Patent Publication Number: US-10334389-B2

Title: Audio reproduction apparatus and game apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a continuation application of PCT International Application No. PCT/JP2014/005780 filed on Nov. 18, 2014, designating the United States of America, which is based on and claims priority of Japanese Patent Applications No. 2013-257342 filed on Dec. 12, 2013, No. 2013-257338 filed on Dec. 12, 2013, and No. 2014-027904 filed on Feb. 17, 2014. The entire disclosures of the above-identified applications, including the specifications, drawings and claims are incorporated herein by reference in their entirety. 
    
    
     FIELD 
     The present disclosure relates to an audio reproduction apparatus that localizes sound to a listener&#39;s ear, and a game apparatus that produces the enjoyment of a game by acoustic effects. 
     BACKGROUND 
     The technology of virtually providing a stereophonic sound field to a listener using two speakers has been developed in recent years. For example, the method of canceling crosstalk which occurs when outputting (reproducing) a binaurally recorded audio signal from two speakers is widely known (see Patent Literature (PTL) 1 as an example). 
     The technology of providing a virtual sound field to a listener using a speaker array is known, too (see PTL 2 as an example). 
     CITATION LIST 
     Patent Literature 
     
         
         [PTL 1] Japanese Unexamined Patent Application Publication No. 9-233599 
         [PTL 2] Japanese Unexamined Patent Application Publication No. 2012-70135 
         [PTL 3] Japanese Patent Publication No. 4840480 
       
    
     Non Patent Literature 
     
         
         [NPL 1] AES 127th Convention, New York N.Y., USA, 2009 Oct. 9-12 Physical and Perceptual Properties of Focused Sources in Wave Field Synthesis 
       
    
     SUMMARY 
     Technical Problem 
     With the technology of canceling crosstalk which occurs when outputting sound from two speakers, the relationship between the position of each speaker and the position of the listener is restricted by transfer characteristics. Accordingly, a desired effect cannot be achieved in the case where a constant relationship between the position of each speaker and the position of the listener is not maintained. In other words, the sweet spot is narrow. 
     The technology of virtually generating a sound field using a speaker array can widen the sweet spot. However, since the plane waves output from the speaker array need to be crossed at the position of the listener, the speaker array needs to be in a crossed arrangement. The speaker arrangement is thus restricted. 
     The present disclosure provides an audio reproduction apparatus that can localize predetermined sound to a listener&#39;s ear without using binaural recording, with an eased restriction on the arrangement of speakers (speaker elements). 
     Solution to Problem 
     An audio reproduction apparatus according to an aspect of the present disclosure is an audio reproduction apparatus that localizes sound to an ear of a listener, and includes: a signal processing unit that converts an audio signal into N channel signals, where N is an integer greater than or equal to 3; and a speaker array including at least N speaker elements that respectively output the N channel signals as reproduced sound, wherein the signal processing unit includes: a beam formation unit that performs a beam formation process of resonating the reproduced sound output from the speaker array at a position of one ear of the listener; and a cancellation unit that performs a cancellation process of preventing the reproduced sound output from the speaker array from reaching a position of the other ear of the listener, and the N channel signals are obtained by performing the beam formation process and the cancellation process on the audio signal. 
     With this structure, the sound (sound image) can be localized to the listener&#39;s ear using a linear speaker array. 
     Moreover, N may be an even number, and the cancellation unit may perform a crosstalk cancellation process which is the cancellation process on each of N/2 pairs of N signals generated by performing the beam formation process on the audio signal, to generate the N channel signals. 
     With this structure, a filter (its constant) used in the crosstalk cancellation process is determined only from the geometric positional relationship between the listener and the combination of speaker elements. The filter used in the crosstalk cancellation process can thus be defined simply. 
     Moreover, the cancellation unit may perform a crosstalk cancellation process which is the cancellation process on the audio signal, based on a transfer function of an input signal to the beam formation unit being output from the speaker array as reproduced sound and reaching the ear of the listener, and the beam formation unit may perform the beam formation process on the audio signal on which the crosstalk cancellation process has been performed, to generate the N channel signals. 
     With this structure, the crosstalk cancellation process is performed on the audio signal before being divided into N channel signals, which requires less computation. 
     Moreover, the beam formation unit may include: a band division filter that generates band signals by dividing the audio signal into predetermined frequency bands; a distribution unit that distributes the generated band signals to each of channels corresponding to the N speaker elements; a position/band-specific filter that performs a filter process on each of the distributed band signals depending on a position of a speaker element to which the band signal is distributed and a frequency band of the band signal, and output a resulting band signal as a filtered signal; and a band synthesis filter that band-synthesizes a plurality of filtered signals belonging to a same channel. 
     With this structure, the beam formation process is controlled for each frequency band, which contributes to higher sound quality. 
     Moreover, the band division filter may divide the audio signal into a high-frequency band signal and a low-frequency band signal, and the position/band-specific filter may, in the case where the filter process is performed on H high-frequency band signals out of N distributed high-frequency band signals where H is a positive integer less than or equal to N, perform the filter process on L low-frequency band signals out of N distributed low-frequency band signals where L is a positive integer less than H. 
     With this structure, the sound in the low-frequency band and the sound in the high-frequency band can be balanced. 
     Moreover, the position/band-specific filter may perform the filter process on the distributed band signal, to cause an amplitude of a filtered signal of a specific channel to be greater than each of amplitudes of filtered signals of channels adjacent to the specific channel on both sides. 
     With this structure, the sound pressure between the channels of the speaker elements can be equalized. 
     Moreover, the signal processing unit may further include a low-pitch enhancement unit that adds a harmonic component of a low-frequency part of the audio signal before the cancellation process, to the audio signal. 
     With this structure, low-pitch sound lost due to the crosstalk cancellation process can be compensated for by utilizing the missing fundamental phenomenon. 
     An audio reproduction apparatus according to an aspect of the present disclosure is an audio reproduction apparatus that localizes sound to an ear of a listener, and includes: a signal processing unit that converts an audio signal into a left channel signal and a right channel signal; a left speaker element that outputs the left channel signal as reproduced sound; and a right speaker element that outputs the right channel signal as reproduced sound, wherein the signal processing unit includes: a low-pitch enhancement unit that adds a harmonic component of a low-frequency part of the audio signal, to the audio signal; and a cancellation unit that performs a cancellation process on the audio signal to which the harmonic component has been added, to generate the left channel signal and the right channel signal, the cancellation process being a process of preventing the reproduced sound output from the right speaker element from reaching a position of a left ear of the listener and preventing the reproduced sound output from the left speaker element from reaching a position of a right ear of the listener. 
     With this structure, in the case where the number of speaker elements is 2, low-pitch sound lost due to the crosstalk cancellation process can be compensated for by utilizing the missing fundamental phenomenon. 
     An audio reproduction apparatus according to an aspect of the present disclosure is an audio reproduction apparatus including: a signal processing unit that converts an audio signal into a left channel signal and a right channel signal; a left speaker element that outputs the left channel signal as reproduced sound; and a right speaker element that outputs the right channel signal as reproduced sound, wherein the signal processing unit includes a filter designed to localize sound of the audio signal to a predetermined position and cause the sound to be enhanced and perceived at a position of one ear of a listener facing the left speaker element and the right speaker element, and converts the audio signal processed by the filter into the left channel signal and the right channel signal, and the predetermined position is in the same area as the one ear of the listener from among two areas separated by a straight line connecting a position of the listener and one of the left speaker element and the right speaker element that corresponds to the one ear, when viewed from above. 
     With this structure, the sound (sound image) can be localized to the listener&#39;s ear using two speaker elements. 
     Moreover, the signal processing unit may further include a crosstalk cancellation unit that performs, on the audio signal, a cancellation process of preventing the sound of the audio signal from being perceived in the other ear of the listener, to generate the left channel signal and the right channel signal, and a straight line connecting the predetermined position and the position of the listener may be approximately in parallel with a straight line connecting the left speaker element and the right speaker element, when viewed from above. 
     With this structure, the sound can be localized to the listener&#39;s ear using two speaker elements and a simple filter structure. 
     An audio reproduction apparatus according to an aspect of the present disclosure is an audio reproduction apparatus that localizes sound to an ear of a listener, and includes: a signal processing unit that converts an audio signal into a left channel signal and a right channel signal; a left speaker element that outputs the left channel signal as reproduced sound; and a right speaker element that outputs the right channel signal as reproduced sound, wherein the signal processing unit performs a filter process using: a first transfer function of sound from a virtual sound source placed on a side of the listener to a first ear of the listener nearer the virtual sound source; a second transfer function of sound from the virtual sound source to a second ear of the listener opposite to the first ear; a first parameter by which the first transfer function is multiplied; and a second parameter by which the second transfer function is multiplied. 
     With this structure, the moving virtual sound source can be recreated with a high sense of realism, using two speaker elements and a simple filter structure. 
     Moreover, in the case where the first parameter is α, the second parameter is β, and a ratio α/β of the first parameter and the second parameter is R, the signal processing unit may: set R to a first value close to 1, when a distance between the virtual sound source and the listener is a first distance; and set R to a second value greater than the first value, when the distance between the virtual sound source and the listener is a second distance that is shorter than the first distance. 
     With this structure, the sense of perspective between the position of the virtual sound source and the position of the listener can be recreated using two speaker elements and a simple filter structure. 
     Moreover, in the case where the first parameter is α, the second parameter is β, and a ratio α/β of the first parameter and the second parameter is R, the signal processing unit may: set R to a value greater than 1, when a position of the virtual sound source is approximately 90 degrees with respect to a front direction of the listener; and set R to be closer to 1, when the position of the virtual sound source deviates more from approximately 90 degrees with respect to the front direction of the listener. 
     With this structure, the acoustic effect of the movement of the virtual sound source on the listener&#39;s side can be produced using two speaker elements and a simple filter structure. 
     A game apparatus according to an aspect of the present disclosure is a game apparatus including: an expectation value setting unit that sets an expectation value of a player winning a game; an acoustic processing unit that outputs an acoustic signal corresponding to the expectation value set by the expectation value setting unit; and at least two sound output units that output the acoustic signal output from the acoustic processing unit, wherein the acoustic processing unit, in the case where the expectation value set by the expectation value setting unit is greater than a predetermined threshold, outputs the acoustic signal processed by a filter with stronger crosstalk cancellation performance than in the case where the expectation value is less than the threshold. 
     With this structure, in the case where the expectation value is high, the acoustic signal processed by the filter with stronger crosstalk cancellation performance than in the case where the expectation value is low is output, so that the player can feel a higher sense of expectation of winning the game from the sound heard in his or her ear. For example, the sense of expectation of the player winning the game can be produced by a whisper or sound effect heard in the player&#39;s ear. The sense of expectation of the player winning the game can be heightened in this way. 
     Moreover, the acoustic processing unit may determine, in a filter process using: a first transfer function of sound from a virtual sound source placed on a side of the player to a first ear of the player nearer the virtual sound source; a second transfer function of sound from the virtual sound source to a second ear of the player opposite to the first ear; a first parameter by which the first transfer function is multiplied; and a second parameter by which the second transfer function is multiplied, the first parameter and the second parameter depending on the expectation value set by the expectation value setting unit, to output the acoustic signal processed by the filter with stronger crosstalk cancellation performance. 
     With this structure, the parameters are determined depending on the expectation value. Accordingly, for example, the degree of the sense of expectation of the player winning the game can be produced by the loudness of a whisper or sound effect heard in the player&#39;s ear. 
     Moreover, the acoustic processing unit may, in the case where the expectation value set by the expectation value setting unit is greater than the threshold, determine the first parameter and the second parameter that differ from each other more than in the case where the expectation value is less than the threshold. 
     With this structure, when the expectation value is higher, the sound heard in one ear increases and the sound heard in the other ear decreases. Accordingly, for example, the degree of the sense of expectation of the player winning the game can be produced by a whisper or sound effect heard in the player&#39;s ear. 
     Moreover, the acoustic processing unit may include: a storage unit that stores a first acoustic signal processed by the filter with stronger crosstalk cancellation performance, and a second acoustic signal processed by a filter with weaker crosstalk cancellation performance than the first acoustic signal; and a selection unit that selects and outputs the first acoustic signal in the case where the expectation value set by the expectation value setting unit is greater than the threshold, and selects and outputs the second acoustic signal in the case where the expectation value set by the expectation value setting unit is less than the threshold. 
     With this structure, the sense of expectation of the player winning the game can be heightened by a simple process. 
     A game apparatus according to an aspect of the present disclosure is a game apparatus including: an expectation value setting unit that sets an expectation value of a player winning a game; an acoustic processing unit that outputs an acoustic signal corresponding to the expectation value set by the expectation value setting unit; and at least two sound output units that output the acoustic signal output from the acoustic processing unit, wherein the acoustic processing unit, in the case where the expectation value set by the expectation value setting unit is greater than a predetermined threshold, adds a larger reverberation component to the acoustic signal than in the case where the expectation value is less than the threshold, and outputs a resulting acoustic signal. 
     With this structure, in the case where the expectation value is high, a larger reverberation component is added to the acoustic signal than in the case where the expectation value is low. Thus, the sense of expectation of the player winning the game can be produced by the surroundness of sound in the space around the player. 
     Moreover, the expectation value setting unit may include: a probability setting unit that sets a probability of winning the game; a timer unit that measures duration of the game; and an expectation value control unit that sets the expectation value, based on the probability set by the probability setting unit and the duration measured by the timer unit. 
     With this structure, the intension of the game apparatus to let the player win the game and the sense of expectation of the player winning the game can be synchronized. 
     Advantageous Effects 
     The audio reproduction apparatus according to the present disclosure can localize predetermined sound to a listener&#39;s ear without using binaural recording, with an eased restriction on the speaker array arrangement. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       These and other objects, advantages and features of the invention will become apparent from the following description thereof taken in conjunction with the accompanying drawings that illustrate a specific embodiment of the present disclosure. 
         FIG. 1  is a diagram illustrating an example of a dummy head. 
         FIG. 2  is a diagram illustrating a typical crosstalk cancellation process. 
         FIG. 3  is a diagram illustrating the wavefronts of sounds output from two speakers and the positions of listeners. 
         FIG. 4  is a diagram illustrating the relationship between the wavefronts of plane waves output from a speaker array and the positions of listeners. 
         FIG. 5  is a diagram illustrating the structure of an audio reproduction apparatus according to Embodiment 1. 
         FIG. 6  is a diagram illustrating the structure of a beam formation unit. 
         FIG. 7  is a flowchart of the operation of the beam formation unit. 
         FIG. 8  is a diagram illustrating the structure of a cancellation unit. 
         FIG. 9  is a diagram illustrating the structure of a crosstalk cancellation unit. 
         FIG. 10  is a diagram illustrating an example of the structure of the audio reproduction apparatus in the case where the number of input audio signals is 2. 
         FIG. 11  is a diagram illustrating another example of the structure of the audio reproduction apparatus in the case where the number of input audio signals is 2. 
         FIG. 12  is a diagram illustrating an example of the structure of the audio reproduction apparatus in the case where a beam formation process is performed after a crosstalk cancellation process. 
         FIG. 13  is a diagram illustrating the structure of an audio reproduction apparatus according to Embodiment 2. 
         FIG. 14  is a diagram illustrating the structure of an audio reproduction apparatus according to Embodiment 3. 
         FIG. 15  is a diagram illustrating the structure of the audio reproduction apparatus in the case of using two input audio signals according to Embodiment 3. 
         FIG. 16  is a diagram illustrating the structure of an audio reproduction apparatus in the case of using two input audio signals according to Embodiment 4. 
         FIG. 17  is a diagram illustrating the position of a virtual sound source in the direction of approximately 90 degrees of a listener according to Embodiment 4. 
         FIG. 18  is a diagram illustrating the position of a virtual sound source on one side of a listener according to Embodiment 4. 
         FIG. 19  is a block diagram illustrating an example of the structure of a game apparatus according to Embodiment 5. 
         FIG. 20  is an external perspective view of an example of the game apparatus according to Embodiment 5. 
         FIG. 21  is a block diagram illustrating an example of the structure of an expectation value setting unit according to Embodiment 5. 
         FIG. 22  is a diagram illustrating an example of signal flow until an acoustic signal reaches a player&#39;s ear according to Embodiment 5. 
         FIG. 23  is a diagram illustrating another example of signal flow until an acoustic signal reaches a player&#39;s ear according to Embodiment 5. 
         FIG. 24  is a block diagram illustrating another example of the structure of the game apparatus according to Embodiment 5. 
         FIG. 25  is a block diagram illustrating another example of the structure of the game apparatus according to Embodiment 5. 
         FIG. 26  is a block diagram illustrating an example of the structure of a game apparatus according to Embodiment 6. 
         FIG. 27  is a block diagram illustrating an example of the structure of a game apparatus according to a modification to Embodiment 6. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     (Underlying Knowledge Forming Basis of the Present Disclosure) 
     The technology of virtually providing a stereophonic sound field to a listener using two speakers has been developed, as described in the Background section. For example, the method of canceling crosstalk when outputting a binaurally recorded audio signal from two speakers is widely known. 
     Binaural recording means recording sound waves reaching both ears of a human, by picking up sounds by microphones fitted in both ears of a dummy head. A listener can perceive spatial acoustics at the time of recording, by listening to the reproduced sound of such a recorded audio signal using headphones. 
     In the case of listening to the sound using speakers, however, the effect of binaural recording is lost because the sound picked up in the right ear also reaches the left ear and the sound picked up in the left ear also reaches the right ear. A conventionally known method to solve this is a crosstalk cancellation process. 
       FIG. 2  is a diagram illustrating a typical crosstalk cancellation process. In  FIG. 2 , hFL denotes the transfer function of sound from a left ch speaker SP-L to a listener&#39;s left ear, hCL denotes the transfer function of sound from the left ch speaker SP-L to the listener&#39;s right ear, hFR denotes the transfer function of sound from a right ch speaker SP-R to the listener&#39;s right ear, and hCR denotes the transfer function of sound from the right ch speaker SP-R to the listener&#39;s left ear. In this case, the matrix M of the transfer functions is the matrix illustrated in  FIG. 2 . 
     In  FIG. 2 , XL denotes a signal recorded in a dummy head&#39;s left ear, XR denotes a signal recorded in the dummy head&#39;s right ear, ZL denotes a signal reaching the listener&#39;s left ear, and ZR denotes a signal reaching the listener&#39;s right ear. 
     When the reproduced sound of the signal [YL, YR] obtained by multiplying the input signal [XL, XR] by the inverse matrix M −1  of the matrix M is output from the left ch speaker SP-L and the right ch speaker SP-R, the signal obtained by multiplying the signal [YL, YR] by the matrix M reaches the listener&#39;s ears. 
     Thus, the input signal [XL, XR] is the signal [ZL, ZR] reaching the listener&#39;s left and right ears. In other words, the crosstalk components (the sound reaching the listener&#39;s right ear out of the sound wave output from the left ch speaker SP-L, and the sound reaching the listener&#39;s left ear out of the sound wave output from the right ch speaker SP-R) are canceled. This method is widely known as a crosstalk cancellation process. 
     With the technology of canceling crosstalk of sound output from two speakers, the relationship between the position of each speaker and the position of the listener is restricted by transfer characteristics. Accordingly, a desired effect cannot be achieved in the case where a constant relationship between the position of each speaker and the position of the listener is not maintained.  FIG. 3  is a diagram illustrating the wavefronts of sounds output from two speakers and the positions of listeners. 
     As illustrated in  FIG. 3 , sound having concentric wavefronts is output from each speaker. The dashed circles indicate the wavefronts of the sound output from the right speaker in  FIG. 3 . The solid circles indicate the wavefronts of the sound output from the left speaker in  FIG. 3 . 
     In  FIG. 3 , when the wavefront at time T of the right speaker reaches the right ear of listener A, the wavefront at time T- 2  of the left speaker reaches the right ear of listener A. When the wavefront at time T of the left speaker reaches the left ear of listener A, the wavefront at time T- 2  of the right speaker reaches the left ear of listener A. 
     Moreover, in  FIG. 3 , when the wavefront at time S of the right speaker reaches the right ear of listener B, the wavefront at time S- 1  of the left speaker reaches the right ear of listener B. When the wavefront at time S of the left speaker reaches the left ear of listener B, the wavefront at time S- 1  of the right speaker reaches the left ear of listener B. 
     Thus, the difference between the time of arrival of the wavefront of the sound from the left speaker and the time of arrival of the wavefront of the sound from the right speaker differs between the position of listener A and the position of listener B in  FIG. 3 . Accordingly, if such transfer characteristics that allow a stereophonic sound field to be perceived most effectively at the position of listener A are set in  FIG. 3 , the sense of realism is lower at the position of listener B than at the position of listener A. 
     In other words, the sweet spot is narrow with the technology of canceling crosstalk of sound output from two speakers. 
     The technology of alleviating such narrowness of the sweet spot using plane waves generated by a speaker array is known (see PTL 2 as an example). 
     This technology of virtually generating a sound field using a speaker array can widen the sweet spot. 
       FIG. 4  is a diagram illustrating the relationship between the wavefronts of plane waves output from a speaker array and the positions of listeners. As illustrated in  FIG. 4 , each speaker array outputs a plane wave that travels perpendicularly to its wavefronts. In  FIG. 4 , the dashed lines indicate the wavefronts of the plane wave output from the right speaker array, and the solid lines indicate the wavefronts of the plane wave output from the left speaker array. 
     In  FIG. 4 , when the wavefront at time T of the right speaker reaches the right ear of listener A, the wavefront at time T- 2  of the left speaker reaches the right ear of listener A. When the wavefront at time T of the left speaker reaches the left ear of listener A, the wavefront at time T- 2  of the right speaker reaches the left ear of listener A. 
     Moreover, in  FIG. 4 , when the wavefront at time S of the right speaker reaches the right ear of listener B, the wavefront at time S- 2  of the left speaker reaches the right ear of listener B. When the wavefront at time S of the left speaker reaches the left ear of listener B, the wavefront at time S- 2  of the right speaker reaches the left ear of listener B. 
     Thus, the difference between the time of arrival of the wavefront of the sound from the left speaker and the time of arrival of the wavefront of the sound from the right speaker is the same at the position of listener A and at the position of listener B in  FIG. 4 . Accordingly, if such transfer characteristics that allow a stereophonic sound field to be perceived most effectively at the position of listener A are set in  FIG. 4 , the stereophonic sound field can be perceived effectively at the position of listener B, too. The sweet spot is therefore wider in  FIG. 4  than in  FIG. 3 . 
     With the technology of virtually generating a sound field using a speaker array, however, the plane waves output from the speaker array need to be crossed at the position of the listener. The structure illustrated in  FIG. 4  cannot be realized solely by a linear speaker array, and a wide space is needed to arrange the speaker array. In other words, the technology of virtually generating a sound field using a speaker array has a restriction (space restriction) on the speaker array arrangement. 
     In view of this, the present disclosure provides an audio reproduction apparatus having an eased restriction on the arrangement of speakers (speaker elements) without using binaural recording. 
     For example, the present disclosure provides an audio reproduction apparatus that can localize predetermined sound from only a linear speaker array, to a listener&#39;s ear. 
     It is known that low-frequency band signals tend to attenuate in the above-mentioned crosstalk cancellation process. This is described in detail in PTL 1. Although PTL 1 discloses a solution to this, a plurality of crosstalk cancellation signal generation filters need to be connected in multiple stages according to the disclosed solution, which requires enormous computation. 
     In view of this, the present disclosure provides an audio reproduction apparatus that can recover low-frequency signals lost as a result of a crosstalk cancellation process, with low computational complexity. 
     The following describes embodiments in detail with reference to drawings as appropriate. In the following, description detailed more than necessary may be omitted. For example, detailed description of well-known matters or repeated description of the substantially same structures may be omitted. This is to avoid unnecessarily redundant description and facilitate the understanding of a person skilled in the art. 
     The accompanying drawings and the following description are provided to help a person skilled in the art to fully understand the present disclosure, and are not intended to limit the subject matter defined in the appended claims. 
     Embodiment 1 
     An audio reproduction apparatus according to Embodiment 1 is described below, with reference to drawings.  FIG. 5  is a diagram illustrating the structure of the audio reproduction apparatus according to Embodiment 1. 
     As illustrated in  FIG. 5 , an audio reproduction apparatus  10  includes a signal processing unit  11  and a speaker array  12 . The signal processing unit  11  includes a beam formation unit  20  and a cancellation unit  21 . 
     The signal processing unit  11  converts an input audio signal into N channel signals. While N=20 in Embodiment 1, N may be an integer greater than or equal to 3. The N channel signals are obtained by performing the below-mentioned beam formation process and cancellation process on the input audio signal. 
     The speaker array  12  includes at least N speaker elements for reproducing the N channel signals (outputting the N channel signals as reproduced sound). In Embodiment 1, the speaker array  12  includes 20 speaker elements. 
     The beam formation unit  20  performs a beam formation process of resonating the reproduced sound output from the speaker array  12  at the position of one ear of a listener  13 . 
     The cancellation unit  21  performs a cancellation process of preventing the reproduced sound of the input audio signal output from the speaker array  12  from reaching the position of the other ear of the listener  13 . 
     The beam formation unit  20  and the cancellation unit  21  constitute the signal processing unit  11 . 
     The following description assumes that the listener  13  faces the speaker array  12 , unless stated otherwise. 
     The operation of the audio reproduction apparatus  10  having the above-mentioned structure is described below. 
     First, the beam formation unit  20  performs the beam formation process on the input audio signal so that the reproduced sound output from the speaker array  12  resonates at the position of one ear of the listener. The beam formation method may be any conventionally known method. For example, the method described in Non Patent Literature (NPL) 1 may be used. 
     A new beam formation process discovered by the inventors is described in Embodiment 1, with reference to  FIGS. 6 and 7 .  FIG. 6  is a diagram illustrating the structure of the beam formation unit  20  according to Embodiment 1. To chiefly describe the beam formation unit  20 , the cancellation unit  21  in  FIG. 5  is omitted in  FIG. 6 . 
     The beam formation unit  20  in  FIG. 6  corresponds to the beam formation unit  20  in  FIG. 5 . The beam formation unit  20  includes a band division filter  30 , a distribution unit  31 , a position/band-specific filter group  32 , and a band synthesis filter group  33 . 
     The band division filter  30  divides the input audio signal into band signals of a plurality of frequency bands. In other words, the band division filter  30  generates a plurality of band signals by dividing the input audio signal into predetermined frequency bands. 
     The distribution unit  31  distributes the band signals to the channels corresponding to the speaker elements in the speaker array  12 . 
     The position/band-specific filter group  32  filters each of the distributed band signals depending on the channel (speaker element position) to which the band signal is distributed and the frequency band of the band signal. The position/band-specific filter group  32  outputs the filtered signals. 
     The band synthesis filter group  33  band-synthesizes the filtered signals output from the position/band-specific filter group  32 , at each position. 
     The operation of the beam formation unit  20  having the above-mentioned structure is described in detail below, with reference to  FIGS. 6 and 7 .  FIG. 7  is a flowchart of the beam formation process according to Embodiment 1. 
     First, the band division filter  30  divides the input audio signal into band signals of a plurality of frequency bands (Step S 101 ). Although the input audio signal is divided into two band signals of a high-frequency signal and a low-frequency signal in Embodiment 1, the input audio signal may be divided into three or more band signals. The low-frequency signal is a part of the input audio signal in a band less than or equal to a predetermined frequency, and the high-frequency signal is a part of the input audio signal in a band greater than the predetermined frequency. 
     Next, the distribution unit  31  distributes each of the band signals (the high-frequency signal and the low-frequency signal) to the 20 channels corresponding to the 20 speaker elements in the speaker array  12  (Step S 102 ). 
     The position/band-specific filter group  32  filters each of the distributed band signals according to the channel (speaker element position) to which the band signal is distributed and the frequency band of the band signal (Step S 103 ). The filter process is described in detail below. 
     The position/band-specific filter group  32  in Embodiment 1 includes a low-frequency signal processing unit  34  and a high-frequency signal processing unit  35 , as illustrated in  FIG. 6 . The low-frequency signal processing unit  34  processes the low-frequency signal, and the high-frequency signal processing unit  35  processes the high-frequency signal. 
     Each of the low-frequency signal processing unit  34  and the high-frequency signal processing unit  35  executes at least a delay process and an amplitude increase/decrease process. Each of the low-frequency signal processing unit  34  and the high-frequency signal processing unit  35  processes the distributed band signal so that a sound wave of a strong (high) sound pressure level is formed in the right ear of the listener  13  in  FIG. 6 . 
     In detail, each of the low-frequency signal processing unit  34  and the high-frequency signal processing unit  35  performs a delay process of assigning a largest delay and an amplification process with a largest gain, on the band signal distributed to the channel (speaker element) nearest the right ear of the listener  13 . 
     Each of the low-frequency signal processing unit  34  and the high-frequency signal processing unit  35  assigns a smaller delay and performs amplification with a smaller gain (attenuation), on the band signal distributed to the channel that is farther from the right ear of the listener  13  in the right or left direction. 
     Thus, each of the low-frequency signal processing unit  34  and the high-frequency signal processing unit  35  performs a delay process of assigning a larger delay and an amplification process of assigning a larger gain, on the band signal distributed to the channel nearer the right ear of the listener  13 . In other words, each of the low-frequency signal processing unit  34  and the high-frequency signal processing unit  35  filters the distributed band signal so that the amplitude of the filtered signal of a specific channel is greater than each of the amplitudes of the filtered signals of the channels adjacent to the specific channel on both sides. In this way, the beam formation unit  20  exercises such control that resonates the sound (sound wave) output from each speaker element at the position of the right ear of the listener  13 . 
     Here, the low-frequency signal does not need to be reproduced in all speaker elements. The low-frequency signal has greater resonance between sound waves output from adjacent speaker elements, than the high-frequency signal. Accordingly, the low-frequency signal may not necessarily be output from all speaker elements that output the high-frequency signal, to keep a perceptual balance between the high-frequency component and the low-frequency component. 
     For example, in the case where the high-frequency signal processing unit  35  filters H high-frequency signals out of the distributed N high-frequency signals (H is a positive integer less than or equal to N), the low-frequency signal processing unit  34  may filter L low-frequency signals out of the distributed N low-frequency signals (L is a positive integer less than H). In this case, the position/band-specific filter group  32  does not output the unfiltered band signal(s). 
     After Step S 103 , the band synthesis filter group  33  band-synthesizes the filtered signals output from the position/band-specific filter group  32 , for each channel (Step S 104 ). In other words, the band synthesis filter group  33  band-synthesizes the filtered signals (the filtered signal of the low-frequency signal and the filtered signal of the high-frequency signal) belonging to the same channel. In detail, the band synthesis filter group  33  has a plurality of (20) band synthesis filters  36  corresponding to the channels, and each band synthesis filter  36  synthesizes the filtered signals of the corresponding channel (speaker element position) to generate a time-axis signal. 
     By the beam formation process described above, sound with a strong sound pressure level is localized to the right ear of the listener  13  in  FIG. 6 . Here, some amount of sound wave also reaches the left ear of the listener  13 , though its sound pressure level is lower than that of the right ear. This impairs the listener  13 &#39;s perceptual psychology that “the input audio signal is being reproduced in the right ear”. 
     In view of this, the cancellation unit  21  in the audio reproduction apparatus  10  reduces the sound wave reaching the left ear of the listener  13 . The operation of the cancellation unit  21  is described below, with reference to  FIGS. 8 and 9 .  FIG. 8  is a diagram illustrating the structure of the cancellation unit  21  according to Embodiment 1.  FIG. 9  is a diagram illustrating the structure of a crosstalk cancellation unit according to Embodiment 1. To chiefly describe the cancellation unit  21 , the detailed structure of the beam formation unit  20  in  FIG. 5  is omitted in  FIG. 8 . 
     In  FIG. 8 , the beam formation unit  20  corresponds to the beam formation unit  20  in  FIG. 5 , and the cancellation unit  21  corresponds to the cancellation unit  21  in  FIG. 5 . The speaker array  12  in  FIG. 8  corresponds to the speaker array  12  in  FIG. 5 , and includes 20 speaker elements (N=20). 
     The cancellation unit  21  in  FIG. 8  includes N/2 (=10) crosstalk cancellation units  40  ( FIG. 9 ). In  FIG. 8, 10  dotted frames (horizontally long boxes) in the cancellation unit  21  each represent a crosstalk cancellation unit  40 . The crosstalk cancellation unit  40  has the structure illustrated in  FIG. 9 . 
     The crosstalk cancellation unit  40  cancels crosstalk of a pair of channels. The pair of channels are channels positioned symmetrically with respect to the center of the linearly arranged speaker elements in the direction of the linear arrangement. Suppose the linearly arranged speaker elements in  FIG. 8  have the channel numbers 1, 2, . . . N (=20) from left to right. Then, the pair of channels are channels whose channel number sum is N+1. 
     When the transfer functions from the speaker elements of the pair of channels (positions) to the listener&#39;s ears are hFL, hCL, hCR, and hFR as illustrated in  FIG. 9 , the matrix M having these transfer functions as elements and the elements (A, B, C, D) of the inverse matrix M −1  of the matrix M have the following relationship. 
     
       
         
           
             
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     The crosstalk cancellation unit  40  multiplies the signals (the two signals corresponding to the pair of channels) input to the crosstalk cancellation unit  40  (the cancellation unit  21 ) by the transfer functions A, B, C, and D, as illustrated in  FIG. 9 . 
     The crosstalk cancellation unit  40  then adds the multiplied signals together, as illustrated in  FIG. 9 . The added signals (channel signals) are output (reproduced) from the corresponding speaker elements. The crosstalk component between the ears resulting from the sound output from the speakers of the pair of channels is canceled in this way. This has been described in the section “Underlying Knowledge Forming Basis of the Present Disclosure”. The crosstalk cancellation method may be any other method. 
     Such a crosstalk cancellation process is performed on N/2 pairs, as illustrated in  FIG. 8 . The N channel signals generated as a result are output (reproduced) from the respective speaker elements of the speaker array  12 . 
     By the crosstalk cancellation process described above, the sound wave of the strong sound pressure level (amplitude) localized to the right ear of the listener  13  by the beam formation process is prevented from reaching the left ear of the listener  13 . This raises the listener  13 &#39;s perceptual psychology that “the input audio signal is being reproduced in the right ear”. 
     Although the number N of speaker elements is N=20 in Embodiment 1, this is an example, and the number N of speaker elements may be any number greater than or equal to 3. 
     As described above, the audio reproduction apparatus  10  according to Embodiment 1 can localize predetermined sound from only the linearly arranged speaker array  12  to the listener&#39;s ear, without using binaural recording. The audio reproduction apparatus  10  according to Embodiment 1 thus allows the listener  13  to fully enjoy a stereophonic sound field even in a space where speakers cannot be arranged three-dimensionally. 
     Although Embodiment 1 describes the case where the number of input audio signals is 1 and the sound is localized to the right ear of the listener, the sound may be localized to the left ear, and the number of input audio signals may be greater than 1. In the case where the number of input audio signals is greater than 1, the sounds of the plurality of input audio signals may be localized to the different ears of the listener  13 . 
       FIG. 10  is a diagram illustrating an example of the structure of the audio reproduction apparatus in the case where the number of input audio signals is 2. An audio reproduction apparatus  10   a  illustrated in  FIG. 10  receives two signals, namely, a first input audio signal and a second input audio signal. 
     The audio reproduction apparatus  10   a  performs the beam formation process and the crosstalk cancellation process on each of the first input audio signal and the second input audio signal. 
     In detail, the first audio signal undergoes the beam formation process by a beam formation unit  20 L so that the reproduced sound localizes to the left ear of the listener  13 , and further undergoes the crosstalk cancellation process by a cancellation unit  21 L. Likewise, the second audio signal undergoes the beam formation process by a beam formation unit  20 R so that the reproduced sound localizes to the right ear of the listener  13 , and further undergoes the crosstalk cancellation process by a cancellation unit  21 R. 
     An addition unit  22  adds the signals after the beam formation process and the crosstalk cancellation process for each channel. The added signals are output (reproduced) from the respective speaker elements of the speaker array  12 . 
     The addition process may be performed before the cancellation process by the cancellation unit  21 , as in an audio reproduction apparatus  10   b  in  FIG. 11 . The addition process may be performed on the filtered signals (the band signals after the process by the position/band-specific filter group  32  and before the process by the band synthesis filter group  33  in the beam formation units  20 L and  20 R), though not illustrated. 
     By doing so, the crosstalk cancellation process by the cancellation unit  21  or the process by the band synthesis filter group  33  is completed in one operation. This reduces computation. 
     Although Embodiment 1 describes the case where the crosstalk cancellation process follows the beam formation process, i.e. the cancellation unit  21  performs the crosstalk cancellation process on the N signals resulting from the beam formation process on the input audio signal for each of the N/2 pairs, the beam formation process may be performed after the crosstalk cancellation process. 
       FIG. 12  is a diagram illustrating an example of the structure of the audio reproduction apparatus in the case where the beam formation process is performed after the crosstalk cancellation process. An audio reproduction apparatus  10   c  illustrated in  FIG. 12  receives two input audio signals. 
     A cancellation unit  50  in the audio reproduction apparatus  10   c  multiplies the two input audio signals by four transfer functions (W, X, Y, Z). The following describes how to find W, X, Y, and Z. 
       FIG. 12  illustrates signal path positions  1 ,  2 ,  3 , and  4 . The signal path positions  1  and  2  are the positions in an intermediate stage of signal processing (immediately before the beam formation process). The signal path position  3  is the position of the left ear of the listener, and the signal path position  4  is the position of the right ear of the listener. 
     Let hBFL be the transfer function from the signal path position  1  to the signal path position  3 , hBCL be the transfer function from the signal path position  1  to the signal path position  4 , hBCR be the transfer function from the signal path position  2  to the signal path position  3 , and hBFR be the transfer function from the signal path position  2  to the signal path position  4 . In this case, the matrix M and the elements W, X, Y, and Z of the inverse matrix M −1  of the matrix M have the following relationship. 
     
       
         
           
             
               
                 
                   
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     In the structure of the audio reproduction apparatus  10   c , the transfer functions of the signals input to the beam formation units  20 L and  20 R are measured or calculated beforehand. The transfer functions mentioned here are the transfer functions when the signals input to the beam formation units  20 L and  20 R and subjected to the beam formation process are output from the speaker array  12  and eventually reach the listener&#39;s ears. The inverse matrix of the matrix having these transfer functions as elements is determined, and the determined inverse matrix is used to perform the crosstalk cancellation process before the beam formation process. Thus, the crosstalk cancellation process is performed before the beam formation process. 
     As described above, the cancellation unit  50  performs the crosstalk cancellation process on the input audio signals, based on the transfer functions when the signals input to the beam formation units  20 L and  20 R are output from the speaker array  12  as reproduced sound and reach the listener&#39;s ears. The beam formation units  20 L and  20 R perform the beam formation process on the input audio signals that have undergone the crosstalk cancellation process, to generate N channel signals. 
     As is clear from the comparison between  FIGS. 8 and 12 , when the crosstalk cancellation process precedes the beam formation process, the crosstalk cancellation process only needs to be performed on one pair of signals. This reduces computation. 
     Embodiment 2 
     An audio reproduction apparatus according to Embodiment 2 is described below, with reference to drawings.  FIG. 13  is a diagram illustrating the structure of the audio reproduction apparatus according to Embodiment 2. 
     As illustrated in  FIG. 13 , an audio reproduction apparatus  10   d  includes a signal processing unit (a cancellation unit  61 , a low-pitch enhancement unit  62 , and a low-pitch enhancement unit  63 ), a crosstalk cancellation filter setting unit  66 , a low-pitch component extraction filter setting unit  67 , a left speaker element  68 , and a right speaker element  69 . The low-pitch enhancement unit  62  includes a low-pitch component extraction unit  64  and a harmonic component generation unit  65 . The low-pitch enhancement unit  63  equally includes a low-pitch component extraction unit and a harmonic component generation unit, though their illustration and description are omitted. 
     The signal processing unit includes the cancellation unit  61 , the low-pitch enhancement unit  62 , and the low-pitch enhancement unit  63 . The signal processing unit converts a first audio signal and a second audio signal into a left channel signal and a right channel signal. 
     The left speaker element  68  outputs the left channel signal as reproduced sound. The right speaker element  69  outputs the right channel signal as reproduced sound. 
     The cancellation unit  61  performs a cancellation process on the first input audio signal to which a harmonic component has been added by the low-pitch enhancement unit  62  and the second input audio signal to which a harmonic component has been added by the low-pitch enhancement unit  63 , to generate the left channel signal and the right channel signal. The cancellation process is a process of preventing the reproduced sound output from the right speaker element  69  from reaching the left ear of the listener  13 , and preventing the reproduced sound output from the left speaker element  68  from reaching the right ear of the listener  13 . 
     The low-pitch enhancement unit  62  adds the harmonic component of the low-frequency part of the first input audio signal, to the first input audio signal. 
     The low-pitch enhancement unit  63  adds the harmonic component of the low-frequency part of the second input audio signal, to the second input audio signal. 
     The low-pitch component extraction unit  64  extracts the low-frequency part (low-pitch component) enhanced by the low-pitch enhancement unit  62 . 
     The harmonic component generation unit  65  generates the harmonic component of the low-pitch component extracted by the low-pitch component extraction unit  64 . 
     The crosstalk cancellation filter setting unit  66  sets the filter coefficient of each crosstalk cancellation filter included in the cancellation unit  61 . 
     The low-pitch component extraction filter setting unit  67  sets the filter coefficient of each low-pitch component extraction filter included in the low-pitch component extraction unit  64 . 
     Although the low-pitch enhancement process and the cancellation process are performed on two input audio signals (the first input audio signal and the second input audio signal) in Embodiment 2, the number of input audio signals may be 1. 
     The operation of the audio reproduction apparatus  10   d  having the above-mentioned structure is described below. 
     First, the low-pitch enhancement units  62  and  63  receive the first input audio signal and the second input audio signal, respectively. The low-pitch enhancement units  62  and  63  each utilize the missing fundamental phenomenon. 
     When a human hears sound that lacks a low pitch (fundamental), he or she can still perceive the low pitch (fundamental) if the harmonic component of the low-pitch (fundamental) is present. This is the missing fundamental phenomenon. 
     In Embodiment 2, the low-pitch enhancement units  62  and  63  each perform signal processing utilizing the missing fundamental phenomenon, in order to auditorily recover the low-pitch component of the first or second input audio signal which attenuates due to the crosstalk cancellation process. 
     In detail, in each of the low-pitch enhancement units  62  and  63 , the low-pitch component extraction unit  64  extracts the signal of the frequency band that attenuates due to the crosstalk cancellation process, and the harmonic component generation unit  65  generates the harmonic component of the low-pitch component extracted by the low-pitch component extraction unit  64 . The method of generating the harmonic component by the harmonic component generation unit  65  may be any conventionally known method. 
     The signals processed by the low-pitch enhancement units  62  and  63  are input to the cancellation unit  61  and subjected to the crosstalk cancellation process. The crosstalk cancellation process is the same as the process described in the section “Underlying Knowledge Forming Basis of the Present Disclosure” and Embodiment 1. 
     Here, the filter coefficient of each crosstalk cancellation filter used in the cancellation unit  61  varies depending on the speaker interval, the speaker characteristics, the positional relationship between the speaker and the listener, etc. The crosstalk cancellation filter setting unit  66  accordingly sets an appropriate filter coefficient. 
     Which band of each of the first and second input audio signals the attenuated low-pitch component belongs to can be determined based on the characteristics of the crosstalk cancellation filter (see PTL 1 as an example). The low-pitch component extraction filter setting unit  67  accordingly sets the low-pitch component extraction filter coefficient, in order to extract the harmonic component of the attenuated band. 
     As described above, in the audio reproduction apparatus  10   d  according to Embodiment 2, the low-pitch enhancement units  62  and  63  add the harmonic components of the low-frequency signals attenuated due to the crosstalk cancellation process by the cancellation unit  61 , respectively to the first and second input audio signals. The audio reproduction apparatus  10   d  can thus perform the crosstalk cancellation process with high sound quality. 
     The audio reproduction apparatus described in Embodiment 1 may include the low-pitch enhancement unit  62  ( 63 ). In this case, the signal processing unit  11  in Embodiment 1 further includes the low-pitch enhancement unit  62  ( 63 ) that adds the harmonic component of the low-frequency signal of the input audio signal before the crosstalk cancellation process, to the input audio signal. 
     Embodiment 3 
     An audio reproduction apparatus according to Embodiment 3 is described below, with reference to drawings.  FIG. 14  is a diagram illustrating the structure of the audio reproduction apparatus according to Embodiment 3. 
     As illustrated in  FIG. 14 , an audio reproduction apparatus  10   e  includes a signal processing unit (a crosstalk cancellation unit  70  and a virtual sound image localization filter  71 ), a left speaker element  78 , and a right speaker element  79 . 
     The signal processing unit (the crosstalk cancellation unit  70  and the virtual sound image localization filter  71 ) converts an input audio signal into a left channel signal and a right channel signal. In detail, the input audio signal processed by the virtual sound image localization filter  71  is converted into the left channel signal and the right channel signal. 
     The left speaker element  78  outputs the left channel signal as reproduced sound. The right speaker element  79  outputs the right channel signal as reproduced sound. 
     The virtual sound image localization filter  71  is designed so that the sound of the input audio signal (the sound represented by the input audio signal) is heard from the left of the listener  13 , i.e. the sound of the input audio signal is localized to the left side of the listener  13 . In other words, the virtual sound image localization filter  71  is designed so that the sound of the input audio signal is localized to a predetermined position and the enhanced sound is perceived at the position of one ear of the listener  13  facing the left speaker element  78  and the right speaker element  79 . 
     The crosstalk cancellation unit  70  performs, on the input audio signal, a cancellation process of preventing the sound of the input audio signal from being perceived in the other ear of the listener  13 , thus generating the left channel signal and the right channel signal. In other words, the crosstalk cancellation unit  70  is designed so that the reproduced sound output from the left speaker element  78  is not perceived in the right ear and the reproduced sound output from the right speaker element  79  is not perceived in the left ear. 
     The operation of the audio reproduction apparatus  10   e  having the above-mentioned structure is described below. 
     First, the virtual sound image localization filter  71  processes the input audio signal. The virtual sound image localization filter  71  is a filter designed so that the sound of the input audio signal is heard from the left of the listener  13 . In detail, the virtual sound image localization filter  71  is a filter representing the transfer function of sound from a sound source placed at the left of the listener  13  to the left ear of the listener  13 . 
     The input audio signal processed by the virtual sound image localization filter  71  is input to one input terminal of the crosstalk cancellation unit  70 . Meanwhile, a null signal (silence) is input to the other input terminal of the crosstalk cancellation unit  70 . 
     The crosstalk cancellation unit  70  performs the crosstalk cancellation process. The crosstalk cancellation process includes a process of multiplication by transfer functions A, B, C, and D, a process of addition of the signal multiplied by the transfer function A and the signal multiplied by the transfer function B, and a process of addition of the signal multiplied by the transfer function C and the signal multiplied by the transfer function D. In other words, the crosstalk cancellation process is a process using the inverse matrix of a 2×2 matrix whose elements are the transfer functions of sounds output from the left speaker element  78  and the right speaker element  79  and reaching the respective ears of the listener  13 . This crosstalk cancellation process is the same as the process described in the section “Underlying Knowledge Forming Basis of the Present Disclosure” and Embodiment 1. The signals which have undergone the crosstalk cancellation process by the crosstalk cancellation unit  70  are output from the left speaker element  78  and the right speaker element  79  to the space as reproduced sound, and the output reproduced sounds reach the ears of the listener  13 . 
     Since the null signal (silence) is input to the other input terminal of the crosstalk cancellation unit  70  and the sound to the right ear of the listener  13  is crosstalk-canceled by the crosstalk cancellation unit  70 , the listener  13  perceives the sound of the input audio signal only in his or her left ear. 
     Although the virtual sound image localization filter  71  in Embodiment 3 is designed so that the sound is localized just beside the listener  13 , this is not a limitation. 
     The sound intended to be created in Embodiment 3 is a whispering sound (whisper) in the left ear of the listener  13 . Such sound is usually heard from approximately just beside the listener  13  or its vicinity, and it is unusual to hear such sound at least from the front. 
     Therefore, the position (predetermined position) to which the sound is localized is desirably on the left side (left rear side) of the straight line connecting the left speaker element  78  and the listener  13  (the straight line forming angle α with the perpendicular line from the position of the listener  13  to the line connecting the left speaker element  78  and the right speaker element  79 ), when the listener  13 , the left speaker element  78 , and the right speaker element  79  are viewed from above (seen vertically) as in  FIG. 14 . In other words, the predetermined position is desirably in the same area as one ear of the listener  13  from among two areas separated by the straight line connecting the position of the listener  13  and one of the left speaker element  78  and the right speaker element  79  that corresponds to the ear when viewed from above. 
     In other words, the virtual sound image localization filter  71  is desirably a filter designed so that the sound of the input audio signal is localized to a position where the listener  13  cannot see the mouth of the whisperer, that is, approximately just beside the listener  13  or its vicinity. Here, “approximately just beside” means that the straight line connecting the predetermined position and the position of the listener  13  is approximately in parallel with the straight line connecting the left speaker element  78  and the right speaker element  79  when viewed from above. 
     The crosstalk cancellation unit  70  does not necessarily need to perform such a crosstalk cancellation process that localizes no sound at all to the right ear of the listener  13  (so that the signal is 0). The term “crosstalk cancellation” is used to suggest that such sound (voice) whispered in the left ear of the listener  13  does not approximately reach the right ear of the listener  13 . Accordingly, sound sufficiently smaller than that of the left ear of the listener  13  may be localized to the right ear of the listener  13 . 
     Although the audio reproduction apparatus  10   e  in Embodiment 3 is designed so that the sound of the input audio signal is perceived in the left ear of the listener  13 , the audio reproduction apparatus  10   e  may be designed so that the sound of the input audio signal is perceived in the right ear of the listener  13 . To cause the sound of the input audio signal to be perceived in the right ear of the listener  13 , the virtual sound image localization filter  71  is designed so that the input audio signal is heard from the right of the listener  13 , and the input audio signal is input to the other input terminal of the crosstalk cancellation unit  70  (the terminal to which the null signal is input in the above description). Meanwhile, the null signal is input to the one input terminal of the crosstalk cancellation unit  70 . 
     In the case of simultaneously localizing sound to the right ear and left ear of the listener  13 , the audio reproduction apparatus has the structure illustrated in  FIG. 15 .  FIG. 15  is a diagram illustrating the structure of the audio reproduction apparatus in the case of using two input audio signals. 
     In an audio reproduction apparatus  10   f  illustrated in  FIG. 15 , a virtual sound image localization filter  81  processes a first input audio signal, and a virtual sound image localization filter  82  processes a second input audio signal. 
     The virtual sound image localization filter  81  is a filter designed so that the sound of the input audio signal to the filter is heard from the left of the listener  13 . The virtual sound image localization filter  82  is a filter designed so that the sound of the input audio signal to the filter is heard from the right of the listener  13 . 
     The first input audio signal processed by the virtual sound image localization filter  81  is input to one input terminal of a crosstalk cancellation unit  80 . The second input audio signal processed by the virtual sound image localization filter  82  is input to the other input terminal of the crosstalk cancellation unit  80 . The crosstalk cancellation unit  80  has the same structure as the crosstalk cancellation unit  70 . The signals which have undergone the crosstalk cancellation process by the crosstalk cancellation unit  80  are output from a left speaker element  88  and a right speaker element  89  to the space as reproduced sound, and the output reproduced sounds reach the ears of the listener  13 . 
     Although Embodiment 3 describes the crosstalk cancellation unit  70  and the virtual sound image localization filter  71  as separate structural elements for the sake of simplicity, the audio reproduction apparatus  10   e  may include a filter operation unit (a structural element combining the crosstalk cancellation unit  70  and the virtual sound image localization filter  71 ) that virtually localizes a sound image and performs signal processing so that the sound is perceived only in one ear of the listener  13 . 
     As described above, the audio reproduction apparatus  10   e  or  10   f  according to Embodiment 3 allows the listener  13  to perceive sound (voice) as if someone is whispering in the ear of the listener  13 . 
     Embodiment 4 
     An audio reproduction apparatus according to Embodiment 4 is described below, with reference to drawings.  FIG. 16  is a diagram illustrating the structure of the audio reproduction apparatus according to Embodiment 4. 
       FIG. 16  is a diagram illustrating signal flow until an acoustic signal reaches a listener&#39;s ear according to Embodiment 4. In detail,  FIG. 16  illustrates signal flow when the sense of reproduction in the ear is increased or decreased by controlling the strength of crosstalk cancellation. 
     In  FIG. 16 , LVD denotes the transfer function of sound from a virtual speaker (virtual sound source) to the left ear of the listener, and LVC denotes the transfer function of sound from the same virtual speaker to the right ear of the listener. 
     As illustrated in  FIG. 16 , the virtual speaker is placed on the light side of the listener. Hence, the transfer function LVD is an example of a first transfer function of sound from a virtual speaker to a listener&#39;s first ear (left ear) nearer the virtual speaker, and the transfer function LVC is an example of a second transfer function of sound from the virtual speaker to the listener&#39;s second ear (right ear) opposite to the first ear. 
     Formula 1 indicates the target characteristics of the ear signal reaching the listener&#39;s ear in the signal flow illustrated in  FIG. 16 . In detail, Formula 1 indicates such target characteristics according to which the signal obtained by multiplying the input signal s by the transfer function LVD, i.e. such a signal that makes the input signal appear to come from the direction of approximately 90 degrees of the listener, reaches the left ear, and the signal obtained by multiplying the input signal s by the transfer function LVC, i.e. such a signal that makes the input signal appear to come from the direction of approximately 90 degrees of the listener, reaches the right ear. 
     
       
         
           
             
               
                 
                   
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     Here, α and β in the left side are parameters for controlling the strength of the sense of reproduction in the left ear. In detail, α is an example of a first parameter by which the first transfer function is multiplied, and β is an example of a second parameter by which the second transfer function is multiplied. 
     Rearranging Formula 1 yields the stereophonic transfer functions [TL, TR] to be the result of multiplying the inverse matrix of the determinant of the spatial acoustic transfer functions by the constant sequence [LVD×α, LVC×β], as shown in Formula 2. 
     
       
         
           
             
               
                 
                   
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                                 LVD 
                                 × 
                                 α 
                               
                             
                           
                           
                             
                               
                                 LVC 
                                 × 
                                 β 
                               
                             
                           
                         
                         ) 
                       
                       . 
                     
                   
                 
               
               
                 
                   ( 
                   
                     Formula 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     2 
                   
                   ) 
                 
               
             
           
         
       
     
     In the case where a is sufficiently greater than β, that is, in the case where the loudness of sound reaching the left ear is sufficiently greater than the loudness of sound reaching the right ear, the sense of reproduction in the left ear is strong. This coincides with an actual phenomenon that whispering voice in the left ear does not reach the right ear, e.g. a phenomenon that buzzing sound of a mosquito heard by the left ear does not reach the right ear. 
     In the case where α and β are approximately equal, that is, in the case where the loudness of sound reaching the left ear is approximately equal to the loudness of sound reaching the right ear, the sense of reproduction in the left ear is weak. This coincides with an actual phenomenon that voice or sound generated far on the left side reaches the right ear, too. 
     By appropriately controlling α and β, it is possible to produce, for example, such an acoustic effect that makes sound appear to approach from far away. This is described below, with reference to  FIG. 17 .  FIG. 17  is a diagram illustrating the position of a virtual sound source in the direction of approximately 90 degrees of a listener according to Embodiment 4. 
     As illustrated in  FIG. 17 , virtual sound source positions A and B each indicate the position of a virtual sound source in the direction of approximately 90 degrees of the listener  13 . Here, “approximately 90 degrees” is the angle with respect to the front (0 degree) of the listener  13 . The direction of approximately 90 degrees of the listener  13  is therefore the direction corresponding to approximately just beside the listener  13 , which is to the left or right of the listener  13 . The virtual sound source position A is farther from the listener  13  than the virtual sound source position B. 
     Let R be the ratio of α and β (α/β). In this embodiment, R is set to a first value close to 1 when the distance between the virtual sound source and the listener  13  is a first distance, and set to a second value greater than the first value when the distance between the virtual sound source and the listener  13  is a second distance that is shorter than the first distance. In other words, R is set to the first value close to 1 when the virtual sound source and the listener  13  are farther from each other, and set to the second value (including infinity) greater than the first value when the virtual sound source and the listener  13  are nearer each other. 
     For example, in the case where the virtual sound source is placed at the virtual sound source position A in  FIG. 17  at the start of sound, the ratio of α and β is controlled to be approximately 1. In the case where the virtual sound source is placed at the virtual sound source position B after a predetermined time, α is set to be sufficiently greater than β. Such an acoustic effect that makes sound appear to approach from far away can be produced in this way. 
     Typically, in the case where the virtual sound source is at approximately 90 degrees of the listener  13  as in  FIG. 17 , the input signal is processed using such transfer functions intended to place the virtual sound source at approximately 90 degrees, while the sense of perspective from the listener  13  is controlled by the sound volume. In this embodiment, on the other hand, α and β are controlled to realize a normally experienced acoustic effect that, in the case where the sound source has approached to the ear, the ear perceives such loud sound that makes the sound of the opposite ear not perceptible. 
     Likewise, such an acoustic effect that makes sound appear to recede into the distance can be produced by setting α to be sufficiently greater than β at the start of sound and, after a predetermined time, setting the ratio of α and β to be approximately 1. 
     Since LVD and LVC are the transfer functions intended to place the virtual speaker (virtual sound source) at approximately 90 degrees, the direction of the above-mentioned “far” or “into the distance” is the direction of approximately 90 degrees of the listener. This direction of “far” or “into the distance” can be changed to a desired direction by changing the direction in which the virtual speaker (virtual sound source) is placed, i.e. by changing LVD and LVC to such transfer functions intended to place the virtual speaker (virtual sound source) in the desired direction. 
     As described above, in the audio reproduction apparatus according to this embodiment, in the filter process using the first transfer function of sound from the virtual speaker placed to one side of the listener  13  to the first ear of the listener nearer the virtual speaker, the second transfer function of sound from the virtual sound source to the second ear opposite to the first ear, the first parameter α by which the first transfer function is multiplied, and the second parameter β by which the second transfer function is multiplied, the signal processing unit controls the first parameter α and the second parameter β. The sense of perspective from the sound source position can be controlled in this way. 
     Although the virtual speaker is placed at approximately 90 degrees of the listener in the example in  FIGS. 16 and 17 , the position of the virtual speaker is not limited to approximately 90 degrees. Although the above describes the process relating to the left ear, the process may relate to the right ear. Alternatively, the process relating to the left ear and the process relating to the right ear may be simultaneously performed to produce the sense of reproduction in both ears. 
     While the above embodiment describes the process of producing the sense of perspective between the virtual sound source and the listener  13 , an example of producing the passage of the virtual sound source on one side of the listener  13  is described below with reference to  FIG. 18 .  FIG. 18  is a diagram illustrating the position of the virtual sound source on one side of the listener according to Embodiment 4. 
     As illustrated in  FIG. 18 , virtual sound source positions C, D, and E each indicate the position of the virtual sound source placed on the side of the listener  13 . 
     Let R be the ratio of α and β(α/β). In this embodiment, R is set to a value greater than 1 when the position of the virtual sound source is approximately 90 degrees with respect to the front of the listener  13 , and set to be closer to 1 when the position of the virtual sound source deviates more from approximately 90 degrees with respect to the front of the listener  13 . In other words, R is set to a value (including infinity) greater than 1 when the virtual sound source is positioned approximately just beside the listener  13 , and set to be closer to 1 when the virtual sound source deviates more from approximately just beside the listener  13 . 
     For example, in the case where the virtual sound source is placed at the virtual sound source position C in  FIG. 18  at the start of sound, the signal of the sound is processed with transfer functions intended to place the virtual sound source at approximately θ degrees (0≤θ&lt;90). In this stage, the ratio R of α and β(=α/β) is set to a value (X) close to 1. 
     In the case where the virtual sound source is placed at the virtual sound source position D after a predetermined time, the signal of the sound is processed with transfer functions intended to place the virtual sound source at approximately 90 degrees, and also the ratio R of α and β is set to a value greater than X. 
     In the case where the virtual sound source is further placed at the virtual sound source position E after a predetermined time, the signal of the sound is processed with transfer functions intended to place the virtual sound source at approximately δ degrees, and also the ratio R of α and β is set to a value (Y) close to 1. X and Y may be the same value. This adds a sense of realism to such an acoustic effect that makes sound appear to pass on the side of the listener  13 . 
     Typically, in the case where the virtual sound source is at approximately θ degrees of the listener  13 , the input signal is processed using such transfer functions intended to place the virtual sound source at approximately θ degrees. In the case where the virtual sound source is at approximately 90 degrees of the listener  13 , the input signal is processed using such transfer functions intended to place the virtual sound source at approximately 90 degrees. In the case where the virtual sound source is at approximately δ degrees (90&lt;δ≤180) of the listener  13 , the input signal is processed using such transfer functions intended to place the virtual sound source at approximately δ degrees. Meanwhile, the sound volume is controlled depending on the distance from the listener  13 . 
     In this embodiment, on the other hand, α and β are controlled to enhance, when the sound source passes on the side of the listener  13 , the sense of the sound source passing just beside the listener  13 . The angles θ and δ illustrated in  FIG. 18  are merely an example, and are not requirements in the present disclosure. 
     Embodiment 5 
     While Embodiments 1 to 4 each describe an audio reproduction apparatus that localizes sound to a listener&#39;s ear, the disclosed technology can also be implemented as a game apparatus that produces the enjoyment of a game by acoustic effects. The game apparatus according to the present disclosure thus includes, for example, any of the audio reproduction apparatuses according to Embodiments 1 to 4. 
     For example, the signal processing unit  11  in Embodiments 1 to 4 corresponds to an acoustic processing unit included in a game apparatus according to the present disclosure, and the speaker array  12  in Embodiments 1 to 4 corresponds to a sound output unit (speaker) included in the game apparatus according to the present disclosure. 
     Recent game apparatuses each produce, in a pachinko machine, a slot machine, or the like, the enjoyment of the game by presenting a sense of expectation of the player winning the game to the player through an image display unit installed in the game apparatus. 
     For example, the game apparatus makes the player recognize that, as the probability of winning the game increases, a person or character which does not appear in the normal state of the game appears on the image display unit, or the colors of the screen change. This heightens the sense of expectation of winning the game, and as a result increases the enjoyment of the game. 
     Regarding acoustic effects, such game apparatuses that increase the enjoyment of the game by changing the acoustic signal processing method depending on the state of the game have been developed. 
     For example, PTL 3 discloses the technique of controlling acoustic signals output from a plurality of speakers in coordination with the operation of a variable display unit of a slot machine. This technique varies the acoustic effects by controlling the output levels and phases of the signals output from the plurality of speakers depending on the state of the game (start, stop, prize type). 
     The conventional technique described in PTL 3, however, coordinates the acoustic effects with the operation of the variable display unit, and cannot produce a sense of expectation of win which is hidden (not visible) in the state of the game. 
     In view of this, the present disclosure provides a game apparatus that can heighten a sense of expectation of a player winning a game. 
     According to the present disclosure, a sense of expectation of a player winning a game can be heightened. 
     A game apparatus according to Embodiment 5 is described below, with reference to drawings. 
       FIG. 19  is a block diagram illustrating the structure of a game apparatus  100  according to Embodiment 5. The game apparatus  100  according to Embodiment 5 produces a sense of expectation of a player winning a game by stereophonic technology. For example, the game apparatus  100  is a game machine such as a pachinko machine or a slot machine as illustrated in  FIG. 20 . 
     As illustrated in  FIG. 19 , the game apparatus  100  includes an expectation value setting unit  110 , an acoustic processing unit  120 , and at least two speakers  150 L and  150 R. The acoustic processing unit  120  includes an acoustic signal storage unit  130  and an acoustic signal output unit  140 . 
     The following describes the structure and operation of each unit in the game apparatus  100 . 
     The expectation value setting unit  110  sets the expectation value of the player winning the game. In detail, the expectation value setting unit  110  sets such an expectation value that makes the player think he or she will win the game. The detailed structure and operation of the expectation value setting unit  110  will be described later with reference to  FIG. 21 . In this embodiment, when the set expectation value is higher, the expectation of the player winning the game is higher. 
     For example, the expectation value setting unit  110  may set the expectation value using a method of generating a state variable representing growing expectation, which has been employed in conventionally widespread game apparatuses to produce a sense of expectation of a player winning a game through an image or electric light. 
     The acoustic processing unit  120  outputs an acoustic signal corresponding to the expectation value set by the expectation value setting unit  110 . In detail, in the case where the expectation value set by the expectation value setting unit  110  is greater than a predetermined threshold, the acoustic processing unit  120  outputs an acoustic signal processed by a filter with stronger crosstalk cancellation performance than in the case where the expectation value is less than the threshold. 
     As illustrated in  FIG. 19 , the acoustic processing unit  120  includes the acoustic signal storage unit  130  that stores acoustic signals provided to the player during the game, and the acoustic signal output unit  140  that changes the output acoustic signal depending on the expectation value set by the expectation value setting unit  110 . 
     The acoustic signal storage unit  130  is memory for storing acoustic signals. The acoustic signal storage unit  130  stores a normal acoustic signal  131  and a sound effect signal  132 . 
     The normal acoustic signal  131  is an acoustic signal provided to the player regardless of the state of the game. The sound effect signal  132  is an acoustic signal sporadically provided depending on the state of the game. The sound effect signal  132  includes a non-stereophonically-processed sound effect signal  133  and a stereophonically-processed sound effect signal  134 . 
     Stereophonic processing is such a process that makes sound appear to be heard in the player&#39;s ear(s). The stereophonically-processed sound effect signal  134  is an example of a first acoustic signal generated by signal processing with strong crosstalk cancellation performance. The non-stereophonically-processed sound effect signal  133  is an example of a second acoustic signal generated by signal processing with weak crosstalk cancellation performance. The method of generating these sound effect signals will be described later with reference to  FIG. 22 . 
     The acoustic signal output unit  140  reads the normal acoustic signal  131  and the sound effect signal  132  from the acoustic signal storage unit  130 , and outputs them to the speakers  150 L and  150 R. As illustrated in  FIG. 19 , the acoustic signal output unit  140  includes a comparator  141 , selectors  142 L and  142 R, and adders  143 L and  143 R. 
     The comparator  141  compares the expectation value set by the expectation value setting unit  110  with the predetermined threshold, and outputs the comparison result to the selectors  142 L and  142 R. In other words, the comparator  141  determines whether or not the expectation value set by the expectation value setting unit  110  is greater than the predetermined threshold, and outputs the determination result to the selectors  142 L and  142 R. 
     The selectors  142 L and  142 R each receive the comparison result from the comparator  141 , and select one of the non-stereophonically-processed sound effect signal  133  and the stereophonically-processed sound effect signal  134 . In detail, the selectors  142 L and  142 R each select the stereophonically-processed sound effect signal  134  in the case where the expectation value is greater than the threshold, and select the non-stereophonically-processed sound effect signal  133  in the case where the expectation value is less than the threshold. 
     The selector  142 L outputs the selected sound effect signal to the adder  143 L, and the selector  142 R outputs the selected sound effect signal to the adder  143 R. 
     The adders  143 L and  143 R each add the normal acoustic signal  131  and the sound effect signal selected by the selector  142 L or  142 R, and output the resulting signal to the corresponding one of the speakers  150 L and  150 R. 
     Thus, in the case where the expectation value set by the expectation value setting unit  110  is less than the predetermined threshold, the acoustic signal output unit  140  reads the non-stereophonically-processed sound effect signal  133  from the acoustic signal storage unit  130 , adds the non-stereophonically-processed sound effect signal  133  to the normal acoustic signal  131 , and outputs the resulting signal. In the case where the expectation value set by the expectation value setting unit  110  is greater than the predetermined threshold, on the other hand, the acoustic signal output unit  140  reads the stereophonically-processed sound effect signal  134  from the acoustic signal storage unit  130 , adds the stereophonically-processed sound effect signal  134  to the normal acoustic signal  131 , and outputs the resulting signal. 
     The speakers  150 L and  150 R are an example of a sound output unit that outputs the acoustic signal output from the acoustic processing unit  120 . The speakers  150 L and  150 R each reproduce the acoustic signal (the acoustic signal obtained by synthesizing the normal acoustic signal  131  and the sound effect signal  132 ) output from the acoustic signal output unit  140 . The game apparatus  100  according to this embodiment includes at least two speakers. The game apparatus  100  may include three or more speakers. 
     The detailed structure of the expectation value setting unit  110  is described below, with reference to  FIG. 21 .  FIG. 21  is a block diagram illustrating an example of the structure of the expectation value setting unit  110  according to Embodiment 5. 
     The expectation value setting unit  110  includes a prize win selection unit  111 , a probability setting unit  112 , a timer unit  113 , and an expectation value control unit  114 , as illustrated in  FIG. 21 . 
     The prize win selection unit  111  determines the win or loss of the game, i.e. prize win or non-prize win, based on a predetermined probability. In detail, the prize win selection unit  111  selects prize win or non-prize win depending on the probability set by the probability setting unit  112 . In the case of prize win, the prize win selection unit  111  outputs a prize win signal. 
     The probability setting unit  112  sets the probability of winning the game. In detail, the probability setting unit  112  sets the probability of prize win or non-prize win for the game. For example, the probability setting unit  112  determines the probability of prize win or non-prize win, based on duration information from the timer unit  113 , the progress of the game in the whole game apparatus  100 , and the like. The probability setting unit  112  changes the probability of prize win or non-prize win, for example, depending on the game skill of the player, an accidental change in state of the game, and the like. The probability setting unit  112  outputs a signal indicating the set probability to the prize win selection unit  111  and the expectation value control unit  114 . 
     The timer unit  113  measures the duration of the game. For example, the timer unit  113  measures the time elapsed from the start of the game by the player. The timer unit  113  outputs a signal indicating the measured duration to the probability setting unit  112  and the expectation value control unit  114 . 
     The expectation value control unit  114  sets the expectation value of the player winning the game, based on the probability set by the probability setting unit  112  and the duration measured by the timer unit  113 . In detail, the expectation value control unit  114  receives the signal output from the probability setting unit  112  and the signal output from the timer unit  113 , and controls the expectation value of the player winning the game which represents the expectation provided to the player. 
     For example, the expectation value control unit  114  increases the expectation value in the case where the duration measured by the timer unit  113  reaches a predetermined time length. For example, the expectation value control unit  114  sets a higher expectation value in the case where the duration is long than in the case where the duration is short. Thus, the expectation value control unit  114  may set the expectation value so as to be positively correlated with the duration. 
     The expectation value control unit  114  varies the expectation value depending on the prize win probability set by the probability setting unit  112 . For example, the expectation value control unit  114  sets a higher expectation value in the case where the prize win probability is high than in the case where the prize win probability is low. Thus, the expectation value control unit  114  may set the expectation value so as to be positively correlated with the prize win probability. 
     As described above, the prize win selection unit  111  and the expectation value control unit  114  respectively perform prize win or non-prize win selection and expectation value setting, based on the probability set by the probability setting unit  112 . This synchronizes the prize win or non-prize win probability and the expectation value, thus synchronizing the sense of expectation of win the player feels from the acoustic signal and the possibility of actually winning the game. 
     The operation of the expectation value setting unit  110  described above is merely illustrative, and any method may be used as long as the possibility of actually winning the game and the expectation of win presented to the player are synchronized. 
     The following describes the method of generating the stereophonically-processed sound effect signal  134 , with reference to  FIG. 22 .  FIG. 22  is a diagram illustrating an example of signal flow until an acoustic signal reaches the player&#39;s ear(s) according to Embodiment 5. In detail,  FIG. 22  illustrates signal flow when an input signal s is stereophonically processed and the processed signal is output from the speakers and reaches the left and right ears of the player. 
     The input signal s is processed by a stereophonic filter TL or TR, and output from the left speaker  150 L or the right speaker  150 R. The input signal s is the source acoustic signal of the non-stereophonically-processed sound effect signal  133  and the stereophonically-processed sound effect signal  134 . Applying the process by the stereophonic filter TL or TR on the input signal s with predetermined strength yields the non-stereophonically-processed sound effect signal  133  and the stereophonically-processed sound effect signal  134 . 
     The sound wave output from the left speaker  150 L is subjected to the action of a spatial transfer function LD, and reaches the left ear of the player. The sound wave output from the left speaker  150 L is subjected to the action of a spatial transfer function LC, and reaches the right ear of the player. 
     Likewise, the sound wave output from the right speaker  150 R is subjected to the action of a spatial transfer function RD, and reaches the right ear of the player. The sound wave output from the right speaker  150 R is subjected to the action of a spatial transfer function RC, and reaches the left ear of the player. 
     Thus, the left ear signal le reaching the left ear and the right ear signal re reaching the right ear satisfy Formula 3. In other words, the ear signal is obtained by multiplying the input signal s by the spatial acoustic transfer functions and the stereophonic transfer functions [TL, TR]. Here, [TL, TR] represents a matrix of two rows and one column (the same applies hereafter). 
     
       
         
           
             
               
                 
                   
                     [ 
                     
                       Math 
                       . 
                       
                           
                       
                       ⁢ 
                       5 
                     
                     ] 
                   
                   ⁢ 
                   
                       
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     ( 
                     
                       
                         
                           le 
                         
                       
                       
                         
                           re 
                         
                       
                     
                     ) 
                   
                   = 
                   
                     
                       ( 
                       
                         
                           
                             LD 
                           
                           
                             RC 
                           
                         
                         
                           
                             LC 
                           
                           
                             RD 
                           
                         
                       
                       ) 
                     
                     × 
                     
                       ( 
                       
                         
                           
                             TL 
                           
                         
                         
                           
                             TR 
                           
                         
                       
                       ) 
                     
                     × 
                     
                       
                         ( 
                         s 
                         ) 
                       
                       . 
                     
                   
                 
               
               
                 
                   ( 
                   
                     Formula 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     3 
                   
                   ) 
                 
               
             
           
         
       
     
     The signal reaching the opposite ear to the speaker due to the action of the spatial transfer function LC or RC is a crosstalk signal. 
     An example of the method of designing a filter with strong crosstalk cancellation performance is described below. Strong crosstalk cancellation causes the input signal s to reach one ear and not to reach the opposite ear in  FIG. 22 . Accordingly, the target characteristics of the ear signal are set so that the left ear signal le is the input signal s and the right ear signal re is 0 as in Formula 4. 
     
       
         
           
             
               
                 
                   
                     [ 
                     
                       Math 
                       . 
                       
                           
                       
                       ⁢ 
                       6 
                     
                     ] 
                   
                   ⁢ 
                   
                       
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     ( 
                     
                       
                         
                           s 
                         
                       
                       
                         
                           0 
                         
                       
                     
                     ) 
                   
                   = 
                   
                     
                       ( 
                       
                         
                           
                             LD 
                           
                           
                             RC 
                           
                         
                         
                           
                             LC 
                           
                           
                             RD 
                           
                         
                       
                       ) 
                     
                     × 
                     
                       ( 
                       
                         
                           
                             TL 
                           
                         
                         
                           
                             TR 
                           
                         
                       
                       ) 
                     
                     × 
                     
                       
                         ( 
                         s 
                         ) 
                       
                       . 
                     
                   
                 
               
               
                 
                   ( 
                   
                     Formula 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     4 
                   
                   ) 
                 
               
             
           
         
       
     
     Rearranging Formula 4 to Formula 5 yields the stereophonic transfer functions [TL, TR] to be the result of multiplying the inverse matrix of the determinant of the spatial acoustic transfer functions by the constant sequence [1, 0] as in Formula 6. 
     
       
         
           
             
               
                 
                   
                     [ 
                     
                       Math 
                       . 
                       
                           
                       
                       ⁢ 
                       7 
                     
                     ] 
                   
                   ⁢ 
                   
                       
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     ( 
                     
                       
                         
                           1 
                         
                       
                       
                         
                           0 
                         
                       
                     
                     ) 
                   
                   = 
                   
                     
                       ( 
                       
                         
                           
                             LD 
                           
                           
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                             LC 
                           
                           
                             RD 
                           
                         
                       
                       ) 
                     
                     × 
                     
                       
                         ( 
                         
                           
                             
                               TL 
                             
                           
                           
                             
                               TR 
                             
                           
                         
                         ) 
                       
                       . 
                     
                   
                 
               
               
                 
                   ( 
                   
                     Formula 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     5 
                   
                   ) 
                 
               
             
             
               
                 
                   
                     [ 
                     
                       Math 
                       . 
                       
                           
                       
                       ⁢ 
                       8 
                     
                     ] 
                   
                   ⁢ 
                   
                       
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     ( 
                     
                       
                         
                           TL 
                         
                       
                       
                         
                           TR 
                         
                       
                     
                     ) 
                   
                   = 
                   
                     
                       
                         ( 
                         
                           
                             
                               LD 
                             
                             
                               RC 
                             
                           
                           
                             
                               LC 
                             
                             
                               RD 
                             
                           
                         
                         ) 
                       
                       
                         - 
                         1 
                       
                     
                     × 
                     
                       
                         ( 
                         
                           
                             
                               1 
                             
                           
                           
                             
                               0 
                             
                           
                         
                         ) 
                       
                       . 
                     
                   
                 
               
               
                 
                   ( 
                   
                     Formula 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     6 
                   
                   ) 
                 
               
             
           
         
       
     
     The stereophonically-processed sound effect signal  134  is generated, for example, by performing a filter process having the stereophonic transfer functions [TL, TR] shown in Formula 6 on the input signal s. 
     Thus, the strength of crosstalk cancellation performance is greater when the ratio in intensity of the signals reaching both ears in the target characteristics of the ear signal is higher. This coincides with an actual physical phenomenon that whispering voice in one ear does not reach the opposite ear. 
     Hence, by increasing the strength of crosstalk cancellation performance when the expectation value set by the expectation value setting unit  110  is higher, the sense of expectation of winning the game can be produced with sound having a stronger sense of reproduction in the ear when the expectation value is higher. Although the above describes an example where the signal reaches the left ear and does not reach the right ear, the signal may reach the right ear instead of the left ear. 
     An example of the method of designing a filter with weak crosstalk cancellation performance is described below. The stereophonic transfer function TL is set to 1 and the stereophonic transfer function TR is set to 0, i.e. the signal is output only from one speaker. This forms a filter with weak crosstalk cancellation performance. In this case, the left ear signal le is s×LD and the right ear signal re is s×LC as in Formula 7, where the signal intensity is not significantly different between the left and right ears. 
     
       
         
           
             
               
                 
                   
                     [ 
                     
                       Math 
                       . 
                       
                           
                       
                       ⁢ 
                       9 
                     
                     ] 
                   
                   ⁢ 
                   
                       
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     ( 
                     
                       
                         
                           le 
                         
                       
                       
                         
                           re 
                         
                       
                     
                     ) 
                   
                   = 
                   
                     
                       
                         ( 
                         
                           
                             
                               LD 
                             
                             
                               RC 
                             
                           
                           
                             
                               LC 
                             
                             
                               RD 
                             
                           
                         
                         ) 
                       
                       × 
                       
                         ( 
                         
                           
                             
                               1 
                             
                           
                           
                             
                               0 
                             
                           
                         
                         ) 
                       
                       × 
                       
                         ( 
                         s 
                         ) 
                       
                     
                     = 
                     
                       
                         ( 
                         
                           
                             
                               
                                 s 
                                 × 
                                 LD 
                               
                             
                           
                           
                             
                               
                                 s 
                                 × 
                                 LC 
                               
                             
                           
                         
                         ) 
                       
                       . 
                     
                   
                 
               
               
                 
                   ( 
                   
                     Formula 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     7 
                   
                   ) 
                 
               
             
           
         
       
     
     Accordingly, the non-stereophonically-processed sound effect signal  133  may be, for example, the signal resulting from the filter process with the stereophonic transfer function TL set to 1 and the stereophonic transfer function TR set to 0. 
     The filter with strong crosstalk cancellation performance shown in Formula 6 is merely illustrative, and the stereophonically-processed sound effect signal  134  may be generated by another filter. 
       FIG. 23  is a diagram illustrating another example of signal flow until an acoustic signal reaches the player&#39;s ear(s) according to Embodiment 5.  FIG. 23  differs from  FIG. 22  in that a virtual speaker is set. 
     The virtual speaker is an example of a virtual sound source placed on the side of the player. In detail, the virtual speaker outputs sound from the direction approximately perpendicular to the direction in which the player faces, toward the player&#39;s ear. A spatial transfer function LV is the transfer function of sound from the speaker to the ear if the actual speaker is placed at the position of the virtual speaker. 
     Formula 8 represents the target characteristics of the ear signal reaching the player&#39;s ear in the signal flow illustrated in  FIG. 23 . In detail, Formula 8 indicates such target characteristics according to which the signal obtained by multiplying the input signal s by the spatial transfer function LV, i.e. such a signal that makes the input signal appear to come from the direction of approximately 90 degrees of the player, reaches the left ear, and no signal reaches the right ear, i.e. the signal is 0. 
     
       
         
           
             
               
                 
                   
                     [ 
                     
                       Math 
                       . 
                       
                           
                       
                       ⁢ 
                       10 
                     
                     ] 
                   
                   ⁢ 
                   
                       
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     ( 
                     
                       
                         
                           
                             s 
                             × 
                             LV 
                           
                         
                       
                       
                         
                           0 
                         
                       
                     
                     ) 
                   
                   = 
                   
                     
                       ( 
                       
                         
                           
                             LD 
                           
                           
                             RC 
                           
                         
                         
                           
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     Rearranging Formula 8 yields the stereophonic transfer functions [TL, TR] to be the result of multiplying the inverse matrix of the determinant of the spatial acoustic transfer functions by the constant sequence [LV, 0], as in Formula 9. 
     
       
         
           
             
               
                 
                   
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     The stereophonically-processed sound effect signal  134  may be generated, for example, by performing a filter process having the stereophonic transfer functions [TL, TR] shown in Formula 9 on the input signal s. 
     Although the virtual speaker is set at the position of approximately 90 degrees of the player in the example illustrated in  FIG. 23 , the virtual speaker does not necessarily need to be at approximately 90 degrees as long as it is on the side of the player. Although the signal reaches the left ear and does not reach the right ear in the above example, the signal may reach the right ear instead of the left ear. 
     As described above, the game apparatus  100  according to this embodiment includes: the expectation value setting unit  110  that sets an expectation value of a player winning a game; the acoustic processing unit  120  that outputs an acoustic signal corresponding to the expectation value set by the expectation value setting unit  110 ; and at least two speakers  150 L and  150 R that output the acoustic signal output from the acoustic processing unit  120 , wherein the acoustic processing unit  120 , in the case where the expectation value set by the expectation value setting unit  110  is greater than a predetermined threshold, outputs the acoustic signal processed by a filter with stronger crosstalk cancellation performance than in the case where the expectation value is less than the threshold. 
     With this structure, in the case where the expectation value is high, the acoustic signal processed by the filter with stronger crosstalk cancellation performance than in the case where the expectation value is low is output, so that the player can feel a higher sense of expectation of winning the game from the sound heard in his or her ear(s). For example, the sense of expectation of the player winning the game can be produced by a whisper or sound effect heard in the player&#39;s ear(s). The sense of expectation of the player winning the game can be heightened in this way. 
     Moreover, in the game apparatus  100  according to this embodiment, the acoustic processing unit  120  includes: the acoustic signal storage unit  130  that stores the stereophonically-processed sound effect signal  134  processed by the filter with stronger crosstalk cancellation performance, and the non-stereophonically-processed sound effect signal  133  processed by a filter with weaker crosstalk cancellation performance than the stereophonically-processed sound effect signal  134 ; and the acoustic signal output unit  140  that selects and outputs the stereophonically-processed sound effect signal  134  in the case where the expectation value set by the expectation value setting unit  110  is greater than the threshold, and selects and outputs the non-stereophonically-processed sound effect signal  133  in the case where the expectation value set by the expectation value setting unit  110  is less than the threshold. 
     With this structure, one of the non-stereophonically-processed sound effect signal  133  and the stereophonically-processed sound effect signal  134  is selected based on the result of comparison between the expectation value and the threshold. The sense of expectation of the player winning the game can thus be heightened by a simple process. The non-stereophonically-processed sound effect signal  133  and the stereophonically-processed sound effect signal  134  may be generated and stored beforehand. 
     Moreover, in the game apparatus  100  according to this embodiment, the expectation value setting unit  110  includes: a probability setting unit  112  that sets a probability of winning the game; a timer unit  113  that measures duration of the game; and an expectation value control unit  114  that sets the expectation value, based on the probability set by the probability setting unit  112  and the duration measured by the timer unit  113 . 
     With this structure, the expectation value is set based on the probability of winning the game and the duration. For example, the intension of the game apparatus  100  to let the player win the game and the sense of expectation of the player winning the game can be synchronized. 
     Although this embodiment describes the case where the acoustic processing unit  120  prepares the non-stereophonically-processed sound effect signal  133  and the stereophonically-processed sound effect signal  134  beforehand and selects one of the signals depending on the expectation value, this is not a limitation. For example, instead of preparing two signals beforehand, the sound effect signal may be changed by switching stereophonic software that runs in real time. In detail, the acoustic processing unit  120  may execute the stereophonic process on the sound effect signal and output the result in the case where the expectation value is greater than the threshold, and output the sound effect signal without executing the stereophonic process in the case where the expectation value is less than the threshold. 
     Although this embodiment describes the case where the acoustic signal storage unit  130  stores two types of signals, namely, the non-stereophonically-processed sound effect signal  133  and the stereophonically-processed sound effect signal  134 , beforehand, this is not a limitation. For example, the acoustic signal storage unit  130  may store a plurality of signals that differ in the degree of stereophonic effect. In this case, the acoustic signal output unit  140  may switch between the plurality of signals depending on the expectation value set by the expectation value setting unit  110 . 
     For example, the acoustic signal storage unit  130  stores three sound effect signals including a first sound effect signal, a second sound effect signal, and a third sound effect signal. Of the three sound effect signals, the first sound effect signal has the weakest stereophonic effect, and the third sound effect signal has the strongest stereophonic effect. 
     The acoustic signal output unit  140  reads and outputs the first sound effect signal, in the case where the expectation value is less than a first threshold. The acoustic signal output unit  140  reads and outputs the second sound effect signal, in the case where the expectation value is greater than the first threshold and less than a second threshold. The acoustic signal output unit  140  reads and outputs the third sound effect signal, in the case where the expectation value is greater than the second threshold. The first threshold is less than the second threshold. 
     The sound effect signal that differs in stereophonic effect is thus output depending on the expectation value. The sound effect signal corresponding to the sense of expectation of the player can be output in this way. 
     Although this embodiment describes the case where the sense of expectation of win of the player is produced in the relationship between the game apparatus  100  and the player, this is not a limitation. For example, among a plurality of players through the game apparatus  100 , the sense of expectation may be produced by an acoustic signal for a player with increased expectation of win. 
     Although this embodiment omits the description of the sound volume when adding the sound effect (sporadically output sound) to the normal acoustic signal  131  (e.g. constantly output background music, etc.) for simplicity&#39;s sake, the sound volume of the normal acoustic signal or sound effect signal may be changed based on the expectation value. 
       FIG. 24  is a block diagram illustrating another example of the structure of the game apparatus according to Embodiment 5. In detail,  FIG. 24  illustrates an example of the structure of a game apparatus  200  capable of controlling the sound volume in the case of adding the sound effect. 
     The game apparatus  200  illustrated in  FIG. 24  differs from the game apparatus  100  illustrated in  FIG. 19  in that an acoustic processing unit  220  is included instead of the acoustic processing unit  120 . The acoustic processing unit  220  differs from the acoustic processing unit  120  in that an acoustic signal output unit  240  is included instead of the acoustic signal output unit  140 . The acoustic signal output unit  240  differs from the acoustic signal output unit  140  in that sound volume adjustment units  244 L and  244 R are further included. 
     The sound volume adjustment units  244 L and  244 R each receive the comparison result from the comparator  141 , and adjusts the sound volume of the normal acoustic signal  131 . In detail, the sound volume adjustment units  244 L and  244 R each decrease the sound volume of the normal acoustic signal  131  in the case of selecting the stereophonically-processed sound effect signal  134  than in the case of selecting the non-stereophonically-processed sound effect signal  133 . This enhances the stereophonic effect (in particular, the effect of localizing the sound image to the ear), and provides the effect to the player. 
     Here, the sound volume of the sound effect signal  132  may be adjusted instead of the sound volume of the normal acoustic signal  131 . In detail, in the case of selecting the stereophonically-processed sound effect signal  134 , the sound volume adjustment unit may increase the sound volume of the stereophonically-processed sound effect signal  134  than in the case of selecting the non-stereophonically-processed sound effect signal  133 . 
     Although this embodiment describes an example where the stereophonic process achieves the acoustic effects at the player&#39;s ear(s), this is not a limitation. For example, the stereophonic process may achieve the surroundness of sound in the space around the player. 
       FIG. 25  is a block diagram illustrating another example of the structure of the game apparatus according to Embodiment 5. In detail,  FIG. 25  illustrates an example of the structure of a game apparatus  300  capable of selectively outputting an artificially added reverberation signal based on the expectation value. 
     The game apparatus  300  illustrated in  FIG. 25  differs from the game apparatus  100  illustrated in  FIG. 19  in that an acoustic processing unit  320  is included instead of the acoustic processing unit  120 . The acoustic processing unit  320  adds a larger reverberation component to the acoustic signal and outputs the resulting acoustic signal in the case where the expectation value set by the expectation value setting unit  110  is greater than the threshold than in the case where the expectation value is less than the threshold. 
     In detail, the acoustic processing unit  320  differs from the acoustic processing unit  120  in that an acoustic signal storage unit  330  is included instead of the acoustic signal storage unit  130 . The acoustic signal storage unit  330  differs from the acoustic signal storage unit  130  in that a reverberation signal  332  is stored instead of the sound effect signal  132 . 
     The reverberation signal  332  is a signal indicating an artificially generated reverberation component. The reverberation signal  332  includes a small reverberation signal  333  and a large reverberation signal  334 . The small reverberation signal  333  has a smaller reverberation signal level and reverberation length than the large reverberation signal  334 . 
     For example, the selectors  142 L and  142 R each receive the comparison result from the comparator  141 , and select one of the small reverberation signal  333  and the large reverberation signal  334 . In detail, the selectors  142 L and  142 R each select the large reverberation signal  334  in the case where the expectation value is greater than the threshold, and select the small reverberation signal  333  in the case where the expectation value is less than the threshold. 
     In the case where the expectation value set by the expectation value setting unit  110  is high, the level and reverberation length of the artificially added reverberation signal can be increased than in the case where expectation value is low. This produces the player&#39;s sense of expectation for the game by the surroundness of sound in the space around the player. 
     Although the acoustic signal storage unit  330  stores two types of reverberation signals in the example in  FIG. 25 , the acoustic signal storage unit  330  may store only one type of reverberation signal. In this case, the selectors  142 L and  142 R each select the reverberation signal in the case where the expectation value is greater than the threshold, and do not select the reverberation signal in the case where the expectation value is less than the threshold. 
     Thus, the game apparatus  300  according to a modification to Embodiment 5 includes: the expectation value setting unit  110  that sets an expectation value of a player winning a game; the acoustic processing unit  320  that outputs an acoustic signal corresponding to the expectation value set by the expectation value setting unit  110 ; and at least two speakers  150 L and  150 R that output the acoustic signal output from the acoustic processing unit  320 , wherein the acoustic processing unit  320 , in the case where the expectation value set by the expectation value setting unit  110  is greater than a predetermined threshold, adds a larger reverberation component to the normal acoustic signal  131  than in the case where the expectation value is less than the threshold, and outputs the resulting normal acoustic signal  131 . 
     With this structure, in the case where the expectation value is high, a larger reverberation component is added to the acoustic signal than in the case where the expectation value is low. By doing so, the player&#39;s sense of expectation for the game can be produced by the surroundness of sound in the space around the player. 
     Embodiment 6 
     A game apparatus according to Embodiment 6 is described below, with reference to drawings. 
       FIG. 26  is a block diagram illustrating the structure of a game apparatus  400  according to Embodiment 6. The game apparatus  400  according to Embodiment 6 produces a sense of expectation of a player winning a game by the technology of adjusting the strength of the sense of reproduction in the ear(s). For example, the game apparatus  400  is a pachinko machine or the like as illustrated in  FIG. 20 , as in Embodiment 5. 
     The game apparatus  400  illustrated in  FIG. 26  differs from the game apparatus  100  illustrated in  FIG. 19  according to Embodiment 5 in that an acoustic processing unit  420  is included instead of the acoustic processing unit  120 . The acoustic processing unit  420  outputs a sound effect signal with a stronger sense of reproduction in the ear, in the case where expectation value set by the expectation value setting unit  110  is greater than the threshold. 
     In detail, the acoustic processing unit  420  differs from the acoustic processing unit  120  in that an acoustic signal storage unit  430  is included instead of the acoustic signal storage unit  130 . The acoustic signal storage unit  430  differs from the acoustic signal storage unit  130  in that a sound effect signal  432  is stored instead of the sound effect signal  132 . 
     The sound effect signal  432  is an acoustic signal sporadically provided depending on the state of the game. The sound effect signal  432  includes a weak-sense-in-ear sound effect signal  433  and a strong-sense-in-ear sound effect signal  434 . 
     The weak-sense-in-ear sound effect signal  433  is an example of a second acoustic signal generated by signal processing with weak crosstalk cancellation performance. For example, the weak-sense-in-ear sound effect signal  433  is such an acoustic signal that is heard with approximately the same loudness in both ears of the player. The strong-sense-in-ear sound effect signal  434  is an example of a first acoustic signal generated by signal processing with strong crosstalk cancellation performance. For example, the strong-sense-in-ear sound effect signal  434  is such an acoustic signal that is heard in one ear of the player but hardly heard in the other ear of the player. 
     For example, the selectors  142 L and  142 R each receive the comparison result from the comparator  141 , and select one of the weak-sense-in-ear sound effect signal  433  and the strong-sense-in-ear sound effect signal  434 . In detail, the selectors  142 L and  142 R each select the strong-sense-in-ear sound effect signal  434  in the case where the expectation value is greater than the threshold, and select the weak-sense-in-ear sound effect signal  433  in the case where the expectation value is less than the threshold. 
     In the case where the expectation value set by the expectation value setting unit  110  is high, the strong-sense-in-ear sound effect signal  434  can be output than in the case where expectation value is low. This produces the player&#39;s sense of expectation for the game by the surroundness of sound in the space around the player. 
     The following describes a filter process for generating signals that differ in the sense of reproduction in the ear(s), with reference to  FIG. 16 . The transfer functions LVD and LVC, the parameters α and β, etc. are the same as those described in Embodiment 4. 
     The parameters α and β in Formulas 1 and 2 are determined based on the expectation value of the player winning the game which is set by the expectation value setting unit  110 . In detail, α and β are set so that the difference between α and β is greater when the expectation value is higher. For example, the enjoyment of the exciting game can be increased by setting α and β to have a large difference (α&gt;&gt;β) when the expectation value is high and setting α and β to be nearly equal (α≈β) when the expectation value is not so high. 
     By determining α and β depending on the expectation value in this way, the weak-sense-in-ear sound effect signal  433  and the strong-sense-in-ear sound effect signal  434  are generated. In detail, the weak-sense-in-ear sound effect signal  433  is generated in the case where α≈β, and the strong-sense-in-ear sound effect signal  434  is generated in the case where α&gt;&gt;β. 
     As described above, in the game apparatus  400  according to this embodiment, the acoustic processing unit  420  determines, in a filter process using: a first transfer function of sound from a virtual speaker placed on a side of the player to a first ear of the player nearer the virtual speaker; a second transfer function of sound from the virtual speaker to a second ear of the player opposite to the first ear; a first parameter by which the first transfer function is multiplied; and a second parameter by which the second transfer function is multiplied, the first parameter and the second parameter depending on the expectation value set by the expectation value setting unit  110 , to output the acoustic signal processed by the filter with stronger crosstalk cancellation performance. 
     With this structure, the parameters are determined depending on the expectation value. Accordingly, for example, the degree of the sense of expectation of the player winning the game can be produced by the loudness of a whisper or sound effect heard in the player&#39;s ear(s). 
     Moreover, in the game apparatus  400  according to this embodiment, the acoustic processing unit  420 , in the case where the expectation value set by the expectation value setting unit  110  is greater than the threshold, determines the first parameter and the second parameter that differ from each other more than in the case where the expectation value is less than the threshold. 
     With this structure, when the expectation value is higher, the sound heard in one ear increases and the sound heard in the other ear decreases. Accordingly, for example, the degree of the sense of expectation of the player winning the game can be produced by a whisper or sound effect heard in the player&#39;s ear(s). 
     Although the virtual speaker is set at the position of approximately 90 degrees of the player in the example illustrated in  FIG. 16 , the virtual speaker does not necessarily need to be at approximately 90 degrees as long as it is on the side of the player. Although the above describes the process relating to the left ear, the process may relate to the right ear. Alternatively, the process relating to the left ear and the process relating to the right ear may be simultaneously performed to produce the sense of reproduction in both ears. 
     Modification to Embodiment 6 
     Although Embodiment 6 describes the case where the acoustic processing unit  420  prepares the weak-sense-in-ear sound effect signal  433  and the strong-sense-in-ear sound effect signal  434  through the process for the sense of reproduction in the ear(s) beforehand and selects one of the signals depending on the expectation value, this is not a limitation. For example, instead of preparing two signals beforehand, the stereophonic transfer functions [TL, TR] are adjusted depending on the expectation value to perform filtering in real time. 
     For example, a game apparatus  500  according to a modification to Embodiment 6 illustrated in  FIG. 27  performs, on the sound effect signal, the filter process using the parameters determined depending on the expectation value in real time.  FIG. 27  is a block diagram illustrating the structure of the game apparatus  500  according to a modification to Embodiment 6. 
     As illustrated in  FIG. 27 , the game apparatus  500  differs from the game apparatus  100  illustrated in  FIG. 19  in that an acoustic processing unit  520  is included instead of the acoustic processing unit  120 . 
     The acoustic processing unit  520  outputs the acoustic signal corresponding to the expectation value set by the expectation value setting unit  110 . For example, the acoustic processing unit  520  determines, in the filter process using the transfer functions LVD and LVC and the parameters α and β, the parameters α and β depending on the expectation value set by the expectation value setting unit  110 . The acoustic signal processed by the filter with stronger crosstalk cancellation performance is thus generated and output. 
     The acoustic processing unit  520  includes an acoustic signal storage unit  530  and an acoustic signal output unit  540 , as illustrated in  FIG. 27 . 
     The acoustic signal storage unit  530  is memory for storing acoustic signals. The acoustic signal storage unit  530  stores the normal acoustic signal  131  and a sound effect signal  532 . The normal acoustic signal  131  is the same as that in Embodiment 5. The sound effect signal  532  is an acoustic signal sporadically provided depending on the state of the game. 
     The acoustic signal output unit  540  generates and outputs a sound effect signal with a weak sense of reproduction in the ear(s) and a sound effect signal with a strong sense of reproduction in the ear(s), depending on the expectation value set by the expectation value setting unit  101 . The acoustic signal output unit  540  includes a parameter determination unit  541  and a filtering unit  542 . 
     The parameter determination unit  541  determines the parameters α and β based on the expectation value set by the expectation value setting unit  110 . In detail, the parameter determination unit  541  determines the parameters α and β so that the difference between α and β is greater in the case where the expectation value set by the expectation value setting unit  110  is greater than the threshold than in the case where the expectation value is less than the threshold. For example, the parameter determination unit  541  determines the parameters α and β to have a larger difference when the expectation value is higher. 
     For example, the parameter determination unit  541  determines α and β described with reference to  FIG. 16 , in coordination with the expectation value of the player winning the game which is set by the expectation value setting unit  110 . In detail, the parameter determination unit  541  determines α and β so that the difference between α and β is greater when the expectation value is higher. For example, the enjoyment of the exciting game can be increased by the parameter determination unit  541  setting α and β to have a large difference (α&gt;&gt;β) when the expectation value is high and setting α and β to be nearly equal (α≈β) when the expectation value is not so high. 
     The filtering unit  542  performs the filter process using the transfer functions LVD and LVC and the parameters α and β, on the sound effect signal. In other words, the filtering unit  542  executes the filter process for adjusting the sense of reproduction in the ear(s), on the sound effect signal. For example, the filtering unit  542  processes the sound effect signal  532  using the stereophonic transfer functions [TL, TR] in Formula 2. 
     The game apparatus  500  according to a modification to Embodiment 6 thus determines the parameters depending on the expectation value. Accordingly, for example, the degree of the sense of expectation of the player winning the game can be produced by the loudness of a whisper or sound effect heard in the player&#39;s ear(s). 
     As described above, in the game apparatus  500  according to a modification to this embodiment, the acoustic processing unit  520  determines, in a filter process using: a first transfer function of sound from a virtual speaker placed on a side of the player to a first ear of the player nearer the virtual speaker; a second transfer function of sound from the virtual speaker to a second ear of the player opposite to the first ear; a first parameter by which the first transfer function is multiplied; and a second parameter by which the second transfer function is multiplied, the first parameter and the second parameter depending on the expectation value set by the expectation value setting unit  110 , to output the acoustic signal processed by the filter with stronger crosstalk cancellation performance. 
     With this structure, the parameters are determined depending on the expectation value. Accordingly, for example, the degree of the sense of expectation of the player winning the game can be produced by a whisper or sound effect heard in the player&#39;s ear(s). 
     Moreover, in the game apparatus  500  according to this embodiment, the acoustic processing unit  520 , in the case where the expectation value set by the expectation value setting unit  110  is greater than the threshold, determines the first parameter and the second parameter that differ from each other more than in the case where the expectation value is less than the threshold. 
     With this structure, when the expectation value is higher, the sound heard in one ear increases and the sound heard in the other ear decreases. Accordingly, for example, the degree of the sense of expectation of the player winning the game can be produced by a whisper or sound effect heard in the player&#39;s ear(s). 
     Other Embodiments 
     Although Embodiments 1 to 6 have been described above to illustrate the disclosed technology, the disclosed technology is not limited to such. Changes, replacements, additions, omissions, etc. may be made to the embodiments as appropriate, and structural elements described in Embodiments 1 to 6 may be combined as a new embodiment. 
     Other embodiments are summarized below. 
     These general and specific embodiments of the audio reproduction apparatus and game apparatus described in the foregoing embodiments may be implemented using a system, a method, an integrated circuit, a computer program, or a computer-readable recording medium such as a CD-ROM, or any combination of systems, methods, integrated circuits, computer programs, or recording media. 
     The disclosed technology includes, for example, a signal processing apparatus in which the speaker array (speaker elements) is omitted from the audio reproduction apparatus described in each of the foregoing embodiments. 
     For example, the structural elements (the expectation value setting unit  110 , the acoustic processing unit  120 , the acoustic signal storage unit  130 , and the acoustic signal output unit  140 ) in the game apparatus according to Embodiment 5 may be implemented by software such as a program executed on a computer including a central processing unit (CPU), random access memory (RAM), ROM, a communication interface, an I/O port, a hard disk, a display, etc., or implemented by hardware such as electronic circuitry. The same applies to the structural elements in each of the game apparatuses  200  to  500  according to the other embodiments. 
     The game apparatus according to the present disclosure provides a sense of expectation of a player winning a game using an acoustic signal, and so can increase the enjoyment of a game in a slot machine or the like. Such technology can be widely used in game apparatuses. 
     Each of the structural elements in each of the foregoing embodiments may be configured in the form of an exclusive hardware product, or may be realized by executing a software program suitable for the structural element. Each of the structural elements may be realized by means of a program executing unit, such as a CPU and a processor, reading and executing the software program recorded on a recording medium such as a hard disk or semiconductor memory. 
     The foregoing embodiments are described to illustrate the disclosed technology, through the detailed description with reference to the accompanying drawings. 
     The structural elements in the detailed description and the accompanying drawings may include not only the structural elements necessary for the solution but also the structural elements not necessary for the solution, to illustrate the disclosed technology. The inclusion of such optional structural elements in the detailed description and the accompanying drawings therefore does not mean that these optional structural elements are necessary structural elements. 
     The foregoing embodiments are intended to be illustrative of the disclosed technology, and so various changes, replacements, additions, omissions, etc. can be made within the scope of the appended Claims and their equivalents. 
     Although only some exemplary embodiments of the present disclosure have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of the present disclosure. Accordingly, all such modifications are intended to be included within the scope of the present disclosure.