Patent Publication Number: US-9414177-B2

Title: Audio signal processing method and audio signal processing device

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application is based on and claims priority of Japanese Patent Applications No. 2013-244519 filed on Nov. 27, 2013, and No. 2014-221715 filed on Oct. 30, 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 signal processing method and an audio signal processing device which change the localization position of a sound by performing signal processing on two audio signals. 
     BACKGROUND 
     There is a conventional technique for canceling a spatial crosstalk by using an L signal and an R signal which are audio signals of two channels (for example, see Patent Literature (PTL) 1). The technique is for widening the sound image of a reproduced sound by reducing a reproduced sound of a right-side speaker arriving at the left ear and a reproduced sound of a left-side speaker arriving at the right ear. 
     CITATION LIST 
     Patent Literature 
     [PTL 1] Japanese Unexamined Patent Application Publication No. 2006-303799 
     [PTL 2] Japanese Patent No. 5248718 
     SUMMARY 
     Technical Problem 
     The above technique cannot change the localization position of a sound localized by the reproduced sounds of two audio signals. 
     The present disclosure provides an audio signal processing method which can change the localization position of a sound localized by the reproduced sounds of two audio signals. 
     Solution to Problem 
     An audio signal processing method according to the present disclosure includes: obtaining a first audio signal and a second audio signal which represent a sound field between a first position and a second position, the first audio signal including a sound localized closer to the first position than to the second position as a major component, the second audio signal including a sound localized closer to the second position than to the first position as a major component; extracting a first signal and a second signal, the first signal being a component of a sound included in the first audio signal and localized closer to the second position than to the first position, the second signal being a component of a sound included in the second audio signal and localized closer to the first position than to the second position; generating (i) a first output signal by subtracting the first signal from the first audio signal and adding the second signal to the first audio signal, and (ii) a second output signal by subtracting the second signal from the second audio signal and adding the first signal to the second audio signal; and outputting the first output signal and the second output signal. 
     Advantageous Effects 
     An audio signal processing method according to the present disclosure can change the localization position of a sound localized by the reproduced sounds of two audio signals. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       These and other objects, advantages and features of the disclosure 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 schematic diagram for illustrating an outline of an audio signal processing method according to Embodiment 1. 
         FIG. 2  illustrates examples of a configuration of an audio signal processing device and peripheral devices according to Embodiment 1. 
         FIG. 3  is a functional block diagram illustrating a configuration of the audio signal processing device according to Embodiment 1. 
         FIG. 4  is a flowchart of an operation of the audio signal processing device according to Embodiment 1. 
         FIG. 5  schematically illustrates a specific configuration of a generating unit. 
         FIG. 6  is a functional block diagram illustrating a detailed configuration of an extracting unit. 
         FIG. 7  is a flowchart of an operation of the extracting unit. 
         FIG. 8  is a first diagram illustrating a specific example of Lin and Rin. 
         FIG. 9  illustrates the localization positions of a sound localized by a reproduced sound of Lin in  FIG. 8  and a reproduced sound of Rin in  FIG. 8 . 
         FIG. 10  is a first diagram illustrating a method of generating Lout and Rout. 
         FIG. 11  is a second diagram illustrating the method of generating Lout and Rout. 
         FIG. 12  is a second diagram illustrating a specific example of Lin and Rin. 
         FIG. 13  illustrates the localization position of a sound localized by a reproduced sound of Lin in  FIG. 12  and a reproduced sound of Rin in  FIG. 12 . 
         FIG. 14  is a first diagram illustrating the signal waveforms obtained when Lout and Rout are generated. 
         FIG. 15  is a second diagram illustrating the signal waveforms obtained when Lout and Rout are generated. 
         FIG. 16  is a third diagram illustrating a specific example of Lin and Rin. 
         FIG. 17  illustrates the localization position of a sound localized by a reproduced sound of Lin in  FIG. 16  and a reproduced sound of Rin in  FIG. 16 . 
         FIG. 18  is a third diagram illustrating the signal waveforms obtained when Lout and Rout are generated. 
         FIG. 19  is a fourth diagram illustrating the signal waveforms obtained when Lout and Rout are generated. 
         FIG. 20  is a first diagram for illustrating an example of a speaker layout. 
         FIG. 21  is a second diagram for illustrating an example of a speaker layout. 
         FIG. 22  is a functional block diagram illustrating a configuration of an audio signal processing device including an input receiving unit. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, non-limiting embodiments will be described in details with reference to the Drawings. However, descriptions more detailed than necessary may be omitted. For example, detailed description of already well known matters or description of substantially identical configurations may be omitted. This is intended to avoid redundancy in the description below, and to facilitate understanding of those skilled in the art. 
     It is to be noted that the attached drawings and the following description are provided so that those skilled in the art can fully understand the present disclosure. Therefore, the drawings and description are not intended to limit the subject matter defined by the claims. 
     Embodiment 1 
     First, an outline of an audio signal processing method according to Embodiment 1 will be described.  FIG. 1  is a schematic diagram for illustrating an outline of the audio signal processing method. 
     In general, an L signal (L-channel signal) and an R signal (R-channel signal) included in a stereo signal include common components (sound components). Such common components have different signal levels depending on the localization position of a sound. In the example of (a) of  FIG. 1 , each of the L signal and the R signal includes components of a drum sound  30   a , a vocal sound  40   a , and a guitar sound  50   a . The L signal has a higher signal level of a sound localized at the left side (drum sound  30   a ) and a lower signal level of a sound localized at the right side (guitar sound  50   a ). The R signal has a lower signal level of a sound localized at the left side (drum sound  30   a ) and a higher signal level of a sound localized at the right side (guitar sound  50   a ). 
     Reproduction of a stereo signal having such a configuration allows a listener to perceive a three-dimensional sound field. 
     However, the stereo signal is based on the assumption that the listener is present near the intermediate position between an L-channel speaker  10 L and an R-channel speaker  10 R. Hence, when the listening position is shifted, stereo perception may be reduced. 
     Specifically, for example, when the listening position of a listener  20  is closer to the R-channel speaker  10 R than to the L-channel speaker  10 L as illustrated in (a) of  FIG. 1 , the vocal sound  40   a  and the guitar sound  50   a  overlap for the listener  20 , which may make it difficult to listen to the sound clearly. Moreover, in such a case, the localization of the guitar sound  50   a  and the drum sound  30   a  may be vague due to phase errors. A typical example of such a situation is inside a car. The position of the driver or the front passenger seat in the car is generally different from the intermediate position between two speakers. 
     Here, according to the audio signal processing method in Embodiment 1, as illustrated in (b) of  FIG. 1 , signal processing is performed on an L signal and an R signal such that the localization position of the drum sound  30   b  is moved toward the left side and the localization position of the guitar sound  50   b  is moved toward the right side. The localization position of the vocal sound  40   a  remains the same. 
     In this way, the listener  20  can listen to the vocal sound  40   a  clearly. 
     Hereinafter, details of the audio signal processing method (audio signal processing device) will be described. 
     [Example of Application] 
     First, an example of the application of the audio signal processing device according to Embodiment 1 will be described.  FIG. 2  illustrates examples of a configuration of the audio signal processing device and peripheral devices according to Embodiment 1. 
     For example, as illustrated in (a) of  FIG. 2 , an audio signal processing device  100  according to Embodiment 1 is implemented as part of a sound reproducing apparatus  201 . In such a case, the sound reproducing apparatus  201  (audio signal processing device  100 ) obtains two audio signals, an L signal and an R signal, from a network, a recording medium (storage medium), radiowave, a sound collecting unit, and the like. The L signal and the R signal are two signals included in a stereo signal. 
     The audio signal processing device  100  generates a first output signal (hereinafter, may also be referred to as Lout) and a second output signal (hereinafter, may also be referred to as Rout) based on the obtained two audio signals which are the L signal (hereinafter, may also be referred to as Lin) and the R signal (hereinafter, may also be referred to as Rin). Here, Lout and Rout respectively correspond to Lin and Rin, and are signals each having a sound localization position which has been changed. Specifically, Lout and Rout are reproduced by the reproduction system of the sound reproducing apparatus  201  including the audio signal processing device  100 , so that a sound, having a localization position which has been changed, is output. 
     In the case of (a) of  FIG. 2 , examples of the audio signal processing device  100  include: an on-vehicle audio device; an audio device including a speaker such as a mobile audio device; a mini component; an audio device connected to a speaker such as an AV center amplifier; a television; a digital still camera; a digital video camera; a mobile terminal device; a personal computer; a TV conference system; a speaker; and a speaker system. 
     Moreover, as illustrated in (b) of  FIG. 2 , the audio signal processing device  100  may be implemented as a device separated from the sound reproducing apparatus  201 . In such a case, the audio signal processing device  100  outputs Lout and Rout to the sound reproducing apparatus  201 . 
     In this case, the audio signal processing device  100  is implemented as, for example, a server and a relay device of a network audio and the like, a mobile audio device, a mini component, an AV center amplifier, a television, a digital still camera, a digital video camera, a mobile terminal device, a personal computer, a TV conference system, a speaker, and a speaker system. An example of the separate sound reproducing apparatus  201  is an on-vehicle audio device. 
     As illustrated in (c) of  FIG. 2 , the audio signal processing device  100  may output (transmit) Lout and Rout to a recording medium  202 . Specifically, the audio signal processing device  100  may record (store) Lout and Rout onto the recording medium  202 . 
     Examples of the recording medium  202  include a packaged media such as a hard disk, a Blu-ray (registered trademark) disc, a digital versatile disc (DVD), and a compact disc (CD), and a flash memory. Such a recording medium  202  may be included in, for example, an on-vehicle audio device, a server and a relay device of a network audio and the like, a mobile audio device, a mini component, an AV center amplifier, a television, a digital still camera, a digital video camera, a mobile terminal device, a personal computer, a television conference system, a speaker, and a speaker system. 
     As described above, the audio signal processing device  100  may have any configuration as long as the audio signal processing device  100  has a function of obtaining Lin and Rin and generating Lout and Rout. Here, Lout has a desired sound localization position changed from the localization position of the obtained Lin, and Rout has a desired sound localization position changed from the localization position of the obtained Rin. 
     [Configuration and Operation] 
     Hereinafter, a specific configuration and an outline of an operation of the audio signal processing device  100  will be described referring to  FIG. 3  and  FIG. 4 . 
       FIG. 3  is a functional block diagram illustrating a configuration of the audio signal processing device  100 .  FIG. 4  is a flowchart of an operation of the audio signal processing device  100 . 
     As  FIG. 3  illustrates, the audio signal processing device  100  includes an obtaining unit  101 , a control unit  105  (an extracting unit  102  and a generating unit  103 ), and an output unit  104 . 
     The obtaining unit  101  obtains Lin and Rin (S 301  in  FIG. 4 ). Lin includes a sound localized closer to the left than to the right relative to the listener as a major component. Rin includes a sound localized closer to the right than to the left relative to the listener as a major component. The obtaining unit  101  is specifically an interface (input interface) provided to the audio signal processing device  100 , for example, for receiving an audio signal. 
     The extracting unit  102  extracts a first signal and a second signal (S 302  in  FIG. 4 ). The first signal is a component of a sound included in the obtained Lin and localized closer to the right. The second signal is a component of a sound included in the obtained Rin and localized closer to the left. The method of extracting the first signal and the second signal performed by the extracting unit  102  will be described later in details. 
     The generating unit  103  generates Lout by subtracting the first signal from Lin and adding the second signal to Lin, and generates Rout by subtracting the second signal from Rin and adding the first signal to Rin (S 303  in  FIG. 4 ).  FIG. 5  schematically illustrates a specific configuration of the generating unit. 
     As  FIG. 5  illustrates, specifically, the generating unit  103  generates Lout by subtracting the first signal from Lin and adding the second signal to the subtraction result, and generates Rout by subtracting the second signal from Rin and adding the first signal to the subtraction result. 
     The generating unit  103  may generate Lout by adding the second signal to Lin and subtracting the first signal from the addition result, and generate Rout by adding the first signal to Rin and subtracting the second signal from the addition result. In other words, any of the subtraction and addition may be performed first. The method of generating Lout and Rout will be described later in details. 
     The extracting unit  102  and the generating unit  103  are included in the control unit  105 . The control unit  105  is specifically implemented by a processor such as a digital signal processor (DSP), a microcomputer, and a dedicated circuit. 
     The output unit  104  outputs the generated Lout and the generated Rout (S 304  in  FIG. 4 ). The output unit  104  is specifically an interface (output interface) provided to the audio signal processing device  100 , for example, for outputting a signal. 
     As described in the above example of application, the destination of Lout and Rout output by the output unit  104  is not particularly limited. In Embodiment 1, the output unit  104  outputs Lout and Rout to speakers. 
     Next, each operation of the audio signal processing device  100  will be described in details. 
     [Operation of Obtaining Lin and Rin] 
     Hereinafter, an operation performed by the obtaining unit  101  to obtain Lin and Rin will be described in details. 
     As already described referring to  FIG. 2 , the obtaining unit  101  obtains Lin and Rin from a network such as the internet, for example. Moreover, for example, the obtaining unit  101  obtains Lin and Rin from a packaged media such as a hard disk, a Blu-ray disc, DVD, and CD, and a recording medium such as a flash memory. 
     Moreover, for example, the obtaining unit  101  obtains Lin and Rin from the radiowave of a television, a mobile phone, a wireless network and the like. Moreover, for example, the obtaining unit  101  obtains, as Lin and Rin, a signal of a sound collected by a sound collecting unit in a smart phone, an audio recorder, a digital still camera, a digital video camera, a personal computer, a microphone and the like. 
     In other words, the obtaining unit  101  may obtain Lin including a sound localized closer to the left than to the right as a major component and Rin including a sound localized closer to the right than to the left as a major component, via any route. 
     As described above, Lin and Rin are included in a stereo signal. In other words, Lin and Rin are an example of signals which represent a sound field between a first position and a second position. Lin is an example of a first audio signal. The sound localized closer to the left is an example of a sound localized closer to the first position than to the second position. Rin is an example of a second audio signal. The sound localized closer to the right is an example of a sound localized closer to the second position than to the first position. The first position and the second position are virtual positions between which the sound field represented by the stereo signal is present. 
     The obtaining unit  101  may obtain, as the first audio signal and the second audio signal, audio signals of two channels selected from among an audio signal of multi channels such as 5.1 channels. In this case, the obtaining unit  101  may obtain a front L signal as the first audio signal and a front R signal as the second audio signal. Alternatively, the obtaining unit  101  may obtain a surround L signal as the first audio signal and a surround R signal as the second audio signal. Moreover, the obtaining unit  101  may obtain the front L signal as the first audio signal and a center signal as the second audio signal. In other words, the obtaining unit  101  may obtain a pair of audio signals used to represent the same sound field. 
     [Operation of Extracting First Signal and Second Signal] 
     Hereinafter, an operation of extracting the first signal and the second signal performed by the extracting unit  102  will be described in details.  FIG. 6  is a functional block diagram illustrating a detailed configuration of the extracting unit  102 .  FIG. 7  is a flowchart of an operation of the extracting unit  102 . 
     As  FIG. 6  illustrates, the extracting unit  102  includes a frequency domain transforming unit  401 , a signal extracting unit  402 , and a time domain transforming unit  403 . 
     The frequency domain transforming unit  401  performs Fourier transform on Lin and Rin to transform a time-domain representation (hereinafter, simply referred to as time domain) to a frequency-domain representation (hereinafter, simply referred to as frequency domain) (S 501  in  FIG. 7 ). In Embodiment 1, the frequency domain transforming unit  401  transforms Lin and Rin from the time domain to the frequency domain by using fast Fourier transform. Lin in the frequency domain is an example of a first frequency signal. Rin in the frequency domain is an example of a second frequency signal. Specifically, the frequency domain transforming unit  401  generates the first frequency signal obtained by transforming Lin to the frequency domain, and the second frequency signal obtained by transforming Rin to the frequency domain. 
     The frequency domain transforming unit  401  may transform Lin and Rin to the frequency domain by using other general frequency transform such as discrete cosine transform and wavelet transform. In other words, the frequency domain transforming unit  401  may use any methods to transform a time domain signal to a frequency domain signal. 
     The signal extracting unit  402  compares the signal levels of Rin and Lin in the frequency domain, and determines the amount of extraction (extraction level, extraction coefficient) of Lin and Rin in the frequency domain based on the comparison result. The signal extracting unit  402  extracts, based on the determined amount of extraction, a first signal in the frequency domain from Lin in the frequency domain and a second signal in the frequency domain from Rin in the frequency domain (S 502  in  FIG. 7 ). In other words, the signal levels of the first frequency signal and the second frequency signal are compared for each of frequencies to determine the amount of extraction of the first signal and the second signal in the frequency domain for the frequency. 
     Here, the amount of extraction refers to a weight coefficient multiplied by Lin in the frequency domain when the first signal in the frequency domain is extracted (a weight coefficient multiplied by Rin when the second signal in the frequency domain is extracted). 
     For example, when the amount of extraction of the first signal in the frequency domain in a given frequency is 0.5, the signal level of the frequency component in the first signal in the frequency domain is equal to a signal level obtained by multiplying the frequency component of Lin in the frequency domain by 0.5. 
     The signal extracting unit  402  determines, for example, the amount of extraction of the first signal in the frequency domain to be greater for a frequency in which the signal level of Lin in the frequency domain is less than that of Rin in the frequency domain and where the difference between the signal levels is greater. In a similar manner, the signal extracting unit  402  determines, for example, the amount of extraction of the second signal in the frequency domain to be greater for a frequency in which the signal level of Rin in the frequency domain is less than that of Lin in the frequency domain and where the difference between the signal levels is greater. 
     For example, in the frequency of f hertz (where f is a real number), a is the signal level of Lin in the frequency domain, b is the signal level of Rin in the frequency domain, and k is a predetermined threshold (where k is a positive real number). In this case, the signal extracting unit  402  determines the amount of extraction of components of frequency f of the first signal in the frequency domain to be b/a when b/a≧k is satisfied and 0 when b/a&lt;k is satisfied. In a similar manner, the signal extracting unit  402  determines the amount of extraction of components of frequency f of the second signal in the frequency domain to be a/b when a/b≧k is satisfied and 0 when a/b&lt;k is satisfied. Typically, k is set to 1. 
     The method of determining the amount of extraction is not limited to the above examples. The amount of extraction may be determined according to the music genre and the like of a sound source as described later, or the amount of extraction calculated by the above determining method can be further adjusted according to the music genre of the sound source. 
     The above described extracting methods are examples, and may be other than the examples. For example, the signal extracting unit  402  subtracts, in the frequency domain, a differential signal αLin−βRin (where α and β are real numbers) from Lin+Rin that is a summed signal of Lin and Rin to extract a frequency signal of the first signal and a frequency signal of the second signal. Note that α and β are appropriately set according to the range of signals to be extracted and the amount of extraction of the signals. Details of such an extracting method are described in PTL 2, and thus, detailed descriptions thereof are omitted. 
     The time domain transforming unit  403  performs inverse Fourier transform on the first signal in the frequency domain extracted from Lin to transform from the frequency domain to the time domain. In this way, the time domain transforming unit  403  generates the first signal. Moreover, the time domain transforming unit  403  performs inverse Fourier transform on the second signal in the frequency domain extracted from Rin to transform from the frequency domain to the time domain. In this way, the time domain transforming unit  403  generates the second signal (S 503  in  FIG. 7 ). In Embodiment 1, the time domain transforming unit  403  uses Fast inverse Fourier transform for inverse transform. 
     [Specific Example 1 of Operation of Audio Signal Processing Device] 
     Hereinafter, referring to  FIG. 8  to  FIG. 11 , a specific example of an operation of the audio signal processing device  100  will be described.  FIG. 8  illustrates a specific example of Lin and Rin. In  FIG. 8 , the horizontal axes represent time and the vertical axes represent amplitude. 
     Lin illustrated in (a) of  FIG. 8  and Rin illustrated in (b) of  FIG. 8  are both sine waves of 3 kHz. Here, Lin and Rin are in phase. As illustrated in (a) of  FIG. 8 , loudness of Lin decreases over time, and as illustrated in (b) of  FIG. 8 , loudness of Rin increases over time. With such a configuration, the horizontal axes in  FIG. 8  may be regarded as the localization position (region) of a sound. 
     In the following descriptions (including specific examples 2 and 3), it is assumed that the listener listens to the sound at the intermediate position of and in front of the speakers which reproduce Lin and Rin. Specifically, the position of the speaker which reproduces Lin is to the left of the listener (L direction), the position of the speaker which reproduces Rin is to the right of the listener (R direction), and the front of the listener is the center (center direction). 
     In  FIG. 8 , in region a (time period corresponding to region a), the signal level of Lin is greater than that of Rin, and the sine waves of 3 kHz are localized to the left of the listener. In region b (time period corresponding to region b), the signal level of Lin is approximately equal to that of Rin, and the sine waves of 3 kHz are localized to the approximately front of the listener. In region c (time period corresponding to region c), the signal level of Lin is less than that of Rin, and the sine waves of 3 kHz are localized to the right of the listener. 
       FIG. 9  illustrates the localization positions of the sound localized by the reproduced sounds of the above Lin and Rin. In  FIG. 9 , the direction of localization is obtained by a panning method (a method of analyzing the localization direction based on ratio of sound pressure of Lin and Rin). In  FIG. 9 , the white portions indicate a high signal level. In  FIG. 9 , the horizontal axes represent time and the vertical axes represent localization direction. The time scale of the horizontal axes in  FIG. 9  is the same as that in  FIG. 8 . Regions a, b, and c in  FIG. 9  respectively correspond to regions a, b, and c in  FIG. 8 . 
     As (a) of  FIG. 9  illustrates, the localization position of the sound localized by the reproduced sounds of Lin and Rin is gradually shifted from the left to the center, and then to the right over time. 
     In  FIG. 9 , (b) and (c) each illustrate the localization position of the sound localized by the reproduced sounds of Lout and Rout generated by the audio signal processing device  100 . The representation method (manner) in (b) and (c) of  FIG. 9  is the same as that in (a) of  FIG. 9 . In  FIG. 9 , (b) illustrates the case where the shift amount of sound localization is small, whereas (c) illustrates the case where the shift amount of sound localization is large. 
     It is understood from the comparison between (a) and (b) in  FIG. 9  that the localization position of the sound localized by the reproduced sounds of Lout and Rout is concentrated in and around region a and region c. In other words, the localization position of the sound is changed by the audio signal processing device  100 . The reproduced sounds of Lout and Rout extend the localization distribution of the sound in and around region b in the left and right directions (vertical direction in (b) of  FIG. 9 ) with respect to the center, while the localization of the sound in region b is maintained. 
     Moreover, it is understood from the comparison between (b) and (c) in  FIG. 9  that the localization position of the sound localized by the reproduced sounds of Lout and Rout is further concentrated in and around region a and region c in (c) of  FIG. 9 . In (c) of  FIG. 9 , the reproduced sounds of Lout and Rout further extend the localization distribution of the sound in and around region b in the left and right directions with respect to the center. 
     Here, a method for generating Lout and Rout providing the localization of the sound illustrated in (b) of  FIG. 9  will be described referring to  FIG. 10 .  FIG. 10  illustrates the method for generating Lout and Rout. In  FIG. 10 , the horizontal axes represent time and the vertical axes represent amplitude. The time scale of the horizontal axes and the amplitude scale of the vertical axes in  FIG. 10  are the same as those in  FIG. 8 . Regions a, b, and c in  FIG. 10  respectively correspond to regions a, b, and c in  FIG. 8 . 
     In  FIG. 10 , (a) illustrates a first signal. The first signal is a signal obtained by extracting a component of a sound included in Lin ((a) of  FIG. 8 ) and localized closer to region c (closer to the right). In  FIG. 10 , (b) illustrates a second signal. As described above, the second signal is a signal obtained by extracting a component of a sound included in Rin ((b) of  FIG. 8 ) and localized closer to region a (closer to the left). 
     In  FIG. 10 , (c) illustrates a signal obtained by subtracting the first signal from Lin. As can be understood from (c) of  FIG. 10 , relative to the signal obtained by subtracting the first signal from Lin, the signal level in region c (right side) is less than that of Lin. In a similar manner, in  FIG. 10 , (d) illustrates a signal obtained by subtracting the second signal from Rin. As can be understood from (d) of  FIG. 10 , relative to the signal obtained by subtracting the second signal from Rin, the signal level in region a (left side) is less than that of Rin. 
     In  FIG. 10 , (e) illustrates Lout that is a signal obtained by subtracting the first signal from Lin and adding the second signal to Lin, and (f) illustrates Rout that is a signal obtained by subtracting the second signal from Rin and adding the first signal to Rin. 
     The signal level of Lout in region a (left side) is greater than that of Lin. The signal level of Rout in region a is less than that of Rin. In other words, with Lout and Rout, the localization position of the sound can be shifted (moved) toward the left side. 
     The signal level of Lout in region c (right side) is less than that of Lin. The signal level of Rout in region c is greater than that of Rin. In other words, with Lout and Rout, the localization position of the sound can be shifted (moved) toward the right side. 
     In order to change the localization position, the addition (addition of the second signal to Lin and addition of the first signal to Rin) is not necessarily needed. However, the addition satisfies the relation of Lin+Rin=Lout+Rout, and thereby maintaining the signal level as a whole and minimizing a change in quality and volume perception after signal processing. 
     As (c) of  FIG. 9  illustrates, the localization position of the sound can be further moved in the left and right directions by changing the amount of extraction of the first signal and the second signal. A method for generating Lout and Rout providing the sound localization illustrated in (c) of  FIG. 9  will be described referring to  FIG. 11 .  FIG. 11  illustrates the method for generating Lout and Rout. In  FIG. 11 , the horizontal axes represent time and the vertical axes represent amplitude. The time scale of the horizontal axes and the amplitude scale of the vertical axes in  FIG. 11  are the same as those in  FIG. 8 . Regions a, b, and c in  FIG. 11  respectively correspond to regions a, b, and c in  FIG. 8 . 
     In  FIG. 11 , (a) illustrates a first signal, and (b) illustrates a second signal. In  FIG. 11 , (c) illustrates a signal obtained by subtracting the first signal from Lin, and (d) illustrates a signal obtained by subtracting the second signal from Rin. It is understood from  FIG. 11  that the amount of extraction of the first signal and the second signal is greater than that in  FIG. 10 . 
     The signal level of Lout in region a illustrated in (e) in  FIG. 11  is greater than that of Lout illustrated in (e) of  FIG. 10 . In other words, Lout illustrated in (e) of  FIG. 11  can further shift (move) the localization position of the sound in the left direction compared to Lout illustrated in (e) of  FIG. 10 . In a similar manner, the signal level of Rout in region c illustrated in (f) of  FIG. 11  is greater than that of Rout illustrated in (f) of  FIG. 10 . In other words, Rout illustrated in (f) of  FIG. 11  can further shift (move) the localization position of the sound in the right direction compared to Rout illustrated in (f) of  FIG. 10 . Here, the relation of Lin+Rin=Lout+Rout is also satisfied, and the signal level as a whole (the signal level of the summed signal of Lin and Rin) remains the same. 
     As described above, according to the audio signal processing method performed by the audio signal processing device  100 , while localizing a sound in and around the center, the localization positions of other sounds can be shifted in the left and right directions, and the shift amount of sound localization in the left and right directions can be changed. In this way, the listener can listen to the sound in and around the center clearly. 
     In the examples of  FIG. 8  to  FIG. 11 , it is assumed that the listener listens to a sound at the intermediate position of and in front of speakers which reproduce Lin and Rin. However, the position of the listener may be other than the above. The listener can clearly listen to the sound in and around the center even when the listener is positioned closer to the speaker which reproduces Lout or when the listener is positioned closer to the speaker which reproduces Rout. 
     [Specific Example 2 of Operation of Audio Signal Processing Device] 
     Hereinafter, another specific example of an operation of the audio signal processing device  100  will be described. Referring to  FIG. 12  to  FIG. 15 , an example where Lin and Rin are used which are included in a stereo sound source of pop music will be described.  FIG. 12  illustrates a specific example of Lin and Rin. In  FIG. 12 , the horizontal axes represent time and the vertical axes represent amplitude. 
       FIG. 13  illustrates the localization position of the sound localized by the reproduced sounds of the above Lin and Rin. In  FIG. 13 , the localization position is obtained by a panning method. The white portions indicate a high signal level. In  FIG. 13 , the horizontal axes represent time and the vertical axes represent localization direction. The time scale of the horizontal axes in  FIG. 13  is the same as that in  FIG. 12 . 
     As (a) of  FIG. 13  illustrates, the localization position of a sound localized by the reproduced sounds of Lin and Rin is concentrated in and around the center. 
     Each of (b) and (c) in  FIG. 13  illustrates the localization position of a sound localized by the reproduced sounds of Lout and Rout generated by the audio signal processing device  100 . The representation method (manner) in (b) and (c) of  FIG. 13  is the same as that in (a) of  FIG. 13 . In  FIG. 13 , (b) illustrates the case where the shift amount of sound localization is small, whereas (c) illustrates the case where the shift amount of sound localization is large. 
     It is understood from the comparison between (a) and (b) of  FIG. 13  that the localization position of the sound in (b) of  FIG. 13  is slightly extended in the left and right directions. 
     It is understood from the comparison between (b) and (c) of  FIG. 13  that the localization position of the sound in (c) of  FIG. 13  is further extended in the left and right directions. 
     Here, the signal waveforms obtained when generating Lout and Rout providing the localization of the sound illustrated in (b) of  FIG. 13  are illustrated in  FIG. 14 .  FIG. 14  illustrates the signal waveforms obtained when Lout and Rout are generated. In  FIG. 14 , the horizontal axes represent time and the vertical axes represent amplitude. The time scale of the horizontal axes and the amplitude scale of the vertical axes in  FIG. 14  are the same as those in  FIG. 12 . 
     In  FIG. 14 , (a) illustrates a first signal, and (b) illustrates a second signal. In  FIG. 14 , (c) illustrates an Lin—first signal, and (d) illustrates an Rin—second signal. In  FIG. 14 , (e) illustrates Lout, and (f) illustrates Rout. 
       FIG. 15  illustrates the signal waveforms obtained when generating Lout and Rout providing the localization of the sound illustrated in (c) of  FIG. 13 .  FIG. 15  illustrates the signal waveforms obtained when Lout and Rout are generated. In  FIG. 15 , the horizontal axes represent time and the vertical axes represent amplitude. The time scale of the horizontal axes and the amplitude scale of the vertical axes in  FIG. 15  are the same as those in  FIG. 12 . 
     In  FIG. 15 , (a) illustrates a first signal, and (b) illustrates a second signal. In  FIG. 15 , (c) illustrates an Lin—first signal, and (d) illustrates an Rin—second signal. In  FIG. 15 , (e) illustrates Lout, and (f) illustrates Rout. 
     In both  FIG. 14  and  FIG. 15 , the relation of Lin+Rin=Lout+Rout is satisfied, and the signal level as a whole is not changed. 
     As described above, according to the audio signal processing method performed by the audio signal processing device  100 , while localizing a sound in and around the center, the localization positions of the other sounds can be shifted in the left and right directions. Additionally, the shift amount of sound localization in the left and right directions can also be changed. In this way, the listener can listen to the sound in and around the center clearly. 
     For example, as  FIG. 12  and (a) of  FIG. 13  illustrate, there may be a case where the localization position of the sound localized by the reproduced sounds of Lin and Rin is concentrated in the center. In such a case, a sound field which greatly expands in the left and right directions can be generated by Lout and Rout generated such that the shift amount of sound localization is large. 
     [Specific Example 3 of Operation of Audio Signal Processing Device] 
     Hereinafter, another specific example of an operation of the audio signal processing device  100  will be described. Referring to  FIG. 16  to  FIG. 19 , an example where Lin and Rin are used which are included in a stereo sound source of classic music will be described. 
       FIG. 16  illustrates a specific example of Lin and Rin. In  FIG. 16 , the horizontal axes represent time and the vertical axes represent amplitude. 
       FIG. 17  illustrates the localization position of a sound localized by the reproduced sounds of the above Lin and Rin. In  FIG. 17 , the localization position is obtained by a panning method. The white portions indicate a high signal level. In  FIG. 17 , the horizontal axes represent time and the vertical axes represent localization direction. The time scale of the horizontal axes in  FIG. 17  is the same as that in  FIG. 16 . 
     As (a) of  FIG. 17  illustrates, the localization position of the sound localized by the reproduced sounds of Lin and Rin is spread in the left and right directions. 
     Each of (b) and (c) in  FIG. 17  illustrates the localization position of a sound localized by the reproduced sounds of Lout and Rout generated by the audio signal processing device  100 . The representation method (manner) in (b) and (c) of  FIG. 17  is the same as that in (a) of  FIG. 17 . In  FIG. 17 , (b) illustrates the case where the shift amount of sound localization is small, whereas (c) illustrates the case where the shift amount of sound localization is large. 
     It is understood from the comparison between (a) and (b) of  FIG. 17  that the localization position of the sound in (b) of  FIG. 17  is slightly extended in the left and right directions. 
     It is understood from the comparison between (b) and (c) of  FIG. 17  that the localization position of the sound in (c) of  FIG. 17  is further extended in the left and right directions. 
     Here, the signal waveforms obtained when generating Lout and Rout providing the localization of the sound illustrated in (b) of  FIG. 17  are illustrated in  FIG. 18 .  FIG. 18  illustrates the signal waveforms obtained when Lout and Rout are generated. In  FIG. 18 , the horizontal axes represent time and the vertical axes represent amplitude. The time scale of the horizontal axes and the amplitude scale of the vertical axes in  FIG. 18  are the same as those in  FIG. 16 . 
     In  FIG. 18 , (a) illustrates a first signal, and (b) illustrates a second signal. In  FIG. 18 , (c) illustrates an Lin—first signal, and (d) illustrates an Rin—second signal. In  FIG. 18 , (e) illustrates Lout, and (f) illustrates Rout. 
     The signal waveforms obtained when generating Lout and Rout providing the localization of the sound illustrated in (c) of  FIG. 17  are illustrated in  FIG. 19 .  FIG. 19  illustrates the signal waveforms obtained when Lout and Rout are generated. In  FIG. 19 , the horizontal axes represent time and the vertical axes represent amplitude. The time scale of the horizontal axes and the amplitude scale of the vertical axes in  FIG. 19  are the same as those in  FIG. 16 . 
     In  FIG. 19 , (a) illustrates a first signal, and (b) illustrates a second signal. In  FIG. 19 , (c) illustrates an Lin—first signal, and (d) illustrates an Rin—second signal. In  FIG. 19 , (e) illustrates Lout, and (f) illustrates Rout. 
     In both  FIG. 18  and  FIG. 19 , the relation of Lin+Rin=Lout+Rout is satisfied, and the signal level as a whole is not changed. 
     As described above, according to the audio signal processing method performed by the audio signal processing device  100 , while localizing a sound in and around the center, the localization positions of the other sounds can be shifted in the left and right directions. Additionally, the shift amount of sound localization in the left and right directions can be changed. In this way, the listener can listen to the sound in and around the center clearly. 
     For example, as  FIG. 16  and (a) of  FIG. 17  illustrate, there may be a case where the localization position of the sound included in Lin and Rin is spread in the left and right directions. In such a case, it is possible to minimize excessive spread of the sound localization position in the left and right directions, by Lout and Rout generated such that the shift amount of sound localization is small. 
     CONCLUSION 
     As described above, according to the audio signal processing method performed by the audio signal processing device  100 , while localizing a sound in and around the center, the localization positions of the other sounds can be shifted in the left and right directions. Additionally, the shift amount of sound localization in the left and right directions can be changed. In other words, the audio signal processing device  100  can change the localization position of the sound localized between the reproduced positions of two audio signals, by performing signal processing. 
     The layout of speakers which reproduce Lout and Rout may be any layout as long as the L-channel speaker is positioned to the left of the R-channel speaker viewed from the listener. However, the audio signal processing method performed by the audio signal processing device  100  is particularly effective in the speaker layout in which a sound is likely to be concentrated in and around the center. Such a layout will be described referring to  FIG. 20  and  FIG. 21 .  FIG. 20  and  FIG. 21  illustrate examples of speaker layout. 
     In  FIG. 20 , an L-channel speaker  60 L and an R-channel speaker  60 R for reproducing a stereo signal are arranged such that the front of the L-channel speaker  60 L faces the front of the R-channel speaker  60 R. In the case where the speaker layout has limitations (for example, on-vehicle audio), such a layout is used. 
     When the L-channel speaker  60 L and the R-channel speaker  60 R are disposed so as to face each other, the localization positions of the sounds are likely to overlap in and around the intermediate position between the two speakers. 
     Moreover, as  FIG. 21  illustrates, in the case where influences of reflection is large due to the layout in which the L-channel speaker  60  and the R-channel speaker  60 R are arranged in a limited space  30 , the localization positions of the sounds are likely to overlap in and around the intermediate positions between the two speakers. 
     In the above cases, the audio signal processing method performed by the audio signal processing device  100  is particularly effective. 
     Other Embodiment 
     Embodiment 1 has been described above as an example of the technique disclosed in the present application. However, the technique according to the present disclosure is not limited thereto, but is also applicable to other embodiments in which changes, replacements, additions, omissions, etc., are made as necessary. Different ones of the components described in Embodiment 1 above may be combined to obtain a new embodiment. 
     Hereinafter, other embodiments will be collectively described. 
     For example, the audio signal processing device  100  may include an input receiving unit which receives input of music genre from a user (listener).  FIG. 22  is a functional block diagram illustrating a configuration of an audio signal processing device including the input receiving unit. An audio signal processing device  100   a  illustrated in  FIG. 22  includes an input receiving unit  106  serving as a user interface such as a remote controller (a light receiving unit of the remote controller) and a touch panel. 
     As described in the above embodiment, the appropriate amount of extraction of the first signal and the second signal is different between the cases where a signal to be processed is a stereo sound source of pop music and classic music. In the audio signal processing device  100   a , an extracting unit  102   a  (a control unit  105   a ) changes the amount of extraction of the first signal according to the music genre received by the input receiving unit  106  and changes the amount of extraction of the second signal according to the music genre received by the input receiving unit  106 . Accordingly, the audio signal processing device  100   a  can appropriately change the localization position of the sound according to the music genre. 
     Each of the constituent elements in the above embodiment may be configured in the form of an exclusive hardware product, or may be realized by executing a software program suitable for the constituent element. The constituent elements may be implemented by a program execution unit such as a CPU or a processor which reads and executes a software program recorded on a recording medium such as a hard disk or a semiconductor memory. 
     For example, each constituent element may be a circuit. These circuits may form a single circuit as a whole or may alternatively form separate circuits. In addition, these circuits may each be a general-purpose circuit or may alternatively be a dedicated circuit. 
     These generic or specific aspects in the present disclosure may be implemented using a system, a method, an integrated circuit, a computer program, or a computer-readable recording medium such as a compact disc read only memory (CD-ROM), and may also be implemented by any combination of systems, methods, integrated circuits, computer programs, or recording media. 
     In the case where the audio signal processing device  100  is implemented as an integrated circuit, the obtaining unit  101  serves as an input terminal of the integrated circuit and the output unit  104  serves as an output terminal of the integrated circuit. 
     As examples of the technique disclosed in the present disclosure, the above embodiments have been described. For this purpose, the accompanying drawings and the detailed description have been provided. 
     Therefore, the constituent elements in the accompanying drawings and the detail description may include not only the constituent elements essential for solving problems, but also the constituent elements that are provided to illustrate the above described technique and are not essential for solving problems. Therefore, such inessential constituent elements should not be readily construed as being essential based on the fact that such inessential constituent elements are illustrated in the accompanying drawings or mentioned in the detailed description. 
     Further, the above described embodiments have been described to exemplify the technique according to the present disclosure, and therefore, various modifications, replacements, additions, and omissions may be made within the scope of the claims and the scope of the equivalents thereof. 
     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. 
     INDUSTRIAL APPLICABILITY 
     The present disclosure is applicable to an audio signal processing device which can change the localization position of a sound by performing signal processing on two audio signals. For example, the present disclosure is applicable to an on-vehicle audio device, an audio reproducing device, a network audio device, and a mobile audio device. Additionally, the present disclosure may be applicable to a disc player of a Blu-ray (registered trademark) disc, DVD, hard disk and the like, a recorder, a television, a digital still camera, a digital video camera, a mobile terminal device, a personal computer, and the like.