Abstract:
An object is to enable accurate calculation of angles and displacements, and to enable reduction of circuit scales. An audio signal processing device, having a digital signal processing circuit ( 31 ) which performs virtual acoustic image localization processing such that an acoustic image is localized at an arbitrary position in the vicinity of the listener, by reproducing, using headphones ( 2 ) or a plurality of speakers, output signals obtained by signal processing of input audio signals, is characterized in that analog detection signals from a sensor ( 1 ) which detects the state of action of the listener are input to the digital signal processing circuit ( 31 ) via an A/D converter ( 30 ), and the transmission characteristics of these audio signals are modified in realtime, according to values derived by processing the values of analog detection signals from the sensor ( 1 ), or by processing the analog detection signals.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention concerns an audio signal processing device which performs virtual acoustic image localization processing, an angular velocity sensor interface device, and a signal processing device.  
           [0003]    2. Description of the Related Art  
           [0004]    In recent years, numerous audio and image reproduction devices have been proposed which use a motion sensor to perform virtual acoustic image localization processing. For example, out-of-head virtual-acoustic image localization headphones have been proposed in which the angle of rotation of the listener&#39;s head is detected, and signal processing is performed to localize, outside the head, the virtual acoustic image of an audio signal corresponding to angle data detected by digital signal processing.  
           [0005]    Below, FIG. 6 through FIG. 10 are used to explain such a conventional audio signal processing device which performs signal processing in order to localize, outside the head, the virtual audio image of an audio signal corresponding to angle data. FIG. 6 is a block diagram of an audio signal processing device having a rotation angle detection function, designed so as to localize the virtual audio image such that the position of localization of the reproduced acoustic image when the audio signals are reproduced by headphones is the same as that for two reproducing speakers, placed before the listener.  
           [0006]    In FIG. 6, when the headphones  2 , having left and right speakers  2 L and  2 R and on which is mounted an angular velocity sensor  1  to detect rotation angles, undergo rotational motion due to rotation of the head of the listener, the angular velocity sensor  1  outputs an analog detection signal with voltage proportional to the angular velocity. This detection signal from the angular velocity sensor  1  passes through a band-limiting filter  3  which removes unnecessary high-frequency components, and is supplied to an A/D converter  4  which converts analog signals into digital signals.  
           [0007]    Digital detection signals, obtained on the output side of the A/D converter  4  by digitizing analog detection signals, are supplied to the microprocessor  5 . In this microprocessor  5 , these digital detection signals for the angular velocity are integrated and processed to obtain angle data. In this microprocessor  5 , the rotation angle for actual localization of the acoustic image is calculated from this angle data, and corresponding signal processing data is supplied to the signal processing circuit  6 .  
           [0008]    On the other hand, audio signals from the sound source, supplied to the audio signal input terminals  7  and  8 , pass through the A/D converters  9  and  10  respectively for conversion from analog signals into digital signals, and are supplied to the digital signal processing circuit  6 .  
           [0009]    In this digital signal processing circuit  6 , audio processing is performed in order to localize, outside the head, the virtual acoustic image of the necessary audio signals corresponding to the angle data calculated by the microprocessor  5 , and the resulting right and left audio signals are supplied to D/A converters  11 R and  11 L, which convert digital signals into analog signals.  
           [0010]    The right and left audio signals resulting when analog signals are converted by the D/A converters  11 R and  11 L pass through the power amplifiers  12 R and  12 L respectively, and are supplied to the right and left speakers  2 R and  2 L of the headphones  2 , so as to apply signals which localize an optimal virtual acoustic image outside the head of the listener listening to the output. The angular velocity sensor  1  is mounted on the headphones  2 , so as to detect rotations of the listener&#39;s head.  
           [0011]    [0011]FIG. 8 shows this digital signal processing circuit  6 , divided into the part the characteristics of which change according to movements of the listener and the part the characteristics of which do not change. In FIG. 8, 7 a  and  8   a  denote input terminals to which are supplied, respectively, digitized audio signals from the audio input terminals  7  and  8 ; the digital audio signals supplied to this input terminal  7   a  pass through the digital filter  13  and are supplied to the adder  17 , and audio signals supplied to this input terminal  7   a  pass through the digital filter  14  and are supplied to the adder  18 .  
           [0012]    Further, digital audio signals supplied to the input terminal  8   a  pass through the digital filter  15  and are supplied to the adder  17 , and digital audio signals supplied to this input terminal  8   a  pass through the digital filter  16  and are supplied to the adder  18 . In this case, the digital filters  13 ,  14 ,  15  and  16  comprise, for example, FIR filters.  
           [0013]    In the drawing of the principle of acoustic image localization shown in FIG. 7, the digital filters  13 ,  14 ,  15  and  16  respectively realize transfer functions HRR, HRL, HLR, and HLL from the speakers SL and SR to both the ears, for the case in which the listener M is facing in a fixed direction (for example, the forward direction, that is, the direction facing the midpoint between the speakers SL and SR).  
           [0014]    The outputs from the digital filter  13  and digital filter  15  are added by the adder  17 , and this addition signal is supplied to the time-difference application circuit  19 ; the outputs from the digital filter  14  and digital filter  16  are added by the adder  18 , and this addition signal is supplied to the time-difference application circuit  20 . The output signals from these time-difference application circuits  19  and  20  pass through the level-difference application circuits  21  and  22 , and are supplied to the D/A converters  11 R and  11 L, respectively.  
           [0015]    Here, changes in the transfer function resulting from movements of the listener&#39;s head are effected through control signals which focus on time differences and level differences in the signals reaching both ears, supplied to the control terminals  19   a  and  20   a  of the time-difference application circuits  19  and  20  respectively and to the control terminals  21   a  and  22   a  of the level-difference application circuits  21  and  22  respectively. In this way signals are simplified; for example, when the listener&#39;s head is facing the forward direction and rotates in the right direction, signals reaching the left ear arrive earlier, compared with the original state, and signals reaching the right ear arrive later, compared with the original state.  
           [0016]    Moreover, the left ear approaches the sound source (the speakers SL and SR), and the right ear recedes from the sound source, so that the level of signals reaching the left ear is high compared with the original state, and the level of signals reaching the right ear is low compared with the original state. Hence by using a microprocessor  5  to control only this change with respect to a reference position, a dynamic transfer function can be simulated.  
           [0017]    The delay time applied by the left-side time-difference application circuit  20  is represented by the characteristic curve Tb, shown as a dash line in the delay time characteristics of FIG. 9; the delay time applied by the right-side time-difference application circuit  19  is represented by the characteristic curve Ta, shown as a long and dash line in the delay time characteristics of FIG. 9.  
           [0018]    The characteristic curves Ta and Tb are curves having completely opposite directions of increase and decrease with respect to the direction of rotation of the head of the listener M. As a result, even when headphones are used, time differences from the sound source to both ears are applied to the headphone reproduction signals similar to the sound differences when listening to sound from a sound source placed within a 180° range in the forward direction while turning the head right and left.  
           [0019]    The level difference applied by the left-side level-difference application circuit  22  is represented by the characteristic curve La, shown as a long and dash line in the relative level characteristics of FIG. 10; the level difference applied by the right-side level-difference application circuit  21  is represented by the characteristic curve Lb, shown as a dash line in the relative level characteristics of FIG. 10. This FIG. 10 shows levels relative to the state in which the head rotation position is 0° (the forward direction).  
           [0020]    The characteristic curves La and Lb are curves having completely opposite directions of increase and decrease with respect to the direction of rotation of the head of the listener M. That is, in the level-difference application circuit  22  the level changes of the characteristic curve La are applied, and in the level-difference application circuit  21  the level changes of the characteristic curve Lb are applied, so that sound volume changes similar to the case of listening to an actual sound source in the forward direction are applied to the headphone reproduction signals as well.  
           [0021]    The above explanation has described a method of localizing an acoustic image before the listener M; by reversing the directions of change of the characteristic selected by the direction of rotation, however, an acoustic image can also be localized behind the listener M. Further, processing can also be performed for an arbitrary number of channels for a plurality of sound sources.  
           [0022]    Hence it is possible to localize high-quality virtual acoustic images both before and behind the listener M.  
           [0023]    However, the rotation angle interface used in the above-described configuration requires that a band-limiting filter  3 , A/D converter  4 , offset-removal filter, and other additional circuits be added externally to the microprocessor  5 ; moreover, it is necessary to send the angle data to the digital signal processing circuit  6  which performs signal processing using the calculated angle data.  
           [0024]    Also, as described above, when an A/D converter is provided separately, and rotation angles are detected, scattering and fluctuations (temperature drift and similar) in DC offsets characteristic to the sensor, amplifier, and A/D converter occur, and consequently problems arise such as the inability to calculate accurate angles and displacements, and the occurrence of overflow in the interface unit due to a DC offset.  
           [0025]    Further, in the above configuration, the circuit scale is large and the mounting area is considerable, and there is the additional problem of high cost. Also, sensor detection and signal processing using detection values are performed by separate devices, specifically, by the microprocessor  5  and the digital signal processing circuit  6 , so that communication processing between them is necessary.  
         SUMMARY OF THE INVENTION  
         [0026]    In light of these problems, one object of this invention is to enable calculation of accurate angles and displacements, while also reducing the circuit scale.  
           [0027]    Hence one object of this invention is to provide an audio signal processing device which performs virtual acoustic image localization processing such that an acoustic image is localized at an arbitrary position in the vicinity of the listener, by reproducing, by means of headphones or a plurality of speakers, output signals resulting from signal processing of input audio signals and comprises digital signal processing means which performs virtual acoustic image localization processing of the input audio signals, an A/D converter which converts into digital signals the analog detection signals from a sensor which detects the state of motion of the listener and control means which performs control so as to change in realtime the transmission characteristics of the digital signal processing means, according to output signals from the A/D converter, and at least part of the A/D converter is comprised within the digital signal processing means.  
           [0028]    By means of this invention, sensor detection signals are acquired by the digital signal processing circuit simultaneously with the input audio signals, so that signal processing of the sensor detection signals and signal processing of these audio signals can be performed within the same device, specifically, within the digital signal processing device, and communication between hardware components is rendered unnecessary.  
           [0029]    The sensor interface can be realized using signal processing software, offsets can be removed by processing within the digital signal processing circuit, there are no errors due to scattering in the characteristics of devices, and there is no need for large capacitors or other external components.  
           [0030]    Another object of this invention is to provide an interface device for a sensor, which supplies analog detection signals from the sensor as digital detection signals and comprises an A/D converter which converts said analog detection signals into digital signals, computation means which converts said A/D converter output signals into detection data in a prescribed unit system and memory which stores detection data computed by the computation means. The detection data stored in the memory can be read by external equipment and at least part of the A/D converter, the computation means and the memory are comprised within digital signal processing means which performs signal processing of and outputs input audio signals.  
           [0031]    By means of this invention, detection signals input as angular velocity data are converted into angle data and can be acquired externally, so that external processing (for example, image processing) can be performed simultaneously with, and in synchronization with, audio processing, and the external equipment can be used to simplify the angular velocity sensor interface device and angle conversion processing.  
           [0032]    Still another object of this invention is to provide an audio signal processing device which, by reproducing, by means of headphones or a plurality of speakers, output signals resulting from signal processing of input audio signals, performs virtual acoustic image localization processing such that an acoustic image is localized at an arbitrary position in the vicinity of the listener, and an image display device which reproduces images before either one eye or both eyes of the listener. The audio signal processing device comprises digital signal processing means which performs virtual acoustic image localization processing of the input audio signals, an A/D converter which converts into digital signals the analog detection signals from a sensor which detects the state of motion of the listener, and control means which performs control so as to change and output in realtime the transmission characteristics of the digital signal processing means, according to output signals from the A/D converter, and which performs control so as to update the display content or display position in the image display device and at least part of the A/D converter is comprised within the digital signal processing means.  
           [0033]    By means of this invention, when the display content in an image display device provided before one eye or both eyes of the listener is changed according to movements of the listener, the interface for this can be provided by interface processing for the sensor mounted on the audio signal processing device, and images and audio can be changed simultaneously using a simple configuration.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0034]    [0034]FIG. 1 is a block diagram showing an example of an embodiment of the audio signal processing device of this invention;  
         [0035]    [0035]FIG. 2 is a functional block diagram showing an example of the digital signal processing circuit of the example of FIG. 1;  
         [0036]    [0036]FIG. 3 is a schematic diagram showing an example of an embodiment of the signal processing device of this invention;  
         [0037]    [0037]FIG. 4 is a functional block diagram showing an example of the digital signal processing circuit of the example of FIG. 3;  
         [0038]    [0038]FIG. 5 is a functional block diagram showing another example of the digital signal processing circuit;  
         [0039]    [0039]FIG. 6 is a schematic diagram showing an example of a conventional audio signal processing device;  
         [0040]    [0040]FIG. 7 is a schematic diagram used to explain the principle of acoustic image localization;  
         [0041]    [0041]FIG. 8 is a functional block diagram showing an example of a conventional digital signal processing circuit;  
         [0042]    [0042]FIG. 9 is a diagram used in the explanation of this invention; and  
         [0043]    [0043]FIG. 10 is a diagram used in the explanation of this invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0044]    Below, examples of embodiments of the audio signal processing device, angular velocity sensor interface device, and signal processing device of this invention are explained, referring to FIG. 1 and FIG. 2. In FIG. 1 and FIG. 2, parts which correspond to parts in FIG. 6 and FIG. 8 are assigned the same symbols.  
         [0045]    The example of FIG. 1 is an audio signal processing device which, in listening to audio signals using headphones, localizes the reproduced audio image in the same position as the audio image localization position when two speakers, placed in front of the listener, are broadcasting.  
         [0046]    In the example of FIG. 1, when the headphones  2 , having left and right speakers  2 L and  2 R and on which is mounted an angular velocity sensor  1  which detects rotation angular velocity, undergo rotating motion, for example due to rotation of the head of the listener, this angular velocity sensor  1  outputs an analog detection signal with voltage proportional to the angular velocity.  
         [0047]    As this angular velocity sensor  1 , for example, a well-known piezoelectric vibratory gyroscope may be used. This piezoelectric vibratory gyroscope can detect rotation angular velocity reliably with a simple configuration; and this piezoelectric vibratory gyroscope can be made small and lightweight, and can be designed to further reduce power consumption.  
         [0048]    Detection signals from the angular velocity sensor are passed through a band-limiting filter  3  to remove unnecessary high-frequency components, and through a part  30   a  of a one-bit A/D converter  30  constituting an interface, and are supplied to the digital signal processing circuit  31 .  
         [0049]    On the other hand, audio signals from a sound source as supplied to audio signal input terminals  7  and  8  of, for example,  2  channels are supplied respectively to this digital signal processing circuit  31  via A/D converters  9  and  10  that convert analog signals into digital signals.  
         [0050]    In this digital signal processing circuit  31 , necessary audio signals corresponding to angle data, as described below, are subjected to signal processing in order to localize an acoustic image outside the head, and the resulting right and left audio signals are supplied to D/A converters  11 R and  11 L which convert digital signals into analog signals.  
         [0051]    The right and left audio signals converted into analog signals by these D/A converters  11 R and  11 L pass through power amplifiers  12 R and  12 L respectively, and are supplied to the right and left speakers  2 R and  2 L of the headphones  2 , so as to apply audio signals which localize an out-of-head virtual acoustic image optimally for the listener who is listening.  
         [0052]    In this example, the digital signal processing circuit  31  is configured as shown by the functional block diagram of FIG. 2. In FIG. 2, 7 a  and  8   a  are the input terminals to which are supplied digitized audio signals from the audio signal input terminals  7  and  8 , respectively.  
         [0053]    Similarly to FIG. 9, the digital audio signals supplied to this input terminal  7   a  pass through a digital filter  13  consisting of, for example, an FIR filter, and are supplied to the adder  17 , and in addition, the digital audio signals supplied to this input terminal  7   a  pass through a digital filter  14  consisting of, for example, an FIR filter, and are supplied to the adder  18 .  
         [0054]    Also, the digital audio signals supplied to this input terminal  8   a  pass through a digital filter  15  consisting of, for example, an FIR filter, and are supplied to the adder  17 , and in addition, the digital audio signals supplied to this input terminal  8   a  pass through a digital filter  16  consisting of, for example, an FIR filter, and are supplied to the adder  18 .  
         [0055]    The digital filters  13 ,  14 ,  15  and  16  respectively realize transfer functions HRR, HRL, HLR, and HLL from the speakers SL and SR in the drawing of the principle of acoustic image localization shown in FIG. 7 to both the ears, for the case in which the listener M is facing in a fixed direction (for example, the forward direction). Through convolution of the audio signals supplied to the input terminals  7   a ,  8   a  and their transfer functions, and reproduction at the ears of the listener, an acoustic image can be localized at the positions of the speakers SL and SR.  
         [0056]    The outputs from the digital filter  13  and digital filter  15  are added by the adder  17 , and this addition signal is supplied to the time-difference application circuit  19 ; the outputs from the digital filter  14  and digital filter  16  are added by the adder  18 , and this addition signal is supplied to the time-difference application circuit  20 . The output signals from these time-difference application circuits  19  and  20  pass through the level-difference application circuits  21  and  22 , and are supplied to the D/A converters  11 R and  11 L, respectively.  
         [0057]    In this example, analog detection signals from the angular velocity sensor  1  are passed through a band-limiting filter  3  to remove unnecessary high-frequency components, and are supplied to an adder  30 b consisting of a one-bit ΔΣ-type A/D converter, which is the one-bit A/D converter  30 . This one-bit ΔΣ-type A/D converter  30  passes output signals from the adder  30   b  through an integrator  30   c  and supplies the signals to a quantizer  30   d  configured within the digital signal processing circuit  31 ; output signals from this quantizer  30   d  pass through the one-sample delay element  30   e  and are supplied to the adder  30   b.    
         [0058]    In this case, detection signals from the angular velocity sensor  1  are acquired by the same one-bit A/D converter  30  within the digital signal processing circuit  31  used for audio signal processing, so that data can be input from the one-bit port of the digital signal processing circuit  31 , and a high-precision angular velocity sensor interface with simple configuration can be realized.  
         [0059]    A low-pass filter  32  is used to limit the frequency band of the output signals from this one-bit A/D converter  30 , and the signals are supplied to a decimation filter  33  which converts the sampling rate. In this decimation filter  33 , the sampling frequency is downsampled from, for example, 48 kHz to 1 kHz.  
         [0060]    Output signals from this decimation filter  33  are passed through a high-pass filter  34  to remove the ultra-low frequency component, that is, the offset and the drift, and are supplied to the integrator  35 ; using this integrator  35 , angle data is obtained. The angle data obtained from this integrator  35  is supplied to the control signal formation circuit  36 , consisting of an angle calculator and memory.  
         [0061]    This control signal formation circuit  36  forms control signals to supply time differences and level differences in the signals reaching both ears, to simulate changes in transfer functions due to movement of the listener&#39;s head.  
         [0062]    Control signals formed by this control signal formation circuit  36  are supplied to the time-difference application circuits  19  and  20 , and to the level-difference application circuits  21  and  22 . For example, when the listener&#39;s head rotates to the right, signals arriving at the left ear arrive earlier than in the original state, and signals arriving at the right ear arrive later than in the original state.  
         [0063]    Because the left ear approaches the sound source (the speakers SL and SR), and the right ear recedes from the sound source, the level of signals reaching the left ear is higher than in the original state, and the level of signals reaching the right ear is lower than in the original state. Hence by controlling only the change due to motion with respect to a reference position using these control signals, a dynamic transfer function can be simulated.  
         [0064]    The delay time applied by the left-side time difference application circuit  20  is represented by the characteristic curve Tb, shown as a dash line in the delay time characteristics of FIG. 9; the delay time applied by the right-side time difference application circuit  19  is represented by the characteristic curve Ta, shown as a long and dash line in the delay time characteristics of FIG. 9.  
         [0065]    The characteristic curves Ta and Tb are curves having completely opposite directions of increase and decrease with respect to the direction of rotation of the head of the listener M. As a result, even when headphones are used, time differences from the sound source to both ears are applied to the headphone reproduction signals similar to the sound differences when listening to sound from a sound source placed within a 180° range in the forward direction while turning the head right and left.  
         [0066]    The level difference applied by the left-side level-difference application circuit  22  is represented by the characteristic curve La, shown as a long and dash line in the relative level characteristics of FIG. 10; the level difference applied by the right-side level-difference application circuit  21  is represented by the characteristic curve Lb, shown as a dash line in the relative level characteristics of FIG. 10. This FIG. 10 shows levels relative to the state in which the head rotation position is 0° (the forward direction).  
         [0067]    The characteristic curves La and Lb are curves having completely opposite directions of increase and decrease with respect to the direction of rotation of the head of the listener M. That is, in the level-difference application circuit  22  the level changes of the characteristic curve La are applied, and in the level-difference application circuit  21  the level changes of the characteristic curve Lb are applied, so that sound volume changes similar to the case of listening to an actual sound source in the forward direction are applied to the headphone reproduction signals as well.  
         [0068]    The above explanation has described a method of localizing an acoustic image in front of the listener M; by reversing the directions of change of the characteristic selected by the direction of rotation, however, an acoustic image can also be localized behind the listener M. Further, processing can also be performed for an arbitrary number of channels for a plurality of sound sources.  
         [0069]    By means of this invention, detection signals from the angular velocity sensor  1  are acquired by the digital signal processing circuit  31  simultaneously with the input audio signals, so that signal processing of the detection signals of the angular velocity sensor  1  and signal processing of these audio signals can be performed within the same device, specifically, within the digital signal processing device  31 , and communication between hardware components is rendered unnecessary. DC offsets and temperature drift occurring due to the angular velocity sensor can be eliminated within the same device, that is, the digital signal processing circuit  31 , and accurate rotation angle calculations are possible.  
         [0070]    In this example, part of the one-bit A/D converter  30  constituting the angular velocity sensor interface is incorporated within the digital signal processing circuit  31 , so that detection signals from the angular velocity sensor  1  can be input from the one-bit input port of the digital signal processing circuit, and a high-precision angular velocity sensor interface can be realized which is inexpensive and has a simple configuration.  
         [0071]    In the above-described example, detection signals from the angular velocity sensor  1  are acquired by a one-bit ΔΣ-type A/D converter, so that input can be performed from the one-bit input port of the digital signal processing circuit  31 , ΔΣ conversion processing can be used to greatly improve the effective conversion precision, and an extremely precise angular velocity sensor interface can be realized. In the above-described example, a first order noise-shaping circuit is configured; of course this may be a secondary or higher-order noise-shaping circuit, and in addition to the configuration of the example described above in which there is negative feedback of the output of the quantizer  30   d  from the one-bit output port, a configuration may be employed in which there is negative feedback of the quantization error of the quantizer  30   d , that is, of the difference signal between the input signal and the output signal of the quantizer  30   d.    
         [0072]    [0072]FIG. 3 and FIG. 4 show another example of an embodiment of this invention. In FIG. 3 and FIG. 4, parts which correspond to parts in FIG. 1 and FIG. 2 are assigned the same symbols, and a detailed explanation is omitted.  
         [0073]    In the example of FIG. 3, an image display device  40 , for example a head-mounted display, is mounted for both the eyes (or one eye) of the listener, and image signals from the image signal input terminal  41  are supplied to the image signal processing circuit  42 ; image signals subjected to signal processing by this image signal processing circuit  42  are then supplied to this image display device  40 .  
         [0074]    In the digital signal processing circuit  31  of this example, as shown in FIG. 4 the control signal formation circuit  36  is provided with an external output terminal  36   a , and digital angle data obtained in this control signal formation circuit  36  is supplied to the image signal processing circuit  42 . At this time, angle data obtained by conversion from angular velocity data is output.  
         [0075]    In this case, angle data is supplied to the image signal processing circuit  42  either at the request of the image signal processing circuit  42 , which is external equipment, or with a fixed period. In the former case, angle data may be requested, for example, from the control signal formation circuit  36  with timing synchronized with the image synchronization signal.  
         [0076]    This image signal processing circuit  42  updates the display content or display position in the image display device  40 , according to this angle data. The examples of FIG. 3 and FIG. 4 are configured similarly to the examples of FIG. 1 and FIG. 2.  
         [0077]    In the examples of FIG. 3 and FIG. 4, when the display content of the image display device  40  mounted on both eyes (or only one eye) of the listener is changed according to movements of the listener, the interface for this can be realized simply by performing interface processing for the angular velocity sensor  1  mounted on the audio signal processing device, so that images and audio signals can be changed simultaneously using a simple configuration.  
         [0078]    In the above-described example, a one-bit ΔΣ-type A/D converter is used as the one-bit A/D converter  30 ; in place of this, a quantizer  30   d  alone may be provided within the digital signal processing circuit  31  as the one-bit A/D converter as shown in FIG. 5, and the device configured from this. In this case, the entirety of the one-bit A/D converter  30  is formed within the digital signal processing circuit  31 , and detection signals of the angular velocity sensor  1  are directly input to the quantizer  30   d.    
         [0079]    In the configuration of FIG. 5, the dynamic range, noise level, and other characteristics of the sensor interface unit are somewhat unfavorable compared with the case in which the above-described one-bit ΔΣ-type A/D converter is used; but the sensor output can be input directly to the digital signal processing circuit  31  via a band-limiting filter, so that still greater compactness is possible.  
         [0080]    In the above-described example, the digital signal processing circuit  31  is explained in a hardware configuration; of course this may also be accomplished using a DSP (digital signal processor), microprocessor or similar device, equipped with a processing program to perform audio signal and sensor signal processing.  
         [0081]    The above-described example is explained as a signal processing device which can be applied to out-of-head acoustic image localization headphones; of course the technology of this invention can also be applied to a signal processing device which provides audio signals which are, for example, reproduced by a plurality of speaker devices placed in front of the listener, to localize an acoustic image in places other than the speaker positions, for example, behind or to one side of the listener. In this case, the entirety of the one-bit A/D converter  30  is formed within the digital signal processing circuit  31 .  
         [0082]    In the above-described example, an angular velocity sensor was used as the sensor; but a geomagnetic direction sensor may be used instead. When such a geomagnetic direction sensor is used, rotation angles can be detected reliably using a simple configuration, and moreover absolute directions are detected, so that there is the advantage that no cumulative errors occur during integration processing of the angular velocity sensor signals in the above example.  
         [0083]    Further, an inclination sensor may be used as this sensor. When using an inclination sensor, a simple configuration can be used to, for example, reliably detect the angle of inclination of th e listener&#39;s head.  
         [0084]    Further, a velocity sensor or acceleration sensor may be used as the sensor, displacement data calculated from A/D-converted velocity or acceleration data, and this calculated displacement data may be used. This displacement data may be output to external equipment as digital signals. When such a velocity sensor or acceleration sensor is used, changes in the listening position of the listener, for example when the listener moves forward or toward the right, can be detected.  
         [0085]    In this case, external equipment processing (for example, image processing) can be performed simultaneously with, and in synchronization with, audio processing, and the sensor interface in the external equipment and velocity-displacement conversion processing can be simplified.  
         [0086]    Further, a plurality of sensors may be provided, and processing of the detection signals of this plurality of sensors may be performed by the same digital signal processing circuit  31 .  
         [0087]    In this case, the detection signals of the plurality of sensors can be acquired by and processed within a single digital signal processing circuit  31 , so that a single device can be used for detection of movements with more degrees of freedom.  
         [0088]    This invention is not limited to the above examples, and of course various configurations can be adopted without deviating from the essence of this invention.  
         [0089]    By means of this invention, the detection signals from a sensor can be acquired by a digital signal processing circuit simultaneously with input audio signals, so that signal processing of the sensor detection signals and signal processing of the audio signals can be realized within the same device, specifically, within a digital signal processing circuit; communication between hardware becomes unnecessary; the circuit scale can be reduced, and processing can be simultaneously performed to eliminate offsets; and accurate calculation of motions can be performed.  
         [0090]    Further, the sensor interface can be realized by means of signal processing software, offsets can be eliminated through processing within the digital signal processing circuit, and there are no errors due to scattering in device characteristics.  
         [0091]    By means of this invention, detection signals input as angular velocity data can be converted into angle data and output externally, so that external processing (for example, image processing) can be performed simultaneously with, and in synchronization with, audio processing, and the angular velocity sensor interface device and angle conversion processing in the external equipment can be simplified.  
         [0092]    By means of this invention, when the display content in an image display device provided before one or both of the listener&#39;s eyes is changed according to movements of the listener, the interface for this can be provided through interface processing for a sensor mounted on the audio signal processing device, so that image and audio signals can be changed simultaneously using a simple configuration.  
         [0093]    Having described preferred embodiments of the present invention with reference to the accompanying drawings, it is to be understood that the present invention is not limited to the above-mentioned embodiments and that various changes and modifications can be effected therein by one skilled in the art without departing from the spirit or scope of the present invention as defined in the appended claims.