JP6609407B2 - Audio signal reproducing apparatus and audio signal processing method - Google Patents

Description

  The present invention relates to an audio signal reproducing apparatus and an audio signal processing method for reproducing and outputting music media, and more particularly to an audio signal reproducing apparatus and an audio signal processing method suitable for realizing a sound field in a passenger compartment.

  To comfortably listen to left and right channel source audio even in the passenger compartment, the sound image must be localized in front of the listener. This is because it is easier to obtain a stereo feeling if the localization information of the audio recorded in the left and right channels is accurately reproduced.

  However, general in-vehicle audio is mainly a 4ch audio system. Therefore, in the prior art disclosed in Patent Document 1, a time alignment function is implemented in an embedded computer such as a DSP, and sound image localization is realized by a preceding sound effect.

  Generally, the preceding sound effect is established by delaying the subsequent sound of the rear speaker by about 1.0 msec or more than the preceding sound of the front speaker. Moreover, the sound quality is cleared by an equalizer and a shelving filter.

Japanese Patent No. 4264686

  The above prior art uses the preceding sound effect to achieve sound image localization, but when the preceding sound effect is used at one listening position of the driver seat or the passenger seat in the passenger compartment, the sound quality is deteriorated. In particular, in the low frequency band, the audio signal output from the front, rear, left, and right speakers causes a dip in the frequency characteristics due to phase interference when the audio signal reaches the listening position, and the amount of information of bass is greatly lost. there were.

  FIG. 2 is a diagram in which the frequency characteristics at the listening position in the driver seat or the passenger seat are obtained by simulation in order to clarify the influence of the dip due to the phase interference. When the arrival time of the left and right rear speakers is delayed by 15 msec relative to the arrival time of the left and right front speakers, a dip occurs in the bands around 33 Hz, 100 Hz, 167 Hz, 233 Hz, and 300 Hz. It was a cause of sound quality degradation.

  In addition, when listening to the driver's seat or passenger's seat in the passenger compartment, the 4ch audio system using the preceding sound effect has a problem that the clarity of the sound image is inferior compared to the left / right home audio system in a normal environment. This is because in the 4ch audio system using the preceding sound effect, the output sound of the rear speaker arrives at the listener with a delay, resulting in an echo effect and a reduction in the clarity of the sound image.

  Furthermore, in the passenger compartment, there is a deterioration in frequency characteristics due to sound absorption by interiors such as seats and reflected sound of glass, which leads to deterioration of sound quality.

  The present invention aims to solve the above problems and improve the audio environment in the passenger compartment.

In order to achieve the above object, an audio signal reproduction apparatus according to a first aspect of the present invention includes a first delay unit that delays an input left channel audio signal and outputs the delayed left channel audio signal to a front left channel speaker, and an input right channel. A second delay device that delays an audio signal and outputs the delayed left audio signal to the front right channel speaker; a third delay device that delays the input left channel audio signal; and a fourth delay device that delays the input right channel audio signal. A localization control unit including the delay unit, and a frequency characteristic and a phase of the rear left channel audio signal delayed by the third delay unit to output to the rear left channel speaker, and the fourth delay unit in an audio signal reproducing apparatus having a sound field control unit, to be output to the rear right ch speaker by controlling the frequency characteristic and the phase of the delayed rear right c h o Dio signal, the localization control unit, The delay amount of each of the first to fourth delay units is determined from the front left channel speaker, the front right channel speaker, the rear left channel speaker, and the rear right channel speaker from the driver seat in the vehicle or Based on the difference in the arrival time of the sound to the passenger seat listening position, the sound image is adjusted to be localized at the listening position, and the sound field control unit attenuates a high frequency band of the left ch audio signal. A first series circuit including a filter and a fifth delay device that delays the left channel audio signal by 0.625 msec; a second filter that attenuates a high frequency band of the right channel audio signal; and the right channel audio And a second series circuit including a sixth delay device that delays the signal by 0.625 msec, and controls the spread of the sound field .

  According to a second aspect of the present invention, in the audio signal reproduction device according to the first aspect, the first and second filters are a high shelf filter having a cutoff frequency of 200 Hz to 500 Hz and an amplification amount of 0 to -12 dB, Alternatively, it is characterized in that it is composed of a plurality of equalizers having a center frequency of 200 Hz to 20 kHz and an amplification amount of 0 to -12 dB.

  According to a third aspect of the present invention, in the audio signal reproduction device according to the first or second aspect, the first series circuit is further provided with a front left channel audio reproduction signal and a rear left channel audio reproduction signal at the listening position. A first FIR filter circuit for improving disturbance of frequency characteristics due to the occurrence of a phase difference is connected in series, and the front right channel audio reproduction signal and the rear right channel audio are further connected to the second series circuit at the listening position. A second FIR filter circuit for improving disturbance of frequency characteristics due to a phase difference in the reproduction signal is connected in series.

  According to a fourth aspect of the present invention, there is provided the audio signal reproducing apparatus according to the third aspect, wherein a third amount of information is improved on the output side of the first delay unit to improve information loss due to the first FIR filter. An FIR filter is connected, and a fourth FIR filter for improving a loss of information amount due to the second FIR filter is connected to an output side of the second delay device.

  According to a fifth aspect of the present invention, in the audio signal reproduction device according to the first, second, third, or fourth aspect, a third filter for frequency characteristic compensation is connected to a preceding stage of the first delay unit, and the first A fourth filter for frequency characteristic compensation is connected to the front stage of the second delay device, a fifth filter for frequency characteristic compensation is connected to the front stage of the third delay device, and a front stage of the fourth delay device. A sixth filter for frequency characteristic compensation is connected to the front left channel speaker, the front right channel speaker, the rear left channel speaker, and the rear left channel speaker by the third to sixth filters. The sound reproduced in (2) has the same frequency characteristics at the listening position.

  According to a sixth aspect of the present invention, in the audio signal reproduction device according to the fifth aspect, the third to sixth filters include the front left ch speaker, the front right ch speaker, the rear left ch speaker, And an FIR filter alone or an FIR filter and a plurality of IIR filters that perform filter calculation processing using a filter coefficient obtained from an inverse transfer function obtained from a measurement result of the impulse response of the rear right ch speaker at the listening position. It is characterized by comprising.

In the audio signal processing method according to the seventh aspect of the present invention, a first delay is applied to the input left channel audio signal and output to the front left channel speaker, and a second delay is applied to the input right channel audio signal. A third delay is applied to the left channel audio signal that is output to the front right channel speaker, and the frequency characteristic and phase are controlled and output to the rear left channel speaker, and the fourth channel is added to the input right channel audio signal. And an audio signal processing method for controlling the frequency characteristic and phase and outputting to the rear right channel speaker, wherein the delay amounts of the first to fourth delays are the front left channel speaker, the front channel part right ch speaker, based on the difference of the rear left ch speaker, and the arrival time of the rear left ch sound from each speaker to the listening position in the vehicle of the driver's seat or the passenger seat, sound There was adjusted to localized at the listening position, the frequency characteristic and phase, have rows by delay processing of the attenuation process and 0.625msec high frequency band of the audio signal to control the spread of the sound field, and characterized in that To do.

  According to an eighth aspect of the present invention, in the audio signal processing method according to the seventh aspect, the high-frequency band attenuation processing of the rear left ch audio signal and the rear right ch audio has a cutoff frequency of 200 Hz to 500 Hz, respectively. A high shelf filter with an amplification amount of 0 to -12 dB or a plurality of equalizers with a center frequency of 200 Hz to 20 kHz and an amplification amount of 0 to -12 dB is characterized.

  According to a ninth aspect of the present invention, in the audio signal processing method according to the seventh or eighth aspect, in addition to the control of the third delay and frequency characteristics and phase, the listening is performed on the rear left channel audio signal. A filtering process using a first FIR filter is performed to improve frequency characteristic disturbance caused by a phase difference between the front left ch audio playback signal and the rear left audio play signal at the position, and the rear right ch audio signal is applied to the rear right ch audio signal. In addition to the control of the fourth delay and frequency characteristics and phase, in order to improve the disturbance of the frequency characteristics caused by the phase difference between the front right channel audio reproduction signal and the rear right audio reproduction signal at the listening position. A filtering process using a second FIR filter is applied to the above.

  According to a tenth aspect of the present invention, in the audio signal processing method according to the ninth aspect, in addition to the application of the first delay to the front left ch audio signal, the rear left ch audio signal In order to improve the loss of information amount due to the filtering of the first FIR filter, a filtering process by a third FIR filter is performed, and the front right ch audio signal is subjected to the second delay, A filtering process using a fourth FIR filter is performed to improve a loss of information amount due to the filtering of the second FIR filter for the rear right channel audio signal.

  According to an eleventh aspect of the present invention, in the audio signal processing method according to the seventh, eighth, ninth, or tenth aspect, a frequency characteristic is compensated by a third filter for the front left ch audio signal, and the front portion Frequency characteristics are compensated for the right channel audio signal by a fourth filter, frequency characteristics are compensated for the rear left channel audio signal by a fifth filter, and a sixth filter is configured for the rear left channel audio signal. The frequency characteristics are compensated for by the third to sixth filters, and the sound reproduced by the front left ch speaker, the front right ch speaker, the rear left ch speaker, and the rear left ch speaker is reproduced by the third to sixth filters. The frequency characteristics are the same at the listening position.

  According to a twelfth aspect of the present invention, in the audio signal processing method according to the eleventh aspect, the third to sixth filters include the front left channel speaker, the front right channel speaker, and the rear left channel speaker. FIR filter alone or FIR filter and a plurality of IIR filters that perform filter operation using a filter coefficient obtained from an inverse transfer function obtained from a measurement result of the impulse response of the rear right ch speaker at the listening position The combination is used.

  According to the present invention, the localization control unit controls the sound image position, and the sound field control unit controls the amplitude characteristic and phase characteristic of the audio signal reproduced by the left and right ch speakers at the rear. The frequency response of the low frequency at the listening position of the driver's seat or passenger's seat in the passenger compartment can be improved, the echo effect due to the preceding sound effect can be improved, and the size of the passenger compartment is matched while maintaining a clear sound image Natural sound field spread can be perceived, and the sound field spread can be controlled.

1 is a functional block diagram of an audio signal reproduction device according to a first embodiment of the present invention. It is a frequency characteristic figure of the conventional audio signal reproducing | regenerating apparatus. It is a frequency characteristic figure of the audio signal reproducing | regenerating apparatus of 1st Example. It is a functional block diagram of the audio signal reproducing device of the second embodiment. It is a frequency characteristic figure of the audio signal reproducing | regenerating apparatus of a 2nd Example. It is a frequency characteristic figure of the audio signal reproducing | regenerating apparatus of a 2nd Example. It is a functional block diagram of the audio signal reproducing device of the third embodiment. It is a frequency characteristic figure of the audio signal reproducing | regenerating apparatus of 3rd Example. It is a functional block diagram of the audio signal reproducing device of the fourth embodiment.

  Hereinafter, in order to explain the present invention in more detail, the present invention will be described by way of examples with reference to the accompanying drawings. Further, FIGS. 2, 3, 5, 6, and 8 attached are frequency characteristic diagrams obtained by simulation in order to clarify the influence of dip caused by phase interference. Note that “FL” added to the rear part of the reference sign shown below represents the front left ch, “FR” represents the front right ch, “RL” represents the rear left ch, and “RR” represents the rear right ch.

<First embodiment>
FIG. 1 is a block diagram showing the configuration of an audio signal reproducing apparatus according to the first embodiment of the present invention. In FIG. 1, reference numeral 10 denotes an input unit for inputting a digital left and right channel audio signal, and includes a left channel input terminal 11L and a right channel input terminal 11R. Reference numeral 20 denotes a localization control unit, which includes delay units 21FL (a delay amount is D1), 21FR (a delay amount is D2), 21RL (a delay amount is D3), and 21RR (a delay amount is D4). A sound field control unit 30 includes filters 31RL and 31RR and delay units 32RL and 32RR (the delay amount is D5). Reference numeral 40 denotes an amplifying unit, which includes amplifiers 41FL, 41FR, 41RL, and 41RR that are power amplifiers having a D / A conversion function. Reference numeral 50 denotes a speaker unit, which includes speakers 51FL, 51FR, 51RL, and 51RR. As described above, the audio signal reproduction device of FIG. 1 inputs the left and right 2ch audio signals and outputs the left and right front and rear 4ch audio reproduction signals.

  Next, the operation of the first embodiment will be described. In FIG. 1, the left channel audio signal input from the input terminal 11L is input to the delay unit 21FL and the delay unit 21RL of the localization control unit 20, and delay amounts D1 and D3 are added thereto, respectively. The right channel audio signal input from the input terminal 11R is input to the delay unit 21RL and the delay unit 21RR of the localization control unit 20, and the delay amounts D2 and D4 are added thereto, respectively.

  The output signal of the delay unit 21FL of the localization control unit 20 is amplified by the amplifier 41FL and input to the speaker 51FL, and the output signal of the delay unit 21FR is amplified by the amplifier 41FR and input to the speaker 51FR.

  The output signal of the delay unit 21RL of the localization control unit 20 is attenuated at a high frequency by the filter 31RL of the sound field control unit 30, added with the delay amount D5 by the delay unit 32RL, amplified by the amplifier 41RL, and input to the speaker 51RL. To do. The output signal of the delay device 21RR is attenuated by the filter 31RR of the sound field control unit 30 and the delay amount D5 is added by the delay device 32RR, and then amplified by the amplifier 41RR and input to the speaker 51RR.

  In the localization control unit 20, the impulse response of each speaker 51FL, 51FR, 51RL, 51RR is observed at the listening position (driver's seat or passenger seat in the passenger compartment), and the listening position and the speakers 51FL, 51FR, 51RL, 51RR are observed. A delay amount is obtained from the transfer function between the two, and a difference in the arrival time of the sound caused by the distance difference is adjusted, so that the amplitude characteristic and the phase characteristic at the listening position are improved, the delay unit 21FL, the delay unit 21FR, the delay unit 21RL and delay amounts D1-D4 of delay device 21RR are adjusted.

  The filters 31RL and 31RR of the sound field control unit 30 are composed of variable high-frequency attenuation filters. For example, when using an IIR type first or second order high shelf filter, a filter having a cutoff frequency of 200 Hz to 500 Hz and an amplification amount of +0 to −12 dB is used. Alternatively, when the filters 31RL and 31RR are realized by a plurality of equalizers, the parameters at that time are a center frequency of 200 Hz to 20 kHz and an amplification amount of +0 to -12 dB.

  The delay amount D5 of the delay devices 32RL and 32RR of the sound field control unit 30 is adjusted to be in the range of 0.5 msec to 1.0 msec. This is to prevent deterioration of the sound quality especially at 300 Hz or less when the audio reproduction signals from the speaker speakers 51FL, 51FR, 51RL, 51RR reach the listening position. By setting the delay amount D5 within the range of 0.5 msec to 1.0 msec, a comb filter effect (comb frequency characteristics) is generated in the high frequency band at the listening position, and the spread of the sound field can be perceived. The spread of the sound field can be adjusted by the cutoff frequency and the amplification amount of the filters 31RL and 31RR.

  For example, when the delay amount D5 is set to 0.625 msec, as shown in FIG. 3, it can be confirmed that the low frequency characteristics are improved compared to the frequency characteristics shown in FIG. 3, in the sound field control unit 30, the delay amount of the front left and right ch audio signal (impulse signal) is set to 0 msec, and the delay amount D5 of the rear left and right ch audio signal (impulse signal) is set to 0.625 msec. It is a frequency characteristic figure in the above-mentioned listening position of the reproduction audio signal which added 4ch of front and rear, right and left.

  According to the first embodiment, the localization control unit 20 controls the sound image position, and the sound field control unit 30 changes the amplitude characteristics and phase characteristics of the rear left and right speakers 51RL and 51RR, thereby driving in the vehicle interior. The frequency response of the low frequency range at the listening position of the seat or passenger seat can be improved, the echo effect due to the preceding sound effect can be improved, and the natural sound field spreads according to the size of the passenger compartment while maintaining a clear sound image And the spread of the sound field can be controlled.

  Incidentally, when the filters 31RL and 31RR of the sound field control unit 30 are high shelf filters or equalizers, the sound field is most widened when the amplification amount in the sound field control unit 30 is set to 0 dB, and the sound field is widened when set to -12 dB. The sound field with clear sound image localization like left and right channel home audio can be realized.

<Second embodiment>
According to the localization control unit 20 and the sound field control unit 30 of the first embodiment described above, the sound image can be localized in front of the listener, but the listener is seated in both the driver seat and the passenger seat. In such a case, only one of the listeners can move the sound image forward.

  Therefore, in the second embodiment, a method of determining the delay amount of the localization control unit 20 when the listening position is set in both the driver seat and the passenger seat will be described.

  In order to have both the driver's seat (right side) and passenger's seat (left side) where the listener is seated, the impulse response of the speakers 51FL and 51RL of the left and right front channels is observed in the front passenger seat and the left and right front and rear The transfer function between the speakers 51FL and 51RL of the ch and the passenger seat is obtained, the delay amount is obtained from the transfer function, and the sound image is obtained based on the difference in the arrival time of the sound caused by the difference in distance between the speakers 51FL and 51RL and the passenger seat. The delay amounts D1 and D3 of the delay devices 21FL and 21RL are adjusted so as to localize the seat.

  Further, the impulse response of the speakers 51FR and 51RR of the right and left front channels is observed in the driver's seat, the transfer function between the speakers 51FR and 51RR of the right and left and right channels and the driver's seat is obtained, and the delay amount is obtained from the transfer function. The delay amounts D2 and D4 of the delay units 21FR and 21RR are adjusted so as to localize the sound image to the driver seat based on the difference in the arrival time of the sound caused by the distance difference between 51FR and 51RR and the driver seat.

  According to the second embodiment, the determination method of the delay amounts D1 to D4 of the localization control unit 20 is made to correspond to the listening positions of the driver seat and the passenger seat, and the sound field control unit 30 uses the amplitudes of the left and right speakers 51RL and 51RR at the rear. By changing the characteristics, it is possible to minimize the deterioration of sound quality while the sound image is localized in front of listeners at both seats.

<Third embodiment>
According to the localization control unit 20 and the sound field control unit 30 of the first and second embodiments described above, when the listener is seated in either the driver seat or the passenger seat, the listener When sitting in both the driver's seat and the passenger seat, sound image localization and sound quality degradation can be minimized.

  However, the delay units 32RL and 32RR of the sound field control unit 30 cause a phase difference between the audio reproduction signal of the front left and right channels and the audio reproduction signal of the rear left and right channels, and the audio reproduction signal of the front left and right channels and the audio of the rear left and right channels. At the frequency at which the phase of the reproduction signal is opposite, a large dip occurs as shown in FIG. 3 and the amount of information is reduced.

  Therefore, in the third embodiment, as shown in the block diagram of FIG. 4, the sound field control unit 30 further includes a rear FIR filter circuit 33R including rear left and right ch FIR filters 33RL and 33RR, and a front left and right circuit. The delay devices 34F and 34FR for the channel are inserted.

  The rear FIR filter circuit 33R corrects a dip generated in the frequency characteristic of a signal obtained by synthesizing the front left and right ch audio output signals and the rear left and right ch audio output signals at the listening position due to the delay of the delay units 32RL and 32RR. To do.

  The filter coefficients (Rh [m]) of the rear FIR filters 33RL and 33RR are obtained from a signal obtained by adding an impulse signal obtained by delaying the delay time (D5) of the delay devices 32RL and 32RR to an impulse signal having a delay of 0 msec.

  As an example, the frequency characteristics of FIG. 3 are given to the filter coefficients (Rh [m]) of the rear FIR filters 33RL and 33RR, and the rear left and right channel audio signals (impulse signals) are convoluted with the filter coefficients (Rh [m]). A frequency characteristic diagram of a signal obtained by adding the rear left and right ch audio reproduction signal obtained by extending by .625 msec and the front left and right ch audio reproduction signal (impulse signal) in which the delays of the delay units 34FL and 34FR are set to 0 msec is shown in FIG. As shown in FIG.

  In FIG. 5, there is no large dip as in FIG. 3, but phase interference occurs in the combined signal of the front left / right ch audio output signal and the rear left / right ch audio playback signal, and a dip of about 12 dB remains.

として、｜Ｒｈ［ｅ^{−ｊ２πｍ／Ｎ}］｜の振幅特性と直線位相特性から求める。 Therefore, by providing a limit value for the amplitude level of the filter coefficients (Rh [m]) of the rear FIR filters 33RL and 33RR, the dip is reduced as shown in the frequency characteristic of FIG. When the limit value of the amplitude level is set, the filter coefficients (Rh [m]) of the rear FIR filters 33RL and 33RR are as follows:

^{Is obtained} from the amplitude characteristic and the linear phase characteristic of | Rh [e ^{−j2πm / N} ] |.

  Here, D5 is the delay amount of the delay units 32RL and 32RR, N is the number of taps of the filter coefficient (Rh [m]) of the FIR filters 33RL and 33RR, and dBthreshold is the filter coefficient (Rh [m]) of the FIR filters 33RL and 33RR. The threshold value set to the limit value of the amplitude level, dBlim, is the limit value of the amplitude level of the filter coefficients (Rh [m]) of the FIR filters 33RL and 33RR. FIG. 6 is a frequency characteristic diagram in the case where −6 dB is given to dBthreshold and −18 dB is given to dBlim.

  In this embodiment, a delay ((number of FIR taps −1) / 2) is generated by the FIR filter circuits 33RL and 33RR inserted in the line of the rear left and right ch audio signals, and the front left and right ch audio reproduction signals and the rear left and right are reproduced. A phase shift occurs in the ch audio playback signal. Therefore, delays 34FL and 34FR with a delay amount D6 are inserted in the front left and right channel audio signal lines to delay the front left and right channel audio signals by the group delay, and the front left and right channel audio playback signals and the rear left and right channels are delayed. Correct the phase shift of the ch audio playback signal.

  According to the third embodiment, the frequency caused by the phase interference shown in FIG. 5 that occurs when the front left / right channel audio reproduction signal and the rear left / right channel audio reproduction signal are synthesized at the listening position by the rear FIR filter circuit 33. The characteristic dip can be reduced as shown in FIG.

<Fourth embodiment>
According to the rear FIR filter circuit 33R of the third embodiment shown in FIG. 4 described above, when the driver seat or the passenger seat is in the listening position, the front left / right channel audio reproduction signal and the rear left / right channel are transmitted by the sound field control unit 20. Although the influence of the phase difference of the audio reproduction signal can be improved and the dip of the frequency characteristic can be eliminated, the information amount of the rear left and right ch audio reproduction signal is reduced by the rear FIR filter circuit 33R.

  Therefore, in the fourth embodiment, as shown in the block diagram of FIG. 7, the front FIR filter circuit 33F having FIR filters 33FL and 33FR is inserted into the sound field control unit 30.

  The filter coefficients (Fh [m]) of the front FIR filters 33FL and 33FR are obtained by doubling the level of the front left / right ch audio signal (impulse signal), and the rear left / right ch audio signal (impulse) of the third embodiment. (Signal) is subtracted from the signal. In order to make the group delay uniform, the number of taps of the filter coefficient (Fh [m]) of the front FIR filter circuit 33F and the filter coefficient (Rh [m]) of the rear FIR filter 33R are the same.

  According to the fourth embodiment, as shown in FIG. 8, the front audio reproduction signal obtained by convolving the front left / right channel audio signal with the filter coefficient (Fh [m]) of the front FIR filter circuit 33F and the third audio signal The frequency characteristic of the signal obtained by synthesizing the rear left and right channel audio reproduction signals in the embodiment at the listening position is flat, and loss of information amount is eliminated.

<Fifth embodiment>
According to the first to fourth embodiments, even if the listener is seated at the listening position of either the driver seat or the passenger seat, and the listener is seated at the listening position of both the driver seat and the passenger seat, Sound quality can be improved by eliminating sound image localization and loss of information, but the frequency characteristics at the listening position described above are different for each front / rear / left / right channel in terms of transfer function depending on the distance between the speakers and the listener and the obstacles. In contrast, the effects of the invention of the above-described embodiment cannot be exhibited to the maximum.

  In the fifth embodiment, therefore, frequency characteristic compensation filters 61FL, 61FR, 61RL, 61RR for front, rear, left and right channels are provided between the localization control unit 20 and the input unit 10 as shown in the block diagram of FIG. The provided frequency characteristic compensator 60 is inserted. The filters 61FL, 61FR, 61RL, and 61RR are configured by FIR filters or a combination of FIR filters and a plurality of IIR filters, and the frequency characteristics at the listening position of the audio reproduction signal of each channel are made equal.

  When the listening position is set to the driver's seat, the filter 61FL is obtained from the inverse transfer function when determining the delay amounts D1 to D4 in the localization control unit 20 described in the first embodiment for frequency characteristic compensation. , 61FR, 61RL, 61RR filter coefficients. The same applies when the listening position is set to the passenger seat.

  When the listening position is set to both the driver seat and the passenger seat, the reverse of determining the delay amounts D1 to D4 of the localization control unit 20 described in the second embodiment is performed for frequency characteristic compensation. The filter coefficients of the filters 61FL, 61FR, 61RL, and 61RR are obtained from the transfer function.

  According to the fifth embodiment, for each of the filters 61FL, 61FR, 61RL, 61RR, the frequency characteristics are individually compensated in a transfer function, so that the front left ch speaker 51FL, the front right ch speaker 51FL, The sound reproduced by the rear left channel speaker 51RL and the rear left channel speaker 51RR can be controlled so as to have the same frequency characteristic at the listening position, so that the localization of the sound image and the sound quality can be improved. The number characteristic compensator 60 can also be applied to the first to fourth embodiments.

  Further, when the filters 61FL, 61FR, 61RL, 61RR of the frequency characteristic compensation unit 60 are constituted by FIR filters, their respective FIR filter coefficients, and the FIR of the front FIR filter circuit 33F of the third and fourth embodiments described above. When the number of taps of the filter coefficients (Fh [m]) of the filters 33FL and 33FR and the filter coefficients (Rh [m]) of the FIR filters 33RL and 33RR of the rear FIR filter circuit 33R are the same, By adding the FIR filter coefficients to obtain the coefficients of the FIR filter corresponding to each channel of the frequency characteristic compensator 60 or the front FIR filter circuit 33F and the rear FIR filter circuit 33R, the calculation processing amount used for the FIR filter Can achieve the intended purpose with a small amount of calculation. .

10: input unit, 10L, 10R: input terminal 20: localization control unit, 20FL, 20FR, 20RL, 20RR: delay unit 30: sound field control unit, 31RL, 31RR: filter, 32RL, 32RR: delay unit, 33FL, 33FR , 33RL, 33RR: FIR filter, 34FL, 34FR: delay device 40: amplification unit, 41FL, 41FR, 41RL, 41RR: amplifier 50: speaker unit, 51FL, 51FR, 51RL, 51RR: speaker 60: frequency characteristic compensation unit, 61FL , 61FR, 61RL, 61RR: Filter

Claims (12)

A first delay unit that delays an input left channel audio signal and outputs the delayed left channel audio signal to the front left channel speaker; a second delay unit that delays an input right channel audio signal and outputs the delayed right channel audio signal to the front right channel speaker; A localization control unit comprising: a third delay unit that delays the input left-ch audio signal; and a fourth delay unit that delays the input right-ch audio signal;
Output to the rear left ch speaker by controlling the third rear left ch audio signal delayed by the delaying unit of the frequency characteristic and phase of the fourth delay unit in a delay the rear right c h o Dio signal Sound field control unit that controls the frequency characteristics and phase and outputs to the rear right channel speaker,
An audio signal reproducing device comprising:
In the localization control unit, the delay amounts of the first to fourth delay units are set so that each of the front left channel speaker, the front right channel speaker, the rear left channel speaker, and the rear right channel speaker. Is adjusted so that the sound image is localized at the listening position based on the difference in the arrival time of the sound from the listening position of the driver's seat or passenger seat in the vehicle ,
The sound field control unit includes a first series circuit including a first filter that attenuates a high frequency band of the left channel audio signal and a fifth delay device that delays the left channel audio signal by 0.625 msec. A second series circuit comprising a second filter for attenuating the high frequency band of the right channel audio signal and a sixth delay unit for delaying the right channel audio signal by 0.625 msec , Control the spread ,
An audio signal reproducing apparatus characterized by the above.
The audio signal reproducing apparatus according to claim 1,
The first and second filters are a high-shelf filter having a cutoff frequency of 200 Hz to 500 Hz and an amplification amount of 0 to -12 dB, or a plurality of equalizers having a center frequency of 200 Hz to 20 kHz and an amplification amount of 0 to -12 dB. An audio signal reproducing device configured to be configured. The audio signal reproduction device according to claim 1 or 2,
In addition, a first FIR filter circuit for improving frequency characteristic disturbance due to a phase difference between the front left channel audio reproduction signal and the rear left channel audio reproduction signal at the listening position is connected in series to the first series circuit. And
In addition to the second series circuit, a second FIR filter circuit for improving frequency characteristic disturbance due to a phase difference between the front right channel audio reproduction signal and the rear right channel audio reproduction signal at the listening position is in series. It is connected,
An audio signal reproducing apparatus characterized by the above. The audio signal reproduction apparatus according to claim 3, wherein
A third FIR filter for improving information loss due to the first FIR filter is connected to the output side of the first delay device,
A fourth FIR filter is connected to the output side of the second delay device to improve the loss of information caused by the second FIR filter;
An audio signal reproducing apparatus characterized by the above. The audio signal reproduction device according to claim 1, 2, 3 or 4,
A third filter for frequency characteristic compensation is connected to the preceding stage of the first delay device,
A fourth filter for frequency characteristic compensation is connected to the preceding stage of the second delay device,
A fifth filter for frequency characteristic compensation is connected to the previous stage of the third delay device,
A sixth filter for frequency characteristic compensation is connected to the preceding stage of the fourth delay device,
The sound reproduced by the front left channel speaker, the front right channel speaker, the rear left channel speaker, and the rear left channel speaker has the same frequency characteristic at the listening position by the third to sixth filters. To be,
An audio signal reproducing apparatus characterized by the above. The audio signal reproduction device according to claim 5, wherein
The third to sixth filters are obtained from the measurement results of the impulse responses of the front left ch speaker, the front right ch speaker, the rear left ch speaker, and the rear right ch speaker at the listening position. An audio signal reproducing apparatus comprising: an FIR filter alone or a combination of an FIR filter and a plurality of IIR filters, which performs a filter calculation process using a filter coefficient obtained from an inverse transfer function.
Apply the first delay to the input left channel audio signal and output it to the front left channel speaker.
Apply a second delay to the input right channel audio signal and output it to the front right channel speaker.
Applying a third delay to the input left channel audio signal and controlling the frequency characteristic and phase to output to the rear left channel speaker,
An audio signal processing method for applying a fourth delay to the input right channel audio signal and controlling the frequency characteristic and phase to output to the rear right channel speaker,
The delay amounts of the first to fourth delays are determined from the driver's seat or the passenger seat in the vehicle from each of the front left channel speaker, the front right channel speaker, the rear left channel speaker, and the rear left channel speaker . Based on the difference in the arrival time of the sound to the listening position, adjust so that the sound image is localized at the listening position,
The frequency characteristic and phase, have rows by delay processing of the attenuation process and 0.625msec high frequency band of the audio signal to control the spread of the sound field,
An audio signal processing method.
The audio signal processing method according to claim 7, wherein
Attenuation processing of the high frequency band of the rear left channel audio signal and the rear right channel audio is a high shelf filter with a cut-off frequency of 200 Hz to 500 Hz and an amplification amount of 0 to −12 dB, or a center frequency of 200 Hz to 20 kHz, respectively. An audio signal processing method characterized by performing with a plurality of equalizers having an amplification amount of 0 to -12 dB.
The audio signal processing method according to claim 7 or 8,
In addition to the control of the third delay and frequency characteristics and phase with respect to the rear left channel audio signal, a phase difference occurs between the front left channel audio playback signal and the rear left audio playback signal at the listening position. In order to improve the disturbance of the frequency characteristics, a filtering process by the first FIR filter is performed,
For the rear right channel audio signal, in addition to the control of the fourth delay and frequency characteristic and phase, a phase difference occurs between the front right channel audio playback signal and the rear right audio playback signal at the listening position. In order to improve the disturbance of the frequency characteristic, a filtering process using a second FIR filter is performed.
An audio signal processing method. The audio signal processing method according to claim 9, wherein
In order to improve the loss of information amount due to the filtering of the first FIR filter for the rear left ch audio signal in addition to the first delay for the front left ch audio signal, a third Apply the filtering process by FIR filter,
In order to improve the loss of information amount due to the filtering of the second FIR filter for the rear right channel audio signal in addition to the second delay for the front right channel audio signal, Apply a filtering process using an FIR filter.
An audio signal processing method. The audio signal processing method according to claim 7, 8, 9 or 10,
A frequency characteristic is compensated by a third filter for the front left channel audio signal,
The front right channel audio signal is compensated for frequency characteristics by a fourth filter,
A frequency characteristic is compensated for the rear left channel audio signal by a fifth filter,
A frequency characteristic is compensated by a sixth filter for the rear left channel audio signal,
The sound reproduced by the front left channel speaker, the front right channel speaker, the rear left channel speaker, and the rear left channel speaker has the same frequency characteristic at the listening position by the third to sixth filters. To be,
An audio signal processing method. The audio signal processing method according to claim 11, wherein
The third to sixth filters are obtained by measuring the impulse responses of the front left channel speaker, the front right channel speaker, the rear left channel speaker, and the rear right channel speaker at the listening position. An audio signal processing method using an FIR filter alone or a combination of an FIR filter and a plurality of IIR filters, which performs filter calculation processing using a filter coefficient obtained from the inverse transfer function.

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