WO2012140764A1

WO2012140764A1 - Audio signal processing device, audio signal processing method and audio signal processing program

Info

Publication number: WO2012140764A1
Application number: PCT/JP2011/059279
Authority: WO
Inventors: 晃広井関; 佳樹太田; 慎一菊池; 快友今西
Original assignee: パイオニア株式会社
Priority date: 2011-04-14
Filing date: 2011-04-14
Publication date: 2012-10-18

Abstract

This audio signal processing device performs processing for audio signals supplied to a front speaker positioned in front of a listening position and a rear speaker positioned behind the listening position. Audio signal supply means supplies identical audio signals to the front speaker and the rear speaker. Phase difference imparting means performs processing for imparting relative phase difference between the audio signal supplied to the front speaker and the audio signal supplied to the rear speaker. Specifically, the phase difference imparting means imparts the phase difference so that the sound pressure level at a rear evaluation point, which is positioned behind the listening position and either at the same front-to-rear direction position as the rear speaker or in front of the rear speaker, is higher than the sound pressure level at a front evaluation point, which is positioned in front of the listening position and behind the front speaker. As a result, it is possible to suitably localize the sound of the rear channel behind the listening position.

Description

Audio signal processing apparatus, audio signal processing method, and audio signal processing program

The present invention relates to an audio signal processing device that is mounted on a vehicle or the like and performs processing for localizing a sound image.

This type of technology is described in Patent Documents 1 and 2, for example. Japanese Patent Application Laid-Open No. H10-228707 gives an audio signal that is given a localization characteristic to an audio signal that is input to one speaker among front and rear speakers in a vehicle interior, and that is assigned a localization characteristic to an audio signal that is input to the other speaker. The technique to add is described. Specifically, in this technology, the localization characteristic is a characteristic obtained by multiplying the acoustic transmission characteristic from one speaker to the seat close to the other speaker and the inverse characteristic of the acoustic transmission characteristic from the other speaker to the seat. Has been granted.

In Patent Document 2, the frequency characteristics of the synthesized sound obtained by synthesizing the output sound output from each speaker at the ear position of the listener is determined based on the frequency at which the comb-like characteristic disturbance starts to appear. Based on the cut-off frequency, the input audio signal is divided into a low-frequency signal and a high-frequency signal, the low-frequency signal is output in advance, and the high-frequency signal is delayed and output subsequently. Are listed. By doing so, a virtual sound image is localized at a required position.

In addition, a technique related to the present invention is described in Patent Document 3.

JP 2009-147487 A Japanese Patent No. 4518151 JP 2008-141524 A

By the way, it is desirable to hear the sound of the rear channel of the surround sound source located rearward at the driver's seat in the passenger compartment. However, since the sound of the rear channel reaches the listener's ear, the sound is blocked by the seat, or the sound is reflected by a window or the like, so the rear channel sound is difficult to be localized backward. In other words, it can be said that the sound of the rear channel in the passenger compartment is ambiguous.

In the technique described in Patent Document 1 described above, since the localization of the transfer function between the rear speaker and the driver's seat is ambiguous, it is difficult to properly localize the sound of the rear channel. In the technique described in Patent Document 2, it is easy to erroneously determine the front-rear localization in the localization using the transfer function. In the above technique, attention is paid only to the characteristics of the listener's both ears, and physical phenomena (such as balance of sound pressure level) around the listener's head are not taken into consideration. For this reason, it has been difficult to properly localize the sound of the rear channel.

The above is one example of problems to be solved by the present invention. An object of the present invention is to provide an audio signal processing device, an audio signal processing method, and an audio signal processing program capable of appropriately localizing a rear channel sound at a desired position.

The invention according to claim 1 is an audio signal processing device that performs processing on an audio signal supplied to a front speaker positioned in front of the listening position and a rear speaker positioned behind the listening position. The audio signal processing device includes audio signal supply means for supplying the same audio signal to the front speaker and the rear speaker, the audio signal supplied to the front speaker, and the audio supplied to the rear speaker. Phase difference providing means for performing a process for providing a relative phase difference with the signal, and the phase difference providing means is located behind the listening position and in the same front-rear direction position as the rear speaker or The phase difference is applied so that the sound pressure level at the rear evaluation point located in front of the rear speaker is higher than the sound pressure level at the front evaluation point located in front of the listening position and behind the front speaker. To do.

The invention according to claim 11 is executed by an audio signal processing apparatus that processes audio signals supplied to a front speaker positioned in front of the listening position and a rear speaker positioned behind the listening position. This is an audio signal processing method. The audio signal processing method includes an audio signal supply step of supplying the same audio signal to the front speaker and the rear speaker, the audio signal supplied to the front speaker, and the audio supplied to the rear speaker. A phase difference providing step for performing a process for giving a relative phase difference between the signal and the signal, wherein the phase difference applying step is located behind the listening position and in the same front-rear direction position as the rear speaker or The phase difference is applied so that the sound pressure level at the rear evaluation point located in front of the rear speaker is higher than the sound pressure level at the front evaluation point located in front of the listening position and behind the front speaker. To do.

According to a twelfth aspect of the present invention, the audio signal supplied to the front speaker located in front of the listening position and the rear speaker located behind the listening position is processed, and the audio signal processing includes a computer. It is an audio signal processing program executed by the apparatus. The audio signal processing program is supplied to the computer from the audio signal supply means for supplying the same audio signal to the front speaker and the rear speaker, and to the audio signal and the rear speaker supplied to the front speaker. Functioning as a phase difference providing unit that performs a process for providing a relative phase difference between the audio signal and the audio signal, the phase difference providing unit being behind the listening position and the same front and rear as the rear speaker. The sound pressure level at the rear evaluation point located in the direction position or in front of the rear speaker is higher than the sound pressure level at the front evaluation point located in front of the listening position and behind the front speaker. Add phase difference.

An example of the acoustic system applied to the vehicle interior is shown. This shows the sound pressure level balance around the listener's head as a physical phenomenon. An example of the front-rear level difference in the passenger compartment is shown. 1 shows a schematic configuration of an audio signal processing apparatus according to the present embodiment. The figure for demonstrating a band pass filter and a phase difference provision part concretely is shown. A specific example of the control band will be shown. The distance defined by the front speaker, the rear speaker, the front evaluation point, and the rear evaluation point is shown. An example of the change of the front-back level difference with respect to a phase difference is shown. It is an image figure which shows the change of the sound pressure level in the vicinity of a listening position when changing a phase difference. An example of the result by a present Example is shown. An example of the result by a present Example and a comparative example is shown.

In one aspect of the present invention, an audio signal processing device that performs processing on an audio signal supplied to a front speaker positioned in front of a listening position and a rear speaker positioned behind the listening position is the front speaker. And an audio signal supply means for supplying the same audio signal to the rear speaker, and a relative position between the audio signal supplied to the front speaker and the audio signal supplied to the rear speaker. Phase difference providing means for performing a process for providing a phase difference, and the phase difference providing means is located behind the listening position and at the same front-rear direction position as the rear speaker or in front of the rear speaker. The sound pressure level at the evaluation point is higher than the sound pressure level at the front evaluation point located in front of the listening position and behind the front speaker. To impart a phase difference.

The above audio signal processing apparatus includes a front speaker positioned in front of the listening position and a rear speaker positioned behind the listening position, and is applied to, for example, a vehicle interior. The audio signal supply means supplies the same audio signal to the front speaker and the rear speaker. For example, the audio signal supply means supplies a rear channel audio signal used for the rear speaker not only to the rear speaker but also to the front speaker. The phase difference providing means is configured to generate a relative phase difference between the audio signal supplied to the front speaker and the audio signal supplied to the rear speaker, and the audio supplied to either the front speaker or the rear speaker. A phase difference is given to the signal. Here, the rear evaluation point is defined as an evaluation point located behind the listening position and in the same front-rear direction position as the rear speaker or in front of the rear speaker, and the front evaluation point is located in front of the listening position and behind the front speaker. It is defined as an evaluation point that is located. In this case, the phase difference providing unit provides the phase difference so that the sound pressure level at the rear evaluation point is higher than the sound pressure level at the front evaluation point. As a result, the rear channel sound can be properly localized behind the listening position. That is, it is possible to eliminate localization ambiguity in the rear channel sound.

In one aspect of the audio signal processing device, the phase difference providing unit may be configured to change the position according to a distance defined by the front speaker, the rear speaker, the front evaluation point, and the rear evaluation point. Add phase difference.

In this aspect, the relationship between the sound pressure level at the rear evaluation point and the sound pressure level at the front evaluation point changes depending on the distance defined by the front speaker, the rear speaker, the front evaluation point, and the rear evaluation point. The phase difference providing means applies the phase difference in consideration of this.

In another aspect of the audio signal processing device, the distance s1F is defined as the distance between the front speaker and the front evaluation point, and the distance s1B is defined as the distance between the front speaker and the rear evaluation point. The distance s2F is defined as the distance between the rear speaker and the front evaluation point, the distance s2B is defined as the distance between the rear speaker and the rear evaluation point, and the wavelength λ is defined as the wavelength of the audio signal. The distance d is defined as the distance obtained by “d = | s1F−s1B | + | s2F−s2B |”, and the predetermined value A is obtained by “A = (s1B−s2B) / λ × 360 °”. When the predetermined value α is defined as a value within a range defined by “d / λ × 180 ° −180 ° ≦ α ≦ d / λ × 180 °”, the phase difference providing means is Based on the predetermined value A and the predetermined value α, “A A phase difference within the range obtained by “+ α” is given.

According to this aspect, the difference between the sound pressure level at the rear evaluation point and the sound pressure level at the front evaluation point is appropriately set to a desired value by giving the phase difference within the range obtained by “A + α”. be able to. That is, the sound pressure level at the rear evaluation point can be maintained appropriately higher than the sound pressure level at the front evaluation point.

In another aspect of the audio signal processing device, the distance acquisition unit that acquires the distances s1F, s1B, s2F, and s2B, and the distance d and the predetermined value A based on the distances s1F, s1B, s2F, and s2B. And a phase difference calculating means for calculating the phase difference within a range obtained by “A + α” by obtaining the predetermined value α, wherein the phase difference providing means is calculated by the phase difference calculating means. The phase difference is given.

In this aspect, the distance acquisition unit acquires the distances s1F, s1B, s2F, and s2B input by the user, for example, and the phase difference calculation unit calculates the phase difference to be given based on the above equation.

Preferably, in the above audio signal processing device, the phase difference providing unit provides the predetermined value A as the phase difference.

When the phase difference is set to the predetermined value A, the audio signal from the front speaker and the audio signal from the rear speaker arrive at the rear evaluation point at approximately the same timing, so that the sound pressure level at the rear evaluation point is maximum. Tend to be. Therefore, the sound pressure level at the rear evaluation point can be maintained appropriately higher than the sound pressure level at the front evaluation point.

In another aspect of the above audio signal processing apparatus, the audio signal processing device further includes a front microphone disposed at the front evaluation point and a rear microphone disposed at the rear evaluation point, and the phase difference providing unit includes the front difference The phase difference to be applied is obtained based on audio signals output from the front speaker and the rear speaker, which are collected by the microphone and the rear microphone.

In this aspect, the phase difference to be applied is obtained by measurement using the front microphone and the rear microphone. By giving the phase difference thus obtained, the sound pressure level at the rear evaluation point can be maintained appropriately higher than the sound pressure level at the front evaluation point.

In another aspect of the above audio signal processing device, the phase difference providing unit provides a phase difference different for each frequency of the audio signal as the phase difference.

The relationship between the sound pressure level at the rear evaluation point and the sound pressure level at the front evaluation point tends to change for each frequency of the audio signal. Therefore, the phase difference providing unit provides a different phase difference for each frequency of the audio signal. Thereby, the sound pressure level at the rear evaluation point can be maintained appropriately higher than the sound pressure level at the front evaluation point regardless of the frequency of the audio signal.

In another aspect of the audio signal processing device, the phase difference providing unit applies the phase difference only when the frequency of the audio signal is in a predetermined band defined by a lower limit value and an upper limit value. .

In this aspect, the phase difference providing means, for example, a band in which the difference between the sound pressure level at the rear evaluation point and the sound pressure level at the front evaluation point is disturbed, or the sound pressure level at the rear evaluation point and the front evaluation point The phase difference can be given only in a band in which the difference from the sound pressure level can be appropriately controlled.

Preferably, the minimum value of the frequency at which the difference between the sound pressure level at the rear evaluation point and the sound pressure level at the front evaluation point is a predetermined value or more is used as the lower limit value.

Preferably, the upper limit value is (1) an absolute value of a difference between a distance between the front speaker and the front evaluation point and a distance between the front speaker and the rear evaluation point, and (2) the rear side. It is defined by the wavelength of the audio signal having a value larger than the sum of the distance between the speaker and the front evaluation point and the absolute value of the difference between the rear speaker and the rear evaluation point.

In another aspect of the present invention, audio executed by an audio signal processing device that processes audio signals supplied to a front speaker positioned in front of the listening position and a rear speaker positioned behind the listening position. The signal processing method includes an audio signal supply step for supplying the same audio signal to the front speaker and the rear speaker, the audio signal supplied to the front speaker, and the audio signal supplied to the rear speaker. A phase difference providing step for performing a process for providing a relative phase difference between the first position and the second position, and the phase difference providing step is performed at a position behind the listening position and in the same front-rear direction position as the rear speaker or the The sound pressure level at the rear evaluation point located in front of the rear speaker is a sound at the front evaluation point located in front of the listening position and behind the front speaker. As is higher than the level, to impart the phase difference.

In another aspect of the present invention, an audio signal is provided that performs processing on an audio signal supplied to a front speaker located in front of the listening position and a rear speaker located behind the listening position and includes a computer. An audio signal processing program executed by a processing device includes: an audio signal supply unit that supplies the computer with the same audio signal to the front speaker and the rear speaker; and the audio signal supplied to the front speaker; Functioning as a phase difference providing unit that performs a process for providing a relative phase difference with the audio signal supplied to the rear speaker, the phase difference providing unit being behind the listening position; The sound pressure level at the same front-rear direction position as the rear speaker or a rear evaluation point located in front of the rear speaker is the listening position. Forward and to be higher than the sound pressure level in the front evaluation point located at the rear of the front speakers, imparting the phase difference.

Also with the above-described audio signal processing method and audio signal processing program, the rear channel sound can be appropriately localized behind the listening position.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

[Basic concept]
First, the basic concept of the present embodiment will be described. FIG. 1 is a diagram illustrating an example of an acoustic system applied to a vehicle interior. As illustrated, the sound system includes a front speaker SP1 disposed in front and a rear speaker SP2 disposed in the rear. Specifically, the front speaker SP1 is arranged in front of the listening position (driver's position, in other words, the driver's seat), and the rear speaker SP2 is arranged behind the listening position. For example, the front speaker SP1 outputs a front channel audio signal, and the rear speaker SP2 outputs a rear channel audio signal of the surround sound source.

Here, it is desirable to hear the sound of the rear channel of the surround sound source located rearward at the driver's seat in the passenger compartment. However, since the sound of the rear channel reaches the ear, the sound is blocked by the seat or reflected by a window or the like, so the rear channel sound is difficult to be localized backward. In other words, it can be said that the sound of the rear channel in the passenger compartment is ambiguous.

For example, in the techniques described in Patent Documents 1 to 3 described above, a process for localizing sound using a transfer function is performed. In localization using such a transfer function, it is easy to erroneously determine front-rear localization. Further, in this technology, attention is paid only to characteristics of the listener (driver) in both ears, and physical phenomena around the listener's head are not taken into consideration. For this reason, it has been difficult to properly localize the sound of the rear channel in the passenger compartment.

FIG. 2 illustrates the sound pressure level balance around the listener's head as a physical phenomenon. In FIG. 2, the size of the broken line area indicates the level of the sound pressure level. From this, it can be seen that the sound pressure level on the side where the speaker SP is located becomes higher and the sound pressure level on the side opposite to the side where the speaker SP is located becomes lower.

Next, with reference to FIG. 3, the difference between the front and rear levels in the passenger compartment will be described. Here, as shown in FIG. 3A, a difference in sound pressure level (front-rear level difference) at the evaluation points P1 and P2 when sound (for example, pink noise) is output from only the rear speaker SP2 is considered. The evaluation point P1 is an evaluation point located in front of the listening position (in other words, in front of the listener (driver)) and behind the front speaker SP1. The evaluation point P2 is an evaluation point located behind the listening position (in other words, behind the listener (driver)) and in front of the rear speaker SP2. Hereinafter, the evaluation point P1 is appropriately referred to as “front evaluation point P1”, and the evaluation point P2 is appropriately referred to as “rear evaluation point P2”. For example, the front evaluation point P1 is located in the vicinity of the frontal part of the listener (driver), and the rear evaluation point P2 is located in the vicinity of the back part of the listener (driver).

In FIG. 3B, the horizontal axis indicates the frequency of the audio signal output from the rear speaker SP2, and the vertical axis indicates the front-rear level difference with respect to the sound pressure level. The “front-rear level difference” means a difference between the sound pressure level at the front evaluation point P1 and the sound pressure level at the rear evaluation point P2 (hereinafter the same). The vertical axis in FIG. 3 (b) indicates that the sound pressure level at the front evaluation point P1 becomes higher than the sound pressure level at the rear evaluation point P2 as it goes up, and the sound goes down as it goes down. It shows that the sound pressure level at the evaluation point P2 is higher than the sound pressure level at the front evaluation point P1. The sound pressure level at the front evaluation point P1 is acquired by the microphone arranged at the front evaluation point P1, and the sound pressure level at the rear evaluation point P2 is acquired by the microphone arranged at the rear evaluation point P2. The front-rear level difference is obtained by subtracting the sound pressure level acquired by the microphone disposed at the rear evaluation point P2 from the sound pressure level acquired by the microphone disposed at the front evaluation point P1.

3 (b), it can be seen that the front / rear level difference varies for each band in the passenger compartment, that is, the rear channel sound localization is ambiguous. In addition, although the sound is generated from the rear speaker SP2, the sound pressure level at the front evaluation point P1 is higher than the sound pressure level at the rear evaluation point P2, as indicated by the broken line area. I understand.

From the above, in this embodiment, control is performed so that the localization ambiguity in the rear channel sound is resolved and the rear channel sound is localized at a desired position between the front and rear. Specifically, in the present embodiment, the sound pressure level balance between the front and rear around the head of the listener is controlled in order to achieve a desired front and rear localization. That is, the front-rear level difference around the listener's head is controlled.

[Control method]
Hereinafter, the control method according to the present embodiment will be specifically described. In the present embodiment, the relative position between the audio signal supplied to the front speaker SP1 and the audio signal supplied to the rear speaker SP2 is set so that the difference between the front and rear levels around the head of the listener becomes a desired value. Control to cause phase difference. Specifically, in this embodiment, a phase difference is given to the audio signal of the front speaker SP1 so that the sound pressure level at the rear evaluation point P2 is higher than the sound pressure level at the front evaluation point P1. . In the present embodiment, the sound pressure level at the rear evaluation point P2 is made higher than the sound pressure level at the front evaluation point P1 in this way, so that the rear channel sound can be localized behind the listener. Yes.

(Configuration of audio signal processing device)
FIG. 4 shows a schematic configuration of the audio signal processing apparatus 10 according to the present embodiment. The audio signal processing apparatus 10 mainly includes a front speaker SP1, a rear speaker SP2, an audio signal supply unit 11, a band pass filter 12, and a phase difference providing unit 13. The audio signal processing device 10 corresponds to, for example, an amplifier.

The front speaker SP1 is arranged in front of the listening position (driver's position, in other words, the driver's seat), and the rear speaker SP2 is arranged behind the listening position. The audio signal supply unit 11 supplies the audio signal from the sound source to the front speaker SP1 and the rear speaker SP2. This audio signal is, for example, a rear channel audio signal in a surround sound source. The audio signal supply unit 11 corresponds to an example of an audio signal supply unit in the present invention.

Although not shown in FIG. 4, a front channel audio signal is also supplied to the front speaker SP1, and the front speaker SP1 outputs an audio signal obtained by synthesizing the rear channel audio signal and the front channel audio signal. .

Here, the band-pass filter 12 and the phase difference providing unit 13 will be described in detail with reference to FIG. As shown in FIG. 5, the bandpass filter 12 extracts a sound signal having a component for each of a plurality of frequency bands obtained by dividing the frequency domain, from the sound signal supplied from the sound signal supply unit 11 to the front speaker SP1. That is, the band-pass filter 12 extracts frequency components in the input audio signal for the desired frequency band. Then, the phase difference providing unit 13 gives a different phase difference for each frequency band to each of the audio signals for each frequency band extracted by the band pass filter 12. The phase difference providing unit 13 corresponds to an example of “phase difference providing means” in the present invention. In the following, the phase difference provided by the phase difference providing unit 13 is appropriately expressed as “phase difference θ”.

(Control bandwidth)
Next, the control band for providing the phase difference θ in the present embodiment will be described. In the present embodiment, the audio signal processing apparatus 10 applies the audio signal of the front speaker SP1 only when the frequency of the audio signal is in a predetermined frequency band (that is, a control band) defined by the lower limit value and the upper limit value. To provide a phase difference θ. Such a control band is set based on an arithmetic expression or measurement.

FIG. 6 is a diagram showing a specific example of the control band. FIG. 6 shows a difference in sound pressure level (front-rear level difference) between the front evaluation point P1 and the rear evaluation point P2 when sound (for example, pink noise) is output from only the rear speaker SP2. Since FIG. 6 is the same diagram as FIG. 3B, detailed description is omitted.

The white arrow in FIG. 6 shows an example of the control band. The lower limit value that defines the control band is the frequency at which the difference between the front and rear levels starts to be disturbed. Specifically, the minimum value of the frequency at which the front-rear level difference (absolute value) is equal to or greater than a predetermined value is used as the lower limit value. In one example, the lower limit value is obtained by measurement. In this example, a graph as shown in FIG. 6 is obtained by measurement, and the lower limit value is determined based on the graph. Specifically, sound pressures acquired by the microphones when microphones are respectively arranged at the positions of the front evaluation point P1 and the rear evaluation point P2 in the vehicle interior and sound (for example, pink noise) is output only from the rear speaker SP2. Based on the level, a graph as shown in FIG. 6 is obtained. In another example, the lower limit value is obtained by estimation without performing such measurement. In this example, it is estimated that the front-rear level difference starts to be disturbed above this frequency in consideration of the vehicle interior space, the position of the front speaker SP1, the rear speaker SP2, the front evaluation point P1, the rear evaluation point P2, etc. in the vehicle interior. The frequency to be used is used as the lower limit value.

On the other hand, the upper limit value that defines the control band is defined according to the distance determined by the front speaker SP1, the rear speaker SP2, the front evaluation point P1, and the rear evaluation point P2. Here, with reference to FIG. 7, the distance defined by the front speaker SP1, the rear speaker SP2, the front evaluation point P1, and the rear evaluation point P2 will be described. As shown in FIG. 7, the distance between the front speaker SP1 and the front evaluation point P1 is “s1F”, the distance between the front speaker SP1 and the rear evaluation point P2 is “s1B”, and the rear speaker SP2 and the front evaluation point P1 are Is the distance “s2F”, and the distance between the rear speaker SP2 and the rear evaluation point P2 is “s2B”. Further, the distance corresponding to the absolute value of the difference between the distance s1F and the distance s1B is “d1”, the distance corresponding to the absolute value of the difference between the distance s2F and the distance s2B is “d2”, and the distance d1 and the distance The distance obtained by adding d1 is “d”. That is, the distance d is obtained from the following equation (1). This distance d is a distance according to the length in the front-rear direction of the head of the listener (driver).

d = d1 + d2 = | s1F−s1B | + | s2F−s2B | Equation (1)
Returning to the description of the upper limit value that defines the control band, the upper limit value is defined based on a wavelength λ that is at least longer than the distance d, that is, a frequency corresponding to the wavelength λ is used. This is because, in an audio signal having a wavelength λ shorter than the distance d, the wavelength of interference fringes generated therebetween becomes shorter than the distance between the front evaluation point P1 and the rear evaluation point P2. That is, it is difficult to appropriately control the difference between the front and rear levels with an audio signal having a wavelength λ shorter than the distance d.

It should be noted that the upper limit value of the control band is not limited to being obtained by the calculation as described above, that is, not limited to being obtained based on the distance d or the like, and may be obtained by measurement. Specifically, microphones may be arranged at the positions of the front evaluation point P1 and the rear evaluation point P2 in the vehicle interior, and the upper limit value of the control band may be obtained based on the sound pressure level acquired by these microphones. good.

The control band is set by the lower limit value and the upper limit value obtained as described above. The control band set in this way is set for the band-pass filter 12 in the audio signal processing device 10. Specifically, the setting for the band-pass filter 12 is performed so that the band-pass filter 12 performs a process of extracting only an audio signal in the control band.

(Range and value of phase difference)
Next, the range and value of the phase difference θ used in the present embodiment will be described. In the present embodiment, the audio signal processing device 10 performs control using the phase difference θ such that the sound pressure level at the rear evaluation point P2 is higher than the sound pressure level at the front evaluation point P1. Such a phase difference θ is set based on the following equations (2) to (4).

θ = A + α Formula (2)
A = (s1B−s2B) / λ × 360 ° Formula (3)
d / λ × 180 ° −180 ° ≦ α ≦ d / λ × 180 ° Formula (4)
As shown in Expression (3), the predetermined value A is a value (fixed value) determined according to the distances s1B and s2B and the wavelength λ. The predetermined value A is determined based on the distance from the front speaker SP1 to the rear evaluation point P2 and the rear speaker SP2 so that the audio signal from the front speaker SP1 and the audio signal from the rear speaker SP2 reach the rear evaluation point P2 at the same timing. This corresponds to a value (phase difference) for correcting the difference from the distance to the rear evaluation point P2. On the other hand, the equation (4) is an equation that defines a range of the predetermined value α determined by the distance d and the wavelength λ obtained from the above equation (1). The range of the phase difference θ to be set is determined by the equation (2) using the predetermined values A and α. The audio signal processing device 10 performs control to give the phase difference θ within the range determined by Expression (2).

As is clear from the above equation, the phase difference θ changes according to the wavelength λ. Therefore, the phase difference θ to be set is determined for each frequency, for example. Specifically, the phase difference θ to be set is determined for each of a plurality of frequency bands obtained by dividing the frequency domain. In the audio signal processing device 10, a plurality of frequency bands obtained by dividing the frequency domain are set in the band pass filter 12, and a phase difference θ determined for each of the plurality of frequency bands is set in the phase difference adding unit 13. . It is assumed that such a plurality of frequency bands are set within the control band set as described above.

Note that the use of the above equations (2) to (4) is based on the condition that the amplitudes of the front speaker SP1 and the rear speaker SP2 in the vicinity of the listener's head are equal. That is, the condition is that the distance from the front speaker SP1 and the rear speaker SP2 to the listener's head is the same.

FIG. 8 shows an example of the change in the level difference before and after the phase difference θ. In FIG. 8, the horizontal axis represents the phase difference θ given to the audio signal of the front speaker SP1, and the vertical axis represents the sound pressure level. The graph shown in FIG. 8 is obtained by microphones arranged at the respective positions of the front evaluation point P1 and the rear evaluation point P2. Specifically, when a sound signal fixed at a predetermined frequency within the control band is output from the front speaker SP1 and the rear speaker SP2 (from the front speaker SP1, the sound signal in which the phase difference θ is changed variously. The sound pressure level acquired by the microphone is used.

A graph 51 indicated by a broken line indicates an example of the sound pressure level at the front evaluation point P1, and a graph 52 indicated by a one-dot chain line indicates an example of the sound pressure level at the rear evaluation point P2. A graph 53 indicated by a solid line shows the difference (front-rear level difference) between the sound pressure level at the front evaluation point P1 and the sound pressure level at the rear evaluation point P2. The sound pressure level at the front evaluation point P1 is acquired by the microphone arranged at the front evaluation point P1, and the sound pressure level at the rear evaluation point P2 is acquired by the microphone arranged at the rear evaluation point P2. The front-rear level difference is obtained by subtracting the sound pressure level acquired by the microphone disposed at the rear evaluation point P2 from the sound pressure level acquired by the microphone disposed at the front evaluation point P1. Regarding the front-rear level difference shown in the graph 53, the sound pressure level at the rear evaluation point P2 becomes higher than the sound pressure level at the front evaluation point P1 as the front-rear level difference becomes smaller (that is, as it goes down on the vertical axis). And

From FIG. 8, when the phase difference θ is set to the predetermined value A (that is, when the predetermined value α is set to “0”), the sound pressure level at the rear evaluation point P2 is the sound pressure at the front evaluation point P1. You can see that it is considerably higher than the level. This is because when the phase difference θ is set to the predetermined value A, the audio signal from the front speaker SP1 and the audio signal from the rear speaker SP2 arrive at the rear evaluation point P2 at substantially the same timing. This is because the sound pressure level at the evaluation point P2 tends to be maximized.

On the other hand, “B1” and “B2” in FIG. 8 indicate phase differences when the predetermined value α is set to “d / λ × 180 ° −180 °” and “d / λ × 180 °”. Yes. When the phase difference θ is set to the phase difference B1 or the phase difference B2, it can be seen that the sound pressure level at the rear evaluation point P2 is substantially equal to the sound pressure level at the front evaluation point P1 (strictly The sound pressure level at the rear evaluation point P2 is slightly higher than the sound pressure level at the front evaluation point P1). Incidentally, the range X1 defined by the phase difference B1 or the phase difference B2 is a range of the phase difference θ obtained by the above equations (2) to (4).

FIG. 8 shows an example of the change in the front-rear level difference with respect to the change in the phase difference θ. When the phase difference θ is obtained by an arithmetic expression as described above, FIG. 8 is used to obtain the phase difference θ. There is no need to obtain a graph as shown in.

FIG. 9 is an image diagram showing a change in sound pressure level near the listening position (near the listener's head) when the phase difference θ is changed. The left side of FIG. 9 shows an image diagram of the sound pressure level in the vicinity of the listening position when using the phase difference θ in which the predetermined value α is set to “d / λ × 180 ° −180 °”. In this case, the sound pressure level at the rear evaluation point P2 and the sound pressure level at the front evaluation point P1 tend to be approximately equal. In the center of FIG. 9, an image diagram of the sound pressure level in the vicinity of the listening position when the phase difference θ with the predetermined value α set to “0” is used, that is, when the phase difference θ is set to the predetermined value A is shown. . In this case, the sound pressure level at the rear evaluation point P2 tends to be considerably higher than the sound pressure level at the front evaluation point P1. The right side of FIG. 9 shows an image diagram of the sound pressure level in the vicinity of the listening position when using the phase difference θ in which the predetermined value α is set to “d / λ × 180 °”. Also in this case, the sound pressure level at the rear evaluation point P2 and the sound pressure level at the front evaluation point P1 tend to be approximately equal.

Here, it is understood from FIGS. 8 and 9 that the phase difference θ is preferably set to the predetermined value A. However, even if the phase difference θ is not set to the predetermined value A, if the phase difference θ is set to a value within the range defined by the predetermined values A and α (see equations (2) to (4)), The level difference can be set to a desired value, that is, the sound pressure level at the rear evaluation point P2 can be appropriately set higher than the sound pressure level at the front evaluation point P1. Therefore, various values can be used as the phase difference θ as long as it is within the range defined by the predetermined values A and α.

In the above description, the example in which the phase difference θ is set based on the equations (2) to (4) is shown. In other words, the example in which the phase difference θ is set by calculation is shown. θ may be set. Specifically, microphones are respectively arranged at the positions of the front evaluation point P1 and the rear evaluation point P2 in the vehicle interior, and a graph as shown in FIG. 8 is obtained from the sound pressure levels acquired by these microphones. The phase difference θ may be set based on In still another example, the phase difference θ may be set using the above-described calculation and measurement in combination.

By the way, in one example, the control band and the phase difference θ are set in advance (for example, before shipment) based on the above-described arithmetic expression and measurement. At the same time, the settings for the bandpass filter 12 and the phase difference providing unit 13 in the audio signal processing apparatus 10 are performed according to the settings of the control band and the phase difference θ. In other examples, such settings can be made after input by the user. In this example, the user inputs distances s1F, s1B, s2F, s2B, and the like to the audio signal processing apparatus 10, and the audio signal processing apparatus 10 A control band and a phase difference θ are set by measurement. Then, the audio signal processing device 10 performs settings for the bandpass filter 12 and the phase difference providing unit 13 in accordance with the control band and the phase difference θ.

[Effects of this embodiment]
Next, the effect of the present embodiment will be described with reference to FIGS.

FIG. 10 shows an example of the result of this example. Specifically, an example of a change in the front-rear level difference due to the phase difference θ is shown. In FIG. 10, the horizontal axis represents the phase difference θ given to the audio signal of the front speaker SP1, and the vertical axis represents the frequency of the audio signal. Further, in FIG. 10, the front-rear level difference is indicated by contour lines. When the numerical value of the front / rear level difference is a positive value, it indicates that the sound pressure level at the front evaluation point P1 is higher than the sound pressure level at the rear evaluation point P2, and the numerical value of the front / rear level difference is negative. In this case, the sound pressure level at the rear evaluation point P2 is higher than the sound pressure level at the front evaluation point P1. Such a front-back level difference is obtained from the sound pressure levels acquired by the microphones arranged at the respective positions of the front evaluation point P1 and the rear evaluation point P2. Specifically, the front-rear level difference is determined by outputting a sound signal in which the phase difference θ is variously changed when the sound signal is output from the front speaker SP1 and the rear speaker SP2. ) And obtained from the sound pressure level acquired by the microphone.

Note that the frequency range shown on the vertical axis corresponds to the control band described above. Further, when the phase difference θ shown on the horizontal axis is a positive value, it indicates that the phase of the audio signal of the front speaker SP1 is delayed from the phase of the audio signal of the rear speaker SP2, and is shown on the horizontal axis. When the phase difference θ is a negative value, it indicates that the phase of the audio signal of the front speaker SP1 is ahead of the phase of the audio signal of the rear speaker SP2.

In FIG. 10, a solid line 61 shows an example of a result when the phase difference θ is set to the predetermined value A (that is, when the predetermined value α is set to “0”). It can be seen from the solid line 61 that the sound pressure level at the rear evaluation point P2 is considerably higher than the sound pressure level at the front evaluation point P1. A broken line 62 shows an example of a result in the case of using the phase difference θ in which the predetermined value α is set to “d / λ × 180 ° −180 °”, and a broken line 63 indicates the predetermined value α as “d / λ. An example of the result when the phase difference θ set to “× 180 °” is used is shown. It can be seen from the

broken lines

62 and 63 that the sound pressure level at the rear evaluation point P2 is slightly higher than the sound pressure level at the front evaluation point P1.

From the above, it can be said that the front-rear level difference around the listener's head can be appropriately set to a desired value by giving the phase difference θ within the range defined by the predetermined values A and α. That is, it can be said that the sound pressure level at the rear evaluation point P2 can be made higher than the sound pressure level at the front evaluation point P1. Therefore, according to the present embodiment, the ambiguity of localization in the sound of the rear channel can be eliminated, and the sound of the rear channel can be appropriately localized behind the listener.

FIG. 11 shows an example of the results of this example and the comparative example. In FIG. 11, the horizontal axis represents the frequency of the audio signal, and the vertical axis represents the front-rear level difference. The front-rear level difference is obtained from the sound pressure levels obtained by arranging microphones at the positions of the front evaluation point P1 and the rear evaluation point P2, respectively. Note that the frequency range shown on the horizontal axis corresponds to the control band described above.

A graph 71 indicated by a solid line and a graph 72 indicated by an alternate long and short dash line show an example of the result according to this example. Specifically, the graph 71 shows the result when the phase difference θ is set to the predetermined value A (that is, when the predetermined value α is set to “0”). Further, the graph 72 shows the results when the phase difference θ is set with the predetermined value α set to “d / λ × 180 ° −180 °” or “d / λ × 180 °”. On the other hand, a graph 73 indicated by a broken line shows an example of the result of the comparative example. Specifically, the graph 73 shows the result when the audio signal is output only from the rear speaker SP2 (it goes without saying that the phase difference θ is not given), and FIG. It is the same as the graph shown.

結果 Compare the result of this example with the result of the comparative example. In the comparative example, the difference between the front and rear levels varies from band to band, and there is a band in the control band where the sound pressure level at the front evaluation point P1 is higher than the sound pressure level at the rear evaluation point P2. Recognize. In contrast, in this embodiment, it can be seen that the sound pressure level at the rear evaluation point P2 is higher than the sound pressure level at the front evaluation point P1 over the entire control band. Specifically, in this embodiment, when the phase difference θ is set to the predetermined value A, the predetermined value α is “d / λ × 180 ° −180 °” or “d / λ × 180 °”. It can be seen that the sound pressure level at the rear evaluation point P2 can be maintained higher than the sound pressure level at the front evaluation point P1 even when the phase difference θ set to “is used.

[Modification]
In the above description, the embodiment has been described in which the phase difference θ is given to the front speaker SP1, but this is not limitative. Instead of giving the phase difference θ to the front speaker SP1, the phase difference θ may be given to the rear speaker SP2. Also when the phase difference θ is applied to the rear speaker SP2, the phase difference θ obtained by the method described above can be used.

The present invention is not limited to application to a configuration in which the rear evaluation point P2 is located in front of the rear speaker SP2, in other words, a configuration in which the rear speaker SP2 is located behind the rear evaluation point P2. The present invention is similarly applied to a configuration in which the rear evaluation point P2 is positioned at the same front-rear direction position as the rear speaker SP2, in other words, a configuration in which the rear speaker SP2 is positioned right next to the rear evaluation point P2. Can do.

In the above, the embodiment in which the audio signal processing apparatus 10 is applied to the vehicle interior is shown, but the present invention is not limited to this. The audio signal processing apparatus 10 can be applied to various acoustic spaces other than the passenger compartment.

In the above, the audio signal processing apparatus 10 having two speakers, the front speaker SP1 and the rear speaker SP2, has been shown. However, the present invention is not limited to application to a system including only two speakers, and three or more The present invention can also be applied to a system having a speaker.

The present invention can be used for various audio devices.

DESCRIPTION OF SYMBOLS 10 Audio | voice signal processing apparatus 11 Audio | voice signal supply part 12 Band pass filter 13 Phase difference provision part P1 Front evaluation point P2 Back evaluation point SP1 Front speaker SP2 Back speaker

Claims

An audio signal processing device that performs processing on an audio signal supplied to a front speaker located in front of a listening position and a rear speaker located behind the listening position,
Audio signal supply means for supplying the same audio signal to the front speaker and the rear speaker;
Phase difference providing means for performing a process for providing a relative phase difference between the audio signal supplied to the front speaker and the audio signal supplied to the rear speaker;
The phase difference providing means has a sound pressure level at a rear evaluation point located behind the listening position and at the same front-rear direction position as the rear speaker or in front of the rear speaker, at the front of the listening position and the front speaker. The audio signal processing apparatus characterized by providing the phase difference so as to be higher than a sound pressure level at a front evaluation point located behind.
The phase difference providing means provides the phase difference according to a distance defined by the front speaker, the rear speaker, the front evaluation point, and the rear evaluation point. The audio signal processing device according to 1.
The distance s1F is defined as the distance between the front speaker and the front evaluation point,
The distance s1B is defined as the distance between the front speaker and the rear evaluation point,
The distance s2F is defined as the distance between the rear speaker and the front evaluation point,
The distance s2B is defined as the distance between the rear speaker and the rear evaluation point,
Define the wavelength λ as the wavelength of the audio signal,
Define the distance d as the distance determined by “d = | s1F−s1B | + | s2F−s2B |”,
The predetermined value A is defined as a value obtained by “A = (s1B−s2B) / λ × 360 °”,
When the predetermined value α is defined as a value within a range defined by “d / λ × 180 ° −180 ° ≦ α ≦ d / λ × 180 °”,
3. The audio signal processing apparatus according to claim 2, wherein the phase difference providing unit provides a phase difference within a range obtained by “A + α” based on the predetermined value A and the predetermined value α. .
Distance acquisition means for acquiring the distances s1F, s1B, s2F, s2B;
A phase difference calculating means for obtaining the distance d, the predetermined value A, and the predetermined value α based on the distances s1F, s1B, s2F, s2B and calculating a phase difference within a range obtained by “A + α”; Further comprising
The audio signal processing apparatus according to claim 3, wherein the phase difference providing unit provides the phase difference calculated by the phase difference calculating unit.
The audio signal processing device according to claim 3 or 4, wherein the phase difference providing unit provides the predetermined value A as the phase difference.
A front microphone disposed at the front evaluation point;
A rear microphone disposed at the rear evaluation point,
The phase difference providing unit obtains the phase difference to be applied based on audio signals output from the front speaker and the rear speaker, which are collected by the front microphone and the rear microphone. The audio signal processing apparatus according to claim 1.
The audio signal processing apparatus according to any one of claims 1 to 6, wherein the phase difference providing unit provides a phase difference different for each frequency of the audio signal as the phase difference.
8. The phase difference adding unit applies the phase difference only when the frequency of the audio signal is in a predetermined band defined by a lower limit value and an upper limit value. 9. The audio signal processing apparatus according to one item.
9. The voice according to claim 8, wherein the lower limit value is a minimum frequency value at which a difference between a sound pressure level at the rear evaluation point and a sound pressure level at the front evaluation point is equal to or greater than a predetermined value. Signal processing device.
The upper limit value is (1) the absolute value of the difference between the distance between the front speaker and the front evaluation point and the distance between the front speaker and the rear evaluation point, and (2) the rear speaker and the front evaluation point. The frequency of the audio signal having a value larger than a value obtained by adding a distance to a point and an absolute value of a difference between a distance between the rear speaker and the rear evaluation point. Item 10. The audio signal processing device according to Item 8 or 9.
An audio signal processing method executed by an audio signal processing device that processes audio signals supplied to a front speaker located in front of a listening position and a rear speaker located behind the listening position,
An audio signal supplying step of supplying the same audio signal to the front speaker and the rear speaker;
A phase difference providing step for performing a process for giving a relative phase difference between the audio signal supplied to the front speaker and the audio signal supplied to the rear speaker,
In the phase difference providing step, the sound pressure level at the rear evaluation point located behind the listening position and in the same front-rear direction position as the rear speaker or in front of the rear speaker is the front of the listening position and the front speaker. The audio signal processing method, wherein the phase difference is given so as to be higher than a sound pressure level at a front evaluation point located behind.
A sound signal processing program for performing processing on a sound signal supplied to a front speaker located in front of the listening position and a rear speaker located behind the listening position, and executed by a sound signal processing device including a computer Because
The computer,
Audio signal supply means for supplying the same audio signal to the front speaker and the rear speaker;
Function as phase difference providing means for performing processing for providing a relative phase difference between the audio signal supplied to the front speaker and the audio signal supplied to the rear speaker;
The phase difference providing means has a sound pressure level at a rear evaluation point located behind the listening position and at the same front-rear direction position as the rear speaker or in front of the rear speaker, at the front of the listening position and the front speaker. An audio signal processing program that gives the phase difference so as to be higher than a sound pressure level at a front evaluation point located behind.