ACOUSTIC PROCESSING DEVICE AND ACOUSTIC PROCESSING METHOD

Abstract

An acoustic processing device unit is provided with: an input reception unit configured to receive an input of a value of a parameter defining a phase difference to be provided between a pair of audio signals; a filter coefficient calculation unit configured to calculate a filter coefficient group corresponding to each of the pair of audio signals based on the input value received by the input reception unit; and a filter processing unit configured to provide a phase difference defined by the input value between the pair of audio signals by performing filter processing on each of the pair of audio signals based on the filter coefficient group calculated by the filter coefficient calculation unit. The parameter above includes a center frequency of the phase difference provided between the pair of audio signals, a quality factor, and a phase difference at the center frequency.

Description

TECHNICAL FIELD

The present invention relates to an acoustic processing device and an acoustic processing method.

BACKGROUND

In a listening environment such as a vehicle interior, for example, standing waves may interfere with each other to cause a dip in a frequency region, thereby deteriorating sound quality or reducing sound pressure.

In order to suppress such a dip, for example, an acoustic processing device that parametrically controls an amplitude characteristic in a frequency domain is known. As an example, an acoustic processing device described in Patent Document 1 reads a filter coefficient group from a memory and applies the filter coefficient group to a filter. The amplitude characteristic is adjusted and the dip is suppressed by the filter processing by the filter. Patent Document 1: Japanese Unexamined Patent Application 2013-219731.

In a conventional acoustic processing device including Patent Document 1, a filter coefficient group calculated under a predetermined condition (for example, under a condition that only a gain is changed by a predetermined value and other parameters are fixed) is stored in advance in a memory. In other words, only a limited filter coefficient group is stored in the memory. Therefore, the degree of freedom of the filter is low.

In order to improve the degree of freedom of the filter, a method of calculating the filter coefficient group under the condition that each parameter is finely changed may be considered. However, in this case, it is necessary to calculate an enormous number of combinations of parameters. Since an enormous amount of time is required for the calculation processing, it is not easy to adopt such a method.

Therefore, in light of the foregoing, an object of the present application is to provide an acoustic processing device and acoustic processing method that can improve the degree of freedom of the filter.

SUMMARY

The acoustic processing device unit according to an embodiment of the present application is provided with: an input reception unit configured to receive an input of a value of a parameter defining a phase difference to be provided between a pair of audio signals; a filter coefficient calculation unit configured to calculate a filter coefficient group corresponding to each of the pair of audio signals based on the input value received by the input reception unit; and a filter processing unit configured to provide a phase difference defined by the input value between the pair of audio signals by performing filter processing on each of the pair of audio signals based on the filter coefficient group calculated by the filter coefficient calculation unit. The parameter above includes a center frequency of the phase difference provided between the pair of audio signals, a quality factor, and a phase difference at the center frequency.

According to an embodiment of the present application, an acoustic processing device and an acoustic processing method are provided wherein it is possible to improve the degree of freedom of a filter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram schematically illustrating a vehicle in which an acoustic processing system according to an embodiment of the present application is installed;

FIG. 2 is a diagram illustrating an example of a phase difference provided by an all-pass filter pair;

FIG. 3 is a diagram illustrating an example of a phase difference provided by an all-pass filter pair;

FIG. 4 is a block diagram illustrating a hardware configuration of an acoustic processing device according to an embodiment of the present application;

FIG. 5 is a functional block diagram of the acoustic processing device according to an embodiment of the present application;

FIG. 6 is a diagram illustrating a flowchart of filter coefficient calculation processing executed in an embodiment of the present application;

FIG. 7 is a diagram illustrating a relationship between a center frequency and a pair of band edge frequencies located around the center frequency in an embodiment of the present application;

FIG. 8A is a diagram illustrating a relationship between a center frequency parameter and a distance between a pair of band edge frequencies on a frequency axis in an embodiment of the present application;

FIG. 8B is a diagram illustrating a relationship between a center frequency parameter and a distance between a pair of band edge frequencies on a frequency axis in an embodiment of the present application;

FIG. 9A is a diagram illustrating a relationship between a quality factor parameter and a distance between a pair of band edge frequencies on a frequency axis in an embodiment of the present application;

FIG. 9B is a diagram illustrating a relationship between a quality factor parameter and a distance between a pair of band edge frequencies on a frequency axis in an embodiment of the present application;

FIG. 10A is a diagram illustrating a relationship between a phase difference parameter and a distance between a pair of band edge frequencies on a frequency axis in an embodiment of the present application;

FIG. 10B is a diagram illustrating a relationship between a phase difference parameter and a distance between a pair of band edge frequencies on a frequency axis in an embodiment of the present application;

FIG. 11A is a diagram for describing the reference term β₀ used for calculating a bandwidth in step S102 of FIG. 6;

FIG. 11B is a diagram for describing the reference term β₀ used for calculating a bandwidth in step S102 of FIG. 6;

FIG. 11C is a diagram for describing the reference term β₀ used for calculating a bandwidth in step S102 of FIG. 6;

FIG. 12A is a diagram for describing the function 131 used for calculating the bandwidth in step S102 of FIG. 6;

FIG. 12B is a diagram for describing the function 131 used for calculating the bandwidth in step S102 of FIG. 6;

FIG. 12C is a diagram for describing the function 131 used for calculating the bandwidth in step S102 of FIG. 6;

FIG. 13A is a diagram for describing the function β₂ used for calculating the bandwidth in step S102 of FIG. 6;

FIG. 13B is a diagram for describing the function β₂ used for calculating the bandwidth in step S102 of FIG. 6;

FIG. 13C is a diagram for describing the function β₂ used for calculating the bandwidth in step S102 of FIG. 6;

FIG. 14 is a diagram illustrating the relationship between the function 3i and the phase difference parameter in the form of a log-log graph;

FIG. 15 is a diagram illustrating a relationship between the function β₂ and the phase difference parameter in a linear graph;

FIG. 16 is a diagram illustrating a relationship between the function β₂ ^(B) and the phase difference parameter in a linear graph according to a variation;

FIG. 17 is a diagram illustrating a relationship between the function β₂ ^(C) and the phase difference parameter in a linear graph according to a variation; and

FIG. 18 is a diagram illustrating a relationship between the product of the function β₁ and the function β₂ ^(C) and the phase difference parameter in a log-log graph.

DETAILED DESCRIPTION OF EMBODIMENTS

The following description relates to an acoustic processing device and acoustic processing method according to an embodiment of the present application.

FIG. 1 is a diagram schematically illustrating a vehicle A (as an example, right-hand steering-wheel car) in which an acoustic processing system 1 according to an embodiment of the present application is installed. As illustrated in FIG. 1, the acoustic processing system 1 is provided with an acoustic processing device 2, a measuring device 3, and a pair of left and right speakers SP_FR and SP_FL.

The acoustic processing device 2 is an example of a computer, and performs phase control by an Infinite Impulse Response (IIR) all-pass filter pair for a pair of transducers to reduce phase interference of a sound field. For example, the acoustic processing device 2 suppresses the occurrence of a dip in a frequency domain due to the interference of standing waves, thereby suppressing the deterioration of sound quality and the reduction of sound pressure.

The speakers SP_FR and SP_FL are an example of a pair of transducers. The speaker SP_FR is a right front speaker embedded in a right door unit (driver's seat side door unit). The speaker SP_FL is a left front speaker embedded in a left door unit (passenger's seat side left door unit).

The vehicle A may have yet another speaker (for example, rear speaker) installed (that is, three or more speakers installed). In this case, the transducer pair to be processed is not limited to the speaker SP_FR and the speaker SP_FL. The transducer pair to be processed may be, for example, two rear speakers installed at left and right positions of a rear seat. Furthermore, the transducer pair to be processed may be the speaker SP_FR and any one of the rear speakers, or may be the speaker SP_FL and any one of the rear speakers.

The measuring device 3 is a well-known device that measures a frequency characteristic of sound, and is installed at a predetermined listening point (a driver's seat, a front passenger's seat, a rear seat, or the like). The measuring device 3 collects sounds output from the speakers SP_FR and SP_FL using a microphone, analyzes a frequency characteristic of the collected sounds, and displays the analyzed frequency characteristic on a display unit.

An operator (user) confirms the frequency characteristic displayed on the display unit of the measuring device 3. For example, when a dip is confirmed, the operator inputs, into the acoustic processing device 2, a parameter value suitable for reducing the phase interference of the sound field at the listening point. Here, the parameters are parameters for calculating a filter coefficient group to be applied to the all-pass filter pair, and specifically, are the center frequency of the phase difference between the pair of audio signals, the quality factor, and the phase difference at the center frequency.

Hereinafter, the parameters of the center frequency, the quality factor (also referred to as Q-value), and the phase difference at the center frequency input by the operator are referred to as a center frequency parameter ω, a quality factor parameter θ, and a phase difference parameter φ, respectively.

The measuring device 3 may not be installed at the listening point. In this case, the operator sits at the listening point and inputs a parameter value suitable for reducing the phase interference of the sound field at the listening point into the acoustic processing device 2 while checking the sound actually heard. That is, the operator may adjust the sound field at the listening point depending on his/her own auditory sense.

Hereinafter, the audio signal of the R channel corresponding to the speaker SP_FR will be referred to as audio signal S_R. Also, the L channel audio signal corresponding to the speaker SP_FL will be referred to as an audio signal S_L.

A phase difference is provided between a pair of audio signals (between the audio signal S_R and the audio signal S_L) by the all-pass filter pair to which the filter coefficient group is applied. Hereinafter, the phase difference between the audio signal S_R and the audio signal S_L is referred to as a phase difference PH in order to be distinguished from the phase difference (phase difference parameter φ) at the center frequency.

In the present embodiment, the operator can provide an appropriate phase difference PH between the audio signal S_R and the audio signal S_L by inputting an appropriate parameter value into the acoustic processing device 2, thereby suppressing occurrence of a dip in a frequency domain due to the interference of standing waves and suppressing the deterioration of sound quality and the reduction in sound pressure.

FIGS. 2 and 3 are diagrams illustrating an example of the phase difference PH provided by the all-pass filter pair. In FIG. 2, the vertical axis (linear axis) represents the phase, and the horizontal axis (logarithmic axis) represents frequency. In FIG. 2, the broken line illustrated by reference numeral APF1 illustrates the phase characteristic of the all-pass filter corresponding to the L channel. Frequencies at intersections of the broken line APF1 and the horizontal axis are band edge frequencies f_C⁻ to be described later. The alternate long and short dash line illustrated by reference numeral APF2 illustrates a phase characteristic of the all-pass filter corresponding to the R channel. The frequencies at the intersections of the alternate long and short dash line APF2 and the horizontal axis are band edge frequencies f_C⁺ to be described later.

In FIG. 3, the vertical axis (linear axis) illustrates the phase difference, and the horizontal axis (logarithmic axis) illustrates the frequency. FIG. 3 illustrates the phase difference PH which is a difference between the phase characteristics illustrated in FIG. 2. As illustrated in FIG. 3, the phase difference PH is determined by each value of the center frequency parameter ω, the quality factor parameter θ, and the phase difference parameter φ.

Here, in the conventional configuration, only the filter coefficient group stored in advance in the memory can be used to execute the filter processing. In this configuration, since only a limited filter coefficient group can be used, it is difficult to realize the adjustment of the phase difference PH by the all-pass filter pair with high resolution. Further, it is necessary to secure a storage area for storing a large number of filter coefficient groups in the memory.

On the other hand, the acoustic processing device 2 is configured to apply the phase difference PH input by the operator (for example, the phase difference defined by the values of the center frequency parameter ω, the quality factor parameter θ, and the phase difference parameter φ illustrated in FIG. 3) between the pair of audio signals by the all-pass filter pair. That is, the acoustic processing device 2 calculates a filter coefficient group based on the values of the center frequency parameter ω, the quality factor parameter θ, and the phase difference parameter input by the operator, performs filter processing based on the calculated filter coefficient group, and gives the phase difference PH indicated by the operator to the audio signal pair.

In the acoustic processing device 2, since the filter can be set based on an arbitrary parameter value, the degree of freedom of the filter is higher than that of the conventional configuration. Further, it is not necessary to secure a storage area for storing a large number of filter coefficient groups in the memory.

FIG. 4 is a block diagram illustrating a hardware configuration of the acoustic processing device 2. As illustrated in FIG. 4, the acoustic processing device 2 is provided with a player 10, an LSI (Large Scale Integration) 11, a D/A converter 12, an amplifier 13, a display unit 14, an operation unit 15, and a flash memory 16.

The player 10 is connected to a sound source. The player 10 plays an audio signal input from the sound source, which is then output to the LSI 11.

Examples of the sound source include disc media such as CDs (Compact Discs), SACDs (Super Audio CDs), and the like, and storage media such as HDDs (Hard Disk Drive), USBs (Universal Serial Bus), and the like that store digital audio data. A telephone (for example, a feature phone or smartphone) may be the sound source. In this case, the player 10 outputs a voice signal during a call input from the telephone through to the LSI 11.

The LSI 11 is provided with a CPU (Central Processing Unit), RAM (Random Access Memory), ROM (Read Only Memory), and the like. The CPU of the LSI 11 includes a single processor or a multiprocessor (in other words, at least one processor) that executes a program written in the ROM of the LSI 11, and comprehensively controls the acoustic processing device 2.

The LSI 11 executes a program developed in a work area such as a RAM to receive input of a value of a parameter (specifically, the center frequency parameter ω, the quality factor parameter θ, and the phase difference parameter φ) defining the phase difference PH to be provided between the pair of audio signals, calculates the filter coefficient group corresponding to each of the pair of audio signals based on the received input value, and perform filter processing on each of the pair of audio signals based on the calculated filter coefficient group to provide the phase difference PH defined by the input value between the pair of audio signals.

By executing the program, for example, a suitable phase difference PH is provided between the audio signal S_R and the audio signal S_L, occurrence of a dip in a frequency domain due to the interference of standing waves is suppressed, and deterioration in sound quality and reduction in sound pressure are suppressed.

The audio signals S_R and S_L after the filter processing by the LSI 11 are converted to an analog signal by the D/A converter 12. The analog signal is amplified by the amplifier 13 and output to the speakers SP_FR and SP_FL. As a result, music recorded in the sound source, for example, is reproduced in the vehicle interior from the speakers SP_FR and SP_FL.

In the present embodiment, a vehicle-mounted acoustic processing system 1 is exemplified. However, even in a listening environment such as a room of a building, a dip may occur in a frequency domain due to interference of standing waves at a listening point. Therefore, the acoustic processing system 1 may be implemented for listening environments other than a vehicle interior.

The display unit 14 is a device that displays various screens, such as a settings screen, and examples include displays such as LCDs (Liquid Crystal Displays) and organic EIs (Electro Luminescence). The display unit 14 may be configured to include a touch panel.

The operation unit 15 includes operators such as switches, buttons, knobs, and wheels, that are mechanical systems, capacitance non-contact systems, membrane systems, or the like. When the display unit 14 includes a touch panel, the touch panel also forms a portion of the operation unit 15.

For example, when the operator inputs values of the center frequency parameter ω, the quality factor parameter θ, and the phase difference parameter φ using the operation unit 15, a phase difference PH (see FIG. 3) corresponding to these input values is displayed on the display unit 14. The operator can change the shape of the curved line (in other words, change the value of at least one of the center frequency parameter ω, the quality factor parameter θ, and the phase difference parameter φ) by touching and sliding a portion of the curved line indicating the phase difference PH on the touch panel, for example.

FIG. 5 is a functional block diagram of the acoustic processing device 2. The functions illustrated in each block in the functional block diagram are executed by cooperation of software and hardware provided in the acoustic processing system 1.

As illustrated in FIG. 5, the acoustic processing device 2 includes, as functional blocks, an input reception unit 210, a filter coefficient calculation unit 220, and a filter processing unit 230. The filter processing unit 230 includes an R filter unit 232 and an L filter unit 234.

The input reception unit 210 receives an input by an operator using the operation unit 15, which is an input of a value of a parameter defining a phase difference to be provided between a pair of audio signals.

The filter coefficient calculation unit 220 calculates a filter coefficient group corresponding to each of the pair of audio signals based on the input value received by the input reception unit 210.

Specifically, the filter coefficient calculation unit 220 calculates a filter coefficient group FC_R (an example of a first filter coefficient group) corresponding to the R channel and a filter coefficient group FC_L (an example of a second filter coefficient group) corresponding to the L channel based on the values of the center frequency parameter ω, the quality factor parameter θ, and the phase difference parameter φ input using the operation unit 15.

The filter processing unit 230 performs filter processing on each of the pair of audio signals based on the filter coefficient group calculated by the filter coefficient calculation unit 220, thereby providing the phase difference PH defined by the input value between the pair of audio signals.

The R filter unit 232 is an example of a first all-pass filter, and the filter coefficient group FC_R is applied thereto. The L filter unit 234 is an example of a second all-pass filter, and the filter coefficient group FC_L is applied thereto. The R filter unit 232 and the L filter unit 234 constitute, for example, a direct form I IIR all-pass filter.

To the R filter unit 232, the audio signal S_R of the R channel is input from the player 10 and the filter coefficient group FC_R is input from the filter coefficient calculation unit 220. The R filter unit 232 performs filter processing on the audio signal S_R using the filter coefficient group FC_R.

To the L filter unit 234, the audio signal S_L of the L channel is input from the player 10 and the filter coefficient group FC_L is input from the filter coefficient calculation unit 220. The L filter unit 234 performs filter processing on the audio signal S_L using the filter coefficient group FC_L.

As a result of the filtering processing performed by the R filter unit 232 and the L filter unit 234, the phase difference PH (the phase difference defined by the values of the center frequency parameter ω, the quality factor parameter θ, and the phase difference parameter φ) specified by the operator is provided given to the audio signal pair. The audio signals S_R and S_L to which the phase difference PH is provided are output as sound into the vehicle interior by the speakers SP_FR and SP_FL via the D/A converter 12 and the amplifier 13. By providing a suitable phase difference PH in the R filter unit 232 and the L filter unit 234, occurrence of a dip in a frequency domain due to the interference of standing waves is suppressed, and deterioration of sound quality and reduction in sound pressure are suppressed.

A method of calculating a filter coefficient group by the filter coefficient calculation unit 220 will be specifically described.

Characteristics of the R filter unit 232 and the L filter unit 234 are expressed as in Equation 1, using a biquad transfer function H(z) of Z transform. In Equation 1, a₀, a₁, and a₂ represent filter coefficients of the denominator of the biquad transfer function H(z). b₀, b₁, and b₂ represent filter coefficients of the numerator of the biquad transfer function H(z). The filter coefficient calculation unit 220 calculates a total of the above six filter coefficients for each of the R channel and the L channel.

$\begin{array}{cc}H\left(z\right)=\frac{b_0+b_1{z}^{-1}+b_2{z}^{-2}}{a_0+a_1{z}^{-1}+a_2{z}^{-2}}& \left(\mathrm{Equation}1\right)\end{array}$

Equation 2 is derived when normalization is performed so that the filter coefficient a₀ becomes 1 in Equation 1. Further, by transforming Equation 2, the characteristics of the R filter unit 232 and the L filter unit 234 implemented as direct form I can be expressed by Equation 3. In Equation 3, y represents the output signal and x represents the input signal.

$\begin{array}{cc}H\left(z\right)=\frac{\left(\frac{b_0}{a_0}\right)+\left(\frac{b_1}{a_0}\right)z^{-1}+\left(\frac{b_2}{a_0}\right)z^{-2}}{1+\left(\frac{{\alpha }_1}{a_0}\right)z^{-1}\left(\frac{a_2}{a_0}\right)z^{-2}}& \left(\mathrm{Equation}2\right)\end{array}$ $\begin{array}{cc}y\left[n\right]-\left(\frac{b_0}{a_0}\right)x\left[n\right]+\left(\frac{b_1}{a_0}\right)x\left[n-1\right]+\left(\frac{b_2}{a_0}\right)x\left[n-2\right]-\left(\frac{{\alpha }_1}{{\alpha }_0}\right)y\left[n-1\right]-\left(\frac{{\alpha }_2}{{\alpha }_0}\right)y\left[n-2\right]& \left(\mathrm{Equation}3\right)\end{array}$

The R filter unit 232 and the L filter unit 234, which are all-pass filters, can be represented as analog prototype filters having a transfer function H(s) as in Equation 4.

$\begin{array}{cc}H\left(s\right)=\frac{s^2-\frac{s}{Q}+1}{s^2+\frac{s}{Q}+1}& \left(\mathrm{Equation}4\right)\end{array}$

A filter coefficient group (six filter coefficients a₀, a₁, a₂, b₀, b₁, and b₂) shown in the following Equation 5 is derived from Equations 3 and 4. In order to derive Equation 5, for example, a known bilinear transform is used, but the method of deriving Equation 5 is not limited thereto.

b ₀=1−α

b ₁=−2 cos ω₀

b ₂=1+α

a ₀=1+α

a ₁=−2 cos ω₀

a ₂=1−α  (Equation 5)

Further, intermediate variables ω₀ and a included in Equation 5 are represented by Equations 6 and 7, respectively. In Equation 6, f₀ represents the center frequency of the filter calculated by the filter coefficient calculation unit 220. In Equation 7, β represents the bandwidth of the filter calculated by the filter coefficient calculation unit 220.

$\begin{array}{cc}{\omega }_0=2\pi f_0& \left(\mathrm{Equation}6\right)\end{array}$ $\begin{array}{cc}\alpha =\sin \left({\omega }_0\right)\sinh \left(\frac{\ln 2}{2}·\beta ·\frac{{\omega }_0}{\sin {\omega }_0}\right)& \left(\mathrm{Equation}7\right)\end{array}$

FIG. 6 illustrates a flowchart of a filter coefficient calculation process executed in the filter coefficient calculation unit 220.

The filter coefficient calculation unit 220 calculates band edge frequencies f_C⁺ and f_C⁻ corresponding to the R channel and the L channel, respectively (step S101).

The filter coefficient calculation unit 220 obtains a bandwidth 13 based on the band edge frequencies f_C⁺ and f_C⁻ calculated in step S101 (step S102).

The filter coefficient calculation unit 220 further substitutes the band edge frequency f_C⁺ as the center frequency f₀ into Equation 6 to calculate the intermediate variable ω₀ corresponding to the R channel, and substitutes the band edge frequency f_C⁻ as the center frequency f₀ into Equation 6 to calculate the intermediate variable ω₀ corresponding to the L channel (step S103).

The filter coefficient calculation unit 220 substitutes the bandwidth 13 and the intermediate variable ω₀ corresponding to the R channel into Equation 7 to calculate the intermediate variable α corresponding to the R channel, and substitutes the bandwidth β and the intermediate variable ω₀ corresponding to the L channel into Equation 7 to calculate the intermediate variable α corresponding to the L channel (step S104).

The filter coefficient calculation unit 220 substitutes the intermediate variables ω₀ and a corresponding to the R channel into Equation 5 to obtain the filter coefficient group FC_R, and substitutes the intermediate variables ω₀ and a corresponding to the L channel into Equation 5 to obtain the filter coefficient group FC_L (step S105).

Next, the filter coefficient calculation processing illustrated in FIG. 6 will be described more specifically.

In step S101, the band edge frequencies f_C⁺ and f_C⁻ are obtained by using the functions f₁(ω, θ, φ) and f₂(ω, θ, φ) with the center frequency parameter ω, the quality factor parameter θ and the phase difference parameter φ as variables, respectively.

The distance D on the frequency axis (logarithmic axis) between the band edge frequencies f_C⁺ and f_C⁻ calculated by the function f₁(ω, θ, φ) and the function f₂(ω, θ, φ) has a negative correlation with the quality factor parameter θ and a positive correlation with the phase difference parameter φ. According to the function f₁(ω, θ, φ) and the function f₂(ω, θ, φ), the band edge frequencies f_C⁺ and f_C⁻ are calculated, being symmetrical centered on a center frequency (a value of the center frequency parameter ω, hereinafter given the reference numeral f_C) on a frequency axis (for example, a logarithmic axis) in consideration of human auditory characteristics.

FIG. 7 is a diagram illustrating the relationship between the center frequency f_C and the band edge frequencies f_C⁺ and f_C⁻. In FIG. 7, the horizontal axis represents frequency, which is represented by a logarithmic axis. As illustrated in FIG. 7, frequencies at positions symmetrical on the logarithmic axis centered on the center frequency f_C are calculated as band edge frequencies f_C⁺ and f_C⁻ by the functions f₁(ω, θ, φ) and f₂(ω, θ, φ).

The characteristics of the function f₁(ω, θ, φ) and the function f₂(ω, θ, φ) will be described with reference to FIG. 8A, FIG. 8B, FIG. 9A, FIG. 9B, FIG. 10A and FIG. 10B.

FIG. 8A and FIG. 8B are diagrams that illustrate the distance D when the values of the quality factor parameter θ and the phase difference parameter φ are fixed and the value of the center frequency parameter ω is changed. In each of FIG. 8A and FIG. 8B, the vertical axis represents the distance D, and the horizontal axis represents the center frequency parameter ω.

FIG. 9A and FIG. 9B are diagrams that illustrate the distance D when the values of the center frequency parameter ω and the phase difference parameter φ are fixed and the value of the quality factor parameter θ (Q value) is changed. In each of FIG. 9A and FIG. 9B, the vertical axis represents the distance D, and the horizontal axis represents the quality factor parameter θ.

FIG. 10A and FIG. 10B are diagrams that illustrate the distance D when the values of the center frequency parameter ω and the quality factor parameter θ are fixed and the value of the phase difference parameter φ is changed. In each of FIG. 10A and FIG. 10B, the vertical axis represents the distance D, and the horizontal axis represents the phase difference parameter φ.

Drawings labeled “Linear diff” show the distance D on the linear axis. Drawings labeled “Log diff” show the distance D on the logarithmic axis. Drawings labeled “Linear plot” show the horizontal axis as a linear axis. Drawings labeled “log-log plot” show a log-log graph (log-log axis).

As illustrated in FIG. 8B, the distance D is constant on the logarithmic axis regardless of the value of the center frequency parameter ω. As illustrated in FIG. 9A and FIG. 9B, the distance D has a negative correlation with the quality factor parameter θ (particularly on the log-log axes). As illustrated in FIG. 10A and FIG. 10B, the distance D has a positive correlation with the phase difference parameter φ.

In step S101, band edge frequencies f_C⁺ and f_C⁻ are calculated using the function f₁(ω, θ, φ) and the function f₂(ω, θ, φ). The distance D on the frequency axis between the band edge frequencies f_C⁺ and f_C⁻ calculated by these functions has a negative correlation with the quality factor parameter θ and a positive correlation with the phase difference parameter φ. Furthermore, the band edge frequencies f_C⁺ and f_C⁻ calculated by these functions appear at positions symmetrical centered on the center frequency f_C on the logarithmic axis in which the human auditory characteristics are taken into consideration.

In this way, the filter coefficient calculation unit 220 calculates the band edge frequency f_C⁺ (an example of the frequency of the first control target for one of the pair of audio signals) and the band edge frequency f_C⁻ (an example of the frequency of the second control target for the other of the pair of audio signals) based on the input values (the values of the center frequency parameter ω, the quality factor parameter θ, and the phase difference parameter φ).

In addition, the filter coefficient calculation unit 220 gives the input values to the function f₁(ω, θ, φ) (an example of a first function) and the function f₂(ω, θ, φ) (an example of a second function) to obtain one of a pair of frequencies (for example, the band-end frequency f_C⁺) located symmetrically around the center frequency on the logarithmic axis as the frequency of the first control object and the other of the pair of frequencies (for example, the band edge frequency f_C⁻) as the frequency of the second control object. The distance D, which is the difference value between the function f₁(ω, θ, φ) and the function f₂(ω, θ, φ), has a negative correlation with the quality factor parameter θ and has a positive correlation with the phase difference parameter φ.

For example, a constant term (numerically, for example, a value in consideration of a ⅓ octave band) in consideration of human auditory characteristics may be incorporated into the function f₁(ω, θ, φ) and the function f₂(ω, θ, φ).

Furthermore, a parametric equalizer is widely known as a technique for adjusting amplitude. In the parametric equalizer, for example, a center frequency, a bandwidth, and a gain are adopted as input parameters. Therefore, an adjustment term for approximating the curve of the peak determined by the input values of the center frequency parameter ω, the quality factor parameter θ, and the phase difference parameter φ (see FIG. 3) to the curve of the Q value determined by the input values (center frequency, bandwidth, gain) of the parametric equalizer may be incorporated into the function f₁(ω, θ, φ) and the function f₂(ω, θ, φ). By incorporating such an adjustment term, for example, an operator who is familiar with the operation of the parametric equalizer can easily perform the adjustment operation of the phase difference by the acoustic processing device 2.

In step S102, the bandwidth β is determined by Equation 8.

$\begin{array}{cc}\beta ={\beta }_0·{\beta }_1·{\beta }_2& \left(\mathrm{Equation}8\right)\end{array}$ $\mathrm{However},$ ${\beta }_0=\frac{f_c^{+}-f_c^{-}}{\omega },{\beta }_1=\frac{180}{❘\Phi ❘},{\beta }_2=\frac{360-❘\Phi ❘}{90}$

The characteristics of Expression 8 will be described using the FIG. 11A to FIG. 11C, FIG. 12A to FIG. 12C, and FIG. 13A to FIG. 13C.

FIG. 11A, FIG. 12A, and FIG. 13A respectively illustrate values of a reference term β₀, the function β₁, and the function β₂ when the values of the quality factor parameter θ and the phase difference parameter φ are fixed and the value of the center frequency parameter ω is changed. In each of FIG. 11A, FIG. 12A, and FIG. 13A, the vertical axis represents the reference term β₀, the function β₁, and the function β₂. The horizontal axis represents the center frequency parameter ω.

FIG. 11B, FIG. 12B, and FIG. 13B are diagrams that respectively show the values of the reference term β₀, the function β₁, and the function β₂ when the values of the center frequency parameter ω and the phase difference parameter φ are fixed and the value of the quality factor parameter θ (Q value) is changed. In each of FIG. 11B, FIG. 12B, and FIG. 13B, the vertical axis represents the reference term β₀, the function β₁, and the function β₂. The horizontal axis represents the quality factor parameter θ.

FIG. 11C, FIG. 12C, and FIG. 13C respectively illustrate values of the reference term β₀, the function β₁, and the function β₂ when the values of the center frequency parameter ω and the quality factor parameter θ are fixed and the value of the phase difference parameter φ is changed. In each of FIG. 11C, FIG. 12C, and FIG. 13C, the vertical axis represents the reference term β₀, the function β₁, and the function β₂. The horizontal axis represents the phase difference parameter φ.

In these drawings, the fixed value of the center frequency parameter ω is 1000 (kHz), the fixed value of the quality factor parameter θ is 1, and the fixed value of the phase difference parameter φ is 180°.

As illustrated in FIG. 11A, the reference term β₀ is constant regardless of the value of the center frequency parameter ω. As illustrated in FIG. 11B and FIG. 11C, the reference term β₀ varies depending on the quality factor parameter θ and the phase difference parameter φ. More specifically, the reference term β₀ changes as the difference absolute value between the band edge frequencies f_C⁺ and f_C⁻ changes in accordance with the quality factor parameter θ. In addition, the reference term β₀ changes as the difference absolute value above changes according to the phase difference parameter Φ. Therefore, the reference term Po can be expressed as, for example, “a term obtained by a difference absolute value between the band edge frequencies f_C⁺ and f_C⁻ and the center frequency parameter ω.”

As illustrated in each of FIG. 12A and FIG. 12B, the function β₁ is constant regardless of the value of the center frequency parameter ω, and is constant regardless of the value of the quality factor parameter θ. However, the function β₁ varies depending on the phase difference parameter φ as illustrated in FIG. 12C.

As illustrated in each of FIG. 13A and FIG. 13B, the function (32 is also constant regardless of the value of the center frequency parameter ω, and is also constant regardless of the value of the quality factor parameter θ. The function (32 also changes according to the phase difference parameter φ as illustrated in FIG. 13C.

FIG. 14 is a diagram illustrating the relationship between the function β₁ and the phase difference parameter φ in the form of a log-log graph. As illustrated in FIG. 14, the function β₁ has a negative correlation with the phase difference parameter φ and decreases substantially linearly on the log-log axis.

For convenience, the value of the function β₁ when the phase difference parameter φ is 0° is assumed to be 180. In this case, the function β₁ can be expressed as, for example, “a function having a negative correlation with the phase difference parameter φ, and a function of the phase difference parameter φ having a predetermined closed interval ([0,180] in the present embodiment) as a domain and a value range.”

FIG. 15 is a diagram illustrating a relationship between the function β₂ and the phase difference parameter φ in a linear graph. As illustrated in FIG. 15, the function β₂ has a negative correlation with the phase difference parameter φ, and decreases substantially linearly with a closed interval [√2, 2] as a range on the linear axis.

As a variation, the function β₂ can also be represented by Equation 9 or Equation 10.

$\begin{array}{cc}{\beta }_2^{\left(B\right)}={\sqrt{2}}^{\frac{360-❘\Phi ❘}{180}}& \left(\mathrm{Equation}9\right)\end{array}$ $$\begin{gathered} \begin{array}{cc}{\beta }_2^{\left(C\right)}=\frac{{\beta }_2^{\left(A\right)}+{\beta }_2^{\left(B\right)}}{2}\text{ \\ However,β2(A)=36⁢❘"[LeftBracketingBar]"Φ❘"[RightBracketingBar]"9⁢0}& \left(\mathrm{Equation}10\right)\end{array} \end{gathered}$$

FIG. 16 is a diagram illustrating the relationship between the function β₂^(B) represented in Equation 9 and the phase difference parameter φ in a linear graph. FIG. 17 is a diagram illustrating the relationship between the function β₂^(C) represented in Equation 10 and the phase difference parameter φ in a linear graph.

According to FIG. 15 to FIG. 17, the function β₂ can be expressed as, for example, “a function having a negative correlation with the phase difference parameter φ and converging from 2 to √2 as the phase difference parameter φ increases.”

FIG. 18 is a diagram illustrating a relationship between the product of the function β₁ and the function β₂ and the phase difference parameter φ in a log-log graph. As illustrated in FIG. 18, the product of two functions also has a negative correlation with the phase difference parameter φ and decreases substantially linearly on the log-log axis. For example, when the phase difference parameter φ is 1°, the function β₁ is 180 and the function β₂ is approximately 2. Furthermore, for example, when the phase difference parameter φ is 180°, the function β₁ is 1, and the function β₂ is √2. Therefore, as illustrated in FIG. 18, the product above takes a value of 360 to approximately √2 according to the phase difference parameter φ.

As described above, in step S102, the filter coefficient calculation unit 220 calculates the bandwidth β of the filter based on the frequencies of the first control target and the frequencies of the second control target (that is, the band edge frequencies f_C⁺ and f_C⁻). In addition, the filter coefficient calculation unit 220 calculates the reference term β₀ based on the difference absolute value between the frequencies of the first and second control objects and the center frequency parameter ω, and obtains the bandwidth β by multiplying the calculated reference term β₀ by a function β₁ (an example of a third function) having a negative correlation with the phase difference parameter φ and having a predetermined closed interval as a domain and a value range, and a function β₂ (an example of a fourth function) having a negative correlation with the phase difference parameter φ and converging from 2 to √2 as the phase difference parameter φ increases.

In step S103, the intermediate variable ω₀ corresponding to the R channel is obtained by Equation 11, and the intermediate variable ω₀ corresponding to the L channel is obtained by Equation 12.

ω₀=2πf_C⁺  (Equation 11)

ω₀=2πf_C⁻  (Equation 12)

In step S104, the intermediate variable α_fC⁺ corresponding to the R channel is obtained by Equation 13, and the intermediate variable α_fC⁻ corresponding to the L channel is obtained by Equation 14. In Equation 13, the notation of “f_C⁺” is exactly ω₀ corresponding to the R channel, that is, “2πf_C⁺.” In addition, in Equation 14, the notation of “f_C⁻” is exactly ω₀ corresponding to the L channel, that is, “2πf_C⁻.”

$\begin{array}{cc}{\alpha }_{f_c^{+}}=\sin \left(f_c^{+}\right)\sinh \left(\frac{\ln 2}{2}·\beta ·\frac{f_c^{+}}{\sin f_c^{+}}\right)& \left(\mathrm{Equation}13\right)\end{array}$ $\begin{array}{cc}{\alpha }_{f_c^{-}}=\sin \left(f_c^{-}\right)\sinh \left(\frac{\ln 2}{2}·\beta ·\frac{f_c^{-}}{\sin f_c^{-}}\right)& \left(\mathrm{Equation}14\right)\end{array}$

In step S105, the filter coefficient group FC_R is obtained by substituting the intermediate variable ω₀ obtained by Equation 11 and the intermediate variable αf_C⁺ obtained by Equation 13 into Equation 5. Further, the filter coefficient group FC_L is obtained by substituting the intermediate variable ω₀ obtained by Equation 12 and the intermediate variable α_fC⁻ obtained by Equation 14 into Equation 5.

As described above, in steps S103 to S105, the filter coefficient calculation unit 220 calculates the filter coefficient group FC_R (an example of the first filter coefficient group corresponding to one audio signal) based on the frequency and bandwidth of the first control target (that is, the band edge frequency f_C⁺ and the bandwidth β), and calculates the filter coefficient group FC_L (an example of the second filter coefficient group corresponding to the other audio signal) based on the frequency and bandwidth of the second control target (that is, the band edge frequency f_C⁻ and the bandwidth β).

By the all-pass filter pair (the R filter unit 232 and the L filter unit 234) to which such a filter coefficient group is provided, the phase difference PH that satisfies the values of the center frequency parameter ω, the quality factor parameter θ, and the phase difference parameter φ designated by the operator is provided to the audio signal S_R and the audio signal S_L.

According to the present embodiment, since the filter can be set based on arbitrary values of the center frequency parameter ω, the quality factor parameter θ, and the phase difference parameter φ, the degree of freedom of the filter is higher than that of the conventional configuration. In other words, since the parameter values can be arbitrarily determined, the resolution of the phase difference that can be set for the audio signal S_R and the audio signal S_L is high. Further, by inputting a parameter value, a phase difference corresponding to the parameter value can be immediately provided to the audio signal S_R and the audio signal S_L. Further, it is not necessary to secure a storage area for storing a large number of filter coefficients in the memory.

The above is a description of an exemplary embodiment of the present application. The embodiments of the present application are not limited to those described above, and various modifications are possible within the scope of the technical concept of the present invention. For example, appropriate combinations of embodiments and the like that are explicitly indicated by way of example in the specification or obvious embodiments and the like are also included in the embodiments of the present application.

For example, in the above description, an acoustic processing device 2 was shown that is provided with only one pair of all-pass filters, but a pair of all-pass filters is required for each band to which a phase difference is to be applied, for example. Therefore, the acoustic processing device 2 may be configured to include a plurality of pairs of all-pass filters so as to be able to apply phase differences to a plurality of bands.

In addition, in the above-described embodiment, the filter coefficient calculation unit 220 performs calculation using, for example, a logarithm, but may perform an equivalent calculation without using a logarithm.

In addition, in the above-described embodiment, the operator inputs each parameter value to the acoustic processing device 2. However, in another embodiment, for example, a higher-level program different from the program installed in the acoustic processing device 2 may automatically provide each parameter value to the acoustic processing device 2.

As an example, a device in which a higher program is installed acquires an image captured by an in-vehicle camera, extracts a person from the acquired captured image, and acquires a seating position of each extracted person. This device provides each parameter value to the acoustic processing device 2 for a transducer pair according to the acquired seating position. For example, when only a person seated in the driver's seat is extracted, the device provides each parameter value for the speakers SP_FR and SP_FL to the acoustic processing device 2. In addition, for example, when a person seated on the driver's seat and a person seated on the rear seat are extracted, the device provides each parameter value for the speakers SP_FR and SP_FL and two rear speakers (that is, each of two transducer pairs) to the acoustic processing device 2.

DESCRIPTION OF REFERENCE NUMERALS

• • 1: Acoustic processing system
  • 2: Acoustic processing device
  • 3: Measuring device
  • 10: Player
  • 11: LSI
  • 12: D/A converter
  • 13: Amplifier
  • 14: Display unit
  • 15: Operation unit
  • 16: Flash memory
  • 210: Input reception unit
  • 220: Filter coefficient calculation unit
  • 230: Filter processing unit
  • 232: R filter unit
  • 234: L filter unit

Claims

1. An acoustic processing device, comprising: an input reception unit configured to receive an input of a value of a parameter defining a phase difference to be provided between a pair of audio signals;a filter coefficient calculation unit configured to calculate a filter coefficient group corresponding to each of the pair of audio signals based on the input value received by the input reception unit; anda filter processing unit configured to provide a phase difference defined by the input value between the pair of audio signals by performing filter processing on each of the pair of audio signals based on the filter coefficient group calculated by the filter coefficient calculation unit;wherein the parameter includes a center frequency of the phase difference provided between the pair of audio signals, a quality factor, and a phase difference at the center frequency.

2. The acoustic processing device according to claim 1, wherein the filter coefficient calculation unit is configured to: calculate a frequency of a first control target with respect to one of the pair of audio signals based on the input value and calculate a frequency of a second control target with respect to the other of the pair of audio signals based on the input value;calculate a bandwidth of a filter based on the frequency of the first control target and the frequency of the second control target;calculate a first filter coefficient group corresponding to the one audio signal based on the frequency and the bandwidth of the first control target; andcalculate a second filter coefficient group corresponding to the other audio signal based on the frequency and the bandwidth of the second control target and the bandwidth.

3. The acoustic processing device according to claim 2, wherein the filter coefficient calculation unit is configured to: provide the input value to a first function and a second function to obtain one of a pair of frequencies located symmetrically around the center frequency on a logarithmic axis as the frequency of the first control target and to obtain the other of the pair of frequencies as the frequency of the second control target, anda difference value between the first function and the second function has a negative correlation with the parameter of the quality factor and a positive correlation with the parameter of the phase difference at the center frequency.

4. The acoustic processing device according to claim 2, wherein the filter coefficient calculation unit is configured to: calculate a reference term based on the center frequency and a difference absolute value between the frequency of the first control target and the frequency of the second control target; andobtain the bandwidth by multiplying the calculated reference term by a third function having a negative correlation with the parameter of the phase difference at the center frequency and having a predetermined closed interval as a domain and a value range, and a fourth function having a negative correlation with the parameter of the phase difference at the center frequency and converging from 2 to √2 as the parameter of the phase difference at the center frequency increases.

5. The acoustic processing device according to claim 2, wherein the filter processing unit comprises a first all-pass filter and a second all-pass filter; the first filter coefficient group is a filter coefficient group applied to the first all-pass filter; andthe second filter coefficient group is a filter coefficient group applied to the second all-pass filter.

6. An acoustic processing method for execution in a computer, the method comprising the steps of: receiving an input of a value of a parameter defining a phase difference to be provided between a pair of audio signals;calculating a filter coefficient group corresponding to each of the pair of audio signals based on the received input value; andproviding the phase difference defined by the input value between the pair of audio signals by performing filter processing on each of the pair of audio signals based on the calculated filter coefficient group;wherein the parameter includes a center frequency of the phase difference provided between the pair of audio signals, a quality factor, and a phase difference at the center frequency.