Generation device, generation method, and program

Abstract

To achieve high suppression performance even at the ear of a user away from an actual error microphone by using a sound collection signal obtained by estimation instead of a sound collection signal collected at an arrangement position of the actual error microphone for estimating the sound collection signal obtained when it is collected at the ear of the user from the sound collection signal collected at the arrangement position of the actual error microphone and actively controlling a cancel signal.SOLUTION: A generation device generates a cancel signal used for active noise control. The generation device generates the cancel signal so that a point in which a suppression amount of noise is maximum is located closer to a user side than an installation position of an error microphone.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to an active noise control (ANC) technique that suppresses external noise at a specific position. [Background technology]

[0002] Non-Patent Document 1 is known as a conventional active noise suppression technology. In active noise suppression, a reference microphone, an error microphone, and a cancellation speaker are generally used. FIG. 1 shows an example of the configuration of a conventional noise suppression device. A reference microphone 91 collects noise emitted from a noise source. A cancellation speaker 92 reproduces a cancellation signal generated by a suppression signal generating device 90 to emit a cancellation sound that cancels the noise. Furthermore, an error microphone 93 collects and feeds back the remaining noise. The suppression signal generating device 90 actively controls and generates a cancellation signal using the collected signal of the reference microphone 91 and the collected signal of the error microphone 93 so that the remaining noise is reduced. Since the cancellation speaker 92 emits a cancellation sound so that the remaining noise is reduced at the installation position of the error microphone 93, the cancellation sound most efficiently suppresses noise at the installation position of the error microphone 93. For this reason, the error microphone 93 is installed close to the user's ear. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Kajikawa, "Recent Topics and Applications of Active Noise Control", Research Report on Music Information Science (MUS), vol. 2015-MUS-107, no. 3, pp. 1-6, May 2015. Summary of the Invention [Problem to be solved by the invention]

[0004] However, in actual use, there are cases where the error microphone 93 cannot be placed close to the user's ear, and if the distance between the installation position of the error microphone 93 and the user's ear is large, as described above, the noise is most efficiently suppressed at the installation position of the error microphone 93, and the noise remaining at the user's ear increases, the suppression performance decreases, and the user may not be able to fully benefit from the noise suppression. For example, it was confirmed by simulation that the suppression performance is -∞ dB when the distance from the noise source to the ear is 100 mm and the error microphone 93 is placed at the user's ear (0 mm), and the suppression performance is -7.38 dB when the error microphone 93 is placed at the midpoint between the noise source and the ear. Figure 2 is a diagram for explaining the difference between the suppression possible area (sweet spot) S1 of the conventional technology and the desired sweet spot S2.

[0005] The present invention aims to provide a generation device, generation method, and program thereof that estimates a picked-up signal that would be obtained if sound were picked up near a user's ear from a picked-up signal picked up at the actual position of the error microphone, and uses the estimated picked-up signal instead of the picked-up signal picked up at the actual position of the error microphone in order to actively control a cancellation signal, thereby achieving high suppression performance even near a user's ear that is far from the actual error microphone. [Means for solving the problem]

[0006] In order to solve the above problems, according to one aspect of the present invention, a generating device generates a cancellation signal for use in active noise control. The generating device generates the cancellation signal so that a point at which the amount of noise suppression is maximized is located closer to the user than the installation position of the error microphone. Effect of the Invention

[0007] According to the present invention, it is possible to achieve an effect of realizing higher suppression performance than in the past when an error microphone cannot be placed close to the user's ear. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram for explaining a conventional active noise control. [Diagram 2] FIG. 1 is a diagram for explaining a suppressible region of the conventional technique. [Diagram 3] 1 is a functional block diagram of a noise suppression system according to a first embodiment. [Figure 4] FIG. 2 is a diagram showing an example of a processing flow of the noise suppression system according to the first embodiment. [Diagram 5] FIG. 1 is a diagram for explaining an estimation method 1. [Figure 6] FIG. 13 is a diagram for explaining estimation method 2. [Figure 7] FIG. 13 is a diagram for explaining estimation method 3. [Figure 8] FIG. 4 is a diagram showing a simulation result of the first embodiment. [Figure 9] FIG. 13 is a diagram showing an example of the configuration of a computer to which the present technique is applied. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment of the present invention will be described. In the drawings used in the following description, components having the same functions and steps performing the same processes are denoted by the same reference numerals, and duplicated explanations will be omitted. In the following description, the symbols "^", " - " etc. should be written directly above the character that immediately follows, but due to limitations in text notation, they are written immediately before the character in question. Within formulas, these symbols are written in the correct position. Furthermore, unless otherwise specified, processing performed on each element of a vector or matrix applies to all elements of that vector or matrix.

[0010] <Key Points of the First Embodiment> In this embodiment, the observed sound pressure at the ear is estimated from the pickup signal of the error microphone installed at a position away from the ear. For example, the pickup signal of a virtual error microphone placed at the ear is estimated from the pickup signal of the actual error microphone, and the pickup signal of the virtual error microphone is used as the pickup signal of the conventional error microphone in the ANC. With this configuration, the position of the sweet spot can be changed from the installation position of the error microphone to the position of the virtual error microphone, and a sound that cancels the residual sound at the ear can be produced.

[0011] There are various methods for estimating the sound pickup signal of a virtual error microphone. For example, the sound pressure is estimated by taking into account the distance attenuation and phase delay from the actual error microphone installation position to the ear. In addition, for example, the sound pressure at the ear is estimated using a spherical harmonic function from the actual error microphone placed on a sphere.

[0012] First Embodiment FIG. 3 is a functional block diagram of the noise suppression system according to the first embodiment, and FIG. 4 shows the processing flow thereof.

[0013] The noise suppression system includes a reference microphone 91, a cancellation speaker 92, an error microphone 93, a suppression signal generation unit 110, and a sound pressure estimation unit 120. The device consisting of the suppression signal generation unit 110 and the sound pressure estimation unit 120 is also called a suppression signal generation device.

[0014] The suppression signal generating device receives as input the pickup signal x(r) of the reference microphone 91 and the pickup signal x(e) of the error microphone 93, generates a cancellation signal (hereinafter also referred to as the "suppression signal") y so that the point at which the amount of noise suppression is maximum is located on the user side relative to the installation position of the error microphone 93, and outputs the cancellation signal y to the cancellation speaker 92.

[0015] The suppression signal generating device is a special device configured by loading a special program into a publicly known or dedicated computer having, for example, a central processing unit (CPU), a main storage device (RAM), and the like. The suppression signal generating device executes each process under the control of, for example, the central processing unit. Data input to the suppression signal generating device and data obtained by each process are stored in, for example, the main storage device, and the data stored in the main storage device is read out to the central processing unit as necessary and used for other processes. At least a part of each processing unit of the suppression signal generating device may be configured by hardware such as an integrated circuit. Each storage unit included in the suppression signal generating device may be configured by, for example, a main storage device such as a RAM (Random Access Memory), or middleware such as a relational database or a key-value store. However, each storage unit does not necessarily need to be included in the suppression signal generating device itself, and may be configured by an auxiliary storage device configured by a semiconductor memory element such as a hard disk, an optical disk, or a flash memory, and may be configured to be provided outside the suppression signal generating device.

[0016] Each part will be explained below.

[0017] <Reference Mike 91> The reference microphone 91 picks up the sound to be suppressed (S91) and outputs a picked-up sound signal x(r). The sound to be suppressed picked up by the reference microphone 91 will be referred to as "noise" hereinafter.

[0018] <Cancel Speaker 92> The cancellation speaker 92 receives the cancellation signal y as input and reproduces the cancellation signal y (S92). When the sound reproduced from the cancellation speaker 92 and the noise to be suppressed are in completely opposite phase, the reproduced sound and the noise to be suppressed overlap, that is, when the sound waves overlap, the waves cancel each other out, and the noise is suppressed.

[0019] <Error Mic 93> The error microphone 93 picks up sounds that are not suppressed by the sound reproduced from the cancellation speaker 92, including residual noise (S93), and outputs a picked-up sound signal x(e). The error microphone 93 is placed at a position closer to the noise source than the observation point (e.g., the user's ear). For example, the error microphone 93 is placed at a position 0.05 m closer to the noise source than the user's ear, as shown in FIG. 5.

[0020] <Sound pressure estimation unit 120> The sound pressure estimation unit 120 receives an output signal (sound pickup signal) x(e) of the error microphone 93 as input, calculates an estimated sound pickup signal x(v) which is a signal estimated to be picked up when the microphone 130 is installed at a position closer to the observation point than the error microphone 93, and outputs the signal. That is, the sound pressure estimation unit 120 estimates a sound pickup signal obtained when a sound that is not suppressed by the sound reproduced from the cancellation speaker 92 is picked up at the installation position of the microphone 130 (S120), and outputs the estimated sound pickup signal as an estimated sound pickup signal x(v). Three examples of methods for estimating the estimated sound pickup signal x(v) are given below. Here, the microphone 130 is not actually installed but is installed virtually, and will be referred to as a virtual microphone 130 below.

[0021] (Estimation method 1) In this estimation method, a pickup signal x(v) of the virtual microphone 130 is estimated from an actual pickup signal x(e) of the error microphone 93 based on distance attenuation and phase delay from the error microphone 93 and the virtual microphone 130. Fig. 5 is a diagram for explaining the positional relationship between the noise source, the error microphone 93, and the virtual microphone 130.

[0022] In this estimation method, the position of a noise source is assumed, and it is assumed that noise propagates from the noise source to the error microphone 93 and the virtual microphone 130 as a plane wave. The sound signal picked up by the virtual microphone 130 is estimated by estimating the distance attenuation and phase shift from the error microphone 93 to the observation point from the transfer function from the noise source to the error microphone 93 and the transfer function from the noise source to the observation point (the position of the virtual microphone 130). The sound pressure estimation unit 120 estimates the sound signal picked up by the virtual microphone 130 from the output signal (picked up signal) x(e) of the error microphone 93 by the following equation, and obtains the estimated picked up signal x(v)=[^G p1 ^G p2 ] is output.

[0023] ^G pn =w n x(e) (n=1,2) (1) Here, if we only consider the gain attenuation, w n teeth w n =|G pn | / |G e | (2) If we only consider the phase shift, n teeth w n =exp((arg G pn -arg G e )j) (3) In equations (2) and (3), G e , G pn is calculated in advance from the assumed noise source position and the observation point prior to the estimation process. For example, a loudspeaker for the noise source is placed at the assumed noise source position, a predetermined signal is played back from the loudspeaker for the noise source, and G is calculated from the sound pickup signal picked up by a microphone placed at the error microphone position. e , and G is calculated from the signal picked up by the microphone placed at the observation point. pn I will ask for it. (Estimation method 2) In this estimation method, the signal picked up by a virtual error microphone is estimated from the signal picked up by multiple error microphones arranged at equal intervals near the head, using spherical harmonic expansion coefficients. Figure 6 is a diagram for explaining the positional relationship of the actual error microphones.

[0024] In this estimation method, the radius r e Error microphones are placed at equal intervals on the spherical surface of and the sound pressure on the spherical surface of radius r is estimated. For example, the distance from the center to the error microphone is r e = 0.15 m, (i) six error microphones are placed at the center of each face of a regular hexahedron (see (i) of FIG. 6), or (ii) twelve error microphones are placed at the center of each face of a regular dodecahedron (see (ii) of FIG. 6), thereby making it possible to place the error microphones at equal intervals. For example, the distance from the center to the observation point (the position of the virtual microphone 130) is estimated as r = 0.08 m.

[0025] By using spherical harmonic expansion, it is possible to estimate the observed sound pressure on any spherical surface from the observed sound pressure on a certain spherical surface.

[0026] radius r e The sound pressure observations p(θ1,φ1),p(θ2,φ2),…,p(θ L ,φ L For example, the collected signals x(e) of the L error microphones 93 are obtained by multiplying the signal x(e) by [p(θ1,φ1),p(θ2,φ2),...,p(θ L ,φ L )].

[0027] The sound pressure estimation unit 120 calculates the spherical harmonic function Y m n Radius r for (·) e Upper sound field coefficient P nm (r e ) is required.

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[0028] The derivation of equation (5) will be explained below.

[0029] When the noise source is a point source and reflection from a hard sphere of radius a is taken into consideration, the sound pressure at point (r, θ, φ) is

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[0030] (N+1) 2 <L Here, the spherical harmonic function Y m n We need the number of speakers to correspond to each mode of (·). If L=6, then N=1, and if L=12, then N=2.

[0031] Furthermore, to prevent spatial aliasing, N is subject to the following constraints:

[0032] kr <N The distance between the head and the virtual error microphone is limited. For example, when the frequency is 300 Hz and N=1, the estimation area is limited to within the distance r=0.18 m from the head.

[0033] (Estimation method 3) In this estimation method, the signal picked up by a virtual error microphone is estimated from the signal picked up by multiple error microphones arranged at non-uniform intervals near the head, using spherical harmonic expansion coefficients estimated by the least squares method. FIG. 7 is a diagram for explaining the positional relationship of the error microphones. For example, error microphones are arranged at four points behind the head (four azimuth angles (0°, 30°, 150°, 180°) × elevation angle 0°) or at 12 points behind the head (four azimuth angles (0°, 30°, 150°, 180°) × three elevation angles (-30°, 0°, 30°)). The installation radius of the error microphones may be determined depending on the environment in which they are installed and the type of sound to be suppressed. For example, when used in a train where running noise is to be suppressed, the installation radius of the error microphones is set to 0.13 m, taking into account the seat size.

[0034] In this estimation method, the radius r e Error microphones are placed at non-uniform intervals on the surface of a sphere of radius r, and the sound pressure on the sphere of radius r is estimated. Since the spherical harmonic expansion cannot be used directly in this estimation method, the spherical harmonic expansion coefficients are estimated by the least squares method to obtain the sound pressure on the sphere of radius r.

[0035] radius r e The sound pressure observations p(r e ,θ1,φ1),p(r e ,θ2,φ2),…,p(r e ,θ L ,φ L ) is obtained. The pickup signal x(e) of the error microphone 93 is - p=[p(r e ,θ1,φ1),p(r e ,θ2,φ2),…,p(r e ,θ L ,φ L )] T Let us assume that. - p is expressed as follows:

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[0036] The sound pressure estimation unit 120 estimates the sound pressure by minimizing the absolute square error. - P(r e ) is found as the solution.

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[0037] <Suppression signal generating unit 110> The suppression signal generation unit 110 receives the collected sound signal x(r) and the estimated collected sound signal x(v) as input, generates a cancellation signal y for suppressing noise at the installation position of the virtual microphone 130 (S110), and outputs the cancellation signal y.

[0038] A conventional technique can be used as a method for generating the cancellation signal. For example, the method described in Non-Patent Document 1 can be used. In this embodiment, a feedforward type ANC is realized by the collected sound signal x(r), the estimated collected sound signal x(v), and the cancellation signal y. The collected sound signal that would be obtained when the interference sound between the noise from the noise source and the reproduced sound of the cancellation signal y is detected by the virtual microphone 130 is estimated, and the noise from the noise source is detected by the reference microphone 91, and the cancellation signal y is generated by inputting it to a noise control filter realized by an adaptive digital filter, and is reproduced by the cancellation speaker 92. It is assumed that the reproduced sound of the cancellation signal y propagates through a secondary path, which is a series of transfer systems from the cancellation speaker 92 to the virtual microphone 130. Then, the coefficients of the noise control filter are updated by an adaptive algorithm so that the input to the virtual microphone 130 is minimized. Since a conventional updating method can be used as a method for updating the coefficients of the noise control filter, a description thereof will be omitted. In the feedforward type ANC, a secondary path model that estimates the secondary path is used to compensate for the influence of the secondary path in the adaptive algorithm.

[0039] <Effects> With the above configuration, it is possible to achieve higher suppression performance than in the past when it is not possible to place an error microphone close to the user's ear. Figure 8 shows the simulation results of the first embodiment. In (A), the noise is a 300 Hz plane wave, and in (B), the noise is a 100 Hz plane wave.

[0040] <Other Modifications> The present invention is not limited to the above-mentioned embodiment and modified examples. For example, the above-mentioned various processes may be executed not only in chronological order as described, but also in parallel or individually depending on the processing capacity of the device executing the processes or as necessary. In addition, appropriate modifications are possible within the scope of the present invention.

[0041] <Programs and recording media> The various processes described above can be implemented by loading a program for executing each step of the above method into the memory unit 2020 of the computer shown in FIG. 9 and operating the control unit 2010, input unit 2030, output unit 2040, etc.

[0042] The program describing the processing contents can be recorded on a computer-readable recording medium, which may be, for example, a magnetic recording device, an optical disk, a magneto-optical recording medium, a semiconductor memory, or any other type of recording medium.

[0043] The program may be distributed, for example, by selling, transferring, lending, etc. portable recording media such as DVDs and CD-ROMs on which the program is recorded. Furthermore, the program may be distributed by storing the program in a storage device of a server computer and transferring the program from the server computer to other computers via a network.

[0044] A computer that executes such a program, for example, first stores the program recorded on a portable recording medium or the program transferred from a server computer in its own storage device. Then, when executing a process, the computer reads the program stored in its own recording medium and executes a process according to the read program. As another execution form of the program, the computer may directly read the program from the portable recording medium and execute a process according to the program, or may execute a process according to the received program each time a program is transferred from the server computer to the computer. The above-mentioned process may be executed by a so-called ASP (Application Service Provider) type service that realizes a processing function only by issuing an execution instruction and obtaining a result, without transferring a program from the server computer to the computer. Note that the program in this embodiment includes information used for processing by an electronic computer and equivalent to a program (data that is not a direct command to the computer but has a nature that specifies the processing of the computer, etc.).

[0045] In addition, in this embodiment, the present device is configured by executing a specific program on a computer, but at least a part of the processing contents may be realized by hardware.

Claims

1. A generating device for generating a cancellation signal for use in active noise control, comprising: A cancellation signal is generated so that the point where the amount of noise suppression is maximum is located closer to the user than the installation position of the error microphone; a sound pressure estimation unit that estimates a sound pickup signal that is picked up when a virtual microphone is installed at a position closer to the observation point than the error microphone, and obtains an estimated sound pickup signal x(v); a suppression signal generation unit that generates a cancellation signal for suppressing noise at an installation position of the virtual microphone by using a pickup signal x(r) that picks up the noise to be suppressed and the estimated pickup signal x(v), The virtual microphone is a microphone that is virtually installed without actually being installed, The sound pressure estimation unit obtains the estimated sound pickup signal x(v) from the sound pickup signals x(e) of the plurality of error microphones arranged at equal intervals near the user's head by using spherical harmonic function expansion coefficients. generator.

2. A generator for generating a cancellation signal for use in active noise control, comprising: A cancellation signal is generated so that the point where the amount of noise suppression is maximum is located closer to the user than the installation position of the error microphone; a sound pressure estimation unit that estimates a sound pickup signal that is picked up when a virtual microphone is installed at a position closer to the observation point than the error microphone, and obtains an estimated sound pickup signal x(v); a suppression signal generation unit that generates a cancellation signal for suppressing noise at an installation position of the virtual microphone by using a pickup signal x(r) that picks up the noise to be suppressed and the estimated pickup signal x(v), The virtual microphone is a microphone that is virtually installed without actually being installed, The sound pressure estimation unit estimates a sound pressure from the sound signal x(e) of the error microphone based on distance attenuation and phase delay from the positional relationship between the error microphone and the virtual microphone. x(v)=[^G p1 ^G p2 ] ^G pn =wnx(e) (n=1,2) The estimated sound pickup signal x(v) is obtained by the above. The transfer characteristic from the assumed noise source position to the error microphone position is G e , and the transfer characteristic from the assumed noise source position to the observation point position is G pn . When only the gain attenuation is taken into consideration, wn is wn = |G pn | / |G e | If we only consider the phase shift, wn is wn =exp((arg G pn -arg G e )j) That is, generator.

3. A generator for generating a cancellation signal for use in active noise control, comprising: A cancellation signal is generated so that the point where the amount of noise suppression is maximum is located closer to the user than the installation position of the error microphone; a sound pressure estimation unit that estimates a sound pickup signal that is picked up when a virtual microphone is installed at a position closer to the observation point than the error microphone, and obtains an estimated sound pickup signal x(v); a suppression signal generation unit that generates a cancellation signal for suppressing noise at an installation position of the virtual microphone by using a pickup signal x(r) that picks up the noise to be suppressed and the estimated pickup signal x(v), The virtual microphone is a microphone that is virtually installed without actually being installed, The sound pressure estimation unit obtains the estimated sound pickup signal x(v) from the sound pickup signals x(e) of the plurality of error microphones arranged at non-equidistant intervals near the user's head by using spherical harmonic function expansion coefficients estimated by a least squares method. generator.

4. 1. A method for generating a cancellation signal for use in active noise control, comprising: A cancellation signal is generated so that the point where the amount of noise suppression is maximum is located closer to the user than the installation position of the error microphone; a sound pressure estimation step of estimating a sound pickup signal that would be picked up if a virtual microphone were installed at a position closer to the observation point than the error microphone, and obtaining an estimated sound pickup signal x(v); a suppression signal generation step of generating a cancellation signal for suppressing noise at an installation position of the virtual microphone by using a pickup signal x(r) that picks up the noise to be suppressed and the estimated pickup signal x(v), The virtual microphone is a microphone that is virtually installed without actually being installed, The sound pressure estimation step obtains the estimated sound pickup signal x(v) from the sound pickup signals x(e) of the plurality of error microphones arranged at equal intervals near the user's head by using spherical harmonic function expansion coefficients. Generation method.

5. A method for generating a cancellation signal for use in active noise control, comprising: A cancellation signal is generated so that the point where the amount of noise suppression is maximum is located closer to the user than the installation position of the error microphone; a sound pressure estimation step of estimating a sound pickup signal that would be picked up if a virtual microphone were installed at a position closer to the observation point than the error microphone, and obtaining an estimated sound pickup signal x(v); a suppression signal generation step of generating a cancellation signal for suppressing noise at an installation position of the virtual microphone by using a pickup signal x(r) that picks up the noise to be suppressed and the estimated pickup signal x(v), The virtual microphone is a microphone that is virtually installed without actually being installed, The sound pressure estimation step is to estimate a sound pressure from the sound signal x(e) of the error microphone based on distance attenuation and phase delay from the positional relationship between the error microphone and the virtual microphone. x(v)=[^G p1 ^G p2 ] ^G pn =wnx(e) (n=1,2) The estimated sound pickup signal x(v) is obtained by the above. The transfer characteristic from the assumed noise source position to the error microphone position is G e , and the transfer characteristic from the assumed noise source position to the observation point position is G pn . When only the gain attenuation is taken into consideration, wn is wn = |G pn | / |G e | If we only consider the phase shift, wn is wn =exp((arg G pn -arg G e )j) That is, Generation method.

6. A method for generating a cancellation signal for use in active noise control, comprising: A cancellation signal is generated so that the point where the amount of noise suppression is maximum is located closer to the user than the installation position of the error microphone; a sound pressure estimation step of estimating a sound pickup signal that would be picked up if a virtual microphone were installed at a position closer to the observation point than the error microphone, and obtaining an estimated sound pickup signal x(v); a suppression signal generation step of generating a cancellation signal for suppressing noise at an installation position of the virtual microphone by using a pickup signal x(r) that picks up the noise to be suppressed and the estimated pickup signal x(v), The virtual microphone is a microphone that is virtually installed without actually being installed, The sound pressure estimation step obtains the estimated sound pickup signal x(v) from the sound pickup signals x(e) of the plurality of error microphones arranged at non-equidistant intervals near the user's head by using spherical harmonic function expansion coefficients estimated by a least squares method. Generation method.

7. A program for causing a computer to function as the generating device according to any one of claims 1 to 3.

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