Active Noise Control System

Abstract

To provide an "active noise control system" that reduces an influence of disturbance to the generation of noise-canceling sound.SOLUTION: A signal e(z) obtained by subtracting echo-canceling sound from output of a second microphone 22 is used as an error of an echo cancellation adaptive filter 33 and a noise cancellation adaptive filter 31, and output of a first sound source device 13 is added to the signal e(z) and output from a first speaker 11. The echo cancellation adaptive filter 33 generates echo-canceling sound from an addition signal of output of a second sound source device 23 and output of a first microphone 12 such that the signal e(z) is minimized. The noise cancellation adaptive filter 31 generates noise-canceling sound from the output of the first sound source device 13 such that the signal e(z) is minimized, and outputs the noise-canceling sound from a second speaker 21.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention mainly relates to an active noise control (ANC) technique that reduces noise by emitting a noise canceling sound that cancels the noise. [Background technology]

[0002] Known active noise control technologies include an active noise control system such as that shown in FIG. 3, in which a sound such as music output from a first sound source device 51, which is a sound source device for a user in a first area, to a speaker 52 for the user in the first area is treated as noise for a user in a second area, and a noise-canceling sound generated using an adaptive filter 53 is added to the output of a second sound source device 56, which is a sound source device for a user in the second area, and output from a speaker 54 in the second area (for example, Patent Document 1).

[0003] This active noise control system uses an error microphone 55 arranged in the second area, and a secondary path reproduction filter 56 that receives the output of the first sound source device 51 as input, and has a transfer function C^(z) set as a transfer function estimated as the transfer function C(z) from a speaker 54 in the second area to the error microphone 55. Also, in the adaptive filter 53, a coefficient update unit 532 updates the filter coefficients of a variable filter 531 that generates a noise cancellation sound from the output of the first sound source device 51 so as to minimize the error by a Filtered-X LMS algorithm that performs an LMS algorithm using the output of the error microphone 55 as an error and the output of the secondary path reproduction filter 56 as a reference signal.

[0004] Also, as shown in FIG. 4, in a system that supports a dialogue between a user in a first area and a user in a second area by outputting the user's voice picked up by a microphone 61 in a first area from a speaker 63 in a second area and outputting the user's voice picked up by a microphone 64 in the second area from a speaker 62 in the first area, an echo cancellation system is also known that uses an adaptive filter 65 to generate a cancellation sound that cancels the echo and adds the cancellation sound to the output of the microphone 64 in the second area with an adder 66, thereby canceling the echo that has leaked from the speaker 63 in the second area to the microphone 64 in the second area. (For example, Patent Document 2).

[0005] In this echo cancellation system, in the adaptive filter 65, the filter coefficient of the variable filter 651 that generates a cancellation sound from the output of the first area microphone 61 is updated by a coefficient update unit 652 using the output of the adder 66 as an error and the output of the first area microphone 61 as a reference signal, using an LMS algorithm or the like to minimize the error. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2010-163054 A [Patent Document 2] JP 2010-16564 A Summary of the Invention [Problem to be solved by the invention]

[0007] According to the active noise control system shown in FIG. 3, the output sound of the second sound source device 56 output from the speaker 54 in the second area is picked up by the error microphone 55 and input to the adaptive filter 53 together with the remaining canceled noise to be processed as an error. However, because this output sound of the second sound source device 56 is not a noise component that should be canceled, it becomes a disturbance for the adaptive filter 53 that prevents it from generating an appropriate noise-canceling sound.

[0008] Therefore, an object of the present invention is to perform good noise cancellation even when the output sound of a sound source device is input to a microphone that detects the noise. [Means for solving the problem]

[0009] In order to achieve the above object, the present invention provides an active noise control system for reducing noise, comprising a first area microphone which is a microphone arranged in a first area, a second area speaker which is a speaker that outputs sound to a second area, a second area microphone which is a microphone arranged in the second area, a second area sound source device which is a sound source device that outputs sound output from the second area speaker, a first adder which adds the output of the first area microphone and the output of the second area sound source device, an echo cancellation adaptive filter having the output of the first adder as an input, a second adder which adds the output of the second area microphone and the output of the echo cancellation adaptive filter, a noise cancellation adaptive filter having an input of a noise signal that represents noise for a user in the second area, and a third adder which outputs a signal obtained by adding the output of the first area microphone, the output of the second area sound source device, and the output of the noise cancellation adaptive filter to the second area speaker. Here, the echo cancellation adaptive filter uses the output of the second adder as an error and updates the filter coefficients so that the error is minimized, and the noise cancellation adaptive filter uses the output of the second adder as an error and updates the filter coefficients so that the error is minimized.

[0010] Here, such an active noise control system may include a secondary path reproduction filter having a transfer function from the second speaker to the first microphone set in advance, the secondary path reproduction filter receiving the noise signal as an input, and the noise cancellation adaptive filter may update a filter coefficient by a Filtered-X LMS algorithm using an output of the second adder as an error and an output of the secondary path reproduction filter as a reference signal.

[0011] Furthermore, in the above active noise control system, in the echo cancellation adaptive filter, the filter coefficient may be updated by an LMS algorithm in which the output of the first adder is a reference signal and the output of the second adder is an error.

[0012] The above active noise control system may further include a first area speaker that receives an output from the second adder and outputs sound to the first area. Alternatively, the above active noise control system may include a first area speaker that outputs sound to a first area, and a first area sound source device that is a sound source device that outputs the sound output from the first area speaker, and the noise signal may be an output of the first area sound source device.

[0013] Alternatively, the above active noise control system may include a first area speaker that outputs sound to a first area, a first area sound source device that is a sound source device that outputs sound output from the first area speaker, and a fourth adder that adds the output of the first area sound source device to the output of the second adder and outputs the result to the first area speaker, and the noise signal may be the output of the first area sound source device.

[0014] Furthermore, the above-described active noise control system may be a system mounted on an automobile, and the first area and the second area may be different areas within the passenger compartment of the automobile. According to the above-described active noise control system, the output of the second adder is the output of the second area microphone excluding the echo of the output of the first area microphone and the output sound of the second area sound source device. Therefore, in the noise cancellation adaptive filter, the output of the second adder is treated as an error, and the filter coefficient is updated so that the error is minimized, thereby enabling good noise cancellation that eliminates the influence of disturbances such as the echo of the output of the first area microphone and the output sound of the second area sound source device.

[0015] Furthermore, when a first area speaker is provided which receives the output of the second adder and outputs sound to the first area to assist a user in the first area in hearing the speech of a user in the second area, the effects of such disturbances can be eliminated with a simple configuration that utilizes an echo cancellation adaptive filter which cancels the echo of the output of the first area microphone that is output to the first area speaker. Effect of the Invention

[0016] As described above, according to the present invention, even if the output sound of a sound source device is input to a microphone for detecting noise, it is possible to perform good noise cancellation. [Brief description of the drawings]

[0017] [Figure 1] 1 is a block diagram showing a configuration of an in-vehicle system according to an embodiment of the present invention; [Diagram 2] 1 is a block diagram showing a configuration of a signal processing device according to an embodiment of the present invention. [Diagram 3] FIG. 1 is a diagram showing the configuration of a known active noise control system. [Figure 4] FIG. 1 is a diagram showing the configuration of a known echo cancellation system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, an embodiment of the present invention will be described taking as an example an application to an in-vehicle system mounted on an automobile. FIG. 1a shows the configuration of an in-vehicle system according to this embodiment. As shown in the figure, the in-vehicle system includes a first speaker 11 which is a speaker for a user in a first area within the vehicle cabin, a first microphone 12 which is a microphone for a user in the first area, a first sound source device 13 which is a sound source device for a user in the first area and outputs sound such as music, a second speaker 21 which is a speaker for a user in a second area within the vehicle cabin, a second microphone 22 which is a microphone for a user in the second area, and a second sound source device 23 which is a sound source device for a user in the second area and outputs sound such as music, as well as a signal processing device 3 to which each of the above components are connected.

[0019] The signal processing device 3 outputs the voice of the user in the first area picked up by the first microphone 12 in the first area to the second speaker 21 in the second area, and outputs the voice of the user in the second area picked up by the second microphone 22 in the second area to the first speaker 11 in the first area after canceling the echo of the voice of the user in the first area that has been transmitted from the second speaker 21 to the second microphone 22 and the output sound of the second sound source device 23 picked up by the second microphone 22, thereby supporting communication through conversation between the user in the first area and the user in the second area.

[0020] Furthermore, the signal processing device 3 outputs the output sound of the first sound source device 13 to the first speaker 11 in the first area, and outputs the output sound of the second sound source device 23 to the second speaker 21 in the second area.

[0021] In addition, the signal processing device 3 treats the output sound of the first sound source device 13 output from the first speaker 11 as the noise of the user in the second area and outputs a noise canceling sound from the second speaker 21 in the second area that cancels the noise at the position of the user in the second area, thereby preventing the user in the second area from being disturbed by the output sound of the first sound source device 13 being listened to by the user in the first area.

[0022] Here, the first area is, for example, the area of ​​the driver's seat of the automobile, as shown in Fig. 1b, and the first speaker 11 and the first microphone 12 are arranged in the first area, while the second area is the area of ​​the seat behind the driver's seat of the automobile, and the second speaker 21 and the second microphone 22 are arranged in the second area.

[0023] Next, the configuration of the signal processing device 3 is shown in FIG. As shown in the figure, the signal processing device 3 includes a noise cancellation adaptive filter 31, a secondary path reproduction filter 32, an echo cancellation adaptive filter 33, a first adder 34, a second adder 35, a third adder 36, and a fourth adder 37.

[0024] The output of the first microphone 12 is sent to a first adder 34, where it is added to the output of the second sound source device 23. The second adder 35 adds the noise cancellation sound output by the noise cancellation adaptive filter 31 to the sum signal of the output of the first microphone 12 and the output of the second sound source device 23 output from the first adder 34, and outputs the result from the second speaker 21.

[0025] The output of the second microphone 22 is sent to a third adder 36, where the echo-canceled sound output by the echo cancellation adaptive filter 33 is subtracted and then sent to a fourth adder 37. The fourth adder 37 adds the output of the first sound source device 13 to the output of the third adder 36 and outputs the result to the first speaker 11.

[0026] The echo cancellation adaptive filter 33 includes an echo cancellation variable filter 331 and an echo cancellation coefficient update unit 332 . The variable filter for echo cancellation 331 receives as input the sum signal of the output of the first microphone 12 and the output of the second sound source device 23 output from the first adder 34, and outputs the output of the variable filter for echo cancellation 331 to the third adder 36 as echo-canceled sound.

[0027] The echo cancellation coefficient update unit 332 uses the output of the third adder 36 as an error and the sum signal of the output of the first microphone 12 and the output of the second sound source device 23 output from the first adder 34 as a reference signal, and updates the filter coefficient of the echo cancellation variable filter 331 so as to minimize the error using an LMS algorithm or the like.

[0028] Next, the secondary path reproduction filter 32 has a transfer function C^(z) that is pre-set as the transfer function thereof, which is the transfer function C(z) from the second speaker 21 to the second microphone 22. The secondary path reproduction filter 32 receives the output of the first sound source device 13 as an input, and outputs the output of the secondary path reproduction filter 32 to the noise cancellation adaptive filter 31 as a reference signal.

[0029] The noise canceling adaptive filter 31 includes a noise canceling variable filter 311 and a noise canceling coefficient updating section 312 . The noise canceling variable filter 311 receives the output of the first sound source device 13 as an input, and outputs the output to the second adder 35 as a noise-canceled sound. The noise cancellation coefficient updating unit 312 receives the output of the third adder 36 as an error signal and the output of the secondary path reproduction filter 32 as a reference signal. The noise canceling coefficient update unit 312 uses the reference signal input from the secondary path reproduction filter 32 to perform the LMS algorithm so as to minimize the error input from the third adder 36, thereby updating the filter coefficients of the noise canceling variable filter 311 by the Filtered-X LMS algorithm.

[0030] More specifically, the echo cancellation coefficient update unit 332 calculates the following in accordance with the Filtered-X LMS algorithm, where x(n) is the filter coefficient of the noise cancellation variable filter 311, μ is a step-size parameter, e(n) is the error input from the third adder 36, and r(n) is the reference signal (filtered reference signal) input from the secondary path reproduction filter 32: x(n+1)=x(n)+μe(n)r(n) The filter coefficient x(n) of the noise canceling variable filter 311 is updated by the above.

[0031] In the above configuration, the output e(z) of the third adder 36 used as an error by the echo cancellation coefficient updating unit 332 and the noise cancellation coefficient updating unit 312 is expressed as follows when the transfer function of the echo cancellation variable filter 331 is W(z), the transfer function of the noise cancellation variable filter 311 is X(z), the transfer function from the first speaker 11 to the second microphone 22 is P(z), the transfer function C(z) from the second speaker 21 to the second microphone 22 is S1(z), the output of the first sound source device 13 is S2(z), and the output of the second sound source device 23 is M1(z), and the speech of the user in the second area is not picked up by the second microphone 22: e(z)=M1(z)C(z)+S2(z)C(z)+S1(z)P(z)-M1(z)W(z)-S2(z)W(z)-S1(z)X(z)C(z) ={M1(z)+S2(z)}C(z)-{M1(z)+S2(z)}W(z)+S1(z){P(z)-X(z)C(z)} is represented by If C(z) = W(z) and P(z) = X(z)C(z), then e(z) = 0.

[0032] Therefore, the transfer function W(z) of the echo cancellation variable filter 331 is set to be equal to the transfer function C(z) from the second speaker 21 to the second microphone 22 by the operation of the echo cancellation coefficient update unit 332 .

[0033] The echo cancellation generated and output by the echo cancellation variable filter 331 using the transfer function W(z) from the sum signal of the output of the first microphone 12 and the output of the second sound source device 23 is a sound that cancels the echo of the output of the first microphone 12 output from the second speaker 21 picked up by the second microphone 22 and the output sound of the second sound source device 23 from the output of the second microphone 22 through subtraction by the third adder 36.

[0034] Further, therefore, by the operation of noise canceling coefficient update unit 312, transfer function X(z) of noise canceling variable filter 311 is set so that transfer function X(z)C(z) from the input of noise canceling variable filter 311 to second microphone 22 becomes equal to transfer function P(z) from first speaker 11 to second microphone 22.

[0035] The noise canceling variable filter 311 generates a transfer function X(z) from the output of the first sound source device 13 and outputs the noise canceling sound from the second speaker 21, which cancels the output sound of the first sound source device 13 output from the first speaker 11 in the area where the second microphone 22 is located.

[0036] In addition, the output e(z) of the third adder 36, which is input as an error to the noise cancellation coefficient update unit 312, is the output of the second microphone 22 excluding the echo of the output of the first microphone 12 and the output sound of the second sound source device 23.

[0037] Therefore, for example, when the second microphone 22 is not picking up the speech of a user in the second area, the output e(z) of the third adder 36 will be S1(z){P(z)-X(z)C(z)}, which represents only the noise remaining after being canceled by the noise canceling sound (the output sound of the first sound source device 13).

[0038] Therefore, according to this embodiment, the noise cancellation adaptive filter 31 can perform good cancellation of the output sound of the first sound source device 13 while eliminating the influence of disturbances such as the echo of the output of the first microphone 12 and the output sound of the second sound source device 23.

[0039] In addition, the elimination of the effects of such disturbances can be achieved with a simple configuration that utilizes the echo cancellation adaptive filter 33 that cancels the echo of the output of the first microphone 12 that is output to the first speaker 11.

[0040] Incidentally, each of the above embodiments may be configured to cancel the echo that has leaked from the second speaker 21 to the second microphone 22 of the signal processing device 3 shown above, and to add a symmetrical configuration for the first and second areas to the signal processing device 3, so that the sound picked up by the first microphone 12 in the first area is output to the second speaker 21 after canceling the echo that has leaked from the first speaker 11 to the first microphone 12.

[0041] In addition, by adding a configuration in which a noise canceling sound that cancels the output sound of the first sound source device 13 output from the first speaker 11 of the signal processing device 3 shown above is output from the second speaker 21 at the user's position in the second area, and a configuration that is symmetrical with respect to the first and second areas to the signal processing device 3, a noise canceling sound that cancels the output sound of the second sound source device 23 output from the second speaker 21 at the user's position in the first area may be output from the first speaker 11.

[0042] Furthermore, in each of the above embodiments, the number of areas is two, but this embodiment may be expanded to accommodate three or more areas. Although the above description has been given taking an example of application to an in-vehicle system, each of the above embodiments can be similarly applied to cases where each area is an area outside a vehicle. [Explanation of symbols]

[0043] 3...signal processing device, 11...first speaker, 12...first microphone, 13...first sound source device, 21...second speaker, 22...second microphone, 23...second sound source device, 31...adaptive filter for noise cancellation, 32...secondary path reproduction filter, 33...adaptive filter for echo cancellation, 34...first adder, 35...second adder, 36...third adder, 37...fourth adder, 311...variable filter for noise cancellation, 312...noise cancellation coefficient update unit, 331...variable filter for echo cancellation, 332...echo cancellation coefficient update unit.

Claims

1. An active noise control system for reducing noise, comprising: a first area speaker that outputs sound to a first area; A first area microphone that is a microphone disposed in the first area; a second area speaker that outputs sound to a second area; A second area microphone that is a microphone disposed in the second area; a first area sound source device which outputs a sound output from the first area speaker; a second area sound source device which outputs a sound output from the second area speaker; a first adder that adds an output of the first area microphone and an output of the second area sound source device; an echo cancellation adaptive filter to which the output of the first adder is input; a second adder that adds the output of the second area microphone and the output of the echo cancellation adaptive filter; a noise canceling adaptive filter that receives as input a noise signal representing noise for a user in the second area; a third adder that outputs a signal obtained by adding together an output of the first area microphone, an output of the second area sound source device, and an output of the noise canceling adaptive filter to the second area speaker; a fourth adder that adds an output of the first area sound source device to an output of the second adder and outputs the result to the first area speaker; the noise signal is an output of the first area sound source device; the echo cancellation adaptive filter updates a filter coefficient using an output of the second adder as an error so as to minimize the error; 2. An active noise control system according to claim 1, wherein said noise cancellation adaptive filter updates a filter coefficient so as to minimize an error obtained by using an output of said second adder as an error.

2. 2. The active noise control system of claim 1, a secondary path reproduction filter that receives the noise signal as an input and has a transfer function from the second area speaker to the first area microphone set in advance; The noise cancellation adaptive filter updates a filter coefficient by a Filtered-X LMS algorithm in which the output of the second adder is used as an error and the output of the secondary path reproduction filter is used as a reference signal.

3. 3. An active noise control system according to claim 1, An active noise control system characterized in that the echo cancellation adaptive filter updates its filter coefficients using an LMS algorithm in which the output of the first adder is used as a reference signal and the output of the second adder is used as an error.

4. An active noise control system according to claim 1, 2 or 3, mounted on a motor vehicle, 2. An active noise control system, wherein the first area and the second area are different areas within a passenger compartment of the automobile.

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