Active Noise Control System

Abstract

To provide an "active noise control system" adapted to a change in a transfer function.SOLUTION: Output of a first channel of an echo cancellation variable filter 331 having output of a first microphone 12 output from a second speaker 21 as input is added to output of a second microphone 22 by a second adder 35. An echo cancellation coefficient updating section 332 updates a filter coefficient of the first channel so that an error that is output of the second adder 35 is minimized. Using output of the second channel that uses the output of a sound source device 13 output from the first speaker 11 as input and shares the filter coefficient with the first channel as a reference signal, and the output of the second microphone 22 as an error, a noise cancellation coefficient updating section 322 updates the filter coefficient of the noise cancellation variable filter 321, which generates noise-canceling sound to be output from the output of the sound source device 13 to the second speaker 21, by a Filtered-X LMS algorithm.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 shown in FIG. 5a, in which music or other audio output from a sound source device 51 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 emitted 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 a sound source device 51 as input and has a transfer function C^(z) set as a transfer function estimated as a 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 sound source device 51 so as to minimize the error by using the Filtered-X LMS algorithm that performs the LMS algorithm with the output of the secondary path reproduction filter 56 as a reference signal, while using the output of the error microphone 55 as an error.

[0004] In addition, in such an active noise control system, in order to correct the difference between the position of the error microphone 55 and the ear of the user in the second area, an active noise control system is also known in which an auxiliary filter 57 is provided to receive the output of the sound source device 51 as its input, as shown in FIG. 5b, and the error output by the error microphone 55 is corrected by subtracting the output of the auxiliary filter 57 (for example, Patent Document 2).

[0005] In this active noise control system, the auxiliary filter 57 has a transfer function H(z) given by H(z)=P(z)-S(z)V(z) / Sv(z) is set in advance.

[0006] Here, P(z) is the transfer function from the speaker 52 for the user in the first area to the error microphone 55, V(z) is the transfer function from the speaker 52 for the user in the first area to the position of the ear of the user in the second area, and Sv(z) is the transfer function from the speaker 54 for the user in the second area to the position of the ear of the user in the second area. Also, S(z) is S(z)=C(z), and is the transfer function from the speaker 54 for the user in the second area to the error microphone 55.

[0007] Also, as shown in FIG. 6, in a system that supports conversation 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 generates a cancellation sound that cancels the echo using an adaptive filter 65 and adds the cancellation sound to the output of the microphone 64 in the second area by 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 3).

[0008] In this echo cancellation system, in an adaptive filter 65, the filter coefficient of a 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 an 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]

[0009] [Patent Document 1] JP 2010-163054 A [Patent Document 2] JP 2018-72770 A [Patent Document 3] JP 2010-16564 A Summary of the Invention [Problem to be solved by the invention]

[0010] The active noise control system shown in Figures 5a and 5b had a problem in that if the actual transfer function C(z) from the speaker 54 in the second area that outputs the noise-canceling sound to the error microphone 55 changes from the transfer function C^(z) set in the secondary path reproduction filter 56 due to fluctuations in the environment or other conditions, it would no longer be possible to cancel the noise effectively.

[0011] Therefore, an object of the present invention is to perform good noise cancellation that adapts to changes in the transfer function from a speaker that outputs a noise-canceling sound that cancels out the noise to a microphone that detects the remaining noise after cancellation. [Means for solving the problem]

[0012] In order to achieve the above object, the present invention provides an active noise control system for reducing noise, the system including: a first area microphone that is a microphone arranged in a first area; a second area speaker that is a speaker arranged in a second area; a second area microphone that is a microphone arranged in the second area; an echo cancellation adaptive filter that receives an output from the first area microphone as an input; an echo cancellation adder that adds the output from the second area microphone and the output from the echo cancellation adaptive filter; a secondary path reproduction filter that receives a noise signal representing noise as an input and is configured to share a filter coefficient with the echo cancellation adaptive filter; a noise cancellation adaptive filter that receives the noise signal as an input; and a noise cancellation adder that adds the output from the first area microphone and the output from the noise cancellation adaptive filter and outputs the result to the second area speaker. Here, the echo cancellation adaptive filter updates a filter coefficient using an output from the echo cancellation adder as an error so as to minimize the error, and the noise cancellation adaptive filter updates a filter coefficient using a Filtered-X LMS algorithm that uses an output from the second area microphone as an error and an output from the secondary path reproduction filter as a reference signal.

[0013] In addition, in order to achieve the above-mentioned 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 arranged in a second area, a second area microphone which is a microphone arranged in the second area, an echo cancellation adaptive filter having an output of the first area microphone as an input, an echo cancellation adder which adds the output of the second area microphone and the output of the echo cancellation adaptive filter, a secondary path reproduction filter having a variable filter coefficient which receives as an input a noise signal representing noise, a noise cancellation adaptive filter which receives as an input the noise signal, a noise cancellation adder which adds the output of the first area microphone and the output of the noise cancellation adaptive filter and outputs the result to the second area speaker, and a secondary path reproduction filter update means which updates the filter coefficient of the secondary path reproduction filter. Here, the echo cancellation adaptive filter updates the filter coefficients using the output of the echo cancellation adder as an error to minimize the error, and the secondary path reproduction filter update means updates the filter coefficients of the secondary path reproduction filter at a predetermined timing so that the filter coefficients become equivalent to the filter coefficients of the echo cancellation adaptive filter. The noise cancellation adaptive filter updates the filter coefficients by a Filtered-X LMS algorithm using the output of the second area microphone as an error and the output of the secondary path reproduction filter as a reference signal.

[0014] According to these active noise control systems, by utilizing the fact that the filter coefficients of the echo cancellation adaptive filter converge to the filter coefficients representing the transfer function from the second area speaker to the second area microphone, the filter coefficients of the secondary path reproduction filter that generates a reference signal used in the Filtered-X LMS algorithm in the noise cancellation adaptive filter can be made to follow changes in the transfer function from the second area speaker to the second area microphone, and as a result, good noise cancellation that adapts to the changes can be performed.

[0015] Here, these active noise control systems may be provided with an auxiliary filter that receives the noise signal as an input, an error correction adder that corrects the output of the second area microphone used as an error by the noise cancellation adaptive filter by adding the output of the auxiliary filter, and an auxiliary filter update means. The auxiliary filter includes a first filter having a transfer function of P(z) that receives the noise signal as an input, a second filter having a transfer function of V(z) / Sv(z) that receives the noise signal as an input, where P(z) is a transfer function from a noise source to the second area microphone, V(z) is a transfer function from the noise source to the sound listening position of a user in the second area, and Sv(z) is a transfer function from a second speaker to the sound listening position of a user in the second area, a third filter with a variable filter coefficient that receives the output of the second filter as an input, and an adder that generates the output of the auxiliary filter by subtracting the output of the first filter from the output of the third filter. Moreover, the auxiliary filter update means updates the filter coefficients of the third filter at a predetermined timing so that the filter coefficients become equivalent to the filter coefficients of the echo cancellation adaptive filter.

[0016] By configuring the active noise control system in this manner, it is possible to correct the difference between the second area microphone and the sound listening position of the user in the second area, and the transfer function of the auxiliary filter used for this correction can be made to follow changes in the transfer function from the second area speaker to the second area microphone.

[0017] Furthermore, it is preferable that these active noise control systems are configured such that the filter coefficients of the echo cancellation adaptive filter are updated by an LMS algorithm in which the output of the first area microphone is used as a reference signal and the output of the echo cancellation adder is used as an error.

[0018] Furthermore, the above active noise control system may be provided with a first area speaker, which is a speaker arranged in the first area to which the output of the echo cancellation adder is input, so as to assist users in the second area in hearing speech by users in the second area.

[0019] An active noise control system comprising: Alternatively, the above-mentioned active noise control system may include a sound source device and a first area speaker that is a speaker arranged in a first area to which the output of the sound source device is input, and the noise signal may be the output of the sound source device.

[0020] Alternatively, the above active noise control system may include a first area speaker which is a speaker arranged in a first area, a sound source device, and an adder for a sound source device which adds the output of the sound source device to the output of the echo cancellation adder and outputs the result to the first area speaker, and the noise signal may be the output of the sound source device.

[0021] Furthermore, the above-mentioned active noise control system may be a system mounted on an automobile, and the first area and the second area may be different areas in the passenger compartment of the automobile. Effect of the Invention

[0022] As described above, according to the present invention, it is possible to perform good noise cancellation that adapts to changes in the transfer function from the speaker that outputs a noise cancellation sound that cancels out the noise to the microphone that detects the remaining noise after cancellation. [Brief description of the drawings]

[0023] [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 a first embodiment of the present invention. [Diagram 3] FIG. 11 is a block diagram showing a configuration of a signal processing device according to a second embodiment of the present invention. [Figure 4] FIG. 11 is a block diagram showing a configuration of a signal processing device according to a third embodiment of the present invention. [Diagram 5] FIG. 1 is a diagram showing the configuration of a known active noise control system. [Figure 6]FIG. 1 is a diagram showing the configuration of a known echo cancellation system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] 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. First, the first embodiment will be described. FIG. 1 shows the configuration of an in-vehicle system according to the first 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 sound source device 13 for a user in the first area, 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 signal processing device 3 to which the above-mentioned components are connected.

[0025] 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, thereby supporting communication through conversation between the user in the first area and the user in the second area.

[0026] In addition, the signal processing device 3 outputs the output sound of the sound source device 13 to the first speaker 11 in the first area, and outputs a noise canceling sound from the second speaker 21 in the second area that cancels the output sound of the sound source device 13 output from the first speaker 11 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 sound source device 13 that is being listened to by the user in the first area.

[0027] 1b, the first area is the area of ​​the driver's seat of the automobile, 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.

[0028] 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 preprocessing unit 31, a noise cancellation adaptive filter 32, an echo cancellation adaptive filter 33, a first adder , a second adder 35, and a third adder .

[0029] The output of the first microphone 12 is subjected to pre-processing in the pre-processing unit 31 to perform noise suppression and amplitude suppression to prevent excessive input, and then sent to the first adder 34, where it is added to the noise-canceled sound output by the noise cancellation adaptive filter 32 and output from the second speaker 21.

[0030] The output of the second microphone 22 is sent to a second adder 35, where the echo-canceled sound output by the echo cancellation adaptive filter 33 is subtracted, and then the output is sent to a third adder 36, where it is added to the output of the sound source device 13 and output to the first speaker 11.

[0031] Echo cancellation adaptive filter 33 includes echo cancellation variable filter 331 and echo cancellation coefficient update unit 332. Echo cancellation variable filter 331 is a two-channel variable filter equipped with two signal processing systems, and the same filter coefficient is set for each channel by echo cancellation coefficient update unit 332. In other words, echo cancellation variable filter 331 is equivalent to two variable filters in which the same filter coefficient is set by echo cancellation coefficient update unit 332.

[0032] A first channel of echo cancellation variable filter 331 receives as input the output of first microphone 12 that has been preprocessed by preprocessing unit 31, and the output of the first channel is output as echo-canceled sound to second adder 35. A second channel of echo cancellation variable filter 331 receives as input the output of sound source device 13, and the output of the second channel is sent to noise cancellation adaptive filter 32 as a reference signal.

[0033] The echo cancellation coefficient update unit 332 uses the output of the second adder 35 as an error and the output of the first microphone 12 preprocessed by the preprocessing unit 31 as a reference signal, and updates the filter coefficient of the first channel of the echo cancellation variable filter 331 so as to minimize the error using an LMS algorithm or the like. The filter coefficient of the first channel is also used as the filter coefficient of the second channel, and when the filter coefficient of the first channel is updated, the filter coefficient of the second channel is also updated so as to be equal to the filter coefficient of the first channel.

[0034] As a result, the echo-canceled sound output from the first channel of echo cancellation variable filter 331 is a sound in which the output sound component of first microphone 12 contained in the output of second microphone 22 is cancelled by subtraction by second adder 35.

[0035] Here, if the transfer function of the secondary path from the second speaker 21 to the second microphone 22 is C(z), the transfer function of the first and second channels of the echo cancellation variable filter 331 is Q(z), and the output of the first microphone 12 that has been preprocessed by the preprocessing unit 31 is M(z), then the error eE(z) output from the second adder 35 to the echo cancellation coefficient update unit 332 is given by eE(z)=M(z)C(z)-M(z)Q(z) Since it is expressed as When the filter coefficients of the first and second channels of the echo cancellation variable filter have converged so that eE(z)=0 by the operation of the echo cancellation coefficient update unit 332.

[0036] eE(z)=M(z)C(z)-M(z)Q(z)=0 Q(z)=C(z) It becomes.

[0037] Next, the noise canceling adaptive filter 32 includes a noise canceling variable filter 321 and a noise canceling coefficient updating section 322 . The noise canceling variable filter 321 receives the output of the sound source device 13 as an input, and outputs the output to the first adder 34 as a noise-canceled sound. The noise cancellation coefficient update section 322 receives the output of the second microphone 22 as an error signal and the output of the second channel of the echo cancellation variable filter 331 as a reference signal. Here, as described above, the filter coefficient of the second channel of the echo cancellation variable filter 331 is controlled by the operation of the echo cancellation coefficient update unit 332 to a filter coefficient that satisfies Q(z)=C(z).

[0038] Therefore, the reference signal output from the second channel of echo cancellation variable filter 331 to noise cancellation coefficient update unit 322 is a signal obtained by convolving the output of sound source device 13 with transfer function C(z) from second speaker 21 to second microphone 22, and this reference signal can be used as a reference signal (filtered reference signal) for the Filtered-X LMS algorithm. In other words, the second channel of echo cancellation variable filter 331 functions as a secondary path reproduction filter used in the Filtered-X LMS algorithm and in which transfer function C^(z) is set.

[0039] Therefore, in echo cancellation coefficient update section 332, the filter coefficient of noise cancellation variable filter 321 is updated by the Filtered-X LMS algorithm by performing the LMS algorithm so as to minimize the error using the second channel output of echo cancellation variable filter 331 as a reference signal.

[0040] More specifically, echo cancellation coefficient update unit 332 calculates the following in accordance with the Filtered-X LMS algorithm, where w(n) is the filter coefficient of noise cancellation variable filter 321, μ is a step size parameter, e(n) is the output of second microphone 22, x(n) is the output of sound source device 13, and r(n) is a reference signal output from the second channel of echo cancellation variable filter 331: w(n+1)=w(n)+μe(n)r(n) The filter coefficient w(n) of the noise canceling variable filter 321 is updated by the above.

[0041] As a result, the noise canceling sound output by the noise canceling variable filter 321, passing through the first adder 34 and output from the second speaker 21, cancels the output sound of the sound source device 13 output from the first speaker 11 in the first area in the region where the second microphone 22 in the second area is located.

[0042] Furthermore, the transfer function Q(z)=C(z) of the second channel of the echo cancellation variable filter 331 is updated by the operation of the echo cancellation coefficient update unit 332 so as to follow the change in the transfer function C(z) from the second speaker 21 to the second microphone 22. Therefore, unlike the case where the secondary path reproduction filter 56 having the transfer function C^(z) set to a fixed value as shown in FIG. 5a is used, even if a change in the transfer function C(z) occurs, it is possible to perform good cancellation of the output sound of the sound source device 13 that follows the change.

[0043] The first embodiment of the present invention has been described above. Next, a second embodiment of the present invention will be described. The second embodiment differs from the first embodiment only in part of the configuration of the signal processing device 3. FIG. 3 shows the configuration of a signal processing device 3 according to the second embodiment. As shown in the figure, the signal processing device 3 according to the second embodiment differs from the first embodiment in that echo cancellation variable filter 331 is a single-channel variable filter corresponding to the first channel of echo cancellation variable filter 331 of the first embodiment, secondary path reproduction filter 311 is provided as a substitute for the second channel of echo cancellation variable filter 331 of the first embodiment, and update control unit 312 is provided which sets the filter coefficient of secondary path reproduction filter 311.

[0044] The secondary path reproduction filter 311 receives the output of the sound source device 13 as an input, and the output of the secondary path reproduction filter 311 is sent to the noise cancellation adaptive filter 32 as a reference signal, similar to the second channel of the echo cancellation variable filter 331 in the first embodiment.

[0045] Update control unit 312 periodically reads out the filter coefficients of echo cancellation variable filter 331, calculates the average of the filter coefficients of echo cancellation variable filter 331 during a specified past period, and if a difference of a specified level or more occurs between the average and the filter coefficient of secondary path reproduction filter 311 that was previously set, updates the filter coefficients of secondary path reproduction filter 311 smoothly to the calculated average of the filter coefficients.

[0046] As a result of such operation, the transfer function C^(z) of the secondary path reproduction filter 311 follows the transfer function Q(z)=C(z) of the echo cancellation variable filter 331 controlled by the operation of the echo cancellation coefficient update unit 332, similar to the second channel of the echo cancellation variable filter 331 in the first embodiment. Therefore, according to the second embodiment as well, it is possible to perform good cancellation of the output sound of the sound source device 13 that adapts to changes in the transfer function C(z) from the second speaker 21 to the second microphone 22.

[0047] The second embodiment of the present invention has been described above. Next, a third embodiment will be described. FIG. 4 shows the configuration of a signal processing device 3 according to the second embodiment. As shown in the figure, the signal processing device 3 according to the third embodiment differs from the first embodiment in that an auxiliary filter 321, a fourth adder 322, and an update processing unit 323 are provided. Auxiliary filter 321 is provided to correct the difference between the position of second microphone 22 and the ears of a user in the second area, and fourth adder 322 outputs a signal obtained by adding the output of auxiliary filter 321 to the output of second microphone 22 to noise cancellation coefficient update unit 322. Then, noise cancellation coefficient update unit 322 updates the filter coefficients of noise cancellation variable filter 321 using the Filtered-X LMS algorithm by performing an LMS algorithm so as to minimize the error using the output of fourth adder 322 as an error and the output of the second channel of echo cancellation variable filter 331 as a reference signal.

[0048] The transfer function H(z) of the auxiliary filter 321 is obtained by inverting the positive and negative transfer function of the auxiliary filter 57 of the active noise control system shown in FIG. 5b because the fourth adder 322 performs addition instead of subtraction as in FIG. 5b. H(z)=S(z)V(z) / Sv(z)-P(z).

[0049] P(z) is the transfer function from the first speaker 11 to the second microphone 22, S(z) is the transfer function from the second speaker 54 to the second microphone 22, V(z) is the transfer function from the first speaker 11 to the position of the user's ear in the second area, and Sv(z) is the transfer function from the second speaker 54 to the position of the user's ear in the second area. Therefore, S(z)=C(z).

[0050] The auxiliary filter 321 consists of a first filter 3211 whose transfer function is P(z), a second filter 3212 whose transfer function is V(z) / Sv(z), a third filter 3213 whose transfer function is S(z), and a fifth adder 3214, and the filter coefficient of the third filter 3213 can be set by the update processing unit 323.

[0051] The output of the sound source device 13 is input to the first filter 3211 and the second filter 3212, the output of the first filter 3211 is sent to the fifth adder 3214, the output of the second filter 3212 is input to the third filter 3213, and the output of the third filter 3213 is sent to the fifth adder 3214.

[0052] Then, the fifth adder 3214 subtracts the output of the first filter 3211 from the output of the third filter 3213 , and sends the result to the fourth adder 322 as the output of the auxiliary filter 321 . The update processing unit 323 periodically reads out the filter coefficients of any one of the channels of the echo cancellation variable filter 331, calculates the average of the filter coefficients read during a specified period in the past, and if a difference of a specified level or more occurs between the average and the filter coefficient of the third filter 3213 previously set, smoothly changes the filter coefficient of the third filter 3213 to the calculated average of the filter coefficients.

[0053] As a result of such operation, the transfer function S(z) of the third filter 3213, which should originally be S(z) = C(z), can be made to follow the transfer function Q(z) = C(z) of each channel of the echo cancellation variable filter 331 controlled by the operation of the echo cancellation coefficient update unit 332, and good cancellation of the output sound of the sound source device 13 can be performed in accordance with the change in the transfer function C(z) from the second speaker 21 to the second microphone 22.

[0054] The third embodiment has been described above. Here, the configuration shown in the third embodiment, which includes the auxiliary filter 321 and updates the filter coefficient of the third filter 3213, may be added to the signal processing device 3 according to the second embodiment shown in FIG.

[0055] Incidentally, in each of the above embodiments, by adding a configuration for canceling the echo that has leaked from the second speaker 21 to the second microphone 22 of the signal processing device 3 shown above, and a configuration that is symmetrical for the first and second areas to the signal processing device 3, the voice picked up by the first microphone 12 in the first area can be output to the second speaker 21 after canceling the echo that has leaked from the first speaker 11 to the first microphone 12.

[0056] In addition, a second sound source device for a user in the second area may be provided, and in the signal processing device 3, the output sound of the sound source device 13 of the signal processing device 3 shown above may be output to the first speaker 11, and a noise canceling sound that cancels the output sound of the sound source device 13 output from the first speaker 11 at the position of the user in the second area may be output from the second speaker 21. By adding a configuration that is symmetrical for the first and second areas to the signal processing device 3, the output sound of the second sound source device may be output to the second speaker 21, and a noise canceling sound that cancels the output sound of the sound source device 13 output from the second speaker 21 at the position of the user in the first area may be output from the first speaker 11.

[0057] 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 outside the vehicle. [Explanation of symbols]

[0058] 3...signal processing device, 11...first speaker, 12...first microphone, 13...sound source device, 21...second speaker, 22...second microphone, 31...pre-processing unit, 32...adaptive filter for noise cancellation, 33...adaptive filter for echo cancellation, 34...first adder, 35...second adder, 36...third adder, 311...secondary path reproduction filter, 312...update control unit, 321...variable filter for noise cancellation, 321...auxiliary filter, 322...noise cancellation coefficient update unit, 322...fourth adder, 323...update processing unit, 331...variable filter for echo cancellation, 332...echo cancellation coefficient update unit, 3211...first filter, 3212...second filter, 3213...third filter, 3214...fifth adder.

Claims

1. An active noise control system for reducing noise, comprising: A first area microphone that is a microphone arranged in a first area; a second area speaker that is a speaker disposed in the second area; A second area microphone that is a microphone arranged in a second area; an echo cancellation adaptive filter that receives an output from the first area microphone; an echo cancellation adder that adds an output of the second area microphone and an output of the echo cancellation adaptive filter; A secondary path reproduction filter configured to share filter coefficients with the echo cancellation adaptive filter, the secondary path reproduction filter receiving an input of a noise signal representing noise; a noise canceling adaptive filter to which the noise signal is input; a noise canceling adder that adds an output of the first area microphone and an output of the noise canceling adaptive filter and outputs the sum to the second area speaker, the echo cancellation adaptive filter updates a filter coefficient using an output of the echo cancellation adder as an error so as to minimize the error; the noise cancellation adaptive filter updates a filter coefficient by a Filtered-X LMS algorithm using an output of the second area microphone as an error and an output of the secondary path reproduction filter as a reference signal; The active noise control system comprises: an auxiliary filter to which the noise signal is input; an error correction adder that corrects the output of the second area microphone used as an error by adding an output of the auxiliary filter; and an auxiliary filter updating means, The auxiliary filter includes: Let P(z) be the transfer function from the noise source to the second area microphone, V(z) be the transfer function from the noise source to the listening position of the user in the second area, and Sv(z) be the transfer function from the second speaker to the listening position of the user in the second area. a first filter having a transfer function of P(z) that receives the noise signal as an input; a second filter having a transfer function of V(z) / Sv(z) that receives the noise signal as an input; a third filter having a variable filter coefficient, the third filter receiving the output of the second filter as an input; an adder for subtracting the output of the first filter from the output of the third filter to generate an output of the auxiliary filter; an auxiliary filter updating means for updating the filter coefficients of the third filter at a predetermined timing so that the filter coefficients become equivalent to the filter coefficients of the echo cancellation adaptive filter;

2. An active noise control system for reducing noise, comprising: A first area microphone that is a microphone arranged in a first area; a second area speaker that is a speaker disposed in the second area; A second area microphone that is a microphone arranged in a second area; an echo cancellation adaptive filter to which the output of the first area microphone is input; an echo cancellation adder that adds an output of the second area microphone and an output of the echo cancellation adaptive filter; a secondary path reproduction filter having variable filter coefficients, the secondary path reproduction filter receiving as input a noise signal representing noise; a noise canceling adaptive filter to which the noise signal is input; a noise canceling adder that adds an output of the first area microphone and an output of the noise canceling adaptive filter and outputs the sum to the second area speaker; a secondary path reproduction filter update means for updating a filter coefficient of the secondary path reproduction filter, the echo cancellation adaptive filter updates a filter coefficient using an output of the echo cancellation adder as an error so as to minimize the error; the secondary path reproduction filter update means updates a filter coefficient of the secondary path reproduction filter at a predetermined timing so that the filter coefficient becomes equal to a filter coefficient of the echo cancellation adaptive filter; the noise cancellation adaptive filter updates a filter coefficient by a Filtered-X LMS algorithm using an output of the second area microphone as an error and an output of the secondary path reproduction filter as a reference signal; The active noise control system comprises: an auxiliary filter to which the noise signal is input; an error correction adder that corrects the output of the second area microphone used as an error by adding an output of the auxiliary filter; and an auxiliary filter updating means, The auxiliary filter includes: Let P(z) be the transfer function from the noise source to the second area microphone, V(z) be the transfer function from the noise source to the listening position of the user in the second area, and Sv(z) be the transfer function from the second speaker to the listening position of the user in the second area. a first filter having a transfer function of P(z) that receives the noise signal as an input; a second filter having a transfer function of V(z) / Sv(z) that receives the noise signal as an input; a third filter having a variable filter coefficient, the third filter receiving an output of the second filter as an input; an adder for subtracting the output of the first filter from the output of the third filter to generate an output of the auxiliary filter; an auxiliary filter updating means for updating the filter coefficients of the third filter at a predetermined timing so that the filter coefficients become equivalent to the filter coefficients of the echo cancellation adaptive filter;

3. An active noise control system according to claim 1 or 2, 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 area microphone is used as a reference signal and the output of the echo cancellation adder is used as an error.

4. An active noise control system according to claim 1, 2 or 3, An active noise control system comprising a first area speaker, the first area speaker being a speaker disposed in a first area to which an output of the echo cancellation adder is input.

5. An active noise control system according to claim 1, 2 or 3, A sound source device; a first area speaker that is disposed in a first area and to which an output of the sound source device is input; An active noise control system, wherein the noise signal is an output of the sound source device.

6. An active noise control system for reducing noise, comprising: A first area microphone that is a microphone arranged in a first area; a second area speaker that is a speaker disposed in the second area; A second area microphone that is a microphone arranged in a second area; an echo cancellation adaptive filter to which the output of the first area microphone is input; an echo cancellation adder that adds an output of the second area microphone and an output of the echo cancellation adaptive filter; A secondary path reproduction filter configured to share filter coefficients with the echo cancellation adaptive filter, the secondary path reproduction filter receiving an input of a noise signal representing noise; a noise canceling adaptive filter to which the noise signal is input; a noise canceling adder that adds an output of the first area microphone and an output of the noise canceling adaptive filter and outputs the sum to the second area speaker, the echo cancellation adaptive filter updates a filter coefficient using an output of the echo cancellation adder as an error so as to minimize the error; the noise cancellation adaptive filter updates a filter coefficient by a Filtered-X LMS algorithm using an output of the second area microphone as an error and an output of the secondary path reproduction filter as a reference signal; The active noise control system comprises: a first area speaker that is a speaker disposed in a first area; A sound source device; a sound source device adder that adds an output of the echo cancellation adder to an output of the sound source device and outputs the result to the first area speaker; An active noise control system, wherein the noise signal is an output of the sound source device.

7. An active noise control system for reducing noise, comprising: A first area microphone that is a microphone arranged in a first area; a second area speaker that is a speaker disposed in the second area; A second area microphone that is a microphone arranged in a second area; an echo cancellation adaptive filter that receives an output from the first area microphone; an echo cancellation adder that adds an output of the second area microphone and an output of the echo cancellation adaptive filter; a secondary path reproduction filter having variable filter coefficients, the secondary path reproduction filter receiving as input a noise signal representing noise; a noise canceling adaptive filter to which the noise signal is input; a noise canceling adder that adds an output of the first area microphone and an output of the noise canceling adaptive filter and outputs the sum to the second area speaker; a secondary path reproduction filter update means for updating a filter coefficient of the secondary path reproduction filter, the echo cancellation adaptive filter updates a filter coefficient using an output of the echo cancellation adder as an error so as to minimize the error; the secondary path reproduction filter update means updates a filter coefficient of the secondary path reproduction filter at a predetermined timing so that the filter coefficient becomes equal to a filter coefficient of the echo cancellation adaptive filter; the noise cancellation adaptive filter updates a filter coefficient by a Filtered-X LMS algorithm using an output of the second area microphone as an error and an output of the secondary path reproduction filter as a reference signal; The active noise control system comprises: a first area speaker that is a speaker disposed in a first area; A sound source device; a sound source device adder that adds an output of the echo cancellation adder to an output of the sound source device and outputs the result to the first area speaker; An active noise control system, wherein the noise signal is an output of the sound source device.

8. An active noise control system according to claim 1, 2, 3, 4, 5, 6 or 7, 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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