Active noise control system

Abstract

The present invention provides an "active noise control system" which reduces the influence of interference on the generation of noise cancellation sound. A signal (e(z)) obtained by subtracting an echo cancellation sound from the output of a second microphone (22) is used as an error for an echo cancellation adaptive filter (33) and a noise cancellation adaptive filter (31), and the 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 an echo cancellation sound in such a manner that the signal (e(z)) is minimized based on the added signal of the output of a second sound source device (23) and a first microphone (12). The noise cancellation adaptive filter (31) generates a noise cancellation sound in such a manner that the signal (e(z)) is minimized based on the output of the first sound source device (13), and outputs from a second speaker (21).

Description

Technical Field

[0001] This invention relates primarily to an active noise control (ANC) technique that reduces noise by emitting noise-canceling sounds to cancel out noise. Background Technology

[0002] As a technology for active noise control, the following technologies are known: Figure 3 As shown in the active noise control system, the sound such as music output from the first sound source device 51, which is a user sound source device for the first area, to the user speaker 52 of the first area, is used as noise for the user in the second area. The noise cancellation sound generated by the adaptive filter 53 is added to the output of the second sound source device 56, which is a user sound source device for the second area, and then output from the speaker 54 of the second area (for example, Patent Document 1).

[0003] In this active noise control system, an error microphone 55 configured in the second region is used, and a transfer function C is set. ^ (z) The quadratic path reproduction filter 56, which takes the output of the first sound source device 51 as its input and serves as the transfer function, is C. ^ (z) is presumed to be the transfer function C(z) from the speaker 54 in the second region to the error microphone 55. Furthermore, in the adaptive filter 53, in the coefficient update unit 532, the filter coefficients of the variable filter 531, which generates noise-canceling tones based on the output of the error microphone 55 as the error and the output of the secondary path reproduction filter 56 as the reference signal, are updated in a manner that minimizes the error by performing the Filtered-X LMS algorithm (Filtered-X Least Mean Square algorithm) of the LMS algorithm.

[0004] In addition, such as Figure 4 As shown, in a system that supports dialogue between a user in the first area and a user in the second area by outputting the user's voice picked up by the microphone 61 in the first area from the speaker 63 in the second area and the user's voice picked up by the microphone 64 in the second area from the speaker 62 in the first area, an echo cancellation system is known (e.g., Patent Document 2): using an adaptive filter 65, an echo cancellation tone is generated, and an adder 66 is used to add the echo cancellation tone to the output of the microphone 64 in the second area, thereby canceling the echo that spreads from the speaker 63 in the second area to the microphone 64 in the second area.

[0005] In this echo cancellation system, in the adaptive filter 65, the output of the adder 66 is used as an error and the output of the microphone 61 in the first region is used as a reference signal ground by the coefficient update unit 652. The filter coefficients of the variable filter 651, which generates the canceled sound based on the output of the microphone 61 in the first region, are updated in a way that minimizes the error by using the LMS algorithm or the like.

[0006] [Existing Technical Documents]

[0007] [Patent Literature]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 2010-163054

[0009] [Patent Document 2] Japanese Patent Application Publication No. 2010-16564 Summary of the Invention

[0010] according to Figure 3 In the active noise control system shown, the output sound of the second sound source device 56, which is output from the speaker 54 in the second area, is picked up by the error microphone 55 and input to the adaptive filter 53 along with the noise that remains after cancellation. It is processed as an error. However, the output sound of the second sound source device 56 is not a component of the noise that should be cancelled. Therefore, for the adaptive filter 53, it becomes an interference that hinders the generation of the appropriate noise cancellation sound.

[0011] Therefore, the technical problem of the present invention is that good noise cancellation can be achieved even when the output sound of the sound source device is input to a microphone for detecting noise.

[0012] To address the aforementioned technical problems, this invention provides an active noise control system for reducing noise, comprising: a first-area microphone disposed in a first area; a second-area speaker outputting sound to a second area; a second-area microphone disposed in the second area; a second-area sound source device outputting sound from the second-area speaker; a first adder adding the output of the first-area microphone and the output of the second-area sound source device; an echo cancellation adaptive filter taking the output of the first adder as input; a second adder adding the output of the second-area microphone and the output of the echo cancellation adaptive filter; a noise cancellation adaptive filter taking a noise signal as input, the noise signal representing noise for a user in the second area; and a third adder outputting a signal to the second-area speaker resulting from the sum of the outputs of the first-area microphone, the second-area sound source device, and the noise cancellation adaptive filter. Here, the echo cancellation adaptive filter updates its coefficients by taking the output of the second adder as an error, and the noise cancellation adaptive filter updates its coefficients by taking the output of the second adder as an error, in a manner that minimizes the error.

[0013] Alternatively, such an active noise control system may include a secondary path reproduction filter that takes the noise signal as input and has a pre-set transfer function from the second speaker to the first microphone. In the noise cancellation adaptive filter, the filter coefficients are updated using the Filtered-X LMS algorithm, which takes the output of the second adder as the error and the output of the secondary path reproduction filter as the reference signal.

[0014] Alternatively, the above active noise control system in the echo cancellation adaptive filter may update the filter coefficients using the LMS algorithm, which uses the output of the first adder as a reference signal and the output of the second adder as an error.

[0015] Alternatively, the above active noise control system may include a first area loudspeaker, which is a loudspeaker that provides the output input of the second adder and outputs sound to the first area.

[0016] Alternatively, the above active noise control system may include: a first area loudspeaker that outputs sound to a first area; and a first area sound source device that outputs sound from the first area loudspeaker, and uses the noise signal as the output of the first area sound source device.

[0017] Alternatively, the above active noise control system may include: a first area loudspeaker that outputs sound to a first area; a first area sound source device that outputs the sound from the first area loudspeaker; 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 loudspeaker, using the noise signal as the output of the first area sound source device.

[0018] Alternatively, the above-mentioned active noise control system can be configured as a system installed in a car, and the first area and the second area can be configured as different areas inside the car's passenger compartment.

[0019] According to the active noise control system described above, the output of the second adder is the output of the second-area microphone after removing the echo from the first-area microphone and the output of the second-area sound source device. Therefore, in the adaptive filter for noise cancellation, the output of the second adder is set as the error, and the filter coefficients are updated in a manner that minimizes this error. This eliminates the influence of interference such as the echo from the first-area microphone and the output of the second-area sound source device, thus achieving good noise cancellation.

[0020] Furthermore, when a speaker, namely a first-area speaker, is provided as the input / output of the second adder and outputs sound to the first area, and supports the listening of the user in the first area to speak to the user in the second area, the effect of such interference can be eliminated by using a simple structure of an echo-cancelling adaptive filter that eliminates the echo output from the first-area microphone of the first-area speaker.

[0021] The effects of the invention

[0022] As described above, according to the present invention, good noise cancellation can be achieved even when the output sound of the sound source device is input to a microphone for detecting noise. Attached Figure Description

[0023] Figure 1 This is a block diagram illustrating the structure of an in-vehicle system according to an embodiment of the present invention.

[0024] Figure 2 This is a block diagram illustrating the structure of a signal processing apparatus according to an embodiment of the present invention.

[0025] Figure 3 This is a diagram showing the structure of a well-known active noise control system.

[0026] Figure 4 This is a diagram showing the structure of a well-known echo cancellation system. Detailed Implementation

[0027] The following description will focus on an in-vehicle system suitable for use in automobiles.

[0028] Figure 1 The 'a' indicates the structure of the vehicle-mounted system in this embodiment.

[0029] As shown in the figure, the vehicle-mounted system includes: a first speaker 11 for users in the first area of ​​the vehicle compartment; a first microphone 12 for users in the first area; a first sound source device 13 for users in the first area, which outputs music and other sounds; a second speaker 21 for users in the second area of ​​the vehicle compartment; a second microphone 22 for users in the second area; a second sound source device 23 for users in the second area, which outputs music and other sounds; and a signal processing device 3 connected to the above components.

[0030] 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 eliminating the echo of the user's voice in the first area spreading 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 conversation-based communication between the user in the first area and the user in the second area.

[0031] In addition, 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.

[0032] In addition, the signal processing device 3 uses the output sound of the first sound source device 13 from the first speaker 11 as noise for the user in the second area, and outputs a noise cancellation sound from the second speaker 21 in the second area to eliminate the noise at the location of the user in the second area. Thus, the user in the second area is prevented from being disturbed by the output sound of the first sound source device 13 that the user in the first area is listening to.

[0033] Here, the first region is, for example, Figure 1 As shown in b, this is the driver's seat area of ​​the car, where the first speaker 11 and the first microphone 12 are located. The second area is the area behind the driver's seat, where the second speaker 21 and the second microphone 22 are located.

[0034] then, Figure 2 The structure of the signal processing device 3 is shown in the figure.

[0035] As shown in the figure, the signal processing device 3 includes an adaptive filter 31 for noise cancellation, a secondary path reproduction filter 32, an adaptive filter 33 for echo cancellation, a first adder 34, a second adder 35, a third adder 36, and a fourth adder 37.

[0036] The output of the first microphone 12 is sent to the first adder 34, where it is added to the output of the second sound source device 23. The second adder 35 further adds a noise-cancelled tone output by the noise-cancelling adaptive filter 31 to the sum of the outputs of the first microphone 12 and the second sound source device 23 from the first adder 34, and outputs it from the second speaker 21.

[0037] The output of the second microphone 22 is sent to the third adder 36. After subtracting the echo cancellation tone output by the echo cancellation adaptive filter 33 from the third adder 36, the output is sent to the 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.

[0038] The echo cancellation adaptive filter 33 includes an echo cancellation variable filter 331 and an echo cancellation coefficient update unit 332.

[0039] The echo cancellation variable filter 331 takes the sum of the output of the first microphone 12 from the first adder 34 and the output of the second sound source device 23 as input, and the output of the echo cancellation variable filter 331 is output to the third adder 36 as the echo cancellation tone.

[0040] The echo cancellation coefficient update unit 332 takes the output of the third adder 36 as the error and takes the sum of the output of the first microphone 12 from the first adder 34 and the output of the second sound source device 23 as the reference signal. It updates the filter coefficients of the echo cancellation variable filter 331 in a way that minimizes the error by using the LMS algorithm or the like.

[0041] Next, the secondary path reproduction filter 32, with its transfer function C pre-set, is... ^ (z) serves as its transfer function, which is C ^ (z) is assumed to be the transfer function C(z) from the second speaker 21 to the second microphone 22. The secondary path reproduction filter 32 takes the output of the first sound source device 13 as input and outputs the output of the secondary path reproduction filter 32 as a reference signal to the noise cancellation adaptive filter 31.

[0042] The noise cancellation adaptive filter 31 includes a noise cancellation variable filter 311 and a noise cancellation coefficient update unit 312.

[0043] The noise cancellation variable filter 311 takes the output of the first sound source device 13 as input, and its output is output as the noise cancellation tone to the second adder 35.

[0044] The output of the third adder 36 is used as an error, and the output of the secondary path reproduction filter 32 is used as a reference signal and input to the noise cancellation coefficient update unit 312.

[0045] The noise cancellation coefficient update unit 312 uses the reference signal input from the secondary path reproduction filter 32 to perform the LMS algorithm in a way that minimizes the error input from the third adder 36, thereby updating the filter coefficients of the noise cancellation variable filter 311 based on the Filtered-X LMS algorithm.

[0046] More specifically, the echo cancellation coefficient update unit 332, according to the Filtered-X LMS algorithm, uses x(n) as the filter coefficient of the noise cancellation variable filter 311, μ as the step size parameter, e(n) as the error input from the third adder 36, and r(n) as the reference signal (filtered reference signal) input from the secondary path reproduction filter 32, and then...

[0047] x(n+1)=x(n)+μe(n)r(n)

[0048] Update the filter coefficients x(n) of the variable filter 311 for noise cancellation.

[0049] Furthermore, in the above structure, the output e(z) of the third adder 36 used for error correction, which is the echo cancellation coefficient update unit 332 and the noise cancellation coefficient update unit 312, is determined by setting the transfer function of the echo cancellation variable filter 331 to W(z), the transfer function of the noise cancellation variable filter 311 to X(z), the transfer function from the first speaker 11 to the second microphone 22 to P(z), the transfer function from the second speaker 21 to the second microphone 22 to C(z), the output of the first sound source device 13 to S1(z), the output of the second sound source device 23 to S2(z), and the output of the first microphone 12 to M1(z), and when the user's speech in the second area is not picked up by the second microphone 22, the output e(z) is determined by the following:

[0050] 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)

[0051] ={M1(z)+S2(z)}C(z)-{M1(z)+S2(z)}W(z)+S1(z){P(z)-X(z)C(z)}

[0052] To indicate,

[0053] When C(z)=W(z) and P(z)=X(z)C(z), e(z)=0.

[0054] Therefore, through the operation of the echo cancellation coefficient update unit 332, 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.

[0055] Furthermore, the echo cancellation variable filter 331 generates and outputs the echo cancellation based on the sum of the output of the first microphone 12 and the output of the second sound source device 23 using the transfer function W(z). This echo cancellation is achieved by the subtraction operation of the third adder 36, which eliminates the echo of the first microphone 12 output from the second microphone 22 and the sound after the output of the second sound source device 23 from the output of the second microphone 22.

[0056] Furthermore, therefore, through the operation of the noise cancellation coefficient update unit 312, the transfer function X(z) of the noise cancellation variable filter 311 is set such that the transfer function X(z)C(z) from the input of the noise cancellation variable filter 311 to the second microphone 22 is equal to the transfer function P(z) from the first speaker 11 to the second microphone 22.

[0057] Furthermore, the noise cancellation variable filter 311 generates a noise cancellation sound based on the output of the first sound source device 13 using the transfer function X(z) and outputs it from the second speaker 21. This sound is the sound after the output sound of the first sound source device 13 from the first speaker 11 is eliminated in the area where the second microphone 22 is located.

[0058] Furthermore, 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 after removing the echo of the first microphone 12 and the output of the second sound source device 23 from the output of the second microphone 22.

[0059] Therefore, for example, when the user's speech in the second area is not picked up by the second microphone 22, the output e(z) of the third adder 36 becomes S1(z){P(z)-X(z)C(z)}, which only represents the noise remaining after the noise cancellation sound is eliminated (the output sound of the first sound source device 13).

[0060] Therefore, according to this embodiment, the noise cancellation adaptive filter 31 can effectively eliminate the output sound of the first sound source device 13, excluding the interference of the echo from the output of the first microphone 12, the output sound of the second sound source device 23, etc.

[0061] Furthermore, the effect of such interference can be eliminated by using the simple structure of the echo cancellation adaptive filter 33, which eliminates the echo output to the first microphone 12 of the first speaker 11.

[0062] In addition, the above embodiments can also employ the structure of the signal processing device 3 shown above to eliminate the echo spreading from the second speaker 21 to the second microphone 22, and the structure of adding a symmetrical structure about the first region and the second region to the signal processing device 3 so that the sound picked up by the first microphone 12 in the first region is output to the second speaker 21 after eliminating the echo spreading from the first speaker 11 to the first microphone 12.

[0063] Alternatively, the above-described structure can be used to output a noise-canceling tone from the signal processing device 3 at the user's position in the second region, which outputs a noise-canceling tone from the first speaker 11 and eliminates the output tone from the first speaker 11 and eliminates the output tone from the second speaker 21 and eliminates the output tone from the second speaker 21 at the user's position in the first region. This can be achieved by adding a symmetrical structure to the signal processing device 3 about the first region and the second region, thereby outputting a noise-canceling tone from the first speaker 11 at the user's position in the first region, which outputs a noise-canceling tone from the second speaker 21 and eliminates the output tone from the second speaker 21 and eliminates the output tone from the second speaker 23 at the user's position in the first region.

[0064] In addition, in the above embodiments, the number of regions is set to 2, but this embodiment can also be extended to correspond to more than 3 regions.

[0065] Furthermore, the above description uses in-vehicle systems as an example, but the above implementation methods are also applicable to areas outside the vehicle.

[0066] Explanation of reference numerals in the attached figures

[0067] 3…Signal processing device, 11…First loudspeaker, 12…First microphone, 13…First sound source device, 21…Second loudspeaker, 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…Coefficient update unit for noise cancellation, 331…Variable filter for echo cancellation, 332…Coefficient update unit for echo cancellation.

Claims

1. An active noise control system, characterized in that, have: The first area microphone is a microphone configured in the first area; The second-zone loudspeaker is a loudspeaker that outputs sound to the second zone; The second area microphone is a microphone configured in the second area; The second zone sound source device is a sound source device that outputs sound from the second zone speaker; The first adder adds the output of the microphone in the first area and the output of the sound source device in the second area; An adaptive filter is used for echo cancellation, with the output of the first adder as the input; The third adder adds the output of the second area microphone and the output of the echo cancellation adaptive filter; The noise cancellation uses an adaptive filter that takes a noise signal as input, which represents the noise as far as the user in the second area is concerned; as well as The second adder outputs a signal to the second area speaker, which is the sum of 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. The echo cancellation uses an adaptive filter to update the filter coefficients in a manner that minimizes the output of the third adder, taking the error as the error. The noise cancellation adaptive filter uses the output of the third adder as an error and updates the filter coefficients in a manner that minimizes this error.

2. The active noise control system as described in claim 1, characterized in that, It includes a secondary path reproduction filter that takes the noise signal as input and has a pre-set transfer function from the second area speaker to the first area microphone. The noise cancellation adaptive filter updates the filter coefficients using the Filtered-X LMS algorithm (also known as the Filtered X Least Mean Square algorithm), which uses the output of the third adder as the error and the output of the secondary path reproduction filter as the reference signal.

3. The active noise control system as described in claim 1 or 2, characterized in that, The echo cancellation adaptive filter updates the filter coefficients using the LMS algorithm (Least Mean Square algorithm), which uses the output of the first adder as the reference signal and the output of the third adder as the error.

4. The active noise control system as described in claim 1 or 2, characterized in that, It has a first-area speaker, which is a speaker that provides sound to the first area from the output of the third adder and the output input of the first-area sound source device.

5. The active noise control system as described in claim 1 or 2, characterized in that, have: A first-area loudspeaker outputs sound to the first area; and The first zone sound source device is a sound source device that outputs sound from the first zone loudspeaker. The noise signal is the output of the sound source device in the first area.

6. The active noise control system as described in claim 1 or 2, characterized in that, have: The first area loudspeaker outputs sound to the first area; The first area sound source device is a sound source device that outputs sound from the first area speaker; as well as The fourth adder adds the output of the first area sound source device to the output of the third adder, and outputs the result to the first area loudspeaker. The noise signal is the output of the sound source device in the first area.

7. The active noise control system as described in claim 1 or 2, characterized in that, The active noise control system is installed in the car. The first area and the second area are different areas inside the passenger compartment of the vehicle.

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