Active noise control system
The active noise control system addresses inefficiencies in existing systems by employing strategically positioned microphones and gain/delay adjustments to achieve effective noise cancellation despite significant transfer function disparities.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- ALPS ALPINE CO LTD
- Filing Date
- 2022-05-18
- Publication Date
- 2026-05-25
AI Technical Summary
Existing active noise control systems face inefficiencies when dealing with large differences in transfer functions from a noise source to multiple error microphones, leading to oversized and burdensome configurations, particularly in scenarios like a car where users listen to music using left and right speakers.
An active noise control system utilizing multiple error microphones positioned strategically near a user's ears, with a gain and delay adjustment mechanism to match the ratio and timing of noise cancellation sounds output from speakers, effectively canceling noise despite significant differences in transfer functions.
The system effectively cancels noise with a simpler configuration by using strategically placed microphones and adjusted gain/delay, ensuring optimal noise cancellation even with large variations in transfer functions.
Smart Images
Figure 0007864426000001 
Figure 0007864426000002 
Figure 0007864426000003
Abstract
Description
Technical Field
[0001] The present invention relates to a technology of active noise control (ANC; Active Noise Control) that reduces noise by radiating noise cancellation sound that cancels out the noise.
Background Art
[0002] As a technology of active noise control, as in the active noise control system shown in FIG. 5, sounds such as music output from a sound source device 51 for a user in a first area to a speaker 52 for a user in the first area are used as noise for a user in a second area, and an active noise control system that radiates noise cancellation sound generated using an adaptive filter 53 from a speaker 54 in the second area is known (for example, Patent Document 1).
[0003] In this active noise control system, the adaptive filter 53 sets the output of an error microphone 55 arranged in the second area as an error, and uses the output of an estimation filter 56 that sets an estimated transfer function Ĉ(z) estimated as the transfer function C(z) from the speaker 54 in the second area to the error microphone 55 as a filtered reference signal. A coefficient update unit updates the tap coefficients of a variable filter 531 that generates noise cancellation sound from the output of the sound source device 51 so that the error is minimized by a Filtered-X LMS algorithm in which the LMS algorithm is performed. [[ID=}18]]
Prior Art Documents
Patent Documents
[0004] <00000{19>
Patent Document 1
Summary of the Invention
Problems to be Solved by the Invention
[0005] Consider a scenario where the active noise control system shown in Figure 5 is applied to a system in a car where each user listens to music using left and right speakers provided for their seat, and the system cancels out the music being listened to by other users as noise. In this case, it is preferable to provide adaptive filters corresponding to each combination of left and right error microphones positioned at the user's left and right ear locations, and left and right speakers for the user's seat, so that music being listened to by other users can be canceled out for each user's left and right ears, and to output noise-canceling sounds generated by the corresponding adaptive filters from the left and right speakers, thereby canceling noise for each of the user's left and right ears.
[0006] However, doing so can result in an excessive number of adaptive filters, leading to an oversized and burdensome system. Therefore, one might consider reducing the number of adaptive filters by combining the output audio from the left and right error microphones into a monaural sound, and then using this monaural sound as the output of a single error microphone to generate a noise cancellation sound with a single adaptive filter, which is then shared as the noise cancellation sound output from the left and right speakers. However, in this case, the same noise cancellation sound will be output from both the left and right speakers, so if there is a relatively large difference in the transfer function such as gain and delay time from the noise source (another user's speaker) to the left and right error microphones (the user's left and right ears), the noise output from the other user's speaker will not be properly canceled.
[0007] Therefore, the present invention aims to provide an active noise control system equipped with multiple error microphones that can effectively cancel noise even when there are relatively large differences in the transfer function from the noise source to each error microphone, using a relatively simple configuration. [Means for solving the problem]
[0008] To achieve the above objectives, the present invention provides an active noise control system for reducing noise, comprising: a first microphone positioned at a location biased toward a first direction relative to the user; a second microphone positioned at a location biased toward a second direction relative to the user; a first speaker that radiates sound toward the vicinity of the position where the first microphone is located; a second speaker that radiates sound toward the vicinity of the position where the second microphone is located; an error signal generation means that generates an added signal by adding the output of the first microphone and the output of the second microphone; an adaptive filter that uses a signal correlated with the noise as a reference signal, treats the added signal as an error, and performs adaptive operations to minimize the error to generate noise cancellation sounds output to the first speaker and the second speaker; and a gain adjustment means that adjusts the ratio of the magnitude of the first noise cancellation sound output to the first speaker to the magnitude of the second noise cancellation sound output to the second speaker. Here, the gain adjustment means performs the adjustment so that the ratio of the magnitude of the second noise cancellation sound to the magnitude of the first noise cancellation sound matches the ratio of the magnitude of the noise transmitted from the noise source to the second microphone to the magnitude of the noise transmitted from the noise source to the first microphone.
[0009] Here, in such an active noise control system, a delay adjustment means may be provided instead of, or together with, the gain adjustment means for adjusting the delay time between the first noise cancellation sound, which is the noise cancellation sound output to the first speaker, and the second noise cancellation sound, which is the noise cancellation sound output to the second speaker. Here, the delay adjustment means makes the adjustment so that the delay time of the second noise cancellation sound relative to the first noise cancellation sound matches the delay time of the noise transmitted from the noise source to the second microphone relative to the noise transmitted from the noise source to the first microphone.
[0010] Furthermore, in the above-described active noise control system, the first microphone may be placed at the first position and the second microphone at the second position, with one of the positions near the user's left ear and the other near the user's right ear designated as the first position and the other as the second position. In this case, one of the left and right seats of the car may be designated as the first seat and the other as the second seat, the user may be the user seated in the first seat, and the noise may be the sound output from a speaker near the second seat towards the person seated in the second seat. With this type of active noise control system, a relationship of gain and delay time that matches the relationship of gain and delay time of the noise from the noise source to the first microphone and the second microphone can be applied between the noise cancellation sound output from the first speaker, which radiates sound toward the area around the position of the first microphone, and the second speaker, which radiates sound toward the area around the position of the second microphone. Therefore, even when the difference in the gain and delay time of the noise is relatively large, the noise can be effectively canceled by using an adaptive filter that treats the summation signal obtained by adding the outputs of the first and second microphones as an error. [Effects of the Invention]
[0011] As described above, according to the present invention, in an active noise control system equipped with multiple error microphones, noise can be effectively canceled even when there is a relatively large difference in the transfer function from the noise source to each error microphone, with a relatively simple configuration. [Brief explanation of the drawing]
[0012] [Figure 1] This is a block diagram showing the configuration of an in-vehicle system according to an embodiment of the present invention. [Figure 2] This is a block diagram showing the arrangement of a microphone and a speaker according to an embodiment of the present invention. [Figure 3] This is a block diagram showing the configuration of the left-seat cancellation sound generation unit according to an embodiment of the present invention. [Figure 4] This is a block diagram showing a method for setting gain and delay time according to an embodiment of the present invention. [Figure 5] This figure shows the configuration of a known active noise control system. [Modes for carrying out the invention]
[0013] The embodiments of the present invention will be described below, using as an example their application to a system in which users in the left front seat and right front seat of an automobile listen to music using left and right speakers provided for those seats, respectively. Figure 1 shows the configuration of the in-vehicle system according to this embodiment. As shown in the figure, the in-vehicle system includes a left-seat sound source device 11, which is a sound source device for the user in the left front seat of the vehicle interior; a left-seat left speaker 12, which is a left-channel speaker for the user in the left front seat; a left-seat right speaker 13, which is a right-channel speaker for the user in the left front seat; a left-seat left-channel adder 14; a left-seat right-channel adder 15; a left-seat left microphone 16; a left-seat right microphone 17; and a left-seat cancellation sound generation unit 18.
[0014] The in-vehicle system also includes a right-seat sound source device 21 for the user in the right front seat of the vehicle, a right-seat left speaker 22 which is the left channel speaker for the user in the right front seat, a right-seat right speaker 23 which is the right channel speaker for the user in the right front seat, a right-seat left channel adder 24, a right-seat right channel adder 25, a right-seat left microphone 26, a right-seat right microphone 27, and a right-seat cancellation sound generation unit 28.
[0015] Here, as shown in Figures 2a and 2b, the left speaker 12 is positioned to the left of the head of the user seated in the left front seat, and the right speaker 13 is positioned to the right of the head of the user seated in the left front seat. In addition, the left microphone 16 is positioned to the left of the head of the user seated in the left front seat, and the right microphone 17 is positioned to the right of the head of the user seated in the left front seat.
[0016] Also, the right seat left speaker 22 is arranged at a position on the left side of the head of the user sitting in the right front seat, and the right seat right speaker 23 is arranged at a position on the right side of the head of the user sitting in the right front seat. Also, the right seat left microphone 26 is arranged at a position on the left side of the head of the user sitting in the right front seat, and the right seat right microphone 27 is arranged at a position on the right side of the head of the user sitting in the right front seat.
[0017] Returning to FIG. 1, the left seat sound source device 11 outputs the left channel audio LA_L and the right channel audio LA_R such as music. The left channel audio LA_L is added to the left seat left channel cancellation sound LC_L output by the left seat cancellation sound generation unit 18 in the left seat left channel adder 14, and then output to the left seat left speaker 12. The right channel audio LA_R is added to the left seat right channel cancellation sound LC_R output by the left seat cancellation sound generation unit 18 in the left seat right channel adder 15, and then output to the left seat right speaker 13.
[0018] The right seat sound source device 21 outputs the left channel audio RA_L and the right channel audio RA_R such as music. The left channel audio RA_L is added to the right seat left channel cancellation sound RC_L output by the right seat cancellation sound generation unit 28 in the right seat left channel adder 24, and then output to the right seat left speaker 22. The right channel audio RA_R is added to the right seat right channel cancellation sound RC_R output by the right seat cancellation sound generation unit 28 in the right seat right channel adder 25, and then output to the right seat right speaker 23.
[0019] Then, the left seat cancellation sound generation unit 18 uses the output LM_L of the left seat left microphone 16 and the output LM_R of the left seat right microphone 17 as errors to generate the left seat left channel cancellation sound LC_L and the left seat right channel cancellation sound LC_R that cancel the noise that propagates from the right direction, which is the left channel audio RA_L and the right channel audio RA_R of the right seat sound source device 21 output from the right seat left speaker 22 and the right seat right speaker 23.
[0020] Furthermore, the right-seat cancellation sound generation unit 28 uses the output RM_L from the right-seat left microphone 26 and the output RM_R from the right-seat right microphone 27 as errors to generate right-seat left-channel cancellation sound RC_L and right-seat right-channel cancellation sound RC_R, which cancel out the noise that propagates from the left direction, using the left-channel audio LA_L and right-channel audio LA_R of the left-seat sound source device 11, which are output from the left-seat left speaker 12 and the left-seat right speaker 13, as noise.
[0021] The left-seat cancellation sound generation unit 18 will be described below. Figure 3 shows the configuration of the left seat cancellation sound generation unit 18. As shown in the figure, the left-seat cancellation sound generation unit 18 includes a reference signal adder 181 that generates a reference signal R by adding the left channel audio RA_L and the right channel audio RA_R of the right-seat sound source device 21; an error adder 182 that generates an error signal E by adding the output LM_L of the left-seat left microphone 16 and the output LM_R of the left-seat right microphone 17; an adaptive filter 183 that performs adaptive operation using the reference signal R and the error signal E to generate a noise cancellation sound LC from the reference signal R; a left channel gain adjustment unit 184; a left channel delay unit 185; a right channel gain adjustment unit 186; and a right channel delay unit 187.
[0022] The adaptive filter 183 includes an estimation filter 1831 which sets a transfer function C^(z) estimated as the transfer function C(z) from the output of the adaptive filter 183 to the output of the error adder 182, a coefficient update unit 1832, and a variable filter 1833. The reference signal R output by the reference signal adder 181 becomes the input to the estimation filter 1831 and the variable filter 1833. The coefficient update unit 1832 updates the transfer function W(z) of the variable filter 1833 by updating the tap coefficients of the variable filter 1833 using the Filtered-X LMS algorithm, which performs the LMS algorithm with the output of the estimation filter 1831 as the filtered reference signal, so as to minimize the power of the error signal E output by the error adder 182.
[0023] Then, the output of the variable filter 1833 is output from the adaptive filter 183 as a noise-canceling LC. The noise cancellation sound LC output by the variable filter 1833 is adjusted in magnitude by a preset gain G_L in the left channel gain adjustment unit 184, then delayed by a preset delay time Z_L in the left channel delay unit 185, and output as the left seat left channel cancellation sound LC_L to the left seat left speaker 12 via the left seat left channel adder 14.
[0024] Furthermore, the noise cancellation sound LC output by the variable filter 1833 is adjusted in magnitude by a preset gain G_R in the right channel gain adjustment unit 186, then delayed by a preset delay time Z_R in the right channel delay unit 187, and output as the left-seat right channel cancellation sound LC_R to the left-seat right speaker 13 via the left-seat right channel adder 15.
[0025] Here, the gain G_L of the left channel gain adjustment unit 184 and the gain G_R of the right channel gain adjustment unit 186 are set so that the gain ratio G_L / G_R matches the ratio M_L / M_R of the magnitude of the noise transmitted from the noise source to the output LM_L of the left microphone 16 in the left seat and the magnitude of the noise transmitted to the output LM_R of the right microphone 17 in the left seat from the noise source.
[0026] Furthermore, the delay time Z_L of the left channel delay unit 185 and the delay time Z_R of the right channel delay unit 187 are set so that the difference in delay times Z_L-Z_R matches the difference d_L-d_R between the delay time d_L of the noise from the noise source to the output LM_L of the left microphone 16 in the left seat and the delay time d_R of the noise from the noise source to the output LM_R of the right microphone 17 in the left seat.
[0027] Here, the noise sources for the noise canceled by the left-seat cancellation sound generation unit 18 are the right-seat left speaker 22 and the right-seat right speaker 23. Therefore, the gain G_L of the left channel gain adjustment unit 184, the gain G_R of the right channel gain adjustment unit 186, the delay time Z_L of the left channel delay unit 185, and the delay time Z_R of the right channel delay unit 187 can be set in advance, for example, as follows.
[0028] In other words, a test sound is output from both the left speaker 22 in the right seat and the right speaker 23 in the right seat, or from a measurement speaker positioned in the center between the left speaker 22 in the right seat and the right speaker 23 in the right seat. Then, the magnitude M_L of the output test sound transmitted to the left microphone 16 (left seat) and the magnitude M_R transmitted to the right microphone 17 (left seat) are determined, and the gain G_L of the left channel gain adjustment unit 184 and the gain G_R of the right channel gain adjustment unit 186 are set so that G_L / G_R matches the determined M_L / M_R.
[0029] Furthermore, the difference d_L-d_R between the output test sound from the left microphone 16 (left seat) to the output LM_L and the output test sound from the right microphone 17 (left seat) to the output LM_R is calculated, and the delay time Z_L of the left channel delay unit 185 and the delay time Z_R of the right channel delay unit 187 are set so that Z_L-Z_R matches the calculated d_L-d_R.
[0030] More specifically, for example, if the waveforms of the output LM_L from the left microphone 16 and the output LM_R from the right microphone 17 obtained in response to the output test sound are as shown in Figure 4, then the magnitude of the peak that first appears in the output LM_L from the left microphone 16 is set to M_L, and the magnitude of the peak that first appears in the output LM_R from the left microphone 26 is set to M_R, and the gain G_L of the left channel gain adjustment unit 184 and the gain G_R of the right channel gain adjustment unit 186 are set so that G_L / G_R matches M_L / M_R.
[0031] Furthermore, the delay between the first peak appearing in the output LM_R of the right-side left microphone 26 and the first peak appearing in the output LM_L of the left-side left microphone 16 is defined as d_L-d_R, and the delay time Z_L of the left channel delay unit 185 and the delay time Z_R of the right channel delay unit 187 are set so that d_L-d_R and Z_L-Z_R match.
[0032] Here, if d_L - d_R is positive, Z_L = d_L - d_R and Z_R = 0 may be set. In this case, the right channel delay section 187 may be omitted. Also, if d_L - d_R is negative, Z_L = 0 and Z_R = -(d_L - d_R). In this case, the left channel delay section 185 may be omitted. The left-seat cancellation sound generation unit 18 has been explained above.
[0033] With this left-seat cancellation sound generation unit 18, a gain and delay time relationship that matches the relationship between the gain and delay time of the noise from the noise source to the output LM_L of the left-seat left microphone 16 and the output LM_R of the left-seat right microphone 17 can be applied between the left-seat left channel cancellation sound LC_L output from the left-seat left speaker 12 and the left-seat right channel cancellation sound LC_R output from the left-seat right speaker 13. Therefore, even when the difference in the gain and delay time of the noise is relatively large, the noise can be effectively canceled using the adaptive filter 183, which treats the sum of the output LM_L of the left-seat left microphone 16 and the output LM_R of the left-seat right microphone 17 as an error.
[0034] Next, the right-seat cancellation sound generation unit 28 is the same as the left-seat cancellation sound generation unit 18 described above, but with the left and right seats swapped. Embodiments of the present invention have been described above. Furthermore, while the above description focused on the application of this embodiment to a system in which users in the left front seat and right front seat of a car listen to music using left and right speakers provided for those seats, this embodiment can be similarly applied to other seat combinations. In this case, the seats do not necessarily have to be seats inside a car. [Explanation of symbols]
[0035] 11...Left seat sound source device, 12...Left seat left speaker, 13...Left seat right speaker, 14...Left seat left channel adder, 15...Left seat right channel adder, 16...Left seat left microphone, 17...Left seat right microphone, 18...Left seat cancellation sound generation unit, 21...Right seat sound source device, 22...Right seat left speaker, 23...Right seat right speaker, 24...Right seat left channel adder, 25...Right seat right channel adder, 26...Right seat left microphone, 27...Right seat right microphone, 28...Right seat cancellation sound generation unit, 181...Reference signal adder, 182...Error adder, 183...Adaptive filter, 184...Left channel gain adjustment unit, 185...Left channel delay unit, 186...Right channel gain adjustment unit, 187...Right channel delay unit, 1831...Estimation filter, 1832...Coefficient update unit, 1833...Variable filter.
Claims
1. An active noise control system for reducing noise, A first microphone is positioned in a location biased toward the first direction relative to the user, A second microphone is positioned to be biased towards the second direction relative to the user, A first speaker is a speaker that radiates sound toward the area surrounding the position where the first microphone is placed, A second speaker is a speaker that radiates sound toward the area surrounding the position where the second microphone is placed, An error signal generation means that generates an added signal by adding the output of the first microphone and the output of the second microphone, An adaptive filter that uses a signal correlated with the noise as a reference signal, treats the summed signal as an error, and performs an adaptive operation to minimize the error to generate noise-canceling sounds output to the first speaker and the second speaker, The system includes a gain adjustment means for adjusting the ratio between the magnitude of the first noise cancellation sound, which is the noise cancellation sound output to the first speaker, and the magnitude of the second noise cancellation sound, which is the noise cancellation sound output to the second speaker. An active noise control system characterized in that the gain adjustment means adjusts the ratio of the magnitude of the second noise cancellation sound to the magnitude of the first noise cancellation sound to match the ratio of the magnitude of the noise transmitted from the noise source to the second microphone to the magnitude of the noise transmitted from the noise source to the first microphone.
2. An active noise control system for reducing noise, A first microphone is positioned in a location biased toward the first direction relative to the user, A second microphone is positioned to be biased towards the second direction relative to the user, A first speaker is a speaker that radiates sound toward the area surrounding the position where the first microphone is placed, A second speaker is a speaker that radiates sound toward the area surrounding the position where the second microphone is placed, An error signal generation means that generates an added signal by adding the output of the first microphone and the output of the second microphone, An adaptive filter that uses a signal correlated with the noise as a reference signal, treats the summed signal as an error, and performs an adaptive operation to minimize the error to generate noise-canceling sounds output to the first speaker and the second speaker, The system includes a delay adjustment means for adjusting the delay time between a first noise cancellation sound, which is the noise cancellation sound output to the first speaker, and a second noise cancellation sound, which is the noise cancellation sound output to the second speaker. The delay adjustment means is characterized by performing the adjustment so that the delay time of the second noise cancellation sound relative to the first noise cancellation sound matches the delay time of the noise transmitted from the noise source to the first microphone relative to the noise transmitted from the noise source to the second microphone.
3. An active noise control system according to claim 2, The system includes a gain adjustment means for adjusting the ratio between the magnitude of the first noise cancellation sound, which is the noise cancellation sound output to the first speaker, and the magnitude of the second noise cancellation sound, which is the noise cancellation sound output to the second speaker. An active noise control system characterized in that the gain adjustment means adjusts the ratio of the magnitude of the second noise cancellation sound to the magnitude of the first noise cancellation sound to match the ratio of the magnitude of the noise transmitted from the noise source to the second microphone to the magnitude of the noise transmitted from the noise source to the first microphone.
4. An active noise control system according to claim 1, 2, or 3, An active noise control system characterized in that one of the positions near the user's left ear and the other near the user's right ear is designated as the first position and the other as the second position, the first microphone is positioned at the first position and the second microphone is positioned at the second position.
5. An active noise control system according to claim 4, In a car, one of the left and right seats is designated as the first seat and the other as the second seat, and the user is the user seated in the first seat. The aforementioned noise is characterized in that the noise is sound emitted from a speaker near the second seat towards the person seated in the second seat.