Active noise control system

Abstract

Provided is an active noise control system capable of well canceling noise regardless of displacement of a user's ear. In a first system signal processing section (111), a first system auxiliary filter (1116) generates a correction signal that corrects an error signal from a noise signal, a first system subtracter (1115) subtracts the correction signal from an output of a first microphone (13) as the error signal, adaptive filters (1111-1114) perform adaptive operation using the error signal, and generate a canceling sound to be output from a first speaker (12). A DMS (18) detects a position of the user's ear. If the position of the user's ear moves, a controller (16) stops the adaptive operation, updates a transfer function of the first system auxiliary filter to a transfer function corresponding to a noise canceling position that matches the position of the user's ear, then gradually changes a transfer function of the adaptive filter to a transfer function corresponding to the matching noise canceling position, and resumes the adaptive operation after the change is completed.

Description

Technical Field

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

[0002] As an active noise control technique that reduces noise by emitting noise-canceling tones to eliminate noise, there is a known technique that includes a microphone and a speaker positioned near the noise cancellation location, and an adaptive filter that generates a noise-canceling tones to be output from the speaker based on the output signal of the noise source or a signal that is similar to the output signal. In the adaptive filter, the signal after the microphone output is corrected using an auxiliary filter is used as an error signal, and its transfer function is adaptive (e.g., Patent Document 1).

[0003] In this technique, an auxiliary filter is configured with a pre-learned transfer function that, when the microphone is positioned at a noise cancellation location, generates a correction signal from the noise signal to correct the signal actually output by the microphone. By using such an auxiliary filter, noise is eliminated at a noise cancellation location that is different from the microphone's position.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2018-72770 Summary of the Invention

[0007] When using the aforementioned technique of using an auxiliary filter to cancel noise at a noise cancellation position different from the microphone to eliminate noise audible to the user, if the user's ear moves away from the noise cancellation position as the user moves, there is a possibility that the noise audible to the user cannot be effectively eliminated.

[0008] Therefore, consider the following process: for different noise cancellation locations, pre-learn the transfer function of the auxiliary filter, and as the user's ear moves, switch the transfer function of the auxiliary filter to the transfer function learned for the noise cancellation location corresponding to the user's ear position, thereby canceling the noise that the user can hear regardless of the user's ear movement.

[0009] However, in this case, after the transfer function of the auxiliary filter is switched, during the period until the transfer function of the adaptive filter adapts to a transfer function that can properly eliminate noise at the user's ear position, the user can sometimes hear noise.

[0010] Therefore, the objective of this invention is to provide an active noise control system that can effectively eliminate noise regardless of the displacement of the user's ear.

[0011] To achieve the above-mentioned objectives, the present invention provides an active noise control system for reducing noise, comprising: a position detection unit for detecting the location where a user hears the sound, i.e., the listening position; a control unit; a loudspeaker for outputting a noise-canceling tone; a microphone for detecting error signals; an auxiliary filter for generating and outputting a correction signal by applying a predetermined transfer function to a noise signal representing noise; an error correction unit for correcting the error signal output by the microphone using the correction signal output by the auxiliary filter, and outputting the corrected error signal as a corrected error signal; an adaptive filter for performing an adaptive operation using the corrected error signal output by the error correction unit, generating a noise-canceling tone to be output from the loudspeaker from the noise signal; and a storage unit for storing multiple noise cancellation positions and setting information, wherein the setting information is setting information for setting the initial transfer function of the adaptive filter corresponding to each noise cancellation position. When the noise cancellation position that matches the listening position detected by the position detection unit among the plurality of noise cancellation positions changes, i.e., the matched noise cancellation position, the control unit performs the following switching operation: the auxiliary filter that outputs the correction signal to the error correction unit is set to an auxiliary filter that has been set with a transfer function for the auxiliary filter corresponding to the matched noise cancellation position, which is one of the transfer functions for the auxiliary filter that is set to correspond to the plurality of noise cancellation positions respectively, and the transfer function of the adaptive filter is updated to the initial transfer function of the adaptive filter corresponding to the matched noise cancellation position using the setting information.

[0012] Here, such an active noise control system can also be configured such that, during the switching operation, the control unit stops the adaptive operation of the adaptive filter and sets the auxiliary filter that outputs the correction signal to the error correction unit to an auxiliary filter with a transfer function set to correspond to the matched noise cancellation position. Then, the control unit gradually changes the transfer function of the adaptive filter to the initial transfer function of the adaptive filter corresponding to the matched noise cancellation position, thereby updating the transfer function of the adaptive filter to the initial transfer function of the adaptive filter, and then restarts the adaptive operation of the adaptive filter.

[0013] Furthermore, more specifically, in the above-described active noise control system, the initial transfer function of the adaptive filter corresponding to each noise cancellation position can be set as follows: when the initial transfer function of the adaptive filter is set, the adaptive filter generates a noise cancellation tone that cancels noise at the noise cancellation position corresponding to the initial transfer function of the adaptive filter under standard conditions; the transfer function of the auxiliary filter corresponding to each noise cancellation position can be set as follows: when the transfer function of the auxiliary filter is set, the auxiliary filter outputs a correction signal, which is a correction signal that corrects the output of the microphone, i.e., the error signal, by the error correction unit in a manner that compensates for the difference between the noise cancellation position corresponding to the transfer function of the auxiliary filter and the microphone position.

[0014] Alternatively, in the above-described active noise control system, the initial transfer function of the adaptive filter corresponding to each noise cancellation position may be set as a transfer function learned using a learning microphone configured at the noise cancellation position corresponding to the initial transfer function of the adaptive filter, and a transfer function for the adaptive filter to generate a noise cancellation tone that cancels noise at the corresponding noise cancellation position; the transfer function of the auxiliary filter corresponding to each noise cancellation position may be a transfer function that has been pre-learned as a transfer function that, when the transfer function of the adaptive filter is fixed to the initial transfer function of the adaptive filter corresponding to the noise cancellation position, the auxiliary filter outputs a correction signal in the error correction unit where the error signal is corrected to 0.

[0015] Alternatively, in the above active noise control system, the position detection unit may detect the position of the user's head or ears while seated in a designated seat in the car as the listening position.

[0016] According to the active noise control system described above, when a displacement occurs in the listening position of the user, in addition to the transfer function of the auxiliary filter, the transfer function of the adaptive filter can also be updated to a transfer function that approximates the transfer function for noise cancellation at the noise cancellation position that matches the listening position. Thus, through subsequent adaptive actions, noise can be quickly cancelled at the noise cancellation position that matches the listening position.

[0017] Furthermore, by gradually updating the transfer function of this adaptive filter, it is possible to suppress the unnatural sound output to the user that accompanies the update.

[0018] Here, the present invention also provides an active noise control system that applies the active noise control system as described above to the elimination of noise at various locations on the left and right ears of a user.

[0019] That is, the present invention also provides an active noise control system comprising: a position detection unit for detecting the position of a user's left and right ears, a control unit, two noise control systems (a right-ear noise control system and a left-ear noise control system), and a storage unit. Each noise control system comprises: a loudspeaker for outputting a noise-canceling tone; a microphone for detecting error signals; an auxiliary filter for generating and outputting a correction signal by applying a predetermined transfer function to the noise signal representing noise; an error correction unit for correcting the output of the microphone (i.e., the error signal) using the correction signal output by the auxiliary filter, and outputting the corrected error signal as a corrected error signal; and an adaptive filter for adaptively operating on the corrected error signal output by the error correction unit of the right-ear noise control system and the corrected error signal output by the error correction unit of the left-ear noise control system, generating a noise-canceling tone to be output from the loudspeaker from the noise signal. In addition, the storage unit stores multiple noise cancellation position sets and setting information, which are used to set the first noise cancellation position and the second noise cancellation position as a noise cancellation position set. The setting information is used to set the first adaptive filter initial transfer function and the second adaptive filter initial transfer function corresponding to each noise cancellation position set for the adaptive filter of the noise control system for the right ear for the first adaptive filter initial transfer function, and to set the first adaptive filter initial transfer function and the second adaptive filter initial transfer function corresponding to each noise cancellation position set for the adaptive filter of the noise control system for the left ear for the second adaptive filter initial transfer function. Furthermore, when the noise cancellation position set matching the user's left and right ear positions detected by the position detection unit changes among the plurality of noise cancellation position sets, the control unit performs the following switching operation: It sets the auxiliary filter that outputs a correction signal to the error correction unit of the right ear noise control system to an auxiliary filter whose transfer function is set to the first auxiliary filter transfer function corresponding to the matching noise cancellation position set among the first auxiliary filter transfer functions corresponding to each of the plurality of pre-set noise cancellation position sets; it updates the transfer function of the adaptive filter of the right ear noise control system to the initial transfer function of the first adaptive filter corresponding to the matching noise cancellation position set using the setting information; it sets the auxiliary filter that outputs a correction signal to the error correction unit of the left ear noise control system to an auxiliary filter whose transfer function is set to the second auxiliary filter transfer function corresponding to the matching noise cancellation position set among the second auxiliary filter transfer functions corresponding to each of the plurality of pre-set noise cancellation position sets; it updates the transfer function of the adaptive filter of the left ear noise control system to the initial transfer function of the second adaptive filter corresponding to the matching noise cancellation position set using the setting information.

[0020] Here, such an active noise control system can also be configured such that, during the switching operation, the control unit stops the adaptive operation of the adaptive filters of the right ear noise control system and the left ear noise control system, and sets the auxiliary filter that outputs the correction signal to the error correction unit of the right ear noise control system to an auxiliary filter with a transfer function set to the first auxiliary filter corresponding to the set of matched noise cancellation positions, and sets the auxiliary filter that outputs the correction signal to the error correction unit of the left ear noise control system to an auxiliary filter with a transfer function set to the second auxiliary filter corresponding to the set of matched noise cancellation positions, by gradually changing the initial transfer function of the first adaptive filter corresponding to the set of matched noise cancellation positions, the transfer function of the adaptive filter of the right ear noise control system is updated to the initial transfer function of the first adaptive filter, and the transfer function of the adaptive filter of the left ear noise control system is updated to the initial transfer function of the second adaptive filter corresponding to the set of matched noise cancellation positions, by gradually changing the initial transfer function of the second adaptive filter, and the adaptive operation of the adaptive filters of the right ear noise control system and the left ear noise control system is restarted.

[0021] Alternatively, such an active noise control system can also be configured such that the set of matched noise cancellation positions is defined as a set of noise cancellation positions where the predicted position of the user's right ear matches a first noise cancellation position, and the predicted position of the user's left ear matches a second noise cancellation position; the initial transfer function of the first adaptive filter and the initial transfer function of the second adaptive filter corresponding to each noise cancellation position set are configured as follows: when the initial transfer function of the first adaptive filter is set to a noise control system for the right ear and the initial transfer function of the second adaptive filter is set to a noise control system for the left ear, the noise cancellation tone is generated under standard conditions by the adaptive filters of the noise control system for the right ear and the noise control system for the left ear, and the noise cancellation tone cancels noise at the first noise cancellation position and the second noise cancellation position of the noise cancellation position set corresponding to the initial transfer function of the first adaptive filter and the initial transfer function of the second adaptive filter; the initial transfer function of the first adaptive filter and the initial transfer function of the second adaptive filter correspond to the noise cancellation position set corresponding to each noise cancellation position set are configured as follows: The first auxiliary filter transfer function is set as follows: in the right ear noise control system, when the first auxiliary filter transfer function is set, the auxiliary filter output correction signal is a transfer function that corrects the microphone output, i.e., the error signal, by means of compensating for the difference between the first noise cancellation position of the noise cancellation position set corresponding to the first auxiliary filter transfer function and the microphone position. The second auxiliary filter transfer function corresponding to each noise cancellation position set is set as follows: in the left ear noise control system, when the second auxiliary filter transfer function is set, the auxiliary filter output correction signal is a transfer function that corrects the microphone output, i.e., the error signal, by means of compensating for the difference between the second noise cancellation position of the noise cancellation position set corresponding to the second auxiliary filter transfer function and the microphone position.

[0022] Alternatively, such an active noise control system can be configured such that the initial transfer function of the first adaptive filter and the initial transfer function of the second adaptive filter corresponding to each noise cancellation position set are set to transfer functions learned by the adaptive filters of the right-ear noise control system and the left-ear noise control system, using the first learning microphone configured at the first noise cancellation position of the noise cancellation position set and the second learning microphone configured at the second noise cancellation position of the noise cancellation position set. The noise cancellation tone is the noise cancellation tone that cancels noise at the first and second noise cancellation positions of the corresponding noise cancellation position set. The transfer function of the first auxiliary filter corresponding to each noise cancellation position set is set to a transfer function that is pre-learned as a transfer function, whereby the transfer function of the adaptive filter of the right-ear noise control system is fixed to the initial transfer function of the first adaptive filter corresponding to the first noise cancellation position of the noise cancellation position set, and the transfer function of the left-ear noise control system is... With the transfer function of the adaptive filter of the system fixed as the initial transfer function of the second adaptive filter corresponding to the second noise cancellation position of the noise cancellation position set, in the right ear noise control system, the auxiliary filter outputs a correction signal in the error correction unit that corrects the error signal to 0. The transfer function of the second auxiliary filter corresponding to each noise cancellation position set is a transfer function that is pre-learned as follows: with the transfer function of the adaptive filter of the right ear noise control system fixed as the initial transfer function of the first adaptive filter corresponding to the first noise cancellation position of the noise cancellation position set, and the transfer function of the adaptive filter of the left ear noise control system fixed as the initial transfer function of the second adaptive filter corresponding to the second noise cancellation position of the noise cancellation position set, in the left ear noise control system, the auxiliary filter is set as a pre-learned transfer function that outputs a correction signal in the error correction unit that corrects the error signal to 0.

[0023] Alternatively, in such an active noise control system, the position detection unit may detect the positions of the left and right ears of a user seated in a designated seat in the car.

[0024] Invention Effects

[0025] As described above, according to the present invention, an active noise control system is provided that can effectively eliminate noise regardless of the displacement of the user's ear. Attached Figure Description

[0026] Figure 1 This is a block diagram illustrating the structure of an active noise control system according to an embodiment of the present invention.

[0027] Figure 2 This is a diagram showing the configuration of the loudspeaker and microphone in an active noise control system according to an embodiment of the present invention.

[0028] Figure 3 This is a block diagram illustrating the structure of the signal processing module according to an embodiment of the present invention.

[0029] Figure 4 This is a diagram illustrating a filter management table according to an embodiment of the present invention.

[0030] Figure 5 This is a diagram illustrating the method for setting elimination points according to an embodiment of the present invention.

[0031] Figure 6 This is a block diagram illustrating the structure for learning the transfer function of the auxiliary filter according to an embodiment of the present invention.

[0032] Figure 7 This is a block diagram illustrating the structure for learning the transfer function of the auxiliary filter according to an embodiment of the present invention.

[0033] Figure 8 This is a flowchart illustrating the elimination point switching process in an embodiment of the present invention. Detailed Implementation

[0034] The embodiments of the present invention will be described below.

[0035] Figure 1 This illustrates the structure of the active noise control system of this embodiment.

[0036] As shown in the figure, the active noise control system 1 includes a signal processing module 11, a first speaker 12, a first microphone 13, a second speaker 14, a second microphone 15, a controller 16, a filter management table 17, and a DMS 18 (Driver Monitoring System 18) for detecting the position of the user's head or ears.

[0037] Furthermore, the active noise control system 1 of this embodiment is a system installed in a car. It is a system that eliminates noise generated by a noise source at each of the two elimination points, with the position of the user's right ear as the first elimination point and the position of the user's left ear as the second elimination point.

[0038] Here, DMS18, for example, according to Figure 2 As shown in a1 and a2, the position of the user's head and ears is detected by images of the user sitting in the noise cancellation seat captured by a near-infrared camera 181 positioned in front of the noise cancellation seat (driver's seat in the figure).

[0039] Here, as Figure 2 As shown in a1 and a2, the first speaker 12 and the first microphone 13 are positioned near the headrest of the noise-cancellation target seat (driver's seat in the figure), which is the standard position for the right ear of the user sitting in the seat. The second speaker 14 and the second microphone 15 are positioned near the headrest of the user's seat, which is the target of noise cancellation, which is the standard position for the left ear of the user sitting in the seat.

[0040] Or, it can be like Figure 2 As shown in b1 and b2, the first speaker 12 is positioned above and in front of the standard position of the right ear of the user seated in the noise-cancellation target seat on the ceiling of the vehicle cabin. The second speaker 14 is positioned above and in front of the standard position of the left ear of the user seated in the noise-cancellation target seat on the ceiling of the vehicle cabin. The first microphone 13 is positioned to the right of the first speaker 12 and closer to the noise-cancellation target seat than the first speaker 12 on the ceiling in front of the user. The second microphone 15 is positioned to the left of the second speaker 14 and closer to the noise-cancellation target seat than the second speaker 14 on the ceiling in front of the user. Furthermore, with the first speaker 12 and the second speaker 14 positioned on the ceiling in this way, super-directional parametric speakers can also be used as the first speaker 12 and the second speaker 14.

[0041] return Figure 1 The signal processing module 11 uses a noise signal x(n) representing the noise generated by the noise source, a sound signal picked up by the first microphone 13 (i.e., the first microphone error signal err1(n)), and a sound signal picked up by the second microphone 15 (i.e., the second microphone error signal err2(n)) to generate a first cancellation signal CA1(n) and output it from the first speaker 12, and generates a second cancellation signal CA2(n) and output it from the second speaker 14.

[0042] Furthermore, noise generated by the noise source is eliminated at the first elimination point and the second elimination point by the first elimination signal CA1(n) output from the first speaker 12 and the second elimination signal CA2(n) output from the second speaker 14.

[0043] Next, as Figure 3 As shown, the signal processing module 11 mainly includes a first system signal processing unit 111 that performs processing related to the generation of the first cancellation signal CA1(n), and a second system signal processing unit 112 that mainly performs processing related to the generation of the second cancellation signal CA2(n).

[0044] Furthermore, the first system signal processing unit 111 includes: a first system variable filter 1111, a first system adaptive algorithm execution unit 1112, a first system first estimation filter 1113 with a preset transfer function S11^(z), a first system second estimation filter 1114 with a preset transfer function S21^(z), a first system subtractor 1115, and a first system auxiliary filter 1116 with a preset transfer function H1(z).

[0045] In the structure of the first system signal processing unit 111, the input noise signal x(n) is output to the first speaker 12 as a first cancellation signal CA1(n) after passing through the first system variable filter 1111.

[0046] Additionally, the input noise signal x(n) is sent to the first system subtractor 1115 after passing through the first system auxiliary filter 1116. The first system subtractor 1115 subtracts the output of the first system auxiliary filter 1116 from the first microphone error signal err1(n) picked up by the first microphone 13, and outputs it as error e1 to the first system adaptive algorithm execution unit 1112 and the second system signal processing unit 112.

[0047] Next, the first system variable filter 1111, the first system adaptive algorithm execution unit 1112, the first system first estimated filter 1113, and the first system second estimated filter 1114 constitute the Filtered-X adaptive filter. In the first system first estimated filter 1113, an estimated transfer characteristic S11^(z) of the transfer function S11(z) from the first system signal processing unit 111 to the first microphone 13, which is calculated through actual measurement, is preset. The first system first estimated filter 1113 convolves the transfer characteristic S11^(z) with the input noise signal x(n) and then inputs it to the first system adaptive algorithm execution unit 1112. In addition, in the second estimation filter 1114 of the first system, there is a preset estimated transfer characteristic S21^(z) that represents the transfer characteristic S21(z) from the signal processing unit 111 of the first system to the second microphone 15 calculated by actual measurement, etc. The second estimation filter 1114 of the first system convolves the transfer characteristic S21^(z) with the input noise signal x(n) and inputs it to the adaptive algorithm execution unit 1112 of the first system.

[0048] Furthermore, the first system adaptive algorithm execution unit 1112 performs the following adaptive operation: taking the noise signal x(n) after convolving the transfer function S11^(z) in the first system first estimation filter 1113, the noise signal x(n) after convolving the transfer function S21^(z) in the first system second estimation filter 1114, the error e1 output from the first system subtractor 1115, and the error e2 output from the second system signal processing unit 112 as inputs, and executing adaptive algorithms such as NLMS to update the transfer function W1(z) of the first system variable filter 1111 so that the error becomes 0.

[0049] The second system signal processing unit 112 also has the same structure as the first system signal processing unit 111. The second system signal processing unit 112 includes: a second system variable filter 1121, a second system adaptive algorithm execution unit 1122, a second system first estimation filter 1123 with a pre-set transfer function S22^(z), a second system second estimation filter 1124 with a pre-set transfer function S12^(z), a second system subtractor 1125, and a second system auxiliary filter 1126 with a set transfer function H2(z).

[0050] In the structure of the second system signal processing unit 112, the input noise signal x(n) is output to the second speaker 14 as the second cancellation signal CA2(n) after passing through the second system variable filter 1121.

[0051] Furthermore, the input noise signal x(n) is sent to the second system subtractor 1125 after passing through the second system auxiliary filter 1126. The second system subtractor 1125 subtracts the output of the second system auxiliary filter 1126 from the second microphone error signal err2(n) picked up by the second microphone 15, and outputs the result as error e2 to the second system adaptive algorithm execution unit 1122 and the first system signal processing unit 111.

[0052] Next, the second system variable filter 1121, the second system adaptive algorithm execution unit 1122, the second system first estimated filter 1123, and the second system second estimated filter 1124 constitute a Filtered-X adaptive filter. In the second system first estimated filter 1123, an estimated transfer characteristic S22^(z) of the transfer function S22(z) from the second system signal processing unit 112 to the second microphone 15, calculated through actual measurements, is preset. The second system first estimated filter 1123 convolves the transfer characteristic S22^(z) with the input noise signal x(n) and inputs it to the second system adaptive algorithm execution unit 1122. Furthermore, in the second estimation filter 1124 of the second system, there is a pre-set estimated transfer characteristic S12^(z) that represents the transfer characteristic S12(z) from the second system signal processing unit 112 to the first microphone 13, which is calculated by means of actual measurement, etc. The second estimation filter 1124 of the second system convolves the transfer characteristic S12^(z) with the input noise signal x(n) and inputs it to the second system adaptive algorithm execution unit 1122.

[0053] Then, the second system adaptive algorithm execution unit 1122 performs the following adaptive operation: taking the noise signal x(n) after convolving the transfer function S22^(z) in the first estimation filter 1123 of the second system, the noise signal x(n) after convolving the transfer function S12^(z) in the second estimation filter 1124 of the second system, the error e2 output from the second system subtractor 1125, and the error e1 output from the first system signal processing unit 111 as inputs, and executing adaptive algorithms such as NLMS to update the transfer function W2(z) of the second system variable filter 1121 so that the error becomes 0.

[0054] Here, the transfer function H1(z) of the first system auxiliary filter 1116 of the first system signal processing unit 111 and the transfer function H2(z) of the second system auxiliary filter 1126 of the second system signal processing unit 112 are configured to be arbitrarily set by the controller 16.

[0055] Furthermore, the execution and cessation of the adaptive action of the first system adaptive algorithm execution unit 1112 of the first system signal processing unit 111, and the execution and cessation of the adaptive action of the second system adaptive algorithm execution unit 1122 of the second system signal processing unit 112, can be controlled by the controller 16.

[0056] Furthermore, when the adaptive operation of the first system adaptive algorithm execution unit 1112 of the first system signal processing unit 111 is stopped, the controller 16 can arbitrarily set the transfer function W1(z) of the first system variable filter 1111 of the first system signal processing unit 111. Additionally, when the adaptive operation of the second system adaptive algorithm execution unit 1122 of the second system signal processing unit 112 is stopped, the controller 16 can arbitrarily set the transfer function W2(z) of the second system variable filter 1121 of the second system signal processing unit 112.

[0057] Next, the contents of filter management table 17 will be explained. Additionally, as... Figure 4 As shown, the filter management table 17 has n entries (rows in the figure) corresponding to each of the n elimination point sets.

[0058] Each elimination point is a pair of a first elimination point and a second elimination point, and different sets of elimination points are different combinations of the first elimination point and the second elimination point.

[0059] That is, a set of n elimination points, for example, Figure 5 As shown in a1, a2, and a3, the positions in different front-to-back directions of the noise cancellation target seat can be set respectively. In this case, the first cancellation point of each cancellation point set is set to the standard right ear position of the user sitting in the noise cancellation target seat located in the corresponding front-to-back direction position, and the second cancellation point is set to the standard left ear position of the user sitting in the noise cancellation target seat located in the corresponding front-to-back direction position.

[0060] In addition, the elimination points in the set of n elimination points can also include elimination points set according to the user's head orientation, front-back, left-right, up-down position, and each combination thereof.

[0061] return Figure 4 In the entry corresponding to the i-th elimination point set in the filter management table 17, the first elimination point P1_i and the second elimination point P2_i of the i-th elimination point set, the first system auxiliary filter setting value H1_i(z), the second system auxiliary filter setting value H2_i(z), the first system variable filter initial value W1_i(z), and the second system variable filter initial value W2_i(z) are registered.

[0062] In addition, the first system auxiliary filter setting value H1_i(z), the second system auxiliary filter setting value H2_i(z), the first system variable filter initial value W1_i(z), and the second system variable filter initial value W2_i(z) registered in the entries of each elimination point set in the filter management table 17 are pre-learned and set in the filter management table 17.

[0063] The learning of the first system auxiliary filter setting value H1_i(z), the second system auxiliary filter setting value H2_i(z), the first system variable filter initial value W1_i(z), and the second system variable filter initial value W2_i(z) is carried out in a standard environment by setting the number i to an integer from 1 to n and performing the following first-stage learning process and second-stage learning process.

[0064] The first stage of learning is handled as follows: Figure 6 As shown, this is carried out in a structure in which the signal processing module 11 is replaced with the first-stage learning processing module 6.

[0065] In addition, the first stage of learning processing is performed by connecting the first learning microphone 51 configured at the first elimination point P1_i in the i-th elimination point set and the second learning microphone 52 configured at the second elimination point P2_i in the i-th elimination point set to the first stage learning processing module 6.

[0066] The settings for the first learning microphone 51 and the second learning microphone 52 are as follows: Figure 5 As shown in b1 and b2, the following processing is performed: a virtual doll with a first learning microphone 51 fixed at the right ear and a second learning microphone 52 fixed at the left ear is seated in the elimination target seat; the position of the elimination target seat, the position of the virtual doll, and the posture are adjusted so that the first learning microphone 51 is located at the first elimination point P1_i of the i-th elimination point set, and the second learning microphone 52 is located at the second elimination point P2_i of the i-th elimination point set.

[0067] like Figure 6 As shown, the first-stage learning processing module 6 includes a first-system first-stage learning processing unit 61 and a second-system first-stage learning processing unit 62.

[0068] Furthermore, the first-stage learning processing unit 61 of the first system has the following structure: From Figure 3The first system signal processing unit 111 of the signal processing module 11 shown removes the first system subtractor 1115 and the first system auxiliary filter 1116, and sets a first system first learning estimation filter 611 to replace the first system first estimation filter 1113. The first system first learning estimation filter 611 is a learning estimation filter that sets the estimated transfer function Sv11^(z) of the transfer function Sv11(z) from the first system first stage learning processing unit 61 to the first learning microphone 51. The first system second learning estimation filter 612 is set to replace the first system second estimation filter 1114. The first system second learning estimation filter 612 is a learning estimation filter that sets the estimated transfer function Sv21^(z) of the transfer function Sv21(z) from the first system first stage learning processing unit 61 to the second learning microphone 52. The outputs of the first learning microphone 51 and the second learning microphone 52 are both input as errors to the first system adaptive algorithm execution unit 1112.

[0069] In addition, the first-stage learning processing unit 62 of the second system has the following structure: From Figure 3 The second system signal processing unit 112 of the signal processing module 11 shown removes the second system subtractor 1125 and the second system auxiliary filter 1126, and sets a second system first learning estimation filter 621 to replace the second system first estimation filter 1123. The second system first learning estimation filter 621 is a learning estimation filter that sets the estimated transfer function Sv22^(z) of the transfer function Sv22(z) from the second system first stage learning processing unit 62 to the second learning microphone 52. The second system second learning estimation filter 622 is set to replace the second system second estimation filter 1124. The second system second learning estimation filter 622 is a learning estimation filter that sets the estimated transfer function Sv12^(z) of the transfer function Sv12(z) from the second system first stage learning processing unit 62 to the first learning microphone 51. The output of the first learning microphone 51 and the output of the second learning microphone 52 are both input as errors to the second system adaptive algorithm execution unit 1122.

[0070] Furthermore, in this structure, the transfer function W1(z) of the first system variable filter 1111 is made to converge and stabilize through the adaptive action of the first system adaptive algorithm execution unit 1112, and the transfer function W2(z) of the second system variable filter 1121 is made to converge and stabilize through the adaptive action of the second system adaptive algorithm execution unit 1122. The converged and stabilized transfer function W1(z) is used as the initial value W1_i(z) of the first system variable filter for the i-th elimination point set for learning, and the converged and stabilized transfer function W2(z) is used as the initial value W2_i(z) of the second system variable filter for the i-th elimination point set for learning.

[0071] The initial values ​​W1_i(z) of the first system variable filter and W2_i(z) of the second system variable filter, which are learned in this way, are the transfer functions of the first system variable filter 1111 and the second system variable filter 1121, respectively. Under the same environmental conditions as during learning, the signal processing module 11 outputs the first cancellation signal CA1(n) and the second cancellation signal CA2(n) that are noise-cancelled in the first cancellation point P1_i and the second cancellation point P2_i of the i-th cancellation point set.

[0072] Next, in the second phase of learning processing, such as Figure 7 As shown, this is carried out in a structure in which the signal processing module 11 is replaced by the second-stage learning processing module 7.

[0073] The second-stage learning processing module 7 includes a first-system second-stage learning processing unit 71 and a second-system second-stage learning processing unit 72.

[0074] Furthermore, the first system second stage learning processing unit 71 includes: a first system fixed filter 711 that sets the initial value W1_i(z) of the first system variable filter obtained as the result of the first stage learning processing as the transfer function; a first system second stage learning variable filter 712; a first system second stage learning adaptive algorithm execution unit 713; and a first system second stage subtractor 714.

[0075] In addition, the second system second stage learning processing unit 72 includes: a second system fixed filter 721 that sets the initial value W2_i(z) of the second system variable filter obtained as the result of the first stage learning processing as the transfer function; a second system second stage learning variable filter 722; a second system second stage learning adaptive algorithm execution unit 723; and a second system second stage subtractor 724.

[0076] The noise signal x(n) input to the second stage learning processing unit 71 of the first system is output to the first speaker 12 after passing through the first system fixed filter 711, and the noise signal x(n) input to the second stage learning processing unit 72 of the second system is output to the second speaker 14 after passing through the second system fixed filter 721.

[0077] Additionally, the noise signal x(n) input to the first system second stage learning processing unit 71 is sent to the first system second stage subtractor 714 after passing through the first system second stage learning variable filter 712. The first system second stage subtractor 714 subtracts the output of the first system second stage learning variable filter 712 from the signal picked up by the first microphone 13, and outputs it as an error to the first system second stage learning adaptive algorithm execution unit 713 and the second system second stage learning adaptive algorithm execution unit 723 of the second system second stage learning processing unit 72.

[0078] Additionally, the noise signal x(n) input to the second system second stage learning processing unit 72 is sent to the second system second stage subtractor 724 after passing through the second system second stage learning variable filter 722. The second system second stage subtractor 724 subtracts the output of the second system second stage learning variable filter 722 from the signal picked up by the second microphone 15 and outputs it as an error to the second system second stage learning adaptive algorithm execution unit 723 and the first system second stage learning adaptive algorithm execution unit 713 of the first system second stage learning processing unit 71.

[0079] Then, the first system second stage learning adaptive algorithm execution unit 713 of the first system second stage learning processing unit 71 updates the transfer function H1(z) of the first system second stage learning variable filter 712 to make the error input from the first system second stage subtractor 714 and the second system second stage subtractor 724 zero, and the second system second stage learning adaptive algorithm execution unit 723 of the second system second stage learning processing unit 72 updates the transfer function H2(z) of the second system second stage learning variable filter 722 to make the error input from the first system second stage subtractor 714 and the second system second stage subtractor 724 zero.

[0080] Furthermore, in this structure, through the adaptive action of the first system second-stage learning adaptive algorithm execution unit 713, the transfer function H1(z) of the first system second-stage learning variable filter 712 is made to converge and stabilize, and the converged and stabilized transfer function H1(z) is used as the first system auxiliary filter setting value H1_i(z) for the i-th elimination point set. Additionally, through the adaptive action of the second system second-stage learning adaptive algorithm execution unit 723, the transfer function H2(z) of the second system second-stage learning variable filter 722 is made to converge and stabilize, and the converged and stabilized transfer function H2(z) is used as the second system auxiliary filter setting value H2_i(z) for the i-th elimination point set.

[0081] Here, with the first system auxiliary filter setting value H1_i(z) and the second system auxiliary filter setting value H2_i(z) being the transfer functions of the first system auxiliary filter 1116 and the second system auxiliary filter 1126, respectively, the first microphone error signal err1(n) output by the first microphone 13 and the second microphone error signal err2(n) output by the second microphone 15 are corrected to the output when the first cancellation point P1_i and the second cancellation point P2_i of the i-th cancellation point set have the first microphone 13 and the second microphone 15.

[0082] Next, the control performed by the controller 16 during the actual operation of the active noise control system 1 will be explained.

[0083] Figure 8 This indicates the steps of the elimination point switching process performed by controller 16.

[0084] As shown in the figure, during the cancellation point switching process, the controller 16 obtains the positions of the right and left ears of the user sitting in the noise cancellation target seat detected by the DMS18 (step 802), and monitors the occurrence of changes in the set of cancellation points that best matches the obtained positions of the right and left ears, i.e., the set of best matching cancellation points (step 804).

[0085] The set of the best matching elimination points is calculated by taking the sum of the distances between the right ear and the first elimination point and the left ear and the second elimination point as the minimum set of elimination points.

[0086] Then, if a change occurs in the set of most matching elimination points (step 804), the adaptive operation of the first system adaptive algorithm execution unit 1112 of the first system signal processing unit 111 and the adaptive operation of the second system adaptive algorithm execution unit 1122 of the second system signal processing unit 112 are stopped (step 806).

[0087] Then, the first system auxiliary filter setting value H1_i(z) registered in the entry of the set of best matching elimination points in the filter management table 17 is set to the transfer function H1(z) of the first system auxiliary filter 1116, and the second system auxiliary filter setting value H2_i(z) registered in the same entry is set to the transfer function H2(z) of the second system auxiliary filter 1126 (step 808).

[0088] Then, the transfer function W1(z) of the first system variable filter 1111 of the first system signal processing unit 111 is gradually changed from its current value to the initial value W1_i(z) of the first system variable filter registered in the entry of the set of best matching elimination points in the filter management table 17, and the transfer function W2(z) of the second system variable filter 1121 of the second system signal processing unit 112 is gradually changed from its current value to the initial value W2_i(z) of the second system variable filter registered in that entry (step 810).

[0089] The changes to the transfer function W1(z) of the first system variable filter 1111 and the transfer function W2(z) of the second system variable filter 1121 can be performed either by changing each unit quantity every unit time, or by changing them to the initial values ​​W1_i(z) of the first system variable filter and W2_i(z) of the second system variable filter at specified times. Furthermore, the changes to the transfer function W1(z) of the first system variable filter 1111 and the transfer function W2(z) of the second system variable filter 1121 are actually performed by gradually updating the values ​​of each tap coefficient of each variable filter to the changed tap coefficient values. Moreover, the values ​​of the tap coefficients at each time point during the change are obtained, for example, by linear interpolation of the tap coefficients before and after the change.

[0090] Then, if the transfer function W1(z) of the first system variable filter 1111 of the first system signal processing unit 111 gradually changes to become the initial value W1_i(z) of the first system variable filter registered in the entry of the best matching elimination point set, and the transfer function W2(z) of the second system variable filter 1121 of the second system signal processing unit 112 gradually changes to become the initial value W2_i(z) of the second system variable filter registered in that entry, then the adaptive operation of the first system adaptive algorithm execution unit 1112 of the first system signal processing unit 111 and the adaptive operation of the second system adaptive algorithm execution unit 1122 of the second system signal processing unit 112 restart (step 812).

[0091] Then, return to the processing from step 802 onwards.

[0092] The above describes the elimination point switching process performed by controller 16.

[0093] Furthermore, the first system auxiliary filter setting value H1_i(z), the second system auxiliary filter setting value H2_i(z), the first system variable filter initial value W1_i(z), and the second system variable filter initial value W2_i(z) registered in the filter management table 17 are not actually the transfer functions themselves. Instead, they are information used to set the first system auxiliary filter setting value H1_i(z) as the transfer function of the first system auxiliary filter 1116, and information used to set the second system auxiliary filter setting value H2_i(z) as the transfer function of the second system auxiliary filter 1126. The information used to set the transfer function, the information used to set the initial value W1_i(z) of the first system variable filter as the transfer function of the first system variable filter 1111, and the information used to set the initial value W2_i(z) of the second system variable filter as the transfer function of the second system variable filter 1121 are used in the elimination point switching process to set the transfer functions of the first system auxiliary filter 1116, the second system auxiliary filter 1126, the first system variable filter 1111, and the second system variable filter 1121 as described above.

[0094] Furthermore, according to the cancellation point switching process described above, if the user's ear shifts, the transfer functions of the first system variable filter 1111, the second system variable filter 1121, the first system auxiliary filter 1116, and the second system auxiliary filter 1126 are updated to the transfer functions of the first cancellation point and the second cancellation point of the set of most matched cancellation points that match the user's left and right ear positions under the environmental conditions described above during learning.

[0095] Furthermore, the updated signal processing module 11 then restarts the adaptive action, performing an adaptive action that absorbs the difference between the environmental conditions during learning and the environmental conditions at the current moment. The transfer function W1(z) of the first system variable filter 1111 and the transfer function W2(z) of the second system variable filter 1121 are updated to transfer functions that eliminate noise at the first and second cancellation points of the best matching cancellation point set.

[0096] Furthermore, since the environmental conditions during learning are not significantly different from those at the current moment, the updated transfer functions of the first system variable filter 1111 and the second system variable filter 1121 are transfer functions that are approximately the same as those that can eliminate noise at the first and second elimination points of the best-matched elimination point set. After the adaptive action restarts, the adaptation of the transfer function W1(z) of the first system variable filter 1111 and the transfer function W2(z) of the second system variable filter 1121 is completed in a short time. Noise is eliminated within a certain range close to the first and second elimination points of the best-matched elimination point set, and noise is eliminated at the user's left and right ear positions close to the first and second elimination points of the best-matched elimination point set.

[0097] Furthermore, the update is performed by gradually changing the transfer functions of the first system variable filter 1111 and the second system variable filter 1121 until the update is completed, while the adaptive operation of the first system variable filter 1111 and the second system variable filter 1121 that generate the first cancellation signal CA1(n) and the second cancellation signal CA2(n) has stopped. Therefore, along with the update, unnatural sounds generated in the user output when the transfer functions of the first system variable filter 1111 and the second system variable filter 1121 change once are also suppressed.

[0098] The embodiments of the present invention have been described above.

[0099] Here, the above implementation can also replace changing the transfer functions of the first system auxiliary filter 1116 and the second system auxiliary filter 1126, and instead set a set of first system auxiliary filters 1116 and second system auxiliary filters with multiple transfer functions corresponding to each noise cancellation point set, and switch the set of first system auxiliary filters 1116 and second system auxiliary filters 1126 currently in use to a group of first system auxiliary filters 1116 and second system auxiliary filters 1126 corresponding to the best matching cancellation point set.

[0100] Furthermore, the above describes the case where there is only one noise source. However, by extending the structure of the signal processing module 11 to consider the propagation of each noise source to each cancellation point, the above implementation can also be applied to the case where there are multiple noise sources.

[0101] Furthermore, in the above embodiments, a case was shown in which a microphone, a speaker, and a signal processing unit were provided for the right ear and the left ear respectively. However, this embodiment can also be applied in the case where a microphone, a speaker, and a signal processing unit are provided for the head, and the noise that can be heard by the right ear and the left ear is concentrated and eliminated by using a microphone, a speaker, and a signal processing unit shared by the right ear and the left ear based on the position of the user's head detected by the DMS18.

[0102] Explanation of reference numerals in the attached figures

[0103] 1…Active noise control system, 6…First-stage learning processing module, 7…Second-stage learning processing module, 11…Signal processing module, 12…First speaker, 13…First microphone, 14…Second speaker, 15…Second microphone, 16…Controller, 17…Filter management table, 18…DMS, 51…First learning microphone, 52…Second learning microphone, 61…First system first-stage learning processing unit, 62…Second system first-stage learning processing unit, 71…First system second-stage learning processing unit, 72…Second system second-stage learning processing unit, 111…First system signal processing unit, 112…Second system signal processing unit, 181…Near-infrared camera, 611…First system first-stage learning estimated filter, 612…First system second-stage learning estimated filter, 621…Second system first-stage learning estimated filter, 622…Second system second-stage learning estimated filter, 711…First system fixed filter 712… Variable filter for second-stage learning of the first system, 713… Adaptive algorithm execution unit for second-stage learning of the first system, 714… Subtractor for second-stage learning of the first system, 721… Fixed filter of the second system, 722… Variable filter for second-stage learning of the second system, 723… Adaptive algorithm execution unit for second-stage learning of the second system, 724… Subtractor for second-stage learning of the second system, 1111… Variable filter of the first system, 1112… Adaptive algorithm execution unit of the first system, 1113… First estimated filter of the first system, 1114… Second estimated filter of the first system, 1115… Subtractor of the first system, 1116… Auxiliary filter of the first system, 1121… Variable filter of the second system, 1122… Adaptive algorithm execution unit of the second system, 1123… First estimated filter of the second system, 1124… Second estimated filter of the second system, 1125… Subtractor of the second system, 1126… Auxiliary filter of the second system.

Claims

1. An active noise control system, which is an active noise reduction control system, comprising: The location detection unit detects the location where the user hears the sound, i.e., the listening location; Control Department; Speaker, outputs noise-canceling sound; Microphone, detecting error signals; An auxiliary filter applies a predetermined transfer function to the noise signal representing the noise to generate a corrected signal and outputs it. The error correction unit corrects the output of the microphone, i.e. the error signal, using the correction signal output by the auxiliary filter, and outputs the corrected error signal as the corrected error signal. An adaptive filter performs adaptive operation using the corrected error signal output by the error correction unit to generate a noise-cancelled tone to be output from the speaker from the noise signal; as well as The storage unit stores multiple noise cancellation positions and setting information. This setting information is used to set the initial transfer function of the adaptive filter corresponding to each noise cancellation position. When the noise cancellation position that matches the listening position detected by the position detection unit changes among the plurality of noise cancellation positions, i.e., the matched noise cancellation position, the control unit performs the following switching operation: the auxiliary filter that outputs the correction signal to the error correction unit is set to an auxiliary filter that has been set with a transfer function for the auxiliary filter corresponding to the matched noise cancellation position, which is one of the transfer functions for the auxiliary filter that is set to correspond to the plurality of noise cancellation positions respectively, and the transfer function of the adaptive filter is updated to the initial transfer function of the adaptive filter corresponding to the matched noise cancellation position using the setting information.

2. The active noise control system according to claim 1, During the switching operation, the control unit stops the adaptive operation of the adaptive filter and sets the auxiliary filter that outputs the correction signal to the error correction unit to an auxiliary filter with a transfer function set to the auxiliary filter corresponding to the matched noise cancellation position. Then, the control unit gradually changes the transfer function of the adaptive filter to the initial transfer function of the adaptive filter corresponding to the matched noise cancellation position. After updating the transfer function of the adaptive filter to the initial transfer function of the adaptive filter, the adaptive operation of the adaptive filter restarts.

3. The active noise control system according to claim 1, The initial transfer function of the adaptive filter corresponding to each noise cancellation position is a transfer function learned using a learning microphone configured at the noise cancellation position corresponding to the initial transfer function of the adaptive filter, and is a transfer function for generating a noise cancellation tone for the adaptive filter at the corresponding noise cancellation position. The transfer function of the auxiliary filter corresponding to each noise cancellation position is a transfer function that is pre-learned as a transfer function that, when the transfer function of the adaptive filter is fixed to the initial transfer function of the adaptive filter corresponding to the noise cancellation position, the auxiliary filter outputs a correction signal in the error correction section where the error signal is corrected to 0.

4. The active noise control system according to claim 3, The position detection unit detects the position of the user's head or ears while seated in the designated seat of the car as the listening position.

5. An active noise control system, which is an active noise reduction control system, comprising: The position detection unit detects the position of the user's left and right ears; Control Department; Two noise control systems: a noise control system for the right ear and a noise control system for the left ear; and Storage Department Each noise control system has: Speaker, outputs noise-canceling sound; Microphone, detecting error signals; An auxiliary filter applies a predetermined transfer function to the noise signal representing the noise to generate a corrected signal and outputs it. The error correction unit corrects the output of the microphone, i.e. the error signal, using the correction signal output by the auxiliary filter, and outputs the corrected error signal as the corrected error signal. as well as An adaptive filter performs adaptive operation using the corrected error signal output by the error correction unit of the right ear noise control system and the corrected error signal output by the error correction unit of the left ear noise control system, generating a noise-cancelling tone to be output from the speaker from the noise signal. The storage unit stores: multiple noise cancellation position sets, with the set of the first noise cancellation position and the second noise cancellation position as the noise cancellation position set; The information includes setting information for setting the initial transfer function of the adaptive filter of the noise control system for the right ear, corresponding to each noise cancellation position set, for the initial transfer function of the first adaptive filter; and setting the initial transfer function of the adaptive filter of the noise control system for the left ear, corresponding to each noise cancellation position set, for the initial transfer function of the second adaptive filter. When the set of noise cancellation positions that matches the set of user's left and right ear positions detected by the position detection unit changes among the plurality of noise cancellation position sets, i.e., the matching noise cancellation position set, the control unit performs the following switching operation: It sets the auxiliary filter that outputs a correction signal to the error correction unit of the right ear noise control system to an auxiliary filter whose transfer function is set to correspond to the first auxiliary filter transfer function corresponding to the matching noise cancellation position set among the first auxiliary filter transfer functions corresponding to each of the plurality of pre-set noise cancellation position sets; it updates the transfer function of the adaptive filter of the right ear noise control system to the initial transfer function of the first adaptive filter corresponding to the matching noise cancellation position set using the setting information; it sets the auxiliary filter that outputs a correction signal to the error correction unit of the left ear noise control system to an auxiliary filter whose transfer function is set to correspond to the second auxiliary filter transfer function corresponding to the matching noise cancellation position set among the second auxiliary filter transfer functions corresponding to each of the plurality of pre-set noise cancellation position sets; it updates the transfer function of the adaptive filter of the left ear noise control system to the initial transfer function of the second adaptive filter corresponding to the matching noise cancellation position set using the setting information.

6. The active noise control system according to claim 5, The control unit during the switching action The adaptive operation of the adaptive filters in the right ear noise control system and the left ear noise control system is stopped. Furthermore, the auxiliary filter that outputs the correction signal to the error correction unit of the right ear noise control system is set to an auxiliary filter with a transfer function set to a first auxiliary filter corresponding to the set of matched noise cancellation positions, and the auxiliary filter that outputs the correction signal to the error correction unit of the left ear noise control system is set to an auxiliary filter with a transfer function set to a second auxiliary filter corresponding to the set of matched noise cancellation positions. The transfer function of the adaptive filter of the right ear noise control system is updated to the first adaptive filter initial transfer function by gradually changing the initial transfer function of the first adaptive filter corresponding to the set of matched noise cancellation positions, and the transfer function of the adaptive filter of the left ear noise control system is updated to the second adaptive filter initial transfer function by gradually changing the initial transfer function of the second adaptive filter corresponding to the set of matched noise cancellation positions. After this, the adaptive operation of the adaptive filters of the right ear noise control system and the left ear noise control system is restarted.

7. The active noise control system according to claim 6, The initial transfer function of the first adaptive filter and the initial transfer function of the second adaptive filter corresponding to each noise cancellation location set are transfer functions learned using the first learning microphone configured at the first noise cancellation location of the noise cancellation location set and the second learning microphone configured at the second noise cancellation location of the noise cancellation location set. These transfer functions are also transfer functions that generate noise-canceling tones through the adaptive filters of the right-ear noise control system and the left-ear noise control system. The noise-canceling tones are noise-canceling tones that cancel noise at the first and second noise cancellation locations of the corresponding noise cancellation location sets. The transfer function of the first auxiliary filter corresponding to each noise cancellation position set is a transfer function pre-learned as follows: In the right ear noise control system, with the transfer function of the adaptive filter of the right ear noise control system fixed to the initial transfer function of the first adaptive filter corresponding to the first noise cancellation position of the noise cancellation position set, and the transfer function of the adaptive filter of the left ear noise control system fixed to the initial transfer function of the second adaptive filter corresponding to the second noise cancellation position of the noise cancellation position set, the auxiliary filter outputs a correction signal in the error correction unit where the error signal is corrected to 0. The transfer function of the second auxiliary filter corresponding to each noise cancellation position set is a transfer function that is pre-learned as a transfer function in the left ear noise control system, wherein the transfer function of the adaptive filter of the right ear noise control system is fixed to the initial transfer function of the first adaptive filter corresponding to the first noise cancellation position of the noise cancellation position set, and the transfer function of the adaptive filter of the left ear noise control system is fixed to the initial transfer function of the second adaptive filter corresponding to the second noise cancellation position of the noise cancellation position set.

8. The active noise control system according to claim 7, The position detection unit detects the position of the left and right ears of a user sitting in a designated seat in the car.

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