Active noise reduction device

Abstract

Even when the input signal contains components with large fluctuations, it stably and effectively reduces noise. [Solution] An active noise reduction device 1 comprises a noise cancellation output device 12 that outputs a cancellation sound y to cancel out noise d, a microphone 13 that generates a microphone signal based on noise d, and a control device 15 that controls the noise cancellation output device 12 based on the microphone signal, wherein the control device 15 includes at least one adaptively updatable filter W1, C^1, H^1, W2, C^2, H^2, calculates the amount of change ΔL of the microphone signal based on the microphone signal, and switches at least one of the operations of an adaptive update process that adaptively updates the filter W1, C^1, H^1, W2, C^2, H^2 according to the amount of change ΔL of the microphone signal and a noise cancellation output process that causes the noise cancellation output device 12 to output a cancellation sound y.

Description

[Technical Field]

[0001] This invention relates to an active noise reduction device. [Background technology]

[0002] Conventionally, active noise reduction devices are known that reduce noise by interfering with the noise with a canceling sound that is in the opposite phase to the noise. An active noise reduction device comprises a canceling sound output device (e.g., a speaker) that outputs a canceling sound to cancel out the noise, and a control device that controls the canceling sound output device based on an input signal (e.g., a microphone signal or an acceleration signal) (see Patent Document 1). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2023-144581 [Overview of the project] [Problems that the invention aims to solve]

[0004] In active noise reduction devices like those described above, there is a risk that noise may not be reduced stably and effectively if the input signal contains components with large fluctuations (for example, if the microphone signal contains voice components or the acceleration signal contains instantaneous vibration components).

[0005] In view of the above background, one aspect of the present invention aims to provide an active noise reduction device that can stably and effectively reduce noise even when the input signal contains components with large fluctuations. [Means for solving the problem]

[0006] To solve the above problems, one aspect of the present invention provides an active noise reduction device comprising: a noise cancellation output device that outputs a noise cancellation sound to cancel out noise; a microphone that generates a microphone signal based on the noise; and a control device that controls the noise cancellation output device based on the microphone signal, wherein the control device includes at least one adaptively updatable filter, calculates the amount of variation of the microphone signal based on the microphone signal, and switches at least one of the operations of an adaptive update process that adaptively updates the filter and a noise cancellation output process that causes the noise cancellation output device to output the noise cancellation sound according to the amount of variation of the microphone signal.

[0007] Another aspect of the present invention is an active noise reduction device comprising: a noise cancellation output device that outputs a noise cancellation sound to cancel out noise; an acceleration sensor that generates an acceleration signal based on the noise; and a control device that controls the noise cancellation output device based on the acceleration signal, wherein the control device includes at least one adaptively updatable filter, calculates a fluctuation amount of the acceleration signal based on the acceleration signal, and switches at least one of the operations of an adaptive update process that adaptively updates the filter and a noise cancellation output process that causes the noise cancellation output device to output the noise cancellation sound according to the fluctuation amount of the acceleration signal. [Effects of the Invention]

[0008] According to the above embodiments, it is possible to provide an active noise reduction device that can stably and effectively reduce noise even when the input signal contains components with large fluctuations. [Brief explanation of the drawing]

[0009] [Figure 1] A schematic diagram showing a vehicle to which an active noise reduction device according to this embodiment is applied. [Figure 2] Block diagram showing an active noise reduction device according to an embodiment. [Figure 3] (A) Waveform diagram showing changes in the amplitude of the microphone signal, and (B) Waveform diagram showing changes in the amount of fluctuation of the microphone signal. [Figure 4](A) A waveform diagram showing a change in amplitude of an acceleration signal, and (B) a waveform diagram showing a change in a variation amount of an acceleration signal [Figure 5] A flowchart showing Execution Example 1 of first switching control according to the embodiment [Figure 6] A flowchart showing Execution Example 2 of first switching control according to the embodiment [Figure 7] A graph showing setting lines of first and second μ tables according to the embodiment [Figure 8] A graph showing setting lines of first and second η tables according to the embodiment [Figure 9] A flowchart showing Execution Example 1 of second switching control according to the embodiment [Figure 10] A flowchart showing Execution Example 2 of second switching control according to the embodiment [Figure 11] A graph showing setting lines of a μ table according to the embodiment MODE FOR CARRYING OUT THE INVENTION

[0010] Hereinafter, an active noise reduction device 1 (hereinafter abbreviated as "noise reduction device 1") according to an embodiment will be described with reference to FIGS. 1 to 11. In the present specification, the "^" (hat) appended together with various reference signs indicates an identified value or an estimated value. In drawings and mathematical formulas, "^" is attached above various reference signs, but in the main text, it is attached after various reference signs.

[0011] <Vehicle 3> FIG. 1 is a schematic diagram showing a vehicle 3 to which the noise reduction device 1 is applied. The vehicle 3 includes a vehicle body 5, a plurality of wheels (not shown) arranged below the vehicle body 5, and a plurality of suspensions 6 arranged between the vehicle body 5 and the plurality of wheels. A vehicle compartment 8 is formed inside the vehicle body 5. A plurality of occupant seats 9 are installed in the vehicle compartment 8. Each occupant seat 9 includes a seat cushion 9A, a seat back 9B arranged rearward and upward of the seat cushion 9A, and a headrest 9C fixed to an upper end of the seat back 9B.

[0012] <Noise Reduction Device 1> Referring to Figure 1, the noise reduction device 1 is an Active Noise Control Device (ANC) for reducing noise d generated inside the passenger compartment 8 of the vehicle 3. More specifically, the noise reduction device 1 generates a canceling sound y that is out of phase with the noise d, and reduces the noise d by causing the generated canceling sound y to interfere with the noise d.

[0013] The noise reduction device 1 includes a plurality of acceleration sensors 11 that generate an acceleration signal x based on noise d, a plurality of speakers 12 (an example of a sound cancellation output device) that output a cancellation sound y to cancel out noise d, a plurality of microphones 13 that generate microphone signals m based on noise d, and a control device 15 that controls the plurality of speakers 12 based on the acceleration signal x and the microphone signals m.

[0014] <Accelerometer 11> Referring to Figure 1, each acceleration sensor 11 is installed on the corresponding suspension 6. The acceleration sensor 11 detects the acceleration of the suspension 6 in response to the noise d and generates an acceleration signal x corresponding to the acceleration of the suspension 6. The acceleration signal x is used as a reference signal corresponding to the noise d.

[0015] <Speaker 12> Referring to Figure 1, each speaker 12 is installed in a location in the vehicle 3 other than the passenger seat 9 (for example, the side door of the passenger seat 9 or the space behind the passenger seat 9). In other embodiments, the speaker 12 may be installed on the passenger seat 9 (for example, the headrest 9C of the passenger seat 9).

[0016] <Mike 13> Referring to Figure 1, each microphone 13 is installed near the headrest 9C of the passenger seat 9 or near the noise source. In other embodiments, the microphones 13 may be installed in locations other than near the passenger seats 9 or noise sources in the vehicle 3 (for example, on the ceiling above the passenger seats 9).

[0017] Microphone 13 is used simultaneously as both a microphone that generates an error signal e corresponding to the error between noise d and cancellation sound y, and a microphone that generates a reference signal r corresponding to noise d. In other words, microphone signal m is used simultaneously as both an error signal e and a reference signal r. For example, in a control channel that controls a speaker 12 adjacent to the driver's seat, microphone 13 installed in the driver's seat generates the error signal e, and microphones 13 installed in other seats or near noise sources generate the reference signal r. On the other hand, in a control channel that controls a speaker 12 adjacent to the passenger seat, microphone 13 installed in the passenger seat generates the error signal e, and microphones 13 installed in other seats or near noise sources generate the reference signal r. Hereinafter, the microphone 13 that generates the error signal e will be referred to as "error microphone 13e," and the microphone 13 that generates the reference signal r will be referred to as "reference microphone 13r."

[0018] <Control device 15> Referring to Figure 2, the control device 15 is composed of a computer having an arithmetic processing unit (processor such as a CPU or MPU) and a storage device (memory such as ROM or RAM). The control device 15 may be configured as a single piece of hardware, or as a unit consisting of multiple pieces of hardware.

[0019] The control device 15 has, as functional components, a plurality of first control signal generation units 16, a plurality of first sound field learning units 17, a plurality of second control signal generation units 18, a plurality of second sound field learning units 19, a control signal addition unit 20, a fluctuation amount calculation unit 21, and a processing control unit 22. The number of first control signal generation units 16 and first sound field learning units 17 corresponds to the number of acceleration sensors 11. The number of second control signal generation units 18 and second sound field learning units 19 corresponds to the number of reference microphones 13r. Note that in Figure 2, only one of each of the first control signal generation unit 16, first sound field learning unit 17, second control signal generation unit 18, and second sound field learning unit 19 is shown.

[0020] <First control signal generation unit 16> Each first control signal generation unit 16 of the control device 15 receives an acceleration signal x (reference signal) from the acceleration sensor 11. Each first control signal generation unit 16 includes a control filter unit 24, a reference signal correction unit 25, and a control update unit 26.

[0021] The control filter unit 24 is composed of a control filter W1. The control filter W1 is composed of an FIR filter (finite impulse response filter). In other embodiments, the control filter W1 may be composed of a SAN filter (single frequency adaptive notch filter) or the like. The control filter unit 24 generates a first control signal u1 by filtering the acceleration signal x (reference signal) with the control filter W1. The control filter unit 24 outputs the generated first control signal u1 to the first sound field learning unit 17 and the control signal summing unit 20.

[0022] The reference signal correction unit 25 is composed of a secondary path filter C^1. The secondary path filter C^1 is a filter that shows an estimated value of the transfer function C of the secondary path from the speaker 12 to the error microphone 13e. The secondary path filter C^1 is composed of an FIR filter. In other embodiments, the secondary path filter C^1 may be composed of a SAN filter or the like. The reference signal correction unit 25 corrects the acceleration signal x (reference signal) by applying filtering to the acceleration signal x using the secondary path filter C^1. The reference signal correction unit 25 outputs the corrected acceleration signal x to the control update unit 26.

[0023] The control update unit 26 adaptively updates the control filter W1 using an adaptive algorithm such as the LMS algorithm (Least Mean Square Algorithm). More specifically, the control update unit 26 adaptively updates the control filter W1 according to equation (1) below so that the error signal e output from the error microphone 13e is minimized.

number

[0024] <First Sound Field Learning Section 17> Each first sound field learning unit 17 of the control device 15 receives an acceleration signal x (reference signal) from the acceleration sensor 11. Each first sound field learning unit 17 includes a cancellation sound estimation signal generation unit 31, a secondary path update unit 32, a noise estimation signal generation unit 33, a primary path update unit 34, a cancellation sound estimation signal inversion unit 35, a noise estimation signal inversion unit 36, and a virtual error signal generation unit 37.

[0025] The negation sound estimation signal generation unit 31, like the reference signal correction unit 25, is configured with a second-order path filter C^1. The negation sound estimation signal generation unit 31 applies filtering to the first control signal u1 using the second-order path filter C^1 to generate a first negation sound estimation signal y^1, which indicates the estimated value of the negation sound y. The negation sound estimation signal generation unit 31 outputs the generated first negation sound estimation signal y^1 to the negation sound estimation signal inversion unit 35.

[0026] The secondary path update unit 32 adaptively updates the secondary path filter C^1 of the cancellation sound estimation signal generation unit 31 using an adaptive algorithm such as the LMS algorithm. More specifically, the secondary path update unit 32 updates the first virtual error signal e output from the virtual error signal generation unit 37. v The quadratic path filter C^1 is adaptively updated by equation (2) below so that 1 (details below) is minimized.

number

[0027] Furthermore, when the secondary path update unit 32 updates the secondary path filter C^1 of the sound cancellation estimation signal generation unit 31 as described above, the updated secondary path filter C^1 is output to the reference signal correction unit 25, and the secondary path filter C^1 of the reference signal correction unit 25 is updated.

[0028] The noise estimation signal generation unit 33 is composed of a primary path filter H^1. The primary path filter H^1 is a filter that shows an estimated value of the transfer function H of the primary path from the noise source to the error microphone 13e. The primary path filter H^1 is composed of, for example, an FIR filter. In other embodiments, the primary path filter H^1 may be composed of a SAN filter or the like. The noise estimation signal generation unit 33 generates a first noise estimation signal d^1 that shows an estimated value of noise d by filtering the acceleration signal x (reference signal) with the primary path filter H^1. The noise estimation signal generation unit 33 outputs the generated first noise estimation signal d^1 to the noise estimation signal inversion unit 36.

[0029] The primary path update unit 34 adaptively updates the primary path filter H^1 using an adaptive algorithm such as the LMS algorithm. More specifically, the primary path update unit 34 uses the first virtual error signal e output from the virtual error signal generation unit 37. v The first-order path filter H^1 is adaptively updated by equation (3) below so that 1 (details below) is minimized.

number

[0030] The negation estimation signal inversion unit 35 inverts the polarity of the first negation estimation signal y^1 output from the negation estimation signal generation unit 31. The negation estimation signal inversion unit 35 outputs the first negation estimation signal y^1 with inverted polarity to the virtual error signal generation unit 37.

[0031] The noise estimation signal inversion unit 36 ​​inverts the polarity of the first noise estimation signal d^1 output from the noise estimation signal generation unit 33. The noise estimation signal inversion unit 36 ​​outputs the first noise estimation signal d^1 with inverted polarity to the virtual error signal generation unit 37.

[0032] The virtual error signal generation unit 37 generates the first virtual error signal e by adding the error signal e output from the error microphone 13e, the first sound cancellation estimation signal y^1 that has passed through the sound cancellation estimation signal inversion unit 35, and the first noise estimation signal d^1 that has passed through the noise estimation signal inversion unit 36. v The virtual error signal generation unit 37 generates the first virtual error signal e vThe value 1 is output to the secondary route update unit 32 and the primary route update unit 34.

[0033] <Second control signal generation unit 18> Each second control signal generation unit 18 of the control device 15 receives a reference signal r from the reference microphone 13r. Each second control signal generation unit 18 includes a control filter unit 44, a reference signal correction unit 45, and a control update unit 46. The components of the second control signal generation unit 18 are the same as those of the first control signal generation unit 16. Below, only the differences between the second control signal generation unit 18 and the first control signal generation unit 16 will be described.

[0034] The control filter unit 44 generates a second control signal u2 by applying a filter to the reference signal r (the reference signal output from the reference microphone 13r) using the control filter W2. The control filter unit 44 outputs the generated second control signal u2 to the second sound field learning unit 19 and the control signal summing unit 20.

[0035] The reference signal correction unit 45 corrects the reference signal r (the reference signal output from the reference microphone 13r) by applying a filter process to it using a second-order path filter C^2. The reference signal correction unit 45 outputs the corrected reference signal r to the control update unit 46.

[0036] The control update unit 46 adaptively updates the control filter W2 according to equation (4) below so that the error signal e output from the error microphone 13e is minimized.

number

[0037] <Second Sound Field Learning Section 19> The reference signal r from the reference microphone 13r is input to each second sound field learning unit 19 of the control device 15. Each second sound field learning unit 19 includes a canceling sound estimated signal generating unit 51, a secondary path updating unit 52, a noise estimated signal generating unit 53, a primary path updating unit 54, a canceling sound estimated signal inverting unit 55, a noise estimated signal inverting unit 56, and a virtual error signal generating unit 57. The constituent elements of the second sound field learning unit 19 are the same as the constituent elements of the first sound field learning unit 17. Hereinafter, only the differences between the second sound field learning unit 19 and the first sound field learning unit 17 will be described.

[0038] The canceling sound estimated signal generating unit 51 filters the second control signal u2 through the secondary path filter C^2, thereby generating a second canceling sound estimated signal y^2 that indicates an estimated value of the canceling sound y. The canceling sound estimated signal generating unit 51 outputs the generated second canceling sound estimated signal y^2 to the canceling sound estimated signal inverting unit 55.

[0039] The secondary path updating unit 52 receives the second virtual error signal e output from the virtual error signal generating unit 57 v 2 (details will be described later) is adaptively updated by the following equation (5) so that 2 becomes minimum.

Math

[0040] The noise estimated signal generating unit 53 filters the reference signal r (the reference signal output from the reference microphone 13r) through the primary path filter H^2, thereby generating a second noise estimated signal d^2 that indicates an estimated value of the noise d. The noise estimated signal generating unit 53 outputs the generated second noise estimated signal d^2 to the noise estimated signal inverting unit 56.

[0041] The primary path updating unit 54 receives the second virtual error signal e output from the virtual error signal generating unit 57 v 2 (details will be described later) is adaptively updated by the following equation (6) so that 2 becomes minimum.

Math

[0042] The sound cancellation estimation signal inversion unit 55 inverts the polarity of the second sound cancellation estimation signal y^2 output from the sound cancellation estimation signal generation unit 51. The sound cancellation estimation signal inversion unit 55 outputs the second sound cancellation estimation signal y^2 with inverted polarity to the virtual error signal generation unit 57.

[0043] The noise estimation signal inversion unit 56 inverts the polarity of the second noise estimation signal d^2 output from the noise estimation signal generation unit 53. The noise estimation signal inversion unit 56 outputs the second noise estimation signal d^2 with inverted polarity to the virtual error signal generation unit 57.

[0044] The virtual error signal generation unit 57 generates a second virtual error signal e by adding the error signal e output from the error microphone 13e, the second sound cancellation estimation signal y^2 that has passed through the sound cancellation estimation signal inversion unit 55, and the second noise estimation signal d^2 that has passed through the noise estimation signal inversion unit 56. v The virtual error signal generation unit 57 generates the second virtual error signal e v Output 2 to the secondary route update unit 52 and the primary route update unit 54.

[0045] <Control signal addition unit 20> The control signal summer 20 of the control device 15 generates a control signal u for controlling the speaker 12 by adding together the first control signals u1 output from each of the multiple first control signal generation units 16 and the second control signals u2 output from each of the multiple second control signal generation units 18. The control signal summer 20 outputs the generated control signal u to the speaker 12. When the control signal u is input to the speaker 12, the speaker 12 generates a cancellation sound y corresponding to the magnitude of the control signal u.

[0046] <Variability Calculation Unit 21> The fluctuation amount calculation unit 21 of the control device 15 receives an error signal e from the error microphone 13e and also receives reference signals r from multiple reference microphones 13r. That is, the fluctuation amount calculation unit 21 receives microphone signals m from multiple microphones 13. Based on the microphone signals m, the fluctuation amount calculation unit 21 calculates the fluctuation amount ΔL of the microphone signals m. More specifically, the fluctuation amount calculation unit 21 calculates the fluctuation amount ΔL of the microphone signals m by the following equation (7).

number

[0047] The first period in Figures 3(A) and 3(B) represents a period when the proportion of road noise components in the microphone signal m is large (for example, a period when vehicle 3 is driving on a rough road). In contrast, the second period in Figures 3(A) and 3(B) represents a period when the proportion of road noise components in the microphone signal m is small (for example, a period when vehicle 3 is driving on a flat road). As shown in Figure 3(B), even if the occupants of vehicle 3 speak loudly during the first period, there is no significant change in the fluctuation amount ΔL of the microphone signal m. This is because the noise component from the road surface is the main component, and the influence of conversation is small. In contrast, as shown in Figure 3(B), if the occupants of vehicle 3 speak loudly during the second period, the fluctuation amount ΔL of the microphone signal m increases sharply. Therefore, by determining whether or not the fluctuation amount ΔL of the microphone signal m exceeds a threshold, it is possible to accurately determine whether or not speech components have been mixed into the microphone signal m.

[0048] Referring to Figure 2, the fluctuation amount calculation unit 21 receives acceleration signals x from multiple acceleration sensors 11. Based on the acceleration signals x, the fluctuation amount calculation unit 21 calculates the fluctuation amount ΔLv of the acceleration signal x. More specifically, the fluctuation amount calculation unit 21 calculates the fluctuation amount ΔLv of the acceleration signal x using the following equation (8).

number

[0049] The third period in Figures 4(A) and 4(B) represents the period during which instantaneous changes occur on the road surface (for example, the period during which vehicle 3 crosses a bump, road joint, road hump, etc.). As shown in Figure 4(A), even if instantaneous changes occur on the road surface during the third period, the amplitude of the acceleration signal x does not fluctuate as much as in other periods. Therefore, it is difficult to accurately determine whether or not an instantaneous vibration component has been mixed into the acceleration signal x based on its amplitude. In contrast, as shown in Figure 4(B), when an instantaneous change occurs on the road surface during the third period, the fluctuation amount ΔLv of the acceleration signal x fluctuates more than in other periods. Therefore, it is possible to accurately determine whether or not an instantaneous vibration component has been mixed into the acceleration signal x by whether or not the fluctuation amount ΔLv of the acceleration signal x exceeds a threshold.

[0050] <Processing Control Unit 22> Referring to Figure 2, the processing control unit 22 of the control device 15 controls the adaptive update process and the sound cancellation output process by transmitting predetermined signals (for example, signals related to the step size parameter μ and the forgetting coefficient η) to the control update unit 26, the secondary path update unit 32, the primary path update unit 34, the control update unit 46, the secondary path update unit 52, and the primary path update unit 54. The adaptive update process is the process of adaptively updating the control filter W1, the secondary path filter C^1, the primary path filter H^1, the control filter W2, the secondary path filter C^2, and the primary path filter H^2 (hereinafter referred to as "adaptive update filters W1~H^2"). The sound cancellation output process is the process of outputting a sound cancellation y to the speaker 12.

[0051] The processing control unit 22 obtains the fluctuation amount ΔL of the microphone signal m and the fluctuation amount ΔLv of the acceleration signal x from the fluctuation amount calculation unit 21. The processing control unit 22 switches the operation of the adaptive update process and the sound cancellation output process according to the fluctuation amount ΔL of the microphone signal m and the fluctuation amount ΔLv of the acceleration signal x. Hereinafter, the control that switches the operation of the adaptive update process and the sound cancellation output process according to the fluctuation amount ΔL of the microphone signal m will be referred to as the "first switching control," and the control that switches the operation of the adaptive update process and the sound cancellation output process according to the fluctuation amount ΔLv of the acceleration signal x will be referred to as the "second switching control."

[0052] <Example 1 of executing the first switching control> Referring to Figure 5, when the first switching control is started, the processing control unit 22 obtains the fluctuation amount ΔL of the microphone signal m from the fluctuation amount calculation unit 21 and determines whether the fluctuation amount ΔL of the microphone signal m exceeds the first threshold T1 (step ST1).

[0053] If the fluctuation amount ΔL of the microphone signal m exceeds the first threshold T1 (step ST1: Yes), the processing control unit 22 determines that audio components are mixed into the microphone signal m and sets the counter D to D off Set to (Step ST2). Counter D is set to an initial value of 0 at the start of the first switching control. Counter D is not reset when the first switching control is completed and is used continuously in the next first switching control. offThis is a pre-set parameter, and it is set to a positive number greater than 1.

[0054] Next, the processing control unit 22 determines whether the microphone signal m (more specifically, the microphone signal m from which the fluctuation amount ΔL was obtained from the fluctuation amount calculation unit 21 in step ST1) is being used as a reference signal r (step ST3).

[0055] If the microphone signal m is used as a reference signal r (step ST3: Yes), the processing control unit 22 stops the adaptive update process in order to suppress the adaptive update of the adaptive update filters W1~H^2 based on the microphone signal m containing voice components. Also, the processing control unit 22 stops the cancellation output process in order to suppress the output of cancellation sound y based on the microphone signal m containing voice components (step ST4).

[0056] If the microphone signal m is not used as the reference signal r (step ST3: No), the processing control unit 22 stops the adaptive update process in order to suppress the adaptive update of the adaptive update filters W1~H^2 based on the microphone signal m which contains voice components. On the other hand, if the microphone signal m which contains voice components is not used as the reference signal r, then since the reference signal r does not contain voice components, the output of the canceling sound y may continue with the control filters W1 and W2 set as fixed filters (adaptive updating of control filters W1 and W2 stopped). For example, for control channels that use the acceleration signal x as the reference signal, the output of the canceling sound y may continue. Therefore, the processing control unit 22 causes the speaker 12 to output the canceling sound y by executing the canceling sound output process with the control filters W1 and W2 set as fixed filters (step ST5).

[0057] If the variation amount ΔL of the microphone signal m is less than or equal to the first threshold T1 (step ST1: No), the processing control unit 22 subtracts 1 from the counter D (step ST6) and then determines whether the counter D has become 0 or less (step ST7).

[0058] If counter D is not 0 or less (step ST7: No), the processing control unit 22 determines whether or not the microphone signal m is being used as the reference signal r (step ST3).

[0059] If counter D is 0 or less (step ST7: Yes), the processing control unit 22 performs adaptive update processing to adaptively update the adaptive update filters W1 to H^2. The processing control unit 22 also performs cancellation sound output processing to output cancellation sound y to the speaker 12 (step ST8).

[0060] Furthermore, in the first switching control, it may be determined that the fluctuation amount ΔL of the microphone signal m exceeds the first threshold T1, and the adaptive update process is stopped. In the next first switching control, it may be determined that the fluctuation amount ΔL of the microphone signal m is less than or equal to the first threshold T1. Even in such a case, the adaptive update process is not immediately resumed, D off Until the corresponding period has elapsed, the adaptive update process remains suspended (see step ST7). This prevents the adaptive update process from being switched ON / OFF frequently in short periods of time.

[0061] <Example 2 of the execution of the first switching control> Referring to Figure 6, when the first switching control is started, the processing control unit 22 obtains the fluctuation amount ΔL of the microphone signal m from the fluctuation amount calculation unit 21 and determines whether the fluctuation amount ΔL of the microphone signal m is greater than or equal to the reference fluctuation amount TL (step ST11). The reference fluctuation amount TL is the fluctuation amount used for table reference. The reference fluctuation amount TL is not reset even after the first switching control is completed and is used continuously in the next first switching control.

[0062] If the variation amount ΔL of the microphone signal m is greater than or equal to the reference variation amount TL (step ST11: Yes), the processing control unit 22 sets the reference variation amount TL to the variation amount ΔL (step ST12).

[0063] If the variation amount ΔL of the microphone signal m is less than the reference variation amount TL (step ST11: No), the processing control unit 22 sets the reference variation amount TL to β × TL (step ST13). β is a preset parameter and is set to a positive number less than 1.

[0064] Next, the processing control unit 22 determines whether the microphone signal m (more specifically, the microphone signal m from which the fluctuation amount ΔL was obtained from the fluctuation amount calculation unit 21 in step ST11) is being used as a reference signal r (step ST14).

[0065] If the microphone signal m is used as the reference signal r (step ST14: Yes), the processing control unit 22 determines the step size parameter μ based on the reference fluctuation amount TL set in step ST12 or step ST13 and the first μ table showing the relationship between the reference fluctuation amount TL and the step size parameter μ (step ST15). Details of the first μ table will be described later.

[0066] Furthermore, the processing control unit 22 determines the forgetting coefficient η based on the reference fluctuation amount TL set in step ST12 or step ST13 and the first η table showing the relationship between the reference fluctuation amount TL and the forgetting coefficient η (step ST15). Details of the first η table will be described later.

[0067] If the microphone signal m is not used as the reference signal r (step ST14: No), the processing control unit 22 determines the step size parameter μ based on the reference fluctuation amount TL set in step ST12 or step ST13 and the second μ table which shows the relationship between the reference fluctuation amount TL and the step size parameter μ (step ST17). Details of the second μ table will be described later.

[0068] Furthermore, the processing control unit 22 determines the forgetting coefficient η based on the reference fluctuation amount TL set in step ST12 or step ST13 and the second η table showing the relationship between the reference fluctuation amount TL and the forgetting coefficient η (step ST18). Details of the second η table will be described later.

[0069] Next, the processing control unit 22 performs adaptive update processing using the step size parameter μ and forgetting coefficient η determined in steps ST15 to ST18 to adaptively update the adaptive update filters W1 to H^2 (see equations (1) to (6) above). Furthermore, the processing control unit 22 performs cancellation sound output processing using the control filters W1 and W2 that have been adaptively updated by the adaptive update processing to output the cancellation sound y to the speaker 12 (step ST19).

[0070] As described above, the processing control unit 22 sets a reference fluctuation amount TL based on the fluctuation amount ΔL of the microphone signal m, determines the step size parameter μ and the forgetting coefficient η based on the reference fluctuation amount TL, and executes adaptive update processing using the step size parameter μ and the forgetting coefficient η. As a result, the update amount of the adaptive update filters W1~H^2 in the adaptive update processing (the second term on the right side of equations (1)~(6) above) is changed according to the fluctuation amount ΔL of the microphone signal m, and the amount by which the current value of the adaptive update filters W1~H^2 is reflected in the updated value of the adaptive update filters W1~H^2 in the adaptive update processing (the first term on the right side of equations (1)~(6) above) is changed.

[0071] Furthermore, if the fluctuation amount ΔL of the microphone signal m is less than the reference fluctuation amount TL, the processing control unit 22 sets the reference fluctuation amount TL to β × TL and determines the step size parameter μ by referring to the first μ table or the second μ table based on the reference fluctuation amount TL. This prevents the step size parameter μ from rapidly increasing when the fluctuation amount ΔL of the microphone signal m rapidly decreases. This effect is also observed for the forgetting coefficient η.

[0072] <First μT table and second μT table> Referring to Figure 7, in the first μ table, the step size parameter μ is kept at its maximum value when the reference fluctuation TL is less than the reference value P1. In the first μ table, when the reference fluctuation TL is greater than or equal to the reference value P1 and less than a reference value P2 which is greater than the reference value P1, the step size parameter μ decreases continuously as the reference fluctuation TL increases. In the first μ table, the step size parameter μ is kept at 0 when the reference fluctuation TL is greater than or equal to the reference value P2.

[0073] In the first μ table, the step size parameter μ is set to a smaller value than in the second μ table, except when the step size parameter μ is 0. Therefore, when μ is determined based on the first μ table in step ST15, the step size parameter μ becomes smaller compared to when μ is determined based on the second μ table in step ST17, resulting in a smaller update amount for the adaptive update filters W1~H^2 in the adaptive update process. Consequently, when the microphone signal m is used as the reference signal r, the update amount for the adaptive update filters W1~H^2 in the adaptive update process is smaller compared to when the microphone signal m is not used as the reference signal r.

[0074] In the second μ table, the step size parameter μ is kept at its maximum value when the reference fluctuation TL is less than the reference value P3. In the second μ table, when the reference fluctuation TL is greater than or equal to the reference value P3 and less than the reference value P4 which is greater than P3, the step size parameter μ decreases continuously as the reference fluctuation TL increases. In the second μ table, the step size parameter μ is kept at 0 when the reference fluctuation TL is greater than or equal to the reference value P4.

[0075] In the first and second μ tables, when the reference fluctuation amount TL, which is set based on the fluctuation amount ΔL of the microphone signal m, is within a predetermined range, the step size parameter μ becomes continuously smaller as the reference fluctuation amount TL increases. Therefore, as the fluctuation amount ΔL of the microphone signal m increases, the step size parameter μ becomes continuously smaller, and the amount of update of the adaptive update filters W1~H^2 in the adaptive update process becomes continuously smaller.

[0076] <Table 1η and Table 2η> Referring to Figure 8, in the first η table, the forgetting coefficient η is kept at 1 when the reference fluctuation TL is less than the reference value Q1. In the first η table, when the reference fluctuation TL is greater than or equal to the reference value Q1 and less than the reference value Q2 which is greater than the reference value Q1, the forgetting coefficient η decreases continuously as the reference fluctuation TL increases. In the first η table, the forgetting coefficient η is kept at its minimum value when the reference fluctuation TL is greater than or equal to the reference value Q2.

[0077] In the first η table, the forgetting coefficient η is set to a smaller value than in the second η table, except when the forgetting coefficient η is 1. Therefore, when η is determined based on the first η table in step ST16, the forgetting coefficient η is smaller compared to when η is determined based on the second η table in step ST18, and the amount by which the current value of the adaptive update filter W1~H^2 is reflected in the updated value of the adaptive update filter W1~H^2 in the adaptive update process is reduced. Therefore, when the microphone signal m is used as the reference signal r, the amount by which the current value of the adaptive update filter W1~H^2 is reflected in the updated value of the adaptive update filter W1~H^2 in the adaptive update process is reduced compared to when the microphone signal m is not used as the reference signal r.

[0078] In the first η table, when the reference fluctuation amount TL, which is set based on the fluctuation amount ΔL of the microphone signal m, is within a predetermined range, the forgetting coefficient η decreases continuously as the reference fluctuation amount TL increases. Therefore, as the fluctuation amount ΔL of the microphone signal m increases, the forgetting coefficient η decreases, and the amount by which the current value of the adaptive update filter W1~H^2 is reflected in the updated value of the adaptive update filter W1~H^2 in the adaptive update process decreases. As a result, the attenuation of the adaptive update filter W1~H^2 increases, and the canceled sound y decreases.

[0079] In the second η table, the forgetting coefficient η is kept at 1 when the reference fluctuation TL is less than the baseline value Q3. In the second η table, the forgetting coefficient η is kept at a value less than 1 when the reference fluctuation TL is greater than or equal to the baseline value Q3 and less than the baseline value Q4 which is greater than the baseline value Q3. In the second η table, the forgetting coefficient η is kept at 1 when the reference fluctuation TL is greater than or equal to the baseline value Q4.

[0080] In the second η table, the range in which the forgetting coefficient η remains less than 1 (the range in which the reference fluctuation amount TL is greater than or equal to the reference value Q3 and less than the reference value Q4) partially overlaps with the range in the second μ table in which the step size parameter μ decreases continuously (the range in which the reference fluctuation amount TL is greater than or equal to the reference value P3 and less than the reference value P4). Therefore, as the update amount of adaptive update filters W1~H^2 gradually decreases due to the continuously decreasing step size parameter μ, the amount in which the current value of adaptive update filters W1~H^2 is reflected in the update value of adaptive update filters W1~H^2 in the adaptive update process decreases.

[0081] In the second η table, the range in which the forgetting coefficient η is kept at 1 (the range in which the reference fluctuation amount TL is greater than or equal to the reference value Q4) partially overlaps with the range in the second μ table in which the step size parameter μ becomes 0 (the range in which the reference fluctuation amount TL is greater than or equal to the reference value P4). Therefore, even if the update amount of the adaptive update filters W1~H^2 becomes 0, the sound cancellation output processing continues.

[0082] <Example 1 of execution of the second switching control> Referring to Figure 9, when the second switching control is started, the processing control unit 22 obtains the fluctuation amount ΔLv of the acceleration signal x from the fluctuation amount calculation unit 21 and determines whether the fluctuation amount ΔLv of the acceleration signal x exceeds the second threshold T2 (step ST21).

[0083] If the fluctuation amount ΔLv of the acceleration signal x exceeds the second threshold T2 (step ST21: Yes), the processing control unit 22 determines that an instantaneous vibration component has been mixed into the acceleration signal x and sets the counter D to D off Set to (Step ST22).

[0084] Next, the processing control unit 22 stops the adaptive update process in order to suppress the adaptive update of the adaptive update filters W1 to H^2 based on the acceleration signal x which contains instantaneous vibration components. The processing control unit 22 also performs the sound cancellation output process with the control filters W1 and W2 in a fixed filter state (adaptive update of control filters W1 and W2 stopped), causing the speaker 12 to output the sound cancellation y (step ST23). As a result, even if instantaneous vibration components are mixed into the acceleration signal x, the noise d based on road surface vibration (the noise controlled by the noise reduction device 1) can be reduced, and the noise reduction performance can be maintained to the maximum extent.

[0085] If the fluctuation amount ΔLv of the acceleration signal x is less than or equal to the second threshold T2 (step ST21: No), the processing control unit 22 subtracts 1 from the counter D (step ST24) and then determines whether the counter D has become 0 or less (step ST25).

[0086] If counter D is not 0 or less (step ST25: No), the processing control unit 22 stops the adaptive update process and performs the sound cancellation output process with control filters W1 and W2 set as fixed filters, thereby outputting the sound cancellation y to the speaker 12 (step ST23).

[0087] If counter D is 0 or less (step ST25: Yes), the processing control unit 22 performs adaptive update processing to adaptively update the adaptive update filters W1 to H^2. The processing control unit 22 also performs cancellation sound output processing to output cancellation sound y to the speaker 12 (step ST26).

[0088] <Example 2 of the execution of the second switching control> Referring to Figure 10, when the second switching control is started, the processing control unit 22 obtains the fluctuation amount ΔLv of the acceleration signal x from the fluctuation amount calculation unit 21 and determines whether the fluctuation amount ΔLv of the acceleration signal x is greater than or equal to the reference fluctuation amount TLv (step ST31).

[0089] If the fluctuation amount ΔLv of the acceleration signal x is greater than or equal to the reference fluctuation amount TLv (step ST31: Yes), the processing control unit 22 sets the reference fluctuation amount TLv to the fluctuation amount ΔLv (step ST32).

[0090] If the fluctuation amount ΔLv of the acceleration signal x is less than the reference fluctuation amount TLv (step ST31: No), the processing control unit 22 sets the reference fluctuation amount TLv to β × TLv (step ST33).

[0091] Next, the processing control unit 22 determines the step size parameter μ based on the reference fluctuation amount TLv set in step ST32 or step ST33 and the μ table showing the relationship between the reference fluctuation amount TLv and the step size parameter μ (step ST34). Details of the μ table will be described later.

[0092] Next, the processing control unit 22 performs an adaptive update process using the step size parameter μ set in step ST34 to adaptively update the adaptive update filters W1 to H^2 (see equations (1) to (6) above). At this time, it is preferable that the forgetting coefficient η be set to 1 in order to continue outputting the canceling sound y from the speaker 12. Furthermore, the processing control unit 22 performs a canceling sound output process using the control filters W1 and W2 that have been adaptively updated by the adaptive update process to output the canceling sound y from the speaker 12 (step ST35).

[0093] As described above, the processing control unit 22 sets a reference fluctuation amount TLv based on the fluctuation amount ΔLv of the acceleration signal x, determines the step size parameter μ based on the reference fluctuation amount TLv, and executes adaptive update processing using the step size parameter μ. As a result, the update amount of the adaptive update filters W1~H^2 in the adaptive update processing (the second term on the right-hand side of equations (1)~(6) above) is changed according to the fluctuation amount ΔLv of the acceleration signal x.

[0094] <μ Table> Referring to Figure 11, in the μ table, the step size parameter μ is kept at its maximum value when the reference fluctuation TLv is less than the reference value A1. In the μ table, when the reference fluctuation TLv is greater than or equal to the reference value A1 and less than the reference value A2 which is greater than the reference value A1, the step size parameter μ decreases continuously as the reference fluctuation TLv increases. In the μ table, the step size parameter μ is kept at 0 when the reference fluctuation TLv is greater than or equal to the reference value A2.

[0095] In the μ table, when the reference fluctuation amount TLv, which is set based on the fluctuation amount ΔLv of the acceleration signal x, is within a predetermined range, the step size parameter μ becomes continuously smaller as the reference fluctuation amount TLv increases. Therefore, as the fluctuation amount ΔLv of the acceleration signal x increases, the step size parameter μ becomes continuously smaller, and the amount of update of the adaptive update filters W1~H^2 in the adaptive update process becomes continuously smaller.

[0096] <Effects> The noise reduction device 1 is designed to have a higher control effect in the vicinity of the microphone 13. Therefore, in this embodiment, the microphone 13 is installed on the headrest 9C of the occupant seat 9. This allows the occupant's head to be brought closer to the microphone 13, thereby increasing the control effect that the occupant can perceive.

[0097] On the other hand, if the microphone 13 is installed on the headrest 9C of the passenger seat 9, the position of the microphone 13 changes significantly when the fore-aft position of the passenger seat 9 is adjusted or when the seat back 9B of the passenger seat 9 is reclined, causing a large change in the transfer function C of the secondary path from speaker 12 to microphone 13. Consequently, if the difference between the transfer function C of the secondary path and the secondary path filters C^1 and C^2 becomes large, there is a risk that the noise reduction device 1 may not be able to sufficiently reduce noise d, or that noise d may be amplified. Therefore, the control device 15 adaptively updates the secondary path filters C^1 and C^2. This allows the secondary path filters C^1 and C^2 to change in response to changes in the transfer function C of the secondary path. As a result, the noise reduction device 1 can sufficiently reduce noise d and suppress the amplification of noise d.

[0098] By the way, if the microphone 13 is installed on the headrest 9C of the passenger seat 9, the microphone 13 will be closer to the passenger's mouth, making it easier for the microphone 13 to pick up the passenger's conversation sounds. In other words, speech components are more likely to be mixed into the microphone signal m. If the microphone signal m mixed with speech components is used as a reference signal r, a control signal u will be generated based on the reference signal r mixed with speech components, and therefore, speech components will also be mixed into the canceling sound y output based on the control signal u. As a result, there is a risk that a voice echo will occur in the passenger compartment 8, causing discomfort to the passenger. Therefore, the control device 15 stops the adaptive update process and the canceling sound output process when the microphone signal m is used as a reference signal r (see Example 1 of First Switching Control). Alternatively, when the microphone signal m is used as the reference signal r, the control device 15 reduces the amount of update of the adaptive update filters W1~H^2 in the adaptive update process, and also reduces the amount by which the current value of the adaptive update filters W1~H^2 is reflected in the updated value of the adaptive update filters W1~H^2 in the adaptive update process (see Example 2 of First Switching Control). This suppresses the generation of a control signal u based on the reference signal r which contains voice components. Therefore, it is possible to suppress the occurrence of voice echoes in the vehicle cabin 8 and stably reduce noise d.

[0099] Furthermore, if the driving conditions of vehicle 3 (e.g., road surface conditions) do not change, the road noise level does not fluctuate significantly, but the conversation noise level does fluctuate significantly. Utilizing this principle, the control device 15 determines that voice components have been mixed into the microphone signal m when the fluctuation amount ΔL of the microphone signal m (i.e., the fluctuation amount of the cumulative value of the amplitude of the microphone signal m at regular intervals) exceeds a first threshold T1. This allows for accurate detection of whether or not voice components are mixed into the microphone signal m (i.e., whether or not voice echoes are likely to occur) based on the fluctuation amount ΔL of the microphone signal m. This more effectively suppresses the occurrence of voice echoes within the vehicle cabin 8 and reduces noise d more stably.

[0100] Incidentally, when vehicle 3 crosses a bump, road joint, road hump, etc., a large vibration is instantaneously input to vehicle 3 from the road surface, which can cause instantaneous vibration components to be mixed into the acceleration signal x. If the adaptive update filters W1~H^2 are adaptively updated based on the acceleration signal x mixed with instantaneous vibration components, the values ​​of the adaptive update filters W1~H^2 may deviate from values ​​suitable for a flat road surface, and there is a risk that the noise reduction performance on a flat road surface will temporarily decrease. Therefore, the control device 15 stops the adaptive update process when the fluctuation amount ΔLv of the acceleration signal x exceeds the second threshold T2 (when instantaneous vibration components are mixed into the acceleration signal x) (see Example 1 of Second Switching Control). Alternatively, the control device 15 reduces the amount of update of the adaptive update filters W1~H^2 in the adaptive update process as the fluctuation amount ΔLv of the acceleration signal x increases (see Example 2 of Second Switching Control). This makes it possible to avoid undesirable adaptive updates of the adaptive update filters W1~H^2 (adaptive updates based on acceleration signals x that contain instantaneous vibration components), thereby maintaining noise reduction performance on flat road surfaces.

[0101] <Variation> In the above embodiment, the control device 15 switches the operation of adaptive update processing and sound cancellation output processing according to the amount of fluctuation ΔL of the microphone signal m and the amount of fluctuation ΔLv of the acceleration signal x. In other embodiments, the control device 15 may switch the operation of adaptive update processing and sound cancellation output processing according to only one of the amount of fluctuation ΔL of the microphone signal m and the amount of fluctuation ΔLv of the acceleration signal x. Furthermore, in other embodiments, the control device 15 may switch the operation of adaptive update processing and sound cancellation output processing according to the amount of fluctuation ΔL of the microphone signal m and / or the amount of fluctuation ΔLv of the acceleration signal x.

[0102] In the above embodiment, the value of the forgetting coefficient η is changed in the second η table (η table when the microphone signal m is not used as the reference signal r). In other embodiments, the value of the forgetting coefficient η may be fixed to 1 in the second η table. Alternatively, when the microphone signal m is not used as the reference signal r, the second η table may not be set, and the value of the forgetting coefficient η may be fixed to 1.

[0103] In the above embodiment, the variation ΔL of the microphone signal m is the variation in the cumulative value of the amplitude of the microphone signal m over a fixed period of time. In other embodiments, the variation ΔL of the microphone signal m may be a value other than the variation in the cumulative value of the amplitude of the microphone signal m over a fixed period of time (for example, the variation in the average value of the amplitude of the microphone signal m over a fixed period of time). The same applies to the variation ΔLv of the acceleration signal x.

[0104] In the above embodiment, the control device 15 adaptively updates the adaptive update filters W1 to H^2 using equations (1) to (6) above. However, equations (1) to (6) above are merely examples of equations used for the adaptive update of the adaptive update filters W1 to H^2. Therefore, in other embodiments, the control device 15 may adaptively update the adaptive update filters W1 to H^2 using equations other than those (1) to (6) above. For example, the control device 15 may use equations (9) to (11) below instead of equations (4) to (6) above (details are omitted, but similar substitutions are possible for equations (1) to (3) above).

number

number

number

number

number

number

number

[0105] In the above embodiment, the control device 15 uses the current values ​​of the adaptive update filters W1 to H^2 (W1(t), C^1(t), H^1(t), W2(t), C^2(t), H^2(t)) as the values ​​of the adaptive update filters W1 to H^2 before adaptive update. In other embodiments, the control device 15 may use the past values ​​of the adaptive update filters W1 to H^2 (for example, W1(t-1), C^1(t-1), H^1(t-1), W2(t-1), C^2(t-1), H^2(t-1)) as the values ​​of the adaptive update filters W1 to H^2 before adaptive update, or it may use both the current and past values ​​of the adaptive update filters W1 to H^2.

[0106] In the above embodiment, the control device 15 includes a plurality of adaptive update filters W1 to H^2. In other embodiments, the control device 15 may include only one adaptive update filter.

[0107] In the above embodiment, both the acceleration signal x and the microphone signal m are used as reference signals. In other embodiments, only one of the acceleration signal x or the microphone signal m may be used as a reference signal.

[0108] In the above embodiment, the noise reduction device 1 is applied to the passenger compartment 8 of the vehicle 3. In other embodiments, the noise reduction device 1 may be applied to the interior space of a moving object other than the vehicle 3 (for example, a ship or an aircraft), or to the interior space of a fixed object (for example, a house).

[0109] This concludes the description of specific embodiments, but the present invention is not limited to the above embodiments or modifications and can be broadly modified and implemented.

[0110] <Summary of Embodiments> An active noise reduction device 1 comprises a noise cancellation output device 12 that outputs a cancellation sound y to cancel out noise d, a microphone 13 that generates a microphone signal m based on the noise d, and a control device 15 that controls the noise cancellation output device 12 based on the microphone signal m, wherein the control device 15 includes at least one adaptively updatable filter W1, C^1, H^1, W2, C^2, H^2, calculates a variation amount ΔL of the microphone signal m based on the microphone signal m, and switches at least one of the operations of an adaptive update process that adaptively updates the filter W1, C^1, H^1, W2, C^2, H^2 according to the variation amount ΔL of the microphone signal m, and a noise cancellation output process that causes the noise cancellation output device 12 to output the cancellation sound y.

[0111] According to this embodiment, when audio components are mixed into the microphone signal m, the operation of adaptive update processing and cancellation output processing can be switched to suppress the adaptive update of filters W1, C^1, H^1, W2, C^2, and H^2 based on the microphone signal m mixed with audio components, as well as the output of cancellation sound y. Therefore, the occurrence of audio echo can be suppressed.

[0112] The control device 15 calculates the amount of change in the cumulative value of the amplitude of the microphone signal m at regular intervals as the amount of change ΔL of the microphone signal m.

[0113] According to this embodiment, it is possible to accurately detect whether or not audio components are mixed into the microphone signal m (i.e., whether or not audio echo is likely to occur) based on the amount of variation ΔL of the microphone signal m.

[0114] The control device 15 determines whether the microphone signal m is being used as a reference signal r corresponding to the noise d, and stops the adaptive update process and the sound cancellation output process if the microphone signal m is being used as the reference signal r, and stops the adaptive update process and executes the sound cancellation output process if the microphone signal m is not being used as the reference signal r.

[0115] According to this embodiment, when the microphone signal m is used as a reference signal r, the occurrence of voice echo can be suppressed by stopping the adaptive update process and the sound cancellation output process. On the other hand, when the microphone signal m is not used as a reference signal r, the noise reduction performance can be maintained to the maximum extent by continuing the sound cancellation output process while stopping the adaptive update process.

[0116] The control device 15 changes the update amounts of the filters W1, C^1, H^1, W2, C^2, and H^2 in the adaptive update process according to the amount of variation ΔL of the microphone signal m.

[0117] According to this embodiment, by changing the update amounts of filters W1, C^1, H^1, W2, C^2, and H^2 according to the variation amount ΔL of the microphone signal m, it is possible to suppress the generation of voice echoes while maintaining maximum noise reduction performance.

[0118] The control device 15 determines whether the microphone signal m is used as a reference signal r corresponding to the noise d, and when the microphone signal m is used as the reference signal r, it reduces the update amount of the filters W1, C^1, H^1, W2, C^2, and H^2 in the adaptive update process compared to when the microphone signal m is not used as the reference signal r.

[0119] According to this embodiment, when the microphone signal m is used as the reference signal r, the occurrence of audio echo can be suppressed by reducing the update amount of filters W1, C^1, H^1, W2, C^2, and H^2. On the other hand, when the microphone signal m is not used as the reference signal r, the noise reduction performance can be maintained to the maximum extent by increasing the update amount of filters W1, C^1, H^1, W2, C^2, and H^2.

[0120] The control device 15 changes the amount by which the pre-adaptive update values ​​of filters W1, C^1, H^1, W2, C^2, and H^2 are reflected in the adaptive update values ​​of filters W1, C^1, H^1, W2, C^2, and H^2 in the adaptive update process, according to the amount of variation ΔL of the microphone signal m.

[0121] According to this embodiment, by changing the amount of reflection according to the amount of fluctuation ΔL of the microphone signal m, it is possible to suppress the generation of voice echoes while maintaining maximum noise reduction performance.

[0122] The control device 15 determines whether the microphone signal m is used as a reference signal r corresponding to the noise d, and when the microphone signal m is used as the reference signal r, it reduces the amount of reflection in the adaptive update process compared to when the microphone signal m is not used as the reference signal r.

[0123] According to this embodiment, when the microphone signal m is used as a reference signal r, the amount of reflection can be reduced to suppress the occurrence of audio echo. On the other hand, when the microphone signal m is not used as a reference signal r, the amount of reflection can be increased to maintain maximum noise reduction performance.

[0124] The control device 15 determines whether the microphone signal m is used as a reference signal r corresponding to the noise d, and when the microphone signal m is used as the reference signal r, it reduces the amount of updates to the filters W1, C^1, H^1, W2, C^2, and H^2 in the adaptive update process compared to when the microphone signal m is not used as the reference signal r, and also reduces the amount of reflection of the pre-adaptive update values ​​of the filters W1, C^1, H^1, W2, C^2, and H^2 to the adaptively updated values ​​of the filters W1, C^1, H^1, W2, C^2, and H^2 in the adaptive update process.

[0125] According to this embodiment, when the microphone signal m is used as a reference signal r, the generation of audio echo can be suppressed by reducing the update and reflection amounts of filters W1, C^1, H^1, W2, C^2, and H^2. On the other hand, when the microphone signal m is not used as a reference signal r, the noise reduction performance can be maximized by increasing the update and reflection amounts of filters W1, C^1, H^1, W2, C^2, and H^2.

[0126] An active noise reduction device 1 comprises a noise cancellation output device 12 that outputs a cancellation sound y to cancel out noise d, an acceleration sensor 11 that generates an acceleration signal x based on the noise d, and a control device 15 that controls the noise cancellation output device 12 based on the acceleration signal x, wherein the control device 15 includes at least one adaptively updatable filter W1, C^1, H^1, W2, C^2, H^2, calculates the amount of change ΔLv of the acceleration signal x based on the acceleration signal x, and switches at least one of the operations of an adaptive update process that adaptively updates the filter W1, C^1, H^1, W2, C^2, H^2 according to the amount of change ΔLv of the acceleration signal x, and a noise cancellation output process that causes the noise cancellation output device 12 to output the cancellation sound y.

[0127] According to this embodiment, when instantaneous vibration components are mixed into the acceleration signal x, the operation of adaptive update processing and sound cancellation output processing can be switched, thereby suppressing the adaptive update of filters W1, C^1, H^1, W2, C^2, and H^2 based on the acceleration signal x mixed with instantaneous vibration components, and the output of sound cancellation y. Therefore, noise reduction performance can be maintained on flat road surfaces.

[0128] The control device 15 calculates the amount of change in the cumulative value of the amplitude of the acceleration signal x at regular intervals as the amount of change ΔLv of the acceleration signal x.

[0129] According to this embodiment, it is possible to accurately detect whether or not instantaneous vibration components are mixed into the acceleration signal x (i.e., whether or not noise reduction performance is likely to temporarily decrease on a flat road surface) based on the fluctuation amount ΔLv of the acceleration signal x.

[0130] The control device 15 determines whether the fluctuation amount ΔLv of the acceleration signal x exceeds the threshold T2, and if the fluctuation amount ΔLv of the acceleration signal x exceeds the threshold T2, it stops the adaptive update process and executes the sound cancellation output process.

[0131] According to this embodiment, by stopping the adaptive update process when the fluctuation amount ΔLv of the acceleration signal x exceeds the threshold T2, it is possible to suppress a temporary decrease in noise reduction performance on a flat road surface. On the other hand, by continuing the sound cancellation output process while stopping the adaptive update process, it is possible to maintain maximum noise reduction performance.

[0132] The control device 15 changes the update amounts of the filters W1, C^1, H^1, W2, C^2, and H^2 in the adaptive update process according to the amount of variation ΔLv of the acceleration signal x.

[0133] According to this embodiment, by changing the update amounts of filters W1, C^1, H^1, W2, C^2, and H^2 in accordance with the fluctuation amount ΔLv of the acceleration signal x, it is possible to maintain maximum noise reduction performance while suppressing a temporary decrease in noise reduction performance on a flat road surface. [Explanation of Symbols]

[0134] 1: Active noise reduction device 11: Accelerometer 12: Speaker (an example of a sound-canceling output device) 13: Mike 15: Control device W1: Control filter (an example of a filter) C^1: Quadratic path filter (an example of a filter) H^1: First-order path filter (an example of a filter) W2: Control filter (an example of a filter) C^2: Quadratic path filter (an example of a filter) H^2: First-order path filter (an example of a filter)

Claims

1. A noise cancellation output device that outputs noise cancellation sound to cancel out noise, A microphone that generates a microphone signal based on the aforementioned noise, An active noise reduction device comprising a control device that controls the sound cancellation output device based on the microphone signal, The control device is Includes at least one adaptively updatable filter, Based on the microphone signal, the amount of variation in the microphone signal is calculated. An active noise reduction device that switches at least one of the following operations in accordance with the amount of fluctuation of the microphone signal: an adaptive update process that adapts and updates the filter, and a sound cancellation output process that causes the sound cancellation output device to output the sound cancellation.

2. The control device calculates the amount of change in the cumulative value of the amplitude of the microphone signal at regular intervals as the amount of change of the microphone signal, according to claim 1.

3. The control device is Determine whether the microphone signal is being used as a reference signal corresponding to the noise, When the microphone signal is used as the reference signal, the adaptive update process and the sound cancellation output process are stopped. The active noise reduction device according to claim 1 or 2, wherein the adaptive update process is stopped and the sound cancellation output process is executed when the microphone signal is not used as the reference signal.

4. The active noise reduction device according to claim 1 or 2, wherein the control device changes the amount of filter update in the adaptive update process according to the amount of fluctuation of the microphone signal.

5. The control device is Determine whether the microphone signal is being used as a reference signal corresponding to the noise, The active noise reduction device according to claim 4, wherein when the microphone signal is used as the reference signal, the amount of update of the filter in the adaptive update process is reduced compared to when the microphone signal is not used as the reference signal.

6. The control device changes the amount by which the value of the filter before adaptive update is reflected in the value of the filter after adaptive update in the adaptive update process, according to the amount of fluctuation of the microphone signal, according to the control device according to claim 1 or 2.

7. The control device is Determine whether the microphone signal is being used as a reference signal corresponding to the noise, The active noise reduction device according to claim 6, wherein when the microphone signal is used as the reference signal, the amount of reflection in the adaptive update process is reduced compared to when the microphone signal is not used as the reference signal.

8. The control device is Determine whether the microphone signal is being used as a reference signal corresponding to the noise, The active noise reduction device according to claim 1 or 2, wherein, when the microphone signal is used as the reference signal, the amount of filter update in the adaptive update process is reduced compared to when the microphone signal is not used as the reference signal, and the amount by which the value of the filter before adaptive update is reflected in the value of the filter after adaptive update in the adaptive update process is reduced.

9. A noise cancellation output device that outputs noise cancellation sound to cancel out noise, An acceleration sensor that generates an acceleration signal based on the aforementioned noise, An active noise reduction device comprising a control device that controls the sound-canceling output device based on the acceleration signal, The control device is Includes at least one adaptively updatable filter, Based on the acceleration signal, the amount of variation in the acceleration signal is calculated, An active noise reduction device that switches at least one of the operations of an adaptive update process that adapts and updates the filter according to the amount of fluctuation of the acceleration signal, and a sound cancellation output process that causes the sound cancellation output device to output the sound cancellation.

10. The control device calculates the amount of change in the cumulative value of the amplitude of the acceleration signal at regular intervals as the amount of change in the acceleration signal, according to claim 9.

11. The control device is Determine whether the amount of fluctuation in the acceleration signal exceeds a threshold, The active noise reduction device according to claim 9 or 10, wherein the adaptive update process is stopped and the sound cancellation output process is executed when the amount of fluctuation of the acceleration signal exceeds the threshold.

12. The active noise reduction device according to claim 9 or 10, wherein the control device changes the amount of filter update in the adaptive update process according to the amount of fluctuation of the acceleration signal.

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