Active noise reduction device and mobile device

Abstract

To provide an active noise reduction device that can improve the degree of freedom in the frequency range in which noise can be reduced.SOLUTION: An active noise reduction device 10 includes: a plurality of first adaptive filters 11; a plurality of feedback filters 12; an addition unit 13 that adds cancel signals respectively outputted by the plurality of first adaptive filters 11, and outputs a cancel signal obtained by addition; and a band elimination filter that is provided in at least one of a first path from each of the plurality of first adaptive filters 11 to a speaker 52 and a second path from a microphone 53 to each of the plurality of first adaptive filters 11.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present disclosure relates to an active noise reduction device that actively reduces noise. [Background technology]

[0002] Patent Document 1 discloses an active vibration noise control device that has a sufficient vibration noise control effect. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-361721 Summary of the Invention [Problem to be solved by the invention]

[0004] The present disclosure provides an active noise reduction device that can improve the degree of freedom of the frequency range in which noise can be reduced. [Means for solving the problem]

[0005] An active noise reduction device according to one embodiment of the present disclosure is an active noise reduction device that reduces noise in a space in which a speaker and a microphone are installed by outputting a cancellation sound from the speaker, and includes: a plurality of first adaptive filters, each of which outputs a cancellation signal used to output the cancellation sound by applying a filter coefficient that is successively updated based on an error signal output from the microphone to a reference signal having a specific frequency; a plurality of feedback filters, each of which multiplies the cancellation signal output by the first adaptive filter corresponding to the feedback filter by a gain coefficient and outputs the result to the first adaptive filter; an adder that adds the cancellation signals output by each of the plurality of first adaptive filters and outputs the added cancellation signal; and a band elimination filter provided on at least one of a first path from each of the plurality of first adaptive filters to the speaker and a second path from the microphone to each of the plurality of first adaptive filters. [Effects of the Invention]

[0006] An active noise reduction device according to one aspect of the present disclosure can improve the degree of freedom of the frequency range in which noise can be reduced. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a block diagram showing the functional configuration of an adaptive filter that corresponds to the SAN algorithm. [Figure 2] FIG. 2 is a diagram showing the relationship between the noise signal and the cancellation signal in the SAN algorithm. [Figure 3] FIG. 3 is a block diagram showing the functional configuration of an adaptive filter corresponding to the SAN Filtered-x LMS algorithm. [Figure 4] FIG. 4 is a diagram showing the relationship between noise and canceled sound in the SAN Filtered-x LMS algorithm. [Figure 5]FIG. 5 is a schematic diagram of a vehicle equipped with an active noise reduction device according to an embodiment. [Figure 6] FIG. 6 is a block diagram showing a functional configuration of an active noise reduction device according to an embodiment. [Figure 7] FIG. 7 is a diagram showing a specific configuration of the first adaptive filter. [Figure 8] FIG. 8 is a diagram showing a specific configuration of the first band elimination filter. [Figure 9] FIG. 9 is a diagram for explaining adjustment of the characteristics of the first band elimination filter. [Figure 10] FIG. 10 is a diagram showing changes in the frequency characteristics (gain characteristics and phase characteristics) of the acoustic transfer function Cm(z) when the first band elimination filter and the second band elimination filter are applied. [Figure 11] FIG. 11 is a diagram showing changes in the frequency characteristics of the acoustic transfer function Cm(z) when only one of the first band elimination filter and the second band elimination filter is applied. [Figure 12] FIG. 12 is a diagram for explaining why the active noise reduction device according to the embodiment can reduce noise over a wide band. [Figure 13] FIG. 13 is a flowchart showing the switching operation of the noise reduction process. [Figure 14] FIG. 14 is a block diagram showing the functional configuration of an active noise reduction device according to the first modification. [Figure 15] FIG. 15 is a block diagram showing a functional configuration of an adaptive filter module according to the first modification. [Figure 16] FIG. 16 is a block diagram showing the functional configuration of an active noise reduction device according to the second modification. [Figure 17] FIG. 17 is a block diagram showing a functional configuration of an adaptive filter module according to the second modification. [Figure 18] FIG. 18 is a block diagram showing the functional configuration of an active noise reduction device according to the third modification. [Figure 19]FIG. 19 is a block diagram showing a functional configuration of an adaptive filter module according to the third modification. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, the embodiments will be described in detail with reference to the drawings. Note that the embodiments described below are all comprehensive or specific examples. The numerical values, shapes, materials, components, component placement and connection forms, steps, and step order shown in the following embodiments are merely examples and are not intended to limit the present disclosure. Furthermore, among the components in the following embodiments, components not recited in independent claims will be described as optional components.

[0009] Furthermore, each drawing is a schematic diagram and is not necessarily an exact illustration. In each drawing, substantially the same components are denoted by the same reference numerals, and duplicated explanations may be omitted or simplified.

[0010] (Embodiment) [Knowledge that formed the basis of the invention] Active noise reduction devices that use adaptive filters to reduce single-frequency noise have been put into practical use to reduce narrow-band noise generated in the interior space of automobiles, etc. However, such active noise reduction devices have the problem that it is difficult to sufficiently reduce noise when the noise frequency deviates by 1 Hz from the expected frequency.

[0011] Additionally, active noise reduction devices using multi-tap adaptive digital filters have been put into practical use to deal with broadband noise, including random noise such as road noise. Realizing such an active noise reduction device requires a sensor for acquiring signals highly correlated with noise, and a digital signal processor for high-speed calculations, which poses a major cost issue.

[0012] To address these issues, the following embodiment describes an active noise reduction device that can reduce broadband noise based on the SAN Filtered-x LMS algorithm. Note that SAN stands for Single frequency Adaptive Notch filter, and LMS stands for Least Mean Square.

[0013] [Noise signal reduction method using SAN algorithm] Before describing the active noise reduction device according to the embodiment, a noise signal reduction method using the SAN algorithm and a noise reduction method using the SAN Filtered-x LMS algorithm will be described.

[0014] First, a noise signal reduction method using the SAN algorithm will be described. Fig. 1 is a block diagram showing the functional configuration of an adaptive filter corresponding to the SAN algorithm. Fig. 2 is a diagram showing the relationship between a noise signal (a sine wave signal of noise) and a cancellation signal in the SAN algorithm. Note that in the noise signal reduction method using the SAN algorithm described below, the noise signal will be described as a sine wave signal of a single frequency.

[0015] 1 and 2, n is an integer equal to or greater than 0 and indicates the sampling number in a discrete-time system. If the frequency of the noise signal to be reduced is f0 [Hz], the normalized angular frequency ω0 [rad] is expressed as follows:

[0016] ω0=2πf0T s =2πf0 / f s [Formula 1]

[0017] In [Equation 1], T s [sec] is the sampling period, and f s [Hz] is the sampling frequency. The normalized angular frequency ω0 is used to represent discrete time, nT s is represented by n.

[0018] Noise sine wave signal n d(n) is expressed as the following [Equation 2] using normalized angular frequency ω0, amplitude R, and phase θ [rad].

[0019] n d (n)=Rsin(ω0n+θ) [Equation 2]

[0020] n d A cancellation signal y(n) is generated to reduce n. d Since it has the same amplitude and opposite phase as (n), it can be expressed as the following [Equation 3].

[0021] y(n)=Rsin{ω0n+(θ-π)} =A(n)sin(ω0n)+B(n)cos(ω0n) [Formula 3]

[0022] A(n) and B(n) are the filter coefficients of the adaptive filter. The amplitude R of the cancellation signal y(n) is A(n). 2 +B(n) 2 and the phase (θ-π) is expressed as the arctangent of B(n) / A(n). Therefore, changing the magnitude of the adaptive filter coefficients A(n) and B(n) changes the amplitude of the cancellation signal, and changing the ratio of the adaptive filter coefficients A(n) and B(n) changes the phase of the cancellation signal.

[0023] Here, the adaptive filter coefficients A(n) and B(n) are optimized using the LMS algorithm to minimize e(n), which is the error signal generated by the interference between the noise signal and the cancellation signal. This reduces the noise signal.

[0024] [Noise reduction method using SAN Filtered-x LMS algorithm] Next, we will explain a noise reduction method using the SAN Filtered-x LMS algorithm. Figure 3 is a block diagram showing the functional configuration of an adaptive filter corresponding to the SAN Filtered-x LMS algorithm. Figure 4 is a diagram showing the relationship between noise and canceled sound in the SAN Filtered-x LMS algorithm. In the following explanation of the noise reduction method using the SAN Filtered-x LMS algorithm, the noise will be described as engine booming noise. Engine booming noise is noise that momentarily resembles a single-frequency sine wave.

[0025] The cancellation signal propagates through the speaker, the vehicle interior, and the microphone and is input to the adaptive filter. This transfer path is represented by the acoustic transfer function C m The SAN Filtered-x LMS algorithm is based on the SAN algorithm and further uses the acoustic transfer function C m This is an algorithm that takes (z) into consideration.

[0026] In Figures 3 and 4, the simulated transfer function C m ^ (z) is the acoustic transfer function C m (z) is a transfer function (filter) that simulates n m (n) is the engine boom noise at the microphone position with frequency f0 [Hz]. m (n) is C m (z) is the discrete time n impulse response. m (n)*y(n) represents the cancellation sound at the microphone position, and * denotes the convolution operator. Note that when actually reducing engine booming noise, the convolution operation is a continuous-time integral, but in the following it will be explained as a discrete-time product-sum operation.

[0027] In the noise reduction method based on the SAN Filtered-x LMS algorithm, the following processes (1) to (5) are repeatedly executed, so that the filter coefficients A(n) and B(n) converge to optimal values.

[0028] (1) Based on the signal indicating the engine rotation frequency, the engine booming noise n m Detect the frequency f0 [Hz] of (n).

[0029] (2) A sine wave x with a frequency of f0 [Hz] s (n) and cosine wave x c (n) is generated, and the result is multiplied by coefficients A(n) and B(n) and added to generate the cancellation signal y(n) shown in [Equation 4].

[0030] y(n)=A(n)x s (n)+B(n)x c (n) [Formula 4]

[0031] (3) A cancellation sound is output from the speaker based on the cancellation signal y(n). At the microphone position, the cancellation sound c m (n)*y(n) and engine booming noise n m The residual sound (error signal) e(n) generated by interference from (n) is detected by a microphone.

[0032] (4) C m ^ (z) sine wave x s (n) and cosine wave x c By filtering each of (n), the sine wave r s (n) and cosine wave r c Generate (n).

[0033] (5) Update the filter coefficients A(n) and B(n) based on the LMS update formulas shown in [Formula 5] and [Formula 6]. Note that μ is a step size parameter that determines the update amount of the filter coefficients A(n) and B(n) per sampling.

[0034] A(n+1)=A(n)-μr s (n)e(n)[Formula 5] B(n+1)=B(n)-μr c (n)e(n)[Formula 6]

[0035] [Configuration of active noise reduction device] Next, the configuration of an active noise reduction device according to an embodiment will be described. Fig. 5 is a schematic diagram of a vehicle equipped with an active noise reduction device according to an embodiment. Fig. 6 is a block diagram showing the functional configuration of the active noise reduction device according to an embodiment.

[0036] As shown in Fig. 5, the active noise reduction device 10 is mounted on a vehicle 50 and reduces noise in a space 51 inside the vehicle cabin. A speaker 52 and a microphone 53 are installed in the space 51. Note that for the sake of simplicity, only one pair of speaker 52 and microphone 53 is shown in Figs. 5 and 6, but in reality, multiple pairs of speakers 52 and microphones 53 are set in the space 51, and multiple pairs of speakers 52 and microphones 53 are used to reduce noise.

[0037] The active noise reduction device 10 is an active noise reduction device that reduces noise at a position where a microphone 53 is installed by using cancellation sound output from a speaker 52. The active noise reduction device 10 is realized by, for example, a microprocessor such as a microcontroller or a DSP (Digital Signal Processor), and a storage unit (memory).

[0038] As shown in Fig. 6, the active noise reduction device 10 specifically includes a plurality of first adaptive filters 11, a plurality of feedback filters 12, an adder 13, a first band elimination filter 14, a first gain adjuster 15, a second band elimination filter 16, and a second gain adjuster 17. In the example of Fig. 6, the active noise reduction device 10 includes two pairs of first adaptive filters 11 and feedback filters 12, but it may include three or more pairs of first adaptive filters 11 and feedback filters 12.

[0039] These components of the active noise reduction device 10 are implemented by a microcontroller executing a computer program (software) stored in a memory unit, but some of them may also be implemented by hardware (circuits). Each component will be described below.

[0040] Each of the plurality of first adaptive filters 11 outputs a cancellation signal by applying a filter coefficient, which is successively updated based on the error signal output from the microphone 53, to a reference signal having a specific frequency. The cancellation signal is a signal used to output a cancellation sound. The first adaptive filter 11 in the upper part of FIG. 6 outputs the cancellation signal y 00 (n), and the first adaptive filter 11 on the lower side outputs the cancellation signal y 01 The upper first adaptive filter 11 outputs (n). The frequency of the reference signal processed by the upper first adaptive filter 11 is different from the frequency of the reference signal processed by the lower first adaptive filter 11, but they may be the same. A specific configuration of the first adaptive filter 11 will be described later.

[0041] The plurality of feedback filters 12 correspond one-to-one to the plurality of first adaptive filters 11. Each of the plurality of feedback filters 12 multiplies the cancellation signal output by the first adaptive filter 11 corresponding to that feedback filter 12 by a gain coefficient and outputs (feeds back) the result to that first adaptive filter 11.

[0042] The upper feedback filter 12 in FIG. 6 receives the cancellation signal y 00 (n) multiplied by a gain coefficient to produce a cancellation signal h 00 6 outputs the cancellation signal y (n) to the upper first adaptive filter 11. The lower feedback filter 12 in FIG. 6 outputs the cancellation signal y 01 (n) multiplied by a gain coefficient to produce a cancellation signal h 01 (n) is output to the first adaptive filter 11 on the lower side.

[0043] The value of the gain coefficient by which the upper feedback filter 12 is multiplied and the value of the gain coefficient by which the lower feedback filter 12 is multiplied may be the same or different.

[0044] The adder 13 adds the cancellation signals output from the plurality of first adaptive filters 11 and outputs the added cancellation signal. In the example of FIG. 6, the adder 13 adds the cancellation signal y 00 (n), and the cancellation signal y 01 (n) and outputs the cancellation signal y(n) after the addition.

[0045] The first band elimination filter 14 is provided on a first path extending from each of the plurality of first adaptive filters 11 to the speaker 52. In the example of Fig. 6, the first band elimination filter 14 is provided on a path extending from the adder 13 to the speaker 52 on the first path, and one first band elimination filter 14 is shared by the plurality of first adaptive filters 11. In Fig. 6, the first band elimination filter 14 is also expressed as G1(z).

[0046] The first band elimination filter 14 is realized by a second adaptive filter. The second adaptive filter is an adaptive filter that performs processing to apply a filter coefficient, which is successively updated based on the input signal (cancellation signal y(n)) to the first band elimination filter 14, to a reference signal having a specific frequency in order to generate an output signal (cancellation signal y'(n)) from the first band elimination filter 14. The specific configuration of the first band elimination filter 14 will be described later.

[0047] The first gain adjustment unit 15 adjusts the gain of the cancellation signal y'(n) output from the first band elimination filter 14 and outputs the result as a cancellation signal y''(n). The first gain adjustment unit 15 is provided on a first path extending from each of the multiple first adaptive filters 11 to the speaker 52. In the example of FIG. 6, the first gain adjustment unit 15 is provided on a path extending from the adder 13 to the speaker 52 on the first path, and one first gain adjustment unit 15 is shared by the multiple first adaptive filters 11. In FIG. 6, the first gain adjustment unit 15 is also expressed as K1.

[0048] The second band elimination filter 16 is provided on the second path from the microphone 53 to each of the multiple first adaptive filters 11. In the example of Fig. 6, the second band elimination filter 16 is provided on the second path up to the branch points corresponding to the multiple first adaptive filters 11, and one second band elimination filter 16 is shared by the multiple first adaptive filters 11. In Fig. 6, the second band elimination filter 16 is also expressed as G2(z).

[0049] The second band elimination filter 16 is realized by a second adaptive filter, similar to the first band elimination filter 14. In this case, the second adaptive filter is an adaptive filter that performs a process of applying a filter coefficient, which is successively updated based on the input signal (error signal e(n)) to the second band elimination filter 16, to a reference signal having a specific frequency in order to generate an output signal (error signal e'(n)) from the second band elimination filter 16.

[0050] The second gain adjustment unit 17 adjusts the gain of the error signal e'(n) output from the second band elimination filter 16 and outputs the result as an error signal e''(n). The second gain adjustment unit 17 is provided on the second path from the microphone 53 to each of the multiple first adaptive filters 11. In the example of FIG. 6, the second gain adjustment unit 17 is provided on the second path up to the path that branches off corresponding to the multiple first adaptive filters 11, and one second gain adjustment unit 17 is shared by the multiple first adaptive filters 11. In FIG. 6, the second gain adjustment unit 17 is also expressed as K2.

[0051] [Specific configuration of the first adaptive filter] Next, a specific configuration of the first adaptive filter 11 will be described. FIG. 7 is a diagram showing a specific configuration of the first adaptive filter 11. As shown in FIG. 7, the first adaptive filter 11 includes a sine wave generating unit 11a, a cosine wave generating unit 11b, a first filter unit 11c, a second filter unit 11d, an adder unit 11e, a first correction unit 11f, a second correction unit 11g, a first update unit 11h, and a second update unit 11i. In the following description using FIG. 7, the specific configuration of the first adaptive filter 11 in the upper part of FIG. 6 will be described. The first adaptive filter 11 in the lower part of FIG. 6 has the same configuration as the first adaptive filter 11 in the upper part, and therefore its description will be omitted.

[0052] The sine wave generating unit 11a outputs a sine wave of a preset frequency as the first reference signal. In FIG. 7, the first reference signal is x S The first reference signal is written as (n), where n is an integer equal to or greater than 0 and indicates a sampling number in a discrete-time system. The first reference signal is output to a first filter unit 11c, a first correction unit 11f, and a first update unit 11h.

[0053] The cosine wave generating unit 11b outputs a predetermined cosine wave having the same frequency as the sine wave as the second reference signal. In FIG. 7, the second reference signal is x C The second reference signal is output to the second filter unit 11d, the second correction unit 11g, and the second update unit 11i.

[0054] The first filter unit 11c multiplies the first reference signal output from the sine wave generating unit 11a by a first filter coefficient A(n). The first filter coefficient A(n) is successively updated by the first updating unit 11h. The first cancellation signal, which is the first reference signal multiplied by the first filter coefficient, is output to the adding unit 11e.

[0055] The second filter unit 11d multiplies the second reference signal output from the cosine wave generating unit 11b by a second filter coefficient B(n). The second filter coefficient B(n) is successively updated by the second updating unit 11i. The second cancellation signal, which is the second reference signal multiplied by the second filter coefficient, is output to the adding unit 11e.

[0056] The adder 11e adds the first cancellation signal output from the first filter 11c and the second cancellation signal output from the second filter 11d. In FIG. 7, the cancellation signal obtained by adding the first cancellation signal and the second cancellation signal is y 00 The adder 11e outputs the cancellation signal y 00 (n) is output to the feedback filter 12 and the adder 13.

[0057] The first correction unit 11f converts the first reference signal into a simulated transfer function C m A first corrected reference signal is generated by correcting (filtering) it using ^(z). In FIG. 7, the first corrected reference signal is generated by filtering it using r S The generated first corrected reference signal is output to the first update unit 11h.

[0058] In addition, the simulated transfer function C m ^(z) is the acoustic transfer function C from the position of the speaker 52 to the position of the microphone 53 m The simulated transfer function C (z) is corrected in consideration of the frequency characteristics of the first band elimination filter 14, the first gain adjustment unit 15, the second band elimination filter 16, and the second gain adjustment unit 17. mSpecifically, ^(z) is the gain and phase (phase lag) for each frequency. m For example, ^(z) is actually measured in advance in space for each frequency and stored in a storage unit (not shown) provided in the active noise reduction device 10. That is, this storage unit stores the frequency, and the gain and phase for correcting the signal of that frequency.

[0059] The second correction unit 11g converts the second reference signal into a simulated transfer function C m A second corrected reference signal is generated by correcting (filtering) the second corrected reference signal using ^(z). In FIG. 7, the second corrected reference signal is generated by filtering the second corrected reference signal using r C The generated second corrected reference signal is output to the second update unit 11i.

[0060] The first updating unit 11h updates the first reference signal acquired from the sine wave generating unit 11a, the first corrected reference signal acquired from the first correcting unit 11f, the error signal (e'(n)) output by the microphone 53, and the output signal (h 00 (n)), and outputs the calculated first filter coefficients to the first filter unit 11c. The first updating unit 11h also updates the first filter coefficients successively.

[0061] The second updating unit 11i calculates second filter coefficients based on the second reference signal acquired from the cosine wave generating unit 11b, the second corrected reference signal acquired from the second correcting unit 11g, the error signal acquired from the microphone 53, and the output signal acquired from the feedback filter 12, and outputs the calculated second filter coefficients to the second filter unit 11d. The second updating unit 11i also sequentially updates the second filter coefficients.

[0062] The LMS update formula for calculating the first filter coefficient and the second filter coefficient will be explained below. 00 (n) is multiplied by the gain coefficient α to obtain the output signal h 00 Generate (n). h 00(n) is expressed as the following [Equation 7] using [Equation 4].

[0063] h 00 (n)=αy 00 (n)=α{A(n)x s (n)+B(n)x c (n)} [Formula 7]

[0064] The LMS update equations shown in [Equation 5] and [Equation 6] can be expressed as the following [Equation 8] and [Equation 9] using [Equation 7].

[0065] A(n+1) =A(n)-μr s (n)e´´(n)-μx s (n)h 00 (n) =A(n)-μr s (n)e´´(n) -μx s (n)α{A(n)x s (n)+B(n)x c (n)} [Formula 8] B(n+1) =B(n)-μr c (n)e´´(n)-μx c (n)h 00 (n) =B(n)-μr c (n)e´´(n) -μx c (n)α{A(n)x s (n)+B(n)x c (n)} [Formula 9]

[0066] As shown in the above [Equation 8] and [Equation 9], the gain coefficient α is a coefficient for adjusting the update speed of the filter coefficients A(n) and B(n). Multiplication by the gain coefficient α adjusts the cancellation sound c at the position of the microphone 53. mThis is equivalent to numerically generating (n)*y(n). Therefore, the stability and noise reduction amount of the first adaptive filter 11 can be adjusted by the value of the gain coefficient α. If the gain coefficient α is greater than 0, the noise reduction characteristics can be made wider in frequency band. In this case, the larger the value of the gain coefficient α, the more stable the first adaptive filter 11 becomes and the more the noise reduction characteristics can be made wider in frequency band, but the less noise reduction amount becomes.

[0067] [Specific configuration of the first band elimination filter] Next, a description will be given of a specific configuration of the first band elimination filter 14. FIG.

[0068] In other words, the first band elimination filter 14 is an equalizer based on the SAN algorithm. The first band elimination filter 14 includes a second adaptive filter 14a, a gain adjustment unit 14b, and an adder 14c.

[0069] The second adaptive filter 14a is configured to convert the output signal v from the first band elimination filter 14 into out (n), the input signal v to the first band elimination filter 14 is in The second adaptive filter 14a is configured by removing the first correction unit 11f and the second correction unit 11g from the first adaptive filter 11. s (n), b c (n), W1(n), and W2(n) are the x s (n), x c (n), A(n), B(n).

[0070] Here, the frequency of the reference signal in the second adaptive filter 14a is f G1 [Hz], the output signal v from the second adaptive filter 14a out_s(n) is expressed as the following [Equation 10]. Note that the frequency f of the reference signal G1 In other words, is the center frequency of the first band elimination filter 14.

[0071] v out_s (n)=W1(n)b s (n)+W2(n)b c (n) [Formula 10]

[0072] In the second adaptive filter 14a, the LMS update equations for the filter coefficients W1(n) and W2(n) are expressed as the following [Equation 11] and [Equation 12].

[0073] W1(n+1)=W1(n)-μ G1 b s (n) {v in (n)+v out_s (n)} [Formula 11] W2(n+1)=W2(n)-μ G1 b c (n) {v in (n)+v out_s (n)} [Formula 12]

[0074] In addition, μ G1 is a step size parameter that determines the amount of update of the filter coefficients W1(n) and W2(n) per sampling.

[0075] The gain adjustment unit 14b adjusts the output signal v out_s (n) is multiplied by the gain coefficient β. The adder 14c multiplies the output signal v out_s (n) and the input signal v in (n) and the output signal v out (n) to generate the output signal v out (n) is expressed as the following [Equation 13].

[0076] v out (n)=v in (n)+βv out_s (n) [Formula 13]

[0077] The gain coefficient β is a function of the center frequency f G1 This is a parameter for adjusting the amount of gain level reduction in f G1 , step size parameter μ G1 , and the gain coefficient β, it is possible to arbitrarily adjust the characteristics of the first band elimination filter 14. Fig. 9 is a diagram for explaining adjustment of the characteristics of the first band elimination filter 14.

[0078] Here, the second band elimination filter 16 has the same configuration as the first band elimination filter 14, and a description of the specific configuration of the second band elimination filter 16 will be omitted. Both of the first band elimination filter 14 and the second band elimination filter 16 have an acoustic transfer function C m It is inserted to make the phase characteristics of (z) gentler.

[0079] The two band elimination filters differ in their insertion locations (first path or second path). However, for example, the same effect can be theoretically obtained whether both band elimination filters are inserted in the first path or both band elimination filters are inserted in the second path.

[0080] The reason for inserting the two band elimination filters at different locations is to effectively use the dynamic range of the signal on the first path (output side) and the second path (input side). Due to software limitations, if a band elimination filter is installed on only one of the first and second paths to attenuate the signal, it may not be possible to obtain the resolution required for noise control.

[0081] As in Modifications 1 to 3 described below, the two band elimination filters may be individually provided in one-to-one correspondence with the plurality of first adaptive filters 11, or may be shared (commonly used) by the plurality of first adaptive filters 11. In these cases, providing a band elimination filter on each of the first path side (output side) and the second path side (input side) can streamline the design.

[0082] By combining multiple band elimination filters provided in the first or second path, the acoustic transfer function C m The frequency characteristic of (z) can be freely changed. The active noise reduction device 10 may include three or more band elimination filters provided in the first path or the second path.

[0083] The center frequency (frequency of the reference signal) of the first band elimination filter 14 and the center frequency of the second band elimination filter 16 are different, but may be the same. For example, when software constraints prevent one band elimination filter from sufficiently attenuating a signal, it may be possible to use two band elimination filters with the same center frequency.

[0084] Here, the acoustic transfer function C m Since (z) includes not only the transfer characteristics from the speaker 52 to the microphone 53 but also the characteristics of the path passing through the first adaptive filter 11, the acoustic transfer function C m 10 shows the acoustic transfer function C when the first band elimination filter 14 and the second band elimination filter 16 are applied. m10 is a diagram showing changes in the frequency characteristics (gain characteristics and phase characteristics) of (z). In the example of Fig. 10, the band targeted for noise reduction is the band of 35 Hz or more and 45 Hz or less, and the center frequency of one of the first band elimination filter 14 and the second band elimination filter 16 is around 31 Hz, and the center frequency of the other is around 49 Hz.

[0085] As shown in FIG. 10, the first band elimination filter 14 and the second band elimination filter 16 generate an acoustic transfer function C m The phase characteristics of (z) can be made gentler. If you want to reduce noise in the 35Hz to 45Hz band, making the phase characteristics of this band gentler can suppress waterbeds (described below).

[0086] The first band elimination filter 14 and the second band elimination filter 16 are used to m The gain of (z) is attenuated. Therefore, in the active noise reduction device 10, the first gain adjustment unit 15 and the second gain adjustment unit 17 adjust the gain. This makes it possible to prevent the filter coefficients of the first adaptive filter 11 from growing excessively large and to prevent the filter coefficients from being clipped to their upper limit due to software constraints.

[0087] The active noise reduction device 10 may include at least one of the first band elimination filter 14 and the second band elimination filter 16. For example, if the active noise reduction device 10 includes only one of the first band elimination filter 14 and the second band elimination filter 16, and the center frequency of the filter is 45 Hz, the acoustic transfer function C m The frequency characteristics of (z) change as shown in Fig. 11. Fig. 11 shows the acoustic transfer function C when only one of the first band elimination filter 14 and the second band elimination filter 16 is applied. m FIG. 10 is a diagram showing changes in frequency characteristics of (z).

[0088] As shown in FIG. 11, even when only one of the first band elimination filter 14 and the second band elimination filter 16 is applied, the acoustic transfer function C m The phase characteristics of (z) can be made gentler.

[0089] In the active noise reduction device 10, the first band elimination filter 14 and the second band elimination filter 16 are each realized by a second adaptive filter 14a (a one-tap adaptive digital filter). However, the first band elimination filter 14 and the second band elimination filter 16 may be realized by a general digital filter. A band elimination filter realized by a general digital filter has a large phase change due to the occurrence of delay on the low frequency side. For this reason, the band elimination filter realized by the second adaptive filter 14a has a larger phase change due to the acoustic transfer function C m This is suitable for the purpose of making the phase characteristics of (z) gentler.

[0090] Furthermore, each of the first band elimination filter 14 and the second band elimination filter 16 may be realized as hardware using circuit components. In this case, the degree of freedom of the first band elimination filter 14 and the second band elimination filter 16 decreases, but the phase change is small, so that the acoustic transfer function C m This is suitable for the purpose of making the phase characteristics of (z) gentler.

[0091] [Effects, etc.] The active noise reduction device 10 can reduce noise over a wide band while suppressing water beds. Figure 12 is a diagram for explaining why the active noise reduction device 10 can reduce noise over a wide band.

[0092] Figure 12(a) shows a schematic diagram (top) of the noise reduction characteristics in a space 51 when an active noise reduction device (corresponding to Figure 3) is used that has only one first adaptive filter 11 without applying a feedback filter 12, and also shows simulation results (bottom) of the frequency characteristics of the noise level when the device is turned on and off. Note that the horizontal axis of the noise reduction characteristics is frequency, and the vertical axis is the amount of noise reduction (the lower the value, the greater the noise reduction).

[0093] Here, in the active noise reduction device corresponding to (a) of Figure 12, if a feedback filter 12 is applied to the first adaptive filter 11 to widen the bandwidth of the noise reduction characteristics of the first adaptive filter 11 alone, the state of (a) of Figure 12 changes to the state of (b) of Figure 12.

[0094] Furthermore, in the active noise reduction device corresponding to Fig. 12(b), by combining a plurality of first adaptive filters 11 with different center frequencies (frequency of the reference signal) of the noise reduction characteristics, the state of Fig. 12(b) changes to the state of Fig. 12(c). In other words, the noise reduction characteristics are made even wider in bandwidth.

[0095] In the active noise reduction device corresponding to Figure 12(c), the first band elimination filter 14 and the second band elimination filter 16 suppress the waterbed that occurs due to the broadening of the frequency band described in Figures 12(b) and (c), thereby changing the state of Figure 12(c) to the state of Figure 12(d). Note that suppressing waterbed means, more specifically, suppressing the increase in noise in the frequency band where waterbed occurs.

[0096] The active noise reduction device 10 is an active noise reduction device corresponding to (d) of Figure 12. In other words, the active noise reduction device 10 can reduce noise over a wide band.

[0097] [Types of noise reduced, etc.] The active noise reduction device 10 can widen or shift the frequency range in which noise can be reduced by changing the frequencies set in the multiple first adaptive filters 11 and the parameters (various parameters such as α, β, K1, and K2) of the feedback filter 12, the first band elimination filter 14, the first gain adjustment unit 15, the second band elimination filter 16, and the second gain adjustment unit 17. Therefore, the active noise reduction device 10 can reduce various noises in the space 51 inside the vehicle.

[0098] For example, the active noise reduction device 10 can reduce road noise, which is a wide-band noise. In this case, the frequency (frequency of the reference signal) set for each of the plurality of first adaptive filters is a fixed frequency that takes into account the frequency band of the road noise. How the frequencies are set for the plurality of first adaptive filters 11 is determined, for example, empirically or experimentally. Furthermore, various parameters are also set to be suitable for reducing road noise. These settings are determined, for example, empirically or experimentally.

[0099] The active noise reduction device 10 can also reduce engine booming, which is a narrow-band noise. In this case, a signal indicating the engine rotation frequency from the vehicle 50 is input to each of the multiple first adaptive filters 11, and the frequency set in each of the multiple first adaptive filters 11 is dynamically changed according to the engine rotation frequency.

[0100] In this case, the frequency synchronized with the rotation order of the engine may be set to each of the multiple first adaptive filters 11, or the set frequency may be shifted so as to obtain a wideband noise reduction characteristic centered on the frequency synchronized with the rotation order of the engine. For example, if the active noise reduction device 10 includes three first adaptive filters 11 and the frequency synchronized with the rotation order of the engine is f0, the frequencies set to the three first adaptive filters 11 may be calculated as f0-Δf E , f0, f0+Δf E The following configuration is possible.E is the amount of frequency shift.

[0101] Furthermore, when reducing engine boom noise, various parameters are set to settings suitable for reducing engine boom noise. These settings are determined empirically or experimentally, for example.

[0102] Furthermore, the active noise reduction device 10 may be realized as a device capable of both processing to reduce broadband noise such as road noise and processing to reduce narrowband noise such as engine booming. Fig. 13 is a flowchart showing the operation of switching between noise reduction processes. In the following explanation of Fig. 13, the active noise reduction device 10 will be described as including a control unit as a functional component that performs the switching operation.

[0103] The control unit acquires a signal indicating the engine rotation frequency from the vehicle 50 (S11), and determines whether the engine is rotating based on the acquired signal (S12). If the control unit determines that the engine is rotating (Yes in S12), it performs processing to reduce narrowband noise (engine booming noise) (S13). Specifically, the control unit sets frequencies synchronized with the engine rotation order (or shifted frequencies) in the multiple first adaptive filters 11, and then sets various parameters for reducing engine booming noise. In other words, the control unit links the frequency of the reference signal to be processed by the multiple first adaptive filters 11 to the running state of the vehicle 50.

[0104] On the other hand, if the control unit determines that the engine is not rotating (No in S12), it performs a process to reduce wideband noise (road noise, etc.) (S14). Specifically, the control unit sets fixed frequencies for the multiple first adaptive filters 11, and then sets various parameters for reducing wideband noise. In other words, the control unit does not link the frequency of the reference signal that is the target of processing by the multiple first adaptive filters 11 with the running state of the vehicle 50.

[0105] The configuration for reducing road noise when the engine is not rotating is useful in a vehicle 50 that runs using both an engine and a motor, such as a PHV (Plug-in Hybrid Vehicle) or a PHEV (Plug-in Hybrid EV).

[0106] In this way, the active noise reduction device 10 can switch the noise reduction process (whether or not to link the frequency set in the first adaptive filter 11 with the vehicle's running state).

[0107] It is not essential that the noise reduction process be switched based on a signal indicating the engine speed, and the noise reduction process may be switched based on a signal indicating the accelerator opening or the vehicle speed, etc. In other words, it is sufficient that the noise reduction process be switched based on information indicating the vehicle's traveling state (information indicating the moving state of the mobile device).

[0108] The control unit may also switch the frequency range for reducing wideband noise based on a signal output from a noise monitoring microphone installed in space 51. The signal output from the noise monitoring microphone is an example of information indicating the state of noise in space 51.

[0109] Specifically, the control unit analyzes the signal output from the microphone, identifies the frequency range of the noise to be reduced, and changes the frequencies and various parameters set in the multiple first adaptive filters 11 so as to reduce the noise in the identified frequency range. For example, the control unit switches the frequency of the reference signal to be processed by the multiple first adaptive filters 11 between a first setting for reducing noise in a first frequency range and a second setting for reducing noise in a second frequency range different from the first frequency range.

[0110] In this way, the active noise reduction device 10 can change (switch) the frequency range when reducing wideband noise, based on the noise conditions in the space 51.

[0111] [Variation 1] Next, a description will be given of an active noise reduction device according to Modification 1. Fig. 14 is a block diagram showing the functional configuration of the active noise reduction device according to Modification 1.

[0112] The active noise reduction device 10a according to the first modification is realized by, for example, a microprocessor such as a microcontroller or a DSP, and a storage unit. As shown in FIG. 14, the active noise reduction device 10a specifically includes a plurality of adaptive filter modules 18a and a cancellation signal (y 00 ´´(n) and y 01 and an adder 13 that adds the adaptive filter modules 18a and 18b to each other and outputs a cancellation signal (y''(n)) after the addition. These components are implemented by a microcontroller executing a computer program (software) stored in a memory unit, but some of them may also be implemented by hardware (circuits). In the example of FIG. 14, the active noise reduction device 10a includes two adaptive filter modules 18a, but may also include three or more adaptive filter modules 18a.

[0113] Fig. 15 is a block diagram showing the functional configuration of adaptive filter module 18a. As shown in Fig. 15, adaptive filter module 18a includes first adaptive filter 11, feedback filter 12, first band elimination filter 14, first gain adjustment unit 15, second band elimination filter 16, and second gain adjustment unit 17. That is, there is a one-to-one correspondence between first adaptive filter 11, first band elimination filter 14, first gain adjustment unit 15, second band elimination filter 16, and second gain adjustment unit 17.

[0114] As described above, the active noise reduction device 10a includes a plurality of adaptive filter modules 18a. Therefore, it can be said that the active noise reduction device 10a includes a plurality of first band elimination filters 14 provided in the first path, which correspond one-to-one to the plurality of first adaptive filters 11. The same applies to the first gain adjustment unit 15.

[0115] Moreover, it can be said that the active noise reduction device 10a is provided with a plurality of second band elimination filters 16 provided in the second path, which correspond one-to-one to the plurality of first adaptive filters 11. The same applies to the second gain adjustment unit 17.

[0116] In such an active noise reduction device 10a, the first band elimination filter 14, the first gain adjustment unit 15, the second band elimination filter 16, and the second gain adjustment unit 17 can be set individually for each of the multiple first adaptive filters 11. The active noise reduction device 10a can operate in the same way as the active noise reduction device 10.

[0117] [Variation 2] Next, a description will be given of an active noise reduction device according to Modification 2. Fig. 16 is a block diagram showing the functional configuration of the active noise reduction device according to Modification 2.

[0118] The active noise reduction device 10b according to the second modification is realized by, for example, a microprocessor such as a microcontroller or a DSP, and a storage unit. As shown in FIG. 16, the active noise reduction device 10b includes a plurality of adaptive filter modules 18b and a cancellation signal (y 00 ´´(n) and y 01The active noise reduction device 10b includes an adder 13 that adds the adaptive filter modules 18b and 18c to output a cancellation signal (y''(n)) after the addition, a second band elimination filter 16, and a second gain adjuster 17. These components are implemented by a microcontroller executing a computer program (software) stored in a memory unit, but some of them may also be implemented by hardware (circuits). In the example of FIG. 16, the active noise reduction device 10b includes two adaptive filter modules 18b, but may also include three or more adaptive filter modules 18b.

[0119] Fig. 17 is a block diagram showing the functional configuration of adaptive filter module 18b. As shown in Fig. 17, adaptive filter module 18b includes a first adaptive filter 11, a feedback filter 12, a first band elimination filter 14, and a first gain adjustment unit 15. That is, there is a one-to-one correspondence between the first adaptive filter 11, the first band elimination filter 14, and the first gain adjustment unit 15.

[0120] As described above, the active noise reduction device 10b includes a plurality of adaptive filter modules 18b. Therefore, it can be said that the active noise reduction device 10b includes a plurality of first band elimination filters 14 provided in the first path, which correspond one-to-one to the plurality of first adaptive filters 11. The same applies to the first gain adjustment unit 15.

[0121] Moreover, it can be said that the active noise reduction device 10b includes a single second band elimination filter 16 provided in the second path, which is common to the plurality of first adaptive filters 11. The same applies to the second gain adjustment unit 17.

[0122] In such an active noise reduction device 10b, the first band elimination filter 14 and the first gain adjuster 15 can be set individually for each of the multiple first adaptive filters 11. Also, in the active noise reduction device 10b, the settings of the second band elimination filter 16 and the second gain adjuster 17 can be made common to the multiple first adaptive filters 11. The active noise reduction device 10b can operate in the same way as the active noise reduction device 10.

[0123] [Variation 3] Next, a description will be given of an active noise reduction device according to Modification 3. Fig. 18 is a block diagram showing the functional configuration of the active noise reduction device according to Modification 3.

[0124] The active noise reduction device 10c according to the third modification is realized by, for example, a microprocessor such as a microcontroller or a DSP, and a storage unit. As shown in FIG. 18, the active noise reduction device 10c specifically includes a plurality of adaptive filter modules 18c and a cancellation signal (y 00 (n) and y 01 The active noise reduction device 10c includes an adder 13 that adds the signals y(n) and y(n) together and outputs a cancellation signal (y(n)) after the addition, a first band elimination filter 14, and a first gain adjuster 15. These components are implemented by a microcontroller executing a computer program (software) stored in a memory unit, but some of them may also be implemented by hardware (circuits). In the example of Fig. 18, the active noise reduction device 10c includes two adaptive filter modules 18c, but may also include three or more adaptive filter modules 18c.

[0125] Fig. 19 is a block diagram showing the functional configuration of adaptive filter module 18c. As shown in Fig. 19, adaptive filter module 18c includes first adaptive filter 11, feedback filter 12, second band elimination filter 16, and second gain adjustment unit 17. That is, there is a one-to-one correspondence between first adaptive filter 11, second band elimination filter 16, and second gain adjustment unit 17.

[0126] As described above, the active noise reduction device 10c includes a plurality of adaptive filter modules 18c. Therefore, it can be said that the active noise reduction device 10c includes a plurality of second band elimination filters 16 provided in the second path, which correspond one-to-one to the plurality of first adaptive filters 11. The same applies to the second gain adjustment unit 17.

[0127] Moreover, it can be said that the active noise reduction device 10c includes a single first band elimination filter 14 provided in the first path, which is common to the plurality of first adaptive filters 11. The same applies to the first gain adjustment unit 15.

[0128] In such an active noise reduction device 10c, the second band elimination filter 16 and the second gain adjuster 17 can be set individually for each of the multiple first adaptive filters 11. Also, in the active noise reduction device 10c, the settings of the first band elimination filter 14 and the first gain adjuster 15 can be made common to the multiple first adaptive filters 11. The active noise reduction device 10c can operate in the same way as the active noise reduction device 10.

[0129] [Effects, etc.] As described above, the active noise reduction device 10 is an active noise reduction device that reduces noise in a space 51 in which a speaker 52 and a microphone 53 are provided by outputting a cancellation sound from the speaker 52. The active noise reduction device 10 includes a plurality of first adaptive filters 11, each of which outputs a cancellation signal used to output a cancellation sound by applying a filter coefficient that is successively updated based on an error signal output from the microphone 53 to a reference signal having a specific frequency, a plurality of feedback filters 12, each of which multiplies the cancellation signal output by the first adaptive filter 11 corresponding to the feedback filter by a gain coefficient and outputs the result to the first adaptive filter, an adder 13 that adds the cancellation signals output by the plurality of first adaptive filters 11 and outputs the added cancellation signal, and a band elimination filter provided on at least one of a first path from each of the plurality of first adaptive filters 11 to the speaker 52 and a second path from the microphone 53 to each of the plurality of first adaptive filters 11.

[0130] Such an active noise reduction device 10 can improve the degree of freedom in the frequency range in which noise can be reduced.

[0131] Moreover, for example, the active noise reduction device 10 further includes a gain adjuster provided in at least one of the paths.

[0132] Such an active noise reduction device 10 can prevent the filter coefficients in the first adaptive filter 11 from growing excessively large, and can prevent the filter coefficients from being clipped to an upper limit due to software constraints.

[0133] Also, for example, a gain adjuster is provided on each of the first path and the second path.

[0134] Such an active noise reduction device 10 can prevent the filter coefficient of the first adaptive filter 11 from growing excessively large while taking into consideration the dynamic range of the signal on both the first path side (output side) and the second path side (input side).

[0135] Also, for example, a band elimination filter is provided in each of the first path and the second path.

[0136] The active noise reduction device 10 calculates the acoustic transfer function C while taking into consideration the dynamic range of the signal on the first path side (output side) and the second path side (input side). m The phase characteristics of (z) can be made gentler.

[0137] Also, for example, the band elimination filter is realized by the second adaptive filter 14a. The second adaptive filter 14a performs a process of applying filter coefficients, which are successively updated based on the input signal to the band elimination filter, to a reference signal having a specific frequency in order to generate an output signal from the band elimination filter.

[0138] Such an active noise reduction device 10 has an acoustic transfer function C m The phase characteristics of (z) can be made gentler.

[0139] Furthermore, for example, the active noise reduction device 10 is provided with a plurality of band elimination filters, and the frequency of the reference signal that is processed by one of the plurality of second adaptive filters 14a corresponding to the plurality of band elimination filters is different from the frequency of the reference signal that is processed by another of the plurality of second adaptive filters 14a.

[0140] Such an active noise reduction device 10 uses a combination of multiple band elimination filters with different center frequencies to achieve an acoustic transfer function C m The phase characteristics of (z) can be made gentler.

[0141] Furthermore, for example, the frequency of the reference signal that one of the plurality of first adaptive filters 11 processes is different from the frequency of the reference signal that another of the plurality of first adaptive filters 11 processes.

[0142] Such an active noise reduction device 10 can achieve a wide bandwidth of noise reduction characteristics by combining a plurality of first adaptive filters 11.

[0143] Also, for example, the active noise reduction device 10a is equipped with, as band elimination filters, a plurality of first band elimination filters 14 provided in the first path that correspond one-to-one to the plurality of first adaptive filters 11, and a plurality of second band elimination filters 16 provided in the second path that correspond one-to-one to the plurality of first adaptive filters 11.

[0144] In such an active noise reduction device 10a, the first band elimination filter 14 and the second band elimination filter 16 can be set individually for each of the plurality of first adaptive filters 11.

[0145] Also, for example, the active noise reduction device 10b is equipped with, as band elimination filters, a plurality of first band elimination filters 14 provided in the first path that correspond one-to-one to the plurality of first adaptive filters 11, and a second band elimination filter 16 provided in the second path that is common to the plurality of first adaptive filters 11.

[0146] In such an active noise reduction device 10b, the first band elimination filter 14 can be set individually for each of the multiple first adaptive filters 11. Also, in the active noise reduction device 10b, the second band elimination filter 16 can be set in common for the multiple first adaptive filters 11.

[0147] Also, for example, the active noise reduction device 10c includes, as band elimination filters, a first band elimination filter 14 provided in the first path that is common to the multiple first adaptive filters 11, and multiple second band elimination filters 16 provided in the second path that correspond one-to-one to the multiple first adaptive filters 11.

[0148] In such an active noise reduction device 10c, the second band elimination filter 16 can be set individually for each of the multiple first adaptive filters 11. Also, in the active noise reduction device 10c, the setting of the first band elimination filter 14 can be made common to the multiple first adaptive filters 11.

[0149] Furthermore, for example, the space 51 is a space inside a mobile device, and the active noise reduction device 10 includes a control unit that acquires information indicating the moving state of the mobile device. Based on the acquired information indicating the moving state of the mobile device, the control unit switches whether or not to link the frequencies of the reference signals that are processed by the multiple first adaptive filters 11 to the moving state of the mobile device.

[0150] Such an active noise reduction device 10 can switch between processing for reducing narrow-band noise and processing for reducing broad-band noise.

[0151] Furthermore, for example, the active noise reduction device 10 includes a control unit that acquires information indicating the state of the noise. Based on the acquired information indicating the state of the noise, the control unit switches the frequency of the reference signal to be processed by the plurality of first adaptive filters between a first setting for reducing noise in a first frequency range and a second setting for reducing noise in a second frequency range different from the first frequency range.

[0152] Such an active noise reduction device 10 can switch the frequency range in which noise is reduced.

[0153] The mobile device also includes an active noise reduction device 10 (or an active noise reduction device 10a, 10b, or 10c), a speaker 52, and a microphone 53.

[0154] In the space inside such a mobile device, the degree of freedom in the frequency range in which noise can be reduced is improved.

[0155] (Other embodiments) Although the embodiments have been described above, the present disclosure is not limited to the above-described embodiments.

[0156] For example, the active noise reduction device according to the above-described embodiment may be mounted on a mobile device other than a vehicle. The mobile device may be, for example, an aircraft or a ship. Furthermore, the present disclosure may be realized as such a mobile device other than a vehicle.

[0157] The configuration of the active noise reduction device according to the above embodiment is an example. For example, the active noise reduction device may include components such as a D / A converter, a low-pass filter (LPF), a high-pass filter (HPF), a power amplifier, or an A / D converter.

[0158] Furthermore, the processing performed by the active noise reduction device according to the above embodiment is merely an example. For example, some of the processing described in the above embodiment may be realized by analog signal processing rather than digital signal processing.

[0159] Furthermore, for example, in the above-described embodiment, the processing performed by a specific processing unit may be performed by another processing unit, the order of multiple processing operations may be changed, or multiple processing operations may be performed in parallel.

[0160] Furthermore, the general or specific aspects of the present disclosure may be realized as a system, an apparatus, a method, an integrated circuit, a computer program, or a non-transitory recording medium such as a computer-readable CD-ROM, or as any combination of a system, an apparatus, a method, an integrated circuit, a computer program, and a computer-readable non-transitory recording medium.

[0161] For example, the present disclosure may be realized as a noise reduction method executed by a computer such as an active noise reduction device (DSP), or as a program for causing a computer (DSP) to execute the active noise reduction method. Furthermore, the present disclosure may be realized as a noise reduction system including an active noise reduction device according to the above-described embodiment, a speaker (sound output device), and a microphone (sound collection device).

[0162] Furthermore, the order of the multiple processes in the operation of the active noise reduction device described in the above embodiment is an example. The order of the multiple processes may be changed, or the multiple processes may be executed in parallel.

[0163] In addition, this disclosure also includes forms obtained by applying various modifications to each embodiment that a person skilled in the art would think of, or forms realized by arbitrarily combining the components and functions of each embodiment within the scope that does not deviate from the intent of this disclosure. [Industrial Applicability]

[0164] The active noise reduction device of the present disclosure is useful, for example, as a device for reducing noise inside a vehicle cabin. [Explanation of symbols]

[0165] 10, 10a, 10b, 10c Active noise reduction device 11 First adaptive filter 11a Sine wave generator 11b Cosine wave generator 11c First filter section 11d Second filter section 11e Addition section 11f 1st correction section 11g 2nd correction section 11h 1st update part 11i 2nd update part 12 Feedback Filter 13 Addition section 14 1st band elimination filter 14a Second adaptive filter 14b Gain adjustment section 14c Addition section 15 First gain adjustment section 16 Second band elimination filter 17 Second gain adjustment section 18a, 18b, 18c Adaptive Filter Modules 50 vehicles 51 Space 52 Speaker 53 Microphone

Claims

1. An active noise reduction device that reduces noise in a space in which a speaker and a microphone are installed by outputting a cancellation sound from the speaker, a plurality of first adaptive filters, each of which outputs a cancellation signal used to output the cancellation sound by applying a filter coefficient that is successively updated based on the error signal output from the microphone to a reference signal having a specific frequency; a plurality of feedback filters, each of which multiplies the cancellation signal output by the first adaptive filter corresponding to the feedback filter by a gain coefficient and outputs the result to the first adaptive filter; an adder that adds the cancellation signals output from the plurality of first adaptive filters and outputs the added cancellation signal; a band elimination filter provided on at least one of a first path from each of the plurality of first adaptive filters to the speaker and a second path from the microphone to each of the plurality of first adaptive filters. Active noise reduction devices.

2. Further, a gain adjuster is provided in at least one of the paths.

2. The active noise reduction device of claim 1.

3. The gain adjuster is provided on each of the first path and the second path.

3. An active noise reduction device according to claim 2.

4. The band elimination filter is provided on each of the first path and the second path.

4. An active noise reduction device according to claim 1.

5. the band elimination filter is realized by a second adaptive filter; The second adaptive filter applies a filter coefficient, which is successively updated based on an input signal to the band elimination filter, to a reference signal having a specific frequency in order to generate an output signal from the band elimination filter. An active noise reduction device according to any one of claims 1 to 4.

6. the active noise reduction device comprises a plurality of the band elimination filters, The frequency of the reference signal to be processed by one of the plurality of second adaptive filters corresponding to the plurality of band elimination filters is different from the frequency of the reference signal to be processed by another of the plurality of second adaptive filters.

6. An active noise reduction device according to claim 5.

7. The frequency of the reference signal that is the target of processing by one of the plurality of first adaptive filters is different from the frequency of the reference signal that is the target of processing by another of the plurality of first adaptive filters. An active noise reduction device according to any one of claims 1 to 6.

8. The active noise reduction device includes, as the band elimination filters, a plurality of first band elimination filters provided in the first path, which correspond one-to-one to the plurality of first adaptive filters, and a plurality of second band elimination filters provided in the second path, which correspond one-to-one to the plurality of first adaptive filters. An active noise reduction device according to any one of claims 4 to 7.

9. The active noise reduction device includes, as the band elimination filters, a plurality of first band elimination filters provided in the first path, which correspond one-to-one to the plurality of first adaptive filters, and a second band elimination filter provided in the second path, which is common to the plurality of first adaptive filters. An active noise reduction device according to any one of claims 4 to 7.

10. The active noise reduction device includes, as the band elimination filters, a first band elimination filter provided in the first path that is common to the plurality of first adaptive filters, and a plurality of second band elimination filters provided in the second path that correspond one-to-one to the plurality of first adaptive filters. An active noise reduction device according to any one of claims 4 to 7.

11. the space is a space within a mobile device, the active noise reduction device includes a control unit that acquires information indicating a moving state of the mobile device; The control unit switches whether or not to link the frequency of the reference signal to be processed by the plurality of first adaptive filters with the moving state of the mobile body device, based on the acquired information indicating the moving state of the mobile body device. An active noise reduction device according to any one of claims 1 to 10.

12. the active noise reduction device includes a control unit that acquires information indicating the noise state, The control unit switches, based on the acquired information indicating the state of the noise, the frequency of the reference signal to be processed by the plurality of first adaptive filters between a first setting for reducing noise in a first frequency range and a second setting for reducing noise in a second frequency range different from the first frequency range. An active noise reduction device according to any one of claims 1 to 10.

13. An active noise reduction device according to any one of claims 1 to 12; the speaker; The microphone Mobile device.

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