JPH0619485A - Noise canceling device - Google Patents

Abstract

PURPOSE:To satisfy both convergence and stability at the same time by controlling the value of a step size parameter mu according to the state of noise cancellation. CONSTITUTION:An adaptive signal processing part 14a determines the coefficient by an adaptive filter 14b by performing adaptive signal processing by using the composite sound signal at a noise cancellation point, a reference signal, and the step size parameter mu so that a noise is canceled, and the adaptive filter filtrates the reference signal corresponding to the coefficient to generate and input a noise canceling signal to a speaker 16 and a secondary sound propagation characteristic granting part 14. The secondary sound propagation characteristic granting part 14e gives the same propagation characteristics with a secondary sound propagation system 18 to the adaptive filter output signal and a step size parameter determination part 14f varies the value of the step size parameter used for the adaptive signal processing according to the ratio of the output signal of the secondary sound propagation characteristic granting part 14e and the composite sound signal detected by a microphone 17.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise canceling device, and more particularly to a noise canceling device capable of canceling noise at a predetermined position (observation point) in a vehicle to provide a comfortable vehicle interior environment.

[0002]

2. Description of the Related Art As a noise countermeasure, a method using a sound absorbing material (passive control) has been conventionally known. However, in the method using the sound absorbing material, it is troublesome to form a quiet area where noise is small, and there is a problem that the bass cannot be effectively eliminated. In particular, in order to prevent noise in the passenger compartment of an automobile, there is a problem that the weight of the automobile increases and the noise cannot be effectively eliminated. For this reason, a method (active control) of radiating a noise canceling sound having a phase opposite to that of the noise from the speaker to reduce the noise has been in the spotlight and is being put to practical use in a part of indoor space such as a factory or an office. Also, a method has been proposed in which noise is reduced by active control even in the passenger compartment of an automobile.

FIG. 6 is a block diagram of a conventional device for realizing noise cancellation, 11 is an engine as a noise source, and 12 is a noise source.
Is a rotation speed sensor for detecting the engine rotation speed R, and 13 is a reference signal generator for generating a sine wave signal having a constant amplitude and having a frequency according to the engine rotation speed R as a reference signal S _N. When the noise source is an engine, noise generated by engine rotation has a periodicity (periodic noise), and its frequency depends on the engine speed. For example, in the case of a four-cylinder engine, when the rotation speed is 600 rpm, the frequency of the periodic noise generated in the vehicle interior is 20 Hz, and the rotation speed is 600.
At 0 rpm, the frequency of the periodic noise generated in the vehicle compartment is 200 Hz, which is the second harmonic of the engine speed. Therefore, the reference signal generator 13 determines that the engine speed R
The sine wave signals having various frequencies are sampled at a predetermined sampling speed in accordance with the above, and stored in the ROM. When the engine speed R is input from the speed sensor 12, the digital sine wave signal corresponding to the speed The values are sequentially read from the ROM at the sampling speed and output.

Reference numeral 14 is a noise canceling controller, which receives the reference signal S _N generated from the reference signal generating unit 13 and also causes noise Sn at a noise canceling position (observation point, for example, near the driver's ear) in the vehicle interior. The synthesized sound signal of the cancel sound Sc is input as an error signal E, and adaptive signal processing is performed so as to minimize the error signal and a noise cancel signal Ya is output. The noise cancellation controller 14 includes an adaptive signal processing unit 14a, an adaptive filter 14b having a digital filter configuration, a DA converter 14c that converts an output of the adaptive filter into an analog noise cancellation signal Ya, and a cancellation sound propagation from a speaker to a noise cancellation point. The filter 14d is created based on the transfer function of the system (secondary sound propagation system) 18 and receives the reference signal S _N. Reference numeral 15 is a power amplifier for amplifying the noise canceling signal Ya, 16 is a canceling speaker for radiating the noise canceling sound Sc, 17 is arranged at the noise canceling point, and a synthesized sound of the noise Sn and the canceling sound Sc is detected and synthesized. An error microphone that outputs a sound signal as an error signal E.

The adaptive signal processing unit 14a has a noise canceling point.
Is input via the filter 14d and the error signal E at
Reference signal S_N'Is input and these signals are used to
Suitable to cancel the noise at the sound cancellation point
The adaptive signal processing is performed to determine the coefficient of the adaptive filter 14b.
It For example, the adaptive signal processing unit 14a is a well-known LMS (Least
 Mean Square)
So that the error signal E input from
The coefficient of the adaptive filter 14b is determined. Adaptive filter 1
4b is in accordance with the coefficient determined by the adaptive signal processing unit 14a.
Reference signal S _NDigital filter is applied to the DA
The noise canceling signal Ya is output from the converter 14c.
It The reference signal S_NHas a high correlation with the noise Sn to be deleted.
Sound that is uncorrelated with the reference signal
I won't leave. When the engine 11 rotates, its rotation speed R
Is detected by the rotation speed sensor 12, and the reference signal generator 1
3 is a reference signal S having a frequency corresponding to the engine speed R
_N(Refer to Fig. 7 (a))
Enter in LA14. At this time, generated from the engine 11
Engine sound with periodicity (periodic noise)
Sky with noise propagation system (first-order sound propagation system) having transfer function
It propagates through and reaches the noise cancellation point. Therefore, the noise
The noise (engine sound) Sn at the cancellation point is the level
Is slightly weakened and slightly delayed, as shown in Fig. 7 (b).
Become.

First, the noise canceling controller 14 has, for example, a noise canceling signal Ya whose phase is opposite to that of the reference signal S _N.
Then, the cancel speaker 16 outputs the cancel sound Sc shown in FIG. 7 (c). However, since the noise Sn is out of phase with the noise Sn, the noise is not canceled by the cancel sound Sc, and the error signal E is generated. The noise canceling controller 14 performs adaptive signal processing so that the error signal E is minimized to determine the coefficient of the adaptive filter 14b. In an ideal case, the canceling sound is finally canceled as shown in FIG. 7 (d). The phase of Sc is made opposite to the phase of noise Sn, and the levels are matched to cancel the noise.

In order to simplify the explanation, the above is an example in which there is one noise source, one cancellation sound source (speaker), and one noise cancellation point (observation point). However, in reality, there are a plurality of noise sources and a plurality of points (observation points) where noise is desired to be canceled. Therefore, one speaker cannot cancel noise at each observation point, and a plurality of speakers exist. FIG. 8 is a configuration diagram of a conventional noise canceling device when there are K noise sources, M speakers, and L observation points. Reference numeral 21 is a noise canceling controller that operates to cancel noise at each observation point, and 22 is a primary sound virtual propagation system (noise propagation system) that represents a system in which noise propagates from each noise source (not shown) to each observation point. ), 23 is a secondary sound propagation system (cancellation sound propagation system) expressing a system in which a cancellation sound propagates from each speaker to each observation point, including characteristics of a speaker (not shown), 24
Is a signal combining unit expressing the function of the microphone at each observation point, the addition units 24 _{1 to} 24 ₁ ′ correspond to the microphones at the first observation point, and the addition units 24 _{2 to} 24 ₂ ′ are the microphones at the second observation point. The addition units 24 _{L to} 24 _L ′ correspond to the microphone at the Lth observation point. _{d d1n} ~d dLn is an external noise is not a cancellation target in each observation point.

[0008] In the noise cancellation controller 21, 21a is (are outputted from the reference signal generating section, not shown) the reference signal x _a1n ~x _AKN corresponding to noise generated from the noise source is input, the noise cancellation signal y _a1n ~y A multi-input-multi-output adaptive filter (hereinafter simply referred to as an adaptive filter) for inputting _aMn to each speaker, and 21b is a secondary sound propagation system 23.
Is a filter for creating a filtered X signal created by using each element (propagation element) of the transfer function matrix of
Reference signal x _a1n ~x _AKN corresponding to noise generated from the noise source
Those enter, 21c are input to filtered-X signal r _111n ~r _LMKn output from the error signal e _1n to e _Ln and the filter 21b at each observation point, the noise at each observation point by using these signals It is an adaptive signal processing unit that performs adaptive signal processing so as to cancel and determines the coefficient of the adaptive filter 21a.

FIG. 9 is an explanatory diagram of the primary sound virtual propagation system 22. As shown in FIG. 9A, _K noise sources NG _{1 to} NG _{K are provided.}
The noise generated from the microphone propagates through the primary sound propagation system 22 having a predetermined frequency / phase characteristic, and the microphone (M
IC _{1 to} MIC _L ). Therefore, assuming that the transfer characteristic of the propagation system in which the noise from the i-th noise source NGi reaches the j-th microphone MIC _j is H _ji , the primary sound virtual propagation system 22
Is expressed as shown in FIG. 9 (b), and its transfer function matrix (H) is as follows.

[0010]

[Equation 1]

Each element H _ij of the transfer function matrix (H) is realized by the FIR type digital filter shown in FIG. That is, the delay element DL that sequentially delays the input signal by one sampling time, and the coefficients h ₀ , h ₁ , and
It is realized by a digital filter including a multiplication unit ML that multiplies h ₂ , ... And an addition unit AD that adds the outputs of the multiplication units. 11 is an explanatory diagram of the secondary sound propagation system 23.
As shown in (a), the noise canceling sound generated from each of the speakers SP _{1 to} SP _M propagates through the secondary sound propagating system 23 having a predetermined frequency / phase characteristic, and the microphone MI is provided at each observation point.
To reach the C ₁ ~MIC _L. Therefore, _assuming that the transfer characteristic of the secondary sound propagating system in which the cancel sound based on the i-th noise cancel signal y _ain reaches the j-th microphone MIC _j is C _ji , the secondary sound propagating system 23 is shown in FIG. It is modeled as shown in b), and its transfer function matrix (C) is as follows.

[0012]

[Equation 2]

Each element of the transfer function matrix (C) has the FIR shown in FIG. 10 as in the case of the primary sound virtual propagation system 22.
Type digital filter. That is, the delay element DL that sequentially delays the input signal by one sampling time
, A multiplication unit ML that multiplies each delay element output by the coefficients c ₀ , c ₁ , c ₂ , ..., And an addition unit A that adds each multiplication unit output.
It is realized by a digital filter composed of D. FIG. 12 shows each element C of the transfer function matrix (C) of the secondary sound propagation system 23.
It is a block diagram of the filter 21b for producing the filtered X signal produced using _ij . Updating adaptive signal processing unit 21c and the reference signal _{x a1n} ~x aKn, the coefficients of the adaptive filter by performing adaptive signal processing based on the synthesized speech signal e _1n to e _Ln between noise and canceling sound at each observation point and the adaptive filter 21a is input to a speaker is inputted to the reference signal x _a1n ~x _AKN generate noise cancellation signals y _a1n ~y _aMn,
Cancel the noise at each observation point.

By the way, the noise cancellation signal y _a1n ~y _{a Mn} output from the adaptive filter 21a is as not to reach the observation point, and reaches under the influence of the frequency and phase characteristics of the secondary sound propagation system 23. Therefore, the adaptive signal processing unit 21c does not use the reference signals x _{a1n to} x _{aKn as} they _are , but uses a filtered X LMS (MEFX LMS) algorithm that uses a signal obtained by adding the characteristics of the secondary sound propagation system 23 to the reference signal. Adopted for more advanced noise cancellation control. That, filtered-X LMS The algorithm reference signal x _a1n ~x _AKN adaptation using the filtered signal by the filter 21b (the filtered-X signal) and the synthesized speech signal at each observation point filter 2
The coefficient of 1a is updated.

In FIG. 12, C _ij is the secondary sound propagation system 23.
12 is an FIR digital filter that realizes each element C _ij (see FIG. 11) of the transfer function matrix (C) in FIG. Filter 21b is (passed through a filter for all of the propagation elements) each reference signal x _a1n ~x _AKN in by the action of all the propagation elements filtered-X signal r _111n ~r _LMKn
Is output. That is, the reference signal x
Propagation elements C _{11 to} C _L1 from the first speaker to all the observation points are _applied to _a1n , and filtered X signals r _{111n to} r _{111n to} r
Outputs _L11n, outputs the filtered-X signal r _121n ~r _L21n the reference signal x _a1n from the second speaker by the action of propagation elements C ₁₂ -C _L2 to full observation point, ... reference signals by the action of propagation elements C _1M -C _{L M} to full observation point from the M-th speaker x _a1n filtered-X signal r _{1M1n
~ R LM1n} are output, and similarly, reference signals x _{a2n to} x _aKn
Act on all propagation elements. _{Incidentally, R 11 = (r 111n,} r 211n, ··· r L11n) R 21 = (r 121n, r 221n, ··· r L21n) ··· R M1 = (r 1M1n, r 2M1n, ··· r _LM1n ) ... R _MK = (r _1MKn , r _2MKn , ... R _LMKn )

FIG. 13 shows a multi-input-multi-output adaptive filter 2.
It is a block diagram of 1a, and has the same structure as the primary sound virtual propagation system 22 and the secondary sound propagation system 23. A _11n- A _MKn is F
For example, delay elements DL1 and D configured by an IR type digital filter for sequentially delaying an input signal by one sampling time
l2 ... And the coefficients a ₀ , a ₁ , a ₂ ...
Are implemented by multiplying units ML1, ML2, ML3 ,. The number of delay stages is not limited to two. Each reference signal x
_{By inputting and} adding _a1n to x _aKn to the digital filters A _{11n to} A _1Kn , the noise cancellation signal y _a1n to be input to the first speaker is obtained, and each reference signal x _{a1n to} x.
noise cancellation signal y _a2n to be input to the second speaker is obtained by adding to input _aKn to the digital filter A _21n ~A _2Kn, ···· each reference signal x _a1n ~x
_By inputting and adding _aKn to the digital filters A _{M1n to} A _MKn , the noise cancellation signal y _aMn input to the M-th speaker is obtained.

Each FIR type digital filter A _{11n to} A _MKn in the adaptive filter 21a has three coefficients (two-stage delay).
In the above configuration, the adaptive signal processing unit 21c performs adaptive signal processing for each of the three coefficients of the FIR digital filters A _{11n to} A _MKn to determine the coefficient value. Ie one FIR
The coefficients a ₀ , a ₁ and a ₂ of the type digital filter A _ij are calculated according to the following equation to determine the coefficients a ₀ , a ₁ and a ₂ .

[0018]

[Equation 3]

In equation (1), (n) is the value at the current sampling time, (n-1) is the value one sampling time before, (n-2) is the value two sampling times before, and (n + 1). Means the value from the current time to the next sampling time. Therefore, R _ij (n-2) is the filter 21 corresponding to the reference signal two sampling times before.
This means the output of b, R _ij (n-1) is the filter output according to the reference signal one sampling time before, and R _ij (n) is the filter output according to the reference signal at the current time. Further, mu is a constant of 1 or less (step size parameter), e _n is the composite signal of the noise and canceling sound in the L each observation point.

[0020] according According to the noise cancellation device, adaptive signal processing unit 21c filtered-X signal r _111n ~r _LMKn and synthesized sound signal (error signal between the noise and the canceling sound at each observation point, which is the output of the filter 21b ) E _1n ~ e
Adaptive filter 2 by executing adaptive signal processing based on _Ln
FIR type digital filters A _{11n to} A constituting 1a
The coefficient of _MKn is determined, and the adaptive filter 21a determines the reference signal x
_{a1n ~} x _aKn is input and the noise cancellation signal y _a1n ~ y
_aMn is generated and input to the speakers SP _{1 to} SP _M (FIG. 11), and each speaker acts to cancel the noise at each observation point by generating a cancel sound. After that, the same operation is repeated to converge the coefficient of the adaptive filter 21a to the optimum value and cancel the noise at the noise cancel point.

In FIG. 14, the number of noise sources K = 2 and the number of speakers M =
2 is a configuration diagram of a specific conventional noise canceling device when the number of observation points (the number of microphones) L = 2, and 21a is configured by four FIR type digital filters A ₁₁ , A ₂₁ , A ₁₂ and A _22. adaptive filter, each propagation elements C ₁₁ and 21b the secondary propagation system transfer function matrix _{(C), C 21, C} 12, C
Filters for creating a filtered X signal in which ₂₂ is a digital filter, 21c-1 to 21c-4 are adaptive signal processing units (MEFs).
X LMS algorithm), SP ₁ and SP ₂ are speakers,
MC ₁ and MC ₂ are microphones installed at the observation points.

[0022]

In adaptive signal processing, if the value of the step size parameter μ in equation (1) is large, the coefficient convergence of the adaptive filter is improved (convergence speed becomes faster), and the optimum value is obtained in a short time. Get closer to you. However, when the value of the step size parameter μ is large, overshoot occurs after approaching the optimum value, and the stability decreases. on the other hand,
When the value of the step size parameter μ is small, the convergence speed of the adaptive filter decreases, and it takes a long time to approach the optimum value. However, after approaching the optimum value, overshoot does not occur and stability is improved.

Convergence and stability are both requirements that must be satisfied in order to effectively cancel noise by following its changes, but as mentioned above, these are contradictory requirements. Therefore, the conventional noise canceling device has a problem that it is not possible to satisfy both convergence and stability at the same time. From the above, an object of the present invention is to provide a noise canceling device capable of satisfying both convergence and stability at the same time, improving followability to noise changes, and sufficiently canceling noise.

[0024]

According to the present invention, the above problem is solved by a cancel sound generation source (speaker), a sensor (microphone) for detecting a synthesized sound of noise and a cancel sound at a noise cancel point, and noise cancel. Noise cancellation controller that performs adaptive signal processing to output noise cancellation signal by performing adaptive signal processing so as to cancel noise at the noise cancellation point using the synthesized sound signal at the point, the reference signal, and the step size parameter μ, and cancels the noise cancellation signal Propagation characteristic imparting means for imparting a propagation characteristic equivalent to that of a cancel sound propagation system from a sound source to a sensor, and a step size parameter used for adaptive signal processing according to a ratio of an output signal of the propagation characteristic imparting means and a synthesized sound signal. and a step size parameter determining means for determining the value of μ.

[0025]

[Operation] The noise canceling controller determines the coefficient of the adaptive filter by performing the adaptive signal processing so as to cancel the noise at the noise canceling point by using the synthesized sound signal at the noise canceling point, the reference signal corresponding to the noise, and the step size parameter. Then, the adaptive filter subjects the reference signal to filter processing according to the coefficient to generate a noise cancellation signal, and inputs the noise cancellation signal to the speaker and the propagation characteristic imparting means. The speaker outputs a cancel sound to cancel the noise at the noise cancel point. The propagation characteristic imparting means imparts to the adaptive filter output (noise cancellation signal) a propagation characteristic equivalent to that of the cancel sound propagation system, and the step size parameter determining means determines the ratio between the output signal of the propagation characteristic imparting means and the synthesized sound signal. The value of the step size parameter used for adaptive signal processing is determined. That is, when the noise is not sufficiently canceled, the value of the step size parameter μ is increased because the synthesized sound signal is large and the ratio is large. Also, depending on the progress of the noise cancellation situation,
That is, as the ratio becomes smaller, the value of the step size parameter becomes smaller. This makes it possible to satisfy both the coefficient convergence and the stability of the adaptive filter. In addition, a bandpass filter that passes only the frequency component of the noise to be canceled that is included in the synthesized sound signal is provided.
The output signal of the bandpass filter is used as a synthesized sound signal to calculate the ratio. By doing so, it is possible to provide a noise canceling device that is not affected by noise other than the noise to be canceled and has a faster convergence speed and excellent stability.

[0026]

【Example】

(a) Overall configuration of the first embodiment of the present invention FIG. 1 is a configuration diagram of a noise canceling device according to an embodiment of the present invention. The same functional parts as those of the conventional device of FIG. There is. In the figure, 11 is an engine which is a noise source,
Reference numeral 2 is a rotation speed sensor that detects the engine rotation speed R, and 13 is a reference signal generation unit that generates a sine wave signal of a constant amplitude having a frequency according to the engine rotation speed R as a reference signal S _N. When the noise source is an engine, noise generated by engine rotation has a periodicity (periodic noise), and the noise frequency depends on the engine speed. Therefore, the reference signal generator 13 samples sine wave signals having various frequencies according to the engine speed R at a predetermined sampling rate and stores them in the ROM, and the engine speed R is input from the engine speed sensor 12. At this time, the digital value of the sine wave signal corresponding to the rotation speed is sequentially read from the ROM at the sampling speed and output.

Reference numeral 14 denotes a noise canceling controller, which receives the reference signal S _N generated from the reference signal generating unit 13 and also causes a noise Sn at a noise canceling position in the passenger compartment (observation point, for example, near the driver's ear). The synthesized sound signal of the cancel sound Sc is input as an error signal E, and adaptive noise signal processing based on the LMS algorithm is performed so as to minimize the error signal and a noise cancel signal Ya is output. Reference numeral 15 is a power amplifier that amplifies the analog noise canceling signal Ya, 16 is a canceling speaker (canceling sound generating source) that emits the noise canceling sound Sc, and 17 is arranged at a noise canceling point (observation point).
An error microphone that detects a synthesized sound of the noise Sn and the cancel sound Sc and outputs the synthesized sound signal as an error signal E. Reference numeral 18 denotes a cancel sound propagation system (secondary sound propagation) in which the cancel sound propagates from the speaker to the noise cancellation point. System). still,
In FIG. 1, in order to simplify the explanation, a noise source, a speaker,
Although the case where there is one error microphone is shown, the present invention is not limited to such a case, but can be applied to a complex system provided with a plurality of noise sources, a plurality of speakers, and a plurality of error microphones.

Noise Canceling Controller The noise canceling controller 14 is the adaptive signal processing unit 1
4a and adaptive filter 14b of digital filter configuration
And a DA converter 14c for converting the digital noise cancellation signal Ya output from the adaptive filter into an analog noise cancellation signal, and the transfer function of the secondary sound propagation system 18 (transfer function matrix in the complex system). , A filter (filtered X signal creation filter) 14d for creating a filtered X signal used for adaptive signal processing, and a noise canceling signal Ya having a propagation characteristic equivalent to that of the secondary sound propagation system 18. The value of the step size parameter μ of the equation (1) used for adaptive signal processing is determined according to the ratio of the output signal Yc ′ of the secondary sound propagation characteristic imparting unit 14e and the output signal Yc ′ of the secondary sound propagation characteristic imparting unit 14e. The step size parameter determining unit 14f is provided.

The adaptive signal processing unit 14a receives the synthesized sound signal (error signal) E at the noise cancellation point and the filtered X signal S _N ′ output through the filter 14d, and uses these signals to obtain the equation (1). Accordingly, adaptive signal processing is performed so as to cancel the noise at the noise canceling point, and the coefficient of the adaptive filter 14b is determined. That is, the adaptive signal processing unit 14a uses the LMS (Least Mean Square)
e) According to the adaptive algorithm, the coefficient of the adaptive filter 14b is determined so that the synthetic sound signal (error signal) E input from the error microphone 17 is minimized. Adaptive filter 1
Reference numeral 4b performs digital filter processing on the reference signal S _N according to the coefficient determined by the adaptive signal processing unit 14a and outputs a noise cancel signal Ya.

Secondary sound propagation characteristic imparting section FIG. 2 is an explanatory diagram of the secondary sound propagation characteristic imparting section 14e, in which the number of noise sources K = 2, the number of speakers M = 2, and the number of observation points (the number of microphones) L = 2. Then, it is configured as follows. In FIG. 2, 14e is a secondary sound propagation characteristic imparting unit, 18 is a secondary sound propagation system, SP _{1 to} SP ₂ are speakers, and MIC _{1 to} MIC ₂ are 2.
It is a microphone installed at two noise canceling points. The noise canceling sounds generated from the speakers SP _{1 to} SP ₂ propagate through the secondary sound propagating system 18 having predetermined frequency / phase characteristics, and the microphones MIC _{1 to} MI ₁ provided at the noise canceling points.
Reach C ₂ . _Assuming that the transfer characteristic of the secondary sound propagation system in which the cancel sound based on the i-th noise cancel signal y _ain reaches the j-th microphone MIC _j is C _ji , the secondary sound propagation characteristic adding unit 14e determines the secondary sound propagation characteristic. It is configured to simulate the sound propagation system 18 and is modeled as shown in FIG. In this secondary sound propagation characteristic imparting unit 14e, 14e-1 to 14e-4 are FIR type digital filters that realize the propagation element C _ji of the secondary sound propagation system, and 14e-5 and 14e-6 are addition units. is there. Adder 1
4e-5 of the output signal y _C1N 'an adder 14e-6 of the output signal y _c2n' each noise cancellation signal y _a1n, can be regarded as a noise cancellation sound in the noise cancellation point when you enter y _a2n the speaker .

Step size parameter determining section The step size parameter determining section 14f changes the value of the step size parameter in the equation (1) according to the magnitude of the volume of the sound at the noise canceling point. When noise cancellation is ideally performed, the synthetic sound signal e
_1n and e _2n (see FIG. 2) are 0, and therefore the ratio η between the noises d _1n and d _2n desired to be canceled and the synthesized sound signals e _1n and e _2n .
(E _1n / d _1n , e _2n / d _2n ) becomes 0. However, when the noise cancellation is not sufficiently performed, the synthesized sound signals e _1n and e _2n become large and the ratio η becomes large. That is, the ratio η increases when the muffling volume is small, and the ratio η decreases when the muffling volume is large. In the ratio calculation, the sign is not taken into consideration and the calculation is performed with an absolute value. Therefore, the step size parameter determination unit 14f calculates the ratio η and changes the value of the step size parameter μ according to the ratio so as to satisfy both high convergence speed and stability. By the way, the ratio η is η = (synthetic sound signal e) / (noise d to be canceled) (4). The synthesized sound signal e is a microphone output and can be detected, but the noise d cannot be detected. However, there is a correlation between the noise d and the cancel sound, and the cancel sound increases as the noise increases, the cancel sound decreases as the noise decreases, and the noise and the cancel sound are equal in an ideal noise canceling state. From this, each noise cancellation point
The loudness of the cancellation sound at the (observation point) can be assumed to be the noise d to be canceled. By making such an assumption, the step size parameter determination unit 14f
Is calculated by the following equation η = (synthesized sound signal e) / (cancellation sound at the observation point) (5). The cancel sound at each observation point is the output signal y _c1n ′, y _c2n ′ of the secondary sound propagation characteristic imparting unit 14e described above.

FIG. 3 shows the step size parameter determining section.
It is a block diagram, the number of noise sources K = 2, the number of speakers M = 2,
This is the case where the number of measurement points (the number of microphones) L = 2. 14f-1 is the ratio
Computation unit, which is a synthetic signal e_1n, E_2nAnd secondary sound propagation characteristics
Output signal y of the sex imparting section 14e_c1n′, Y_c2nEnter '
The ratio η₁(= E_1n/ Y_c1n′), Η₂
(= E_2n/ Y_c2n′) Is calculated. 14f-2 corresponds to the ratio η value
Corresponding step size parameter value μ (to change
Is an η-μ coefficient correspondence table to be stored.
If the ratio is 1 or more, the noise canceling operation is effective.
Cancel operation is stopped because it is not working properly. 14f-
3 is a step size parameter determination unit, and each ratio
η₁, Η₂Step size parameter μ according to₁, μ ₂To
Calculated from the η-μ coefficient correspondence table, and the average value is
The minimum or maximum value is the step size parameter.
, And input to the adaptive signal processing unit 14a.
Note that if the minimum value is used, stability is emphasized and maximum
If a value is used, the convergence is relatively important.

[0033] When the entire operation the engine 11 is rotated, the rotation speed R is detected by the rotational speed sensor 12, the reference signal generator 13 generates a reference signal S _N having a frequency corresponding to the engine speed R, the noise cancellation Input to the controller 14. At this time, a periodic engine sound (periodic noise) generated from the engine 11 propagates through the air having a noise propagation system (primary sound propagation system) having a predetermined transfer function and reaches a noise cancellation point. The error microphone 17 detects the synthesized sound of the noise and the cancel sound at the noise cancel point, and inputs the synthesized sound signal (error signal) E to the adaptive signal processing unit 14a. In parallel with the above, the reference signal S _N is input to the filtered X signal generation filter 14 d, and the filtered X signal S _N ′ used for adaptive signal processing is input to the adaptive signal processing unit 14 a. The adaptive signal processing unit 14a is a synthetic sound signal (error signal).
Using E and the filtered X signal S _N ′ output from the filter 14d and the step size parameter μ (the initial value is 0.5, for example), adaptive signal processing is performed according to the equation (1), and the coefficient of the adaptive filter 14b is calculated. decide.

The adaptive filter 14b is an adaptive signal processing unit 14
The reference signal S _N is digitally filtered according to the coefficient determined by a, and the noise cancellation signal Ya is output. The DA converter 14c outputs the adaptive filter output to DA.
It is converted and input to the speaker 16. As a result, the noise canceling sound is output from the speaker, and the secondary sound propagation system 18
To reach the noise canceling point and act to cancel the noise. The error microphone 17 detects the synthesized sound at the noise cancellation point and inputs it to the adaptive signal processing unit 14a and the step size parameter determination unit 14f. In parallel with this, the secondary sound propagation characteristic imparting unit 14e imparts the noise cancellation signal Ya output from the adaptive filter 14b with a propagation characteristic equivalent to that of the cancellation sound propagation system 18 to cancel noise signal Yc 'at the noise cancellation point. Is generated and input to the step size parameter determination unit 14f. The step size parameter determination unit 14f determines the step size parameter μ used for adaptive signal processing according to the ratio η (= E / Yc ') between the output signal Yc' of the secondary sound propagation characteristic imparting unit 14e and the synthesized sound signal E. Then, the adaptive signal processing unit 14
Enter in a. The adaptive signal processing unit 14a executes adaptive signal processing using the input step size parameter μ. Thereafter, in the same manner, the noise is canceled by executing the adaptive signal processing while changing μ according to the value of the ratio η, that is, according to the noise canceling state. In this way, when the noise cancellation state is bad, the value of the step size parameter μ can be increased to improve the convergence, and the coefficient value of the adaptive filter can be brought close to the optimum value in a short time. Since μ is reduced according to the degree of noise cancellation, sufficient stability can be maintained at the time when the value approaches the optimum value, and a sufficient noise prevention effect can be exhibited.

(B) Second Embodiment of the Present Invention FIG. 4 is a block diagram of another embodiment of the present invention, in which the same parts as those in the first embodiment are designated by the same reference numerals. The second embodiment is different from the first embodiment in that a tracking control filter (bandpass filter) that passes only the frequency component of the noise to be canceled included in the synthesized sound signal E is included.
19 is provided, and the step size parameter determination unit 14f determines that the tracking control filter 19
This is the point where the ratio η is calculated by using the signal output from the synthesized sound signal. The noise at the noise cancellation point includes noise to be canceled and external noise that is not a target of cancellation. For this reason, the synthesized sound signal E output from the error microphone 17 includes noise that is not the cancellation target, the accurate ratio η cannot be calculated, and an incorrect step size parameter μ may be determined. Therefore, in the second embodiment, only the frequency component of the noise to be truly canceled from the synthesized sound signal E is extracted to calculate the ratio η, and the step size parameter μ is determined based on the ratio η. By doing so, the step size parameter μ can be correctly determined without being affected by external noise other than the noise to be canceled, and it is possible to provide a noise canceling device that is more excellent in convergence and stability.

Tracking Control Filter The tracking control filter 19 includes a plurality of filters having a center frequency and a band corresponding to the frequency of periodic noise (eg engine sound), and selects a predetermined filter based on the engine speed R. The signal that has passed through the filter is output as a synthesized sound signal E '. FIG. 5 shows the tracking control filter 19
19a to 19n are filters having center frequencies and bandwidths corresponding to some engine speed ranges, in other words, some frequency ranges of periodic noise, and 19p is an engine. This is a filter selection circuit that inputs the synthesized sound signal E only to the filter corresponding to the rotation speed R. When the engine speed R is 600 rpm, the frequency of the periodic noise is 20 Hz. Therefore, rotation speed 6
A filter corresponding to 00 rpm has a cutoff frequency of 3
It becomes a low-pass filter of about 0 Hz. Further, when the engine speed R is 6000 rpm, the frequency of the periodic noise is 200 Hz. Therefore, the filter corresponding to the engine speed is a bandpass filter having a center frequency of 200 Hz and a bandwidth of about 50 Hz.

When the entire operation engine 11 rotates, the rotation speed R is detected by the rotation speed sensor 12 and input to the reference signal generator 13 and the tracking control filter 19. When the engine speed R is input, the reference signal generator 13 generates a reference signal S _N having a frequency corresponding to the engine speed R and inputs the reference signal S _N to the noise canceling controller 14. The tracking control filter 19 is set to a frequency band according to the rotation speed. That is, a predetermined filter corresponding to the rotation speed is selected. A periodic engine sound (periodic noise) generated from the engine 11 propagates through the air having a noise propagation system (primary sound propagation system) having a predetermined transfer function and reaches a noise cancellation point. The error microphone 17 detects the synthesized sound of the noise and the cancellation sound at the noise cancellation point,
The synthetic sound signal (error signal) E is input to the adaptive signal processing unit 14a. In parallel with the above, the filtered X signal generation filter 14d receives the reference signal S _N and outputs the filtered X signal S _N ′ used for adaptive signal processing to the adaptive signal processing unit 1.
Input to 4a. The adaptive signal processing unit 14a receives the synthesized sound signal (error signal) E, the filtered X signal S _N ′ output from the filter 14d, and the step size parameter μ.
Using (the initial value is, for example, 0.5), adaptive signal processing is performed according to the equation (1) to determine the coefficient of the adaptive filter 14b.

The adaptive filter 14b is an adaptive signal processing unit 14
The reference signal S _N is digitally filtered according to the coefficient determined by a, and the noise cancellation signal Ya is output. The DA converter 14c outputs the adaptive filter output to DA.
It is converted and input to the speaker 16. As a result, the noise canceling sound is output from the speaker, and the secondary sound propagation system 18
To reach the noise canceling point and act to cancel the noise. The error microphone 17 detects the synthesized sound at the noise cancellation point and inputs it to the adaptive signal processing unit 14a and the tracking control filter 19. Since the frequency band of the periodic noise according to the engine speed is set in the tracking control filter 19, the tracking control filter 19 removes the noise signal outside the band of the periodic noise, in other words, the periodic noise. Only the component in the same band as is passed as a synthesized sound signal E ', and is input to the step size parameter determination unit 14f. In parallel with this, the secondary sound propagation characteristic imparting unit 14e causes the noise cancel signal Y output from the adaptive filter 14b.
Propagation characteristics equivalent to those of the cancel sound propagation system 18 are added to a to generate a cancel sound signal Yc ′ at the noise cancel point, which is input to the step size parameter determination unit 14f. The step size parameter determining unit 14f uses the step size parameter μ for adaptive signal processing according to the ratio η (= E ′ / Yc ′) between the output signal Yc ′ of the secondary sound propagation characteristic imparting unit 14e and the synthesized sound signal E ′. Is determined and input to the adaptive signal processing unit 14a.

The adaptive signal processing unit 14a executes adaptive signal processing using the input step size parameter μ, and thereafter, similarly changes μ according to the value of the ratio η, that is, according to the noise canceling state. Meanwhile, the adaptive signal processing is executed to cancel the noise. As described above, since the filter in which the band of the periodic noise is set is provided, noise other than the periodic noise that is truly desired to be canceled can be removed from the synthesized sound signal, and therefore, the step size parameter μ can be correctly determined and the time can be reduced in a short time. And, the noise can be canceled stably. Although the present invention has been described above with reference to the embodiments, the present invention can be variously modified according to the gist of the present invention described in the claims, and the present invention does not exclude these.

[0040]

As described above, according to the present invention, a propagation characteristic giving means for giving a noise canceling signal a propagation characteristic equivalent to that of a cancel sound propagating system and a ratio of an output signal of the propagation characteristic giving means and a synthesized sound signal are provided. When the noise is not sufficiently canceled (when the synthesized sound signal is large and the ratio is large), the step size parameter μ of the step size parameter μ is changed. By increasing the value and decreasing the value of the step size parameter according to the degree of noise cancellation (as the ratio decreases), it is possible to satisfy both the coefficient convergence and stability of the adaptive filter. It can be canceled effectively. Further, according to the present invention, since the bandpass filter that passes only the frequency component of the noise to be canceled from the synthesized sound signal is provided and the output signal of this bandpass filter is used as the synthesized sound signal, the ratio is calculated. ,
It is possible to provide a noise canceling device that is not affected by noise other than the noise to be canceled and has a faster convergence speed and excellent stability.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of a secondary sound propagation characteristic imparting unit.

FIG. 3 is a configuration diagram of a step size parameter determination unit.

FIG. 4 is a configuration diagram of a second embodiment of the present invention.

FIG. 5 is a configuration diagram of a tracking control filter.

FIG. 6 is a configuration diagram of a conventional noise canceling device.

FIG. 7 is a waveform diagram for explaining a noise canceling operation.

FIG. 8 is a configuration diagram of a conventional noise canceling device when there are a plurality of noise sources, speakers, and observation points.

FIG. 9 is an explanatory diagram of a primary sound virtual propagation system.

FIG. 10 is a configuration diagram of a digital filter that realizes each element of a transfer function matrix.

FIG. 11 is an explanatory diagram of a secondary sound propagation system.

FIG. 12 is a configuration diagram of a filter for generating a filtered X signal.

FIG. 13 is a configuration diagram of an adaptive filter.

FIG. 14 is a configuration diagram of a conventional noise canceling device when there are two noise sources, speakers, and observation points.

[Explanation of symbols]

 13 ... Reference signal generator 14 Noise cancel controller 14a Adaptive signal processor 14b Adaptive filter 14d Filtered X signal creation filter 14e Secondary sound propagation characteristic imparting unit 14f Step size Parameter determining unit 16 · Speaker 17 · Error microphone 18 · Secondary sound propagation system 19 · Tracking control filter

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shuji Sawada 1-4-1 Chuo, Wako-shi, Saitama Inside the Honda R & D Co., Ltd. Stock Company Honda Technical Research Institute

Claims (2)

[Claims] 1. A cancel sound generation source for outputting a cancel sound for canceling noise at a noise cancel point, a sensor for detecting a synthesized sound of noise and a cancel sound at the noise cancel point, and a synthesized sound at the noise cancel point. A signal and a reference signal corresponding to the noise generated from the noise source are input, and adaptive signal processing is performed to cancel the noise at the noise cancellation point using these signals and a step size parameter that is a coefficient for signal processing. In a noise canceling device equipped with a noise canceling controller that generates a noise canceling signal and inputs it to the canceling sound generating source, the noise canceling signal is given a propagation characteristic equivalent to that of the canceling sound propagation system from the canceling sound generating source to the sensor. A propagation characteristic imparting means, and the propagation characteristic imparting means Noise canceling device being characterized in that a step size parameter determining means for determining a value of the step size parameter used in adaptive signal processing in accordance with the ratio of the force signal and the synthesized sound signal. 2. A bandpass filter that passes a frequency component of noise to be canceled included in a synthesized sound signal, wherein the step size parameter determining means calculates the ratio by using an output signal of the bandpass filter as a synthesized sound signal. The noise canceling device according to claim 1, wherein: