JP3419911B2 - Noise cancellation system - Google Patents

Description

Detailed Description of the Invention

[0001]

The present invention relates to Filered-X LMS (Least M
noise cancellation system that cancels noise by adaptive signal processing based on the (ean square) algorithm, especially the propagation characteristics (transfer characteristics) of the canceled sound propagation system
And a noise canceling system for canceling noise by identifying propagation characteristics of a noise propagation system online.

[0002]

2. Description of the Related Art Active noise control (ANC) for canceling noise by radiating a noise canceling sound having a phase opposite to that of noise from a speaker cancels noise in the interior space of a factory, office, etc., or in the interior space of an automobile. It has been put to practical use for that. FIG. 6 is a configuration diagram of a conventional noise canceling system that reduces noise by active control, and is a case where the engine sound of a vehicle is reduced. Reference numeral 11 is an engine which is a noise source, 12 is a rotation speed sensor for detecting the engine rotation speed R, and 13 is a reference signal generation for generating a sine wave signal of a constant amplitude having a frequency according to the engine rotation speed R as a reference signal x _n. It is a department. When the noise source is an engine, noise generated by engine rotation has a periodicity, and its frequency depends on the engine speed. For example, in the case of a four-cylinder engine, the periodic noise generated in the vehicle compartment is dominated by the second harmonic of the engine speed, and the engine speed is 600r.
At pm (10 rps), the frequency of noise generated in the passenger compartment is 20 Hz, and the rotation speed is 6000 rpm (100 rp).
In the case of s), the frequency of noise generated in the vehicle compartment is 200H
z. The reference signal generating unit 13 stores the sine wave data of the second harmonic in the ROM, reads the data as needed, and outputs the data to generate the reference signal x _n . The timing of reading / outputting this data is controlled according to the engine speed R, whereby a reference signal having the frequency of periodic noise generated according to the engine speed R is output.

Reference numeral 14 is a noise canceling controller, which receives the reference signal x _n generated from the reference signal generating section 13 and also generates a noise S at a noise canceling point (observation point, for example, near the driver's ear) in the passenger compartment. The synthesized sound signal of _n and the cancel sound Sc _n is input as an error signal e _n , and the Filered-X LMS is used so that the error signal is minimized.
The adaptive signal processing based on the algorithm is performed and the noise cancellation signal y _n is output. The noise cancellation controller 14 is adapted by convolving the adaptive signal processing unit 14a, the adaptive filter 14b having a digital filter configuration, and the reference signal _xn with the propagation characteristics (transfer function) of the cancellation sound propagation system from the speaker to the noise cancellation point. Filter for creating processing reference signal (filtered reference signal) u _n (filter for creating filtered reference signal) 14
have c. Reference numeral 15 is a DA converter for converting the output of the adaptive filter (noise canceling signal y _n ) into an analog noise canceling signal, 16 is a power amplifier for amplifying the noise canceling signal, and 17 is a canceling speaker for radiating the noise canceling sound Sc _n. , 18 are arranged at the noise canceling points, detect a synthesized sound of the noise S _n and the cancel sound Sc _n , and output the synthesized sound signal as an error signal e _n.
Mike, 19 amplifier for amplifying an error signal e _n, 20
Is a low-pass filter for removing aliases, and 20 'is an AD converter for converting the output of the low-pass filter to digital.

The adaptive signal processing unit 14a has a noise canceling point.
Error signal e at_nAnd input via the filter 14c
Reference signal u for processing_nInput and use these signals
And cancel the noise at the noise cancellation point.
Adaptive signal processing is performed to determine the coefficient of the adaptive filter 14b.
decide. For example, the adaptive signal processing unit 14a is a well-known Filere
From the error microphone 18 according to the d-X LMS algorithm
In order to minimize the power of the input error signal en
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 x _nNoise is applied to the digital filter
Cancel signal y_nTo cancel the noise.
The reference signal x_nIs the noise S you want to erase_nHigh correlation with
Sound that has no correlation with the reference signal is erased.
I can't.

The adaptive filter 14b, as shown in FIG.
For example, delay elements DL and D configured by an FIR digital filter and sequentially delaying an input signal by one sampling time
L ... and the coefficients w _0n , w _1n , w _2n
.... Multiplying units ML, ML, and the like for multiplying w _{(N-1) n} ,
It is realized by adders AD, AD, ... Which sequentially add the outputs of the respective multipliers. The number of coefficients is called the number of taps. Current time n
If the reference signal at Ts is x _n , the coefficients of the respective multiplication units at that time are w _0n , w _1n , w _2n ... w _{(N-1) n} , and the output (noise cancellation signal) is y _n , then adaptive filter 14b performs computation of the following equation _{y n = Σw in · x ni} (i = 0~N-1) ·· (1), and outputs the noise cancellation signal y _n.

The filter 14c, as shown in FIG.
For example, delay elements DL, DL.
.. and coefficients c ₀ , c ₁ , c ₂ , ... C for each delay element output
It is realized by multiplying units ML, ML, ... For multiplying _J−1, and adder units AD, AD ,. Coefficients c ₀ , c ₁ , c ₂ ... c _J-1 are determined so as to simulate the propagation characteristics (transfer characteristics) of the secondary sound propagation system (cancellation sound propagation system: system from the speaker to the observation point). ing. Assuming that the reference signal at time n · Ts is x _n and the output (reference signal for signal processing) is u _n , the signal processing filter 14c has the following expression u _n = Σci · x _ni (i = 0 to J-1). The calculation of (2) is executed and the signal processing reference signal u _n is output.

The adaptive signal processing section 14a uses one sampling
Adaptive filter at the next time (n + 1) · Ts after time Ts
14b coefficient w_{0n + 1}, W_{1n + 1}, W_{2n + 1}... w_{(N-1) n + 1}
Is the coefficient w at the current time n · T_0n, W_1n, W_2n...
w_{(N-1) n}And error signal e_nAnd the reference signal u for adaptive processing_nFor
Next formula (coefficient update formula) w_{jn + 1}= W_jn−∇_n = W_jn-2μ ・ u_n・ E_n(3) (However, j = 0, 1, ... N-1). Equation (3)
Where suffix n is the value at the current sampling time,
Suffix (n + 1) is the value one sampling time later,
Six (n-1) is the value one sampling time before, the suffix
Cous (n-2) means the value two sampling times before, ...
There is. Also, μ is the step of updating the coefficient of the adaptive filter.
Is a constant (step size parameter) that determines
It is set to an appropriate value according to the sound cancellation system.

When the engine 11 rotates, its rotation speed R
Is detected by the rotation speed sensor 12, and the reference signal generator 1
3 generates a reference signal _xn having a frequency corresponding to the engine speed R and inputs it to the filter 14c and the adaptive filter 14b. At this time, a periodic engine sound 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 filter 14 c convolves the transfer characteristic C ′ of the cancel sound propagation system with the reference signal x _n to obtain the adaptive processing reference signal u.
_n is generated and input to the adaptive signal processing unit 14c. In parallel with the above, the synthetic sound of the noise and canceling sound (error signal) e _n is detected by the error microphone 18 in the noise cancellation point, the amplifier is input low-pass filter, the adaptive signal processing unit 14a via the AD converter .

The adaptive signal processor 14a uses the error signal e _n and the signal processing reference signal u _n to filter the signal according to the equation (3).
-X Performs adaptive signal processing based on the LMS algorithm to determine the coefficient of the adaptive filter 14b. Adaptive filter 14
The signal b is subjected to digital filter processing on the reference signal x _n according to the coefficient determined by the adaptive signal processing unit 14 a to generate a noise cancel signal y _n, which is input to the speaker 17 via the DA converter and the power amplifier. As a result, the noise canceling sound is output from the speaker 17, reaches the noise canceling point via the canceling sound propagation system, and acts to cancel the noise. Thereafter, the above operation is repeated to cancel the noise. FIG. 9 represents a noise cancellation system using a primary sound virtual propagation system (noise propagation system) h from a noise source to an observation point and a secondary sound propagation system (canceled sound propagation system) c from a speaker to a noise cancellation point. 6 is a block diagram of the same, and the same parts as those in FIG. 6 are denoted by the same reference numerals. In the figure, 21 is a noise propagation system having an impulse response characteristic h, 22 is a canceling sound propagating system having an impulse response characteristic c, and the canceling sound propagation system 22 also includes a speaker characteristic.

Since the Filtered-X LMS algorithm has excellent advantages such as a small amount of calculation for adaptation,
It is currently used in many active noise control (ANC) systems. However, the variation characteristics c cancellation sound propagation system, 'when deviated from, if (3) ∇ _n is ideal (c = c' characteristic c of the filter 14c becomes different from). Therefore, the adaptation progresses in a direction different from the true gradient direction, and the stability condition, the convergence speed, and the convergence value of the adaptive filter 14b change accordingly.
Further, as a result, there is a problem that the muffling performance of the ANC system is generally deteriorated. A deviation between the characteristic c of the cancel sound propagation system 22 and the characteristic c'of the filter 14c is called a modeling error. The most direct method for eliminating the malfunction caused by the modeling error is to identify the transfer characteristic c of the cancel sound propagation system online. Such an online identification method has been conventionally proposed.

The first identification method is the Ericsson ((Eriksson)
Radiated from the secondary sound source a random noise y _N that is uncorrelated with the output y _n of the adaptive filter.
The unknown system c is identified using the adaptive filter c ″. FIG. 10 is a block diagram of such an online identification method.
14b is an adaptive filter whose coefficient is determined by the Filtered-X LMS algorithm so as to cancel noise, 18
Is a microphone at a noise canceling point, 21 is a noise propagation system having a transfer characteristic h, 22 is a cancel sound propagation system having a transfer characteristic c, and 23 is an output signal (noise canceling signal) y _n of the adaptive filter 14b and a secondary sound source (not shown). An arithmetic unit for adding the output random noise y _N , 24 is an identifying unit for identifying the transfer characteristic of the cancel sound propagation system 22 by adaptive signal processing, and 24 a is an adaptive unit to which a coefficient determined by adaptive signal processing is set. It is a filter. Reference numeral 25 is a calculator for calculating the difference ε _n between the error signal e _n output from the adaptive filter 24a and the microphone 18. The adaptive filter 14b operates so as to cancel noise having a correlation only with the reference signal x _n . Further, the identification unit 24 for identifying the cancel sound propagation system 22, random noise y _N power E of the difference signal of the output signal of the adaptive filter 24a for outputting the random noise y _N of the cancel sound propagation system 22 for [epsilon _n] is Operates to be the minimum. Here, since x _N and y _N are uncorrelated, when E [ε _n ] becomes minimum, c ″ = c, and the coefficient of the adaptive filter 24a matches the impulse response of the cancel sound propagation system.

The second identification method is proposed by Tapia et al. And identifies the unknown system (h, c) without using special identification noise. FIG. 11 is a block diagram of the second online identification method. 14b is a Filter
An adaptive filter whose coefficient is determined to cancel noise by the ed-X LMS algorithm, 18 is a microphone at a noise canceling point, 21 is a noise propagation system with transfer characteristic h, and 22 is a cancel sound propagation system with transfer characteristic c. . Reference numeral 26 is a first identification unit that identifies the transfer characteristic h of the noise propagation system 21 by adaptive signal processing, and 26a is an adaptive filter whose coefficient is set by adaptive signal processing. 27
Is a second identifying unit that identifies the transfer characteristic c of the cancel sound propagation system 22 by adaptive signal processing, and 27a is an adaptive filter whose coefficient is set by adaptive signal processing. 28
Is an adder that adds the output signals of the adaptive filters 26a and 27a, and 29 is a calculator that calculates the difference signal ε _n between the output signal e _n ′ of the adder 28 and the error signal e _n output from the microphone 18. The adaptive filter 14b operates so that the power E | e _n ² | of the error signal e _n is minimized, and the first and second identification units 26 and 27 operate on the power E of the difference signal ε _n .
It operates to minimize [ε _n ² ].

[0013]

The first on-line identification method is to use random noise other than the true noise to be canceled. In order to prevent this random noise (identification noise) from becoming noise at the noise cancellation point, it is necessary to reduce its level. However, if the level of the identification noise y _N is small, the identification error becomes large, and it is necessary to secure a certain level. However, when the level is increased, there is a problem that the identification noise increases at the noise cancellation point. The second online identification method does not require the use of special identification noise, and there is no problem with the first online identification method. However, this method may not correctly identify the unknown system (h, c).

FIG. 12 is a block diagram of a noise canceling system using the second online identification method. Reference numeral 14 is a noise canceling controller, 14a is an adaptive processing unit that performs adaptive signal processing by the Filtered-X LMS algorithm, and 14b.
Is an adaptive filter, and 14c is a signal processing filter. 1
8 is a microphone that outputs an error signal e _n at a noise canceling point, 21 is a noise propagation system, 22 is a canceling sound propagation system, and 26 is a first identifying unit that identifies the transfer characteristic h of the noise propagation system 21 by adaptive signal processing. 26a is an adaptive signal processing unit and 26b is an adaptive filter. Reference numeral 27 is a second identification unit that identifies the transfer characteristic c of the cancel sound propagation system 22 by adaptive signal processing, 27b is an adaptive signal processing unit, and 27b is an adaptive filter. Reference numeral 28 is a calculation unit that adds the output signals of the adaptive filters 26b and 27b, and 29 is a calculation unit that calculates the difference ε _n between the output signal e _n ′ of the calculation unit 28 and the error signal e _n output from the microphone 18.

The first and second identification units 26 and 27 calculate the coefficients of the adaptive filters 26b and 27b by the following coefficient updating formula.

[Equation 1] Determined by On the other hand, the error ε _n is

[Equation 2] Given in. Therefore, the above coefficient update formula is

[Equation 3] Becomes

Taking the expected values on both sides, the above equation becomes

[Equation 4] Becomes Applying the theory of independence to this,

[Equation 5] Becomes Therefore, the convergence values of the adaptive filters 26b and 27b are

[Equation 6] That is,

[Equation 7] It is a value that satisfies.

Therefore, the correlation matrix

[Equation 8] Is regular, then

[Equation 9] And the unknown transmission system can be correctly identified. But the correlation matrix

[Equation 10] Are often singular, in which case unknown systems cannot be accurately identified.

For example, h is 1 tap, c is 1 tap, w
Considering the case where is 1 tap, the noise cancellation system of FIG. 12 is as shown in FIG. 13, and the coefficient updating formula of the identifying unit is as follows.

[Equation 11] The error ε _n is given by

[Equation 12] Given in.

Where the correlation matrix

[Equation 13] Considering the regularity of y _n = w _n x _n ,

[Equation 14] Becomes Therefore, the correlation matrix is

[Equation 15] Becomes For ease of discussion, in the following, w _n = w
= Constant (when the adaptive filter 14b for canceling sound converges, a state close to this).

Therefore, the correlation matrix is

[Equation 16] This matrix can be written as

[Equation 17] The first matrix on the right side is a lower triangular matrix, and its determinant is given by the product of diagonal terms. Therefore, it is a singular matrix because det (Δ) = 0.

The second matrix on the right side is an autocorrelation matrix, which is almost always a positive definite value and is almost always regular. The third matrix on the right side is an upper triangular matrix, and its determinant is given by the product of diagonal terms. Therefore, it is a singular matrix because det (Δ) = 0. From the result of, it can be understood that the correlation matrix is singular. Therefore, it is not always possible to correctly identify h and c. Although the case where h, c, and w are 1 taps has been described above, the same applies when the number of taps of the adaptive filter 14b is generally equal to or less than the number of taps of the noise propagation system 21. For example, when h is 4 taps, c is 3 taps, and w is 2 taps, the correlation matrix is

[Equation 18] The above can be said similarly.

From the above, the first object of the present invention is to improve the second online identification method of the related art to reliably identify the transfer characteristics h and c of an unknown system (noise propagation system, cancellation sound propagation system). It is to provide a noise cancellation system that can. A second object of the present invention is to provide a noise canceling system capable of canceling noise by performing adaptive signal processing based on the Filtered-X LMS algorithm using the identified transfer characteristic. A third object of the present invention is to provide a noise canceling system capable of identifying and canceling noises online even if the transfer characteristics h and c change.

[0023]

According to the present invention, the above object is to provide a first identifying means for identifying propagation characteristics of a noise propagation system from a noise source to a noise cancellation point by adaptive signal processing, and a cancellation sound propagation system. Second identification means for identifying the propagation characteristic of the noise propagation signal by adaptive signal processing, and when the propagation characteristic of the noise propagation system is specified by K tap coefficients, the number of tap coefficients of the adaptive filter that outputs the noise cancellation signal is K + 1 or more. And a coefficient determination unit that makes at least one coefficient after the (K + 1) th non-zero, and is achieved by a noise cancellation system that identifies the propagation characteristics of the canceled sound propagation system and the propagation characteristics of the noise propagation system online. .

[0024]

The adaptive signal processing unit for noise canceling includes an error signal which is a synthesized sound of noise and cancel sound at the noise canceling point, and a reference signal for adaptive processing in which the propagation characteristic of the cancel sound propagating system is convoluted with the reference signal. Using Filtered-
The adaptive filter performs adaptive signal processing based on the X LMS algorithm to determine the coefficient of the adaptive filter, the adaptive filter filters the reference signal to generate a noise cancellation signal, and the cancellation sound generation unit receives the noise cancellation signal. The cancel sound is emitted, and the power of the error signal is controlled to be the minimum. In parallel with the noise cancellation control, the first and second identifying means respectively identify the propagation characteristic h of the noise propagation system and the propagation characteristic c of the canceled sound propagation system online by adaptive signal processing. in this case,
If the first identifying means specifies the propagation characteristic h of the noise propagation system with K tap coefficients, the number of tap coefficients of the adaptive filter that outputs the noise canceling signal is set to K + 1 or more. Then, the coefficient determination unit controls so that at least one coefficient after the (K + 1) th coefficient is non-zero. In this way, the propagation characteristic h of the noise propagation system and the propagation characteristic c of the cancel sound propagation system can be definitely determined.

[0025]

【Example】

(a) Identification principle of the present invention In the second conventional online identification method, the correlation matrix may not be regular, and the propagation characteristic h of the noise propagation system and the propagation characteristic c of the cancel sound propagation system are uniquely determined. I can't. In other words, there are cases where the second conventional online identification method can create only independent equations of unknown numbers or less, and there are innumerable solutions to the equations. Therefore, the unknown system (h, c) could not be identified accurately. Therefore, if the number of taps in the noise propagation system is K and the number of taps in the cancellation sound propagation system is J, the total number of unknowns is K +.
Since there are J, it can be said that these unknowns can be uniquely determined by constructing K + J independent equations by some method. When the number of taps of the noise canceling adaptive filter is I, the number of taps I is set to (K + 1) or more, and at least one tap coefficient (w _{K to} w _I-1 ) after (K + 1) th The convergence value of one coefficient) is controlled to be a value other than 0. In this way, unknown equations (K + J) or more independent equations can always be obtained. When more than unknown (K + J) independent equations are obtained, the correlation matrix becomes regular,
The optimal solution that minimizes E [ε _n ² ] can be uniquely determined.

(B) Noise Canceling System of the Present Invention (b-1) Configuration FIG. 1 is a block diagram of the noise canceling system of the present invention. Reference numeral 31 denotes a noise canceling controller, which receives the reference signal x _n generated from the reference signal generating unit and also outputs a composite sound signal of the noise d _n and the cancel sound d _n ′ at the noise canceling point in the vehicle interior as an error signal e. _It is input as _n , and the Filere is set to minimize the power of the error signal.
Adaptive noise signal processing based on dX LMS is performed to output a noise cancellation signal y _n . Noise cancellation controller 3
Reference numeral 1 is an adaptive signal processing unit 31a, an adaptive filter 31b having a digital filter configuration, and a reference signal _xn by convolving a propagation characteristic (transfer function) c'of a cancel sound propagation system from a speaker to a noise cancellation point to adaptive processing. Processing filter (filter for creating filtered X signal) 31 for creating a reference signal for filtering (filtered reference signal) u _n ′
have c.

Reference numeral 32 denotes a noise propagation system having a transfer characteristic h, 3
3 is a canceling sound propagation system having a transfer characteristic c, 34 is a microphone for outputting a composite sound signal of the noise d _{n at} the noise canceling point in the vehicle interior and the canceling sound d _n ′ as an error signal e _n , and 35 is a noise propagation system 35a is a first identification unit for identifying the transfer characteristic h of 32 by adaptive signal processing;
Is an adaptive signal processor, 35b is an adaptive filter in which the transfer characteristic h ″ of the noise propagation system 32 identified by the adaptive signal processing is set. Reference numeral 36 identifies the transfer characteristic of the cancel sound propagation system 33 by the adaptive signal processing. The second identification part,
36a is an adaptive signal processing unit, 36b is an adaptive filter in which the transfer characteristic c ″ of the cancel sound propagation system 33 identified by the adaptive signal processing is set. 37 is an arithmetic unit, 3
Reference numeral 7a is an adder that adds the output signals of the adaptive filters 35b and 36b, and 37b is an arithmetic circuit that calculates the difference ε _n between the output signal of the adder 37a and the error signal e _n output from the microphone 34.

In the present invention, if the number of taps of the noise propagation system 32 and the adaptive filter 35b is K, the number of taps of the cancel sound propagation system and the adaptive filter 36b is J, and the number of taps of the adaptive filter 31b in the noise cancellation controller is I. , The number of taps I is I ≧ K + 1. Reference numeral 38 denotes a tap coefficient control unit that determines the coefficient of at least one tap after the (K + 1) th tap of the adaptive filter 31b so as not to be zero. If the number of taps of the noise canceling adaptive filter 31b is I, the number of taps I
Is set to (K + 1) or more, and the convergence value of at least one (K + 1) th and subsequent tap coefficients (at least one coefficient from w _{K to} w _I−1 ) is controlled to be a value other than 0. With this configuration, the first and second identification units 35 and 36
Can uniquely determine the optimum solution (h ″, c ″) that minimizes the power E [ε _n ² ] of the difference signal ε _n .

(B-2) Configuration of tap coefficient control unit FIG. 2 is a block diagram of the tap coefficient control unit 38, where 38a is
(K + 1) th in a predetermined time (called a block)
Tap coefficient w_KnAverage value w_nA block that calculates and outputs
The lock average calculator, 38b is the same as the previous block average value.
Difference Δw between block averages_nDifference operation to calculate ′
Part, 38c is the difference Δw_n'And set value TΔ _wCompare the size of
And then | Δw_n′ ｜ <TΔ_wWhen, the convergence completion signal CED is
Convergence determining unit for outputting, 38d outputs (K + 1) when the convergence is completed.
Th tap coefficient w_KnAverage value w _n'And set value T_wBig and small
, W_n′ ｜ ≧ T_wIn the case of, the adaptive signal processing unit
Tap coefficient w calculated by 31a_KnWithout changing
w_n′ ｜ <T_wIn the case of, by the adaptive signal processing unit 31a
Calculated tap coefficient w_KnSet value w_BChange to (≠ 0)
It is a convergent value determining unit. The tap coefficient control unit 38
Tap coefficient w at number convergence_KnIs the set value T_w
In the following cases, that is, tap coefficient w_KnThe convergence value of is almost 0
, The tap coefficient w_KnSet value w_BChange to (≠ 0)
Control so that it does not become zero.

(B-3) Operation The filter 31c shown in FIG. 1 executes the operation of (2) using the coefficients c ₀ , c ₁ , c ₂ ... c _J-1 for specifying the cancel sound propagation system. The signal processing reference signal u _n ′ is output. The adaptive signal processing unit 31a receives the error signal e _{n at the} noise canceling point and the signal processing reference signal u _n ′, performs the calculation of equation (3) using these signals, and outputs the coefficient w _{0n of} the adaptive filter 31b. w _1n , w _2n ... W _{(I-1) n} are determined. The adaptive filter 31b executes the calculation of the equation (1) using the coefficients w _0n , w _1n , w _2n ... W _{(I-1 ) n} determined by the adaptive signal processing unit 31a to execute the noise cancellation signal y _n. Is output. The noise canceling signal y _n reaches the noise canceling point via the canceling sound propagation system 33 and becomes the canceling sound signal d _n ′, and the noise (reference signal) reaches the noise canceling point via the noise propagation system 32. It The microphone 34 detects the error signal e _n which is a composite sound signal of the cancel sound signal d _n ′ and the noise signal d _n, and detects the noise cancel controller 3
Enter 1. After that, the above processing is repeated, and the coefficient of the adaptive filter 31b converges to a predetermined value so that the power E [e _n ² ] of the error signal e _n is minimized.

In parallel with the above, the adaptive signal processing unit 35a in the first identifying unit 35 receives the reference signal x _n and the difference signal ε _n , and uses these signals to perform adaptive signal processing based on the LMS algorithm. By performing the adaptive signal processing, the coefficient of the adaptive filter 35b is determined so that the power E [ε _n ² ] of the difference signal ε _n is minimized. When the coefficient of the adaptive filter 35b is determined so that E [ε _n ² ] is minimized, the adaptive filter 35b exhibits a transfer characteristic h ″ that is substantially the same as the transfer characteristic h of the noise propagation system 32. The LMS algorithm is an adaptive signal processing algorithm in which u _n = x _{n in} equation (3).

The adaptive signal processing unit 36a in the second identifying unit 36 receives the noise cancellation signal y _n and the difference signal ε _n , performs adaptive signal processing based on the LMS algorithm using these signals, By the adaptive signal processing, the coefficient of the adaptive filter 36b is determined so that the power E [ε _n ² ] of the difference signal ε _n becomes the minimum. When the coefficient of the adaptive filter 36b is determined so that E [ε _n ² ] is minimized, the adaptive filter 36b determines the transfer characteristic c of the cancel sound propagation system 33.
And it will exhibit substantially the same transfer characteristics c ". Noise cancellation controller 31 the error signal e _n power E [e _n
² ] is minimized, and the first and second identification units 3
5 and 36 operate so that the power E [ε _n ² ] of the difference signal ε _n is minimized. Considering that the power E [e _n ² ] of the error signal e _n is minimized by the noise canceling process, the first and second identification units 35 and 36 have the minimum power of the output signal e _n ′ of the adder 37a. Means to work as follows. Therefore, the first identification unit 35 uses the reference signal x _n
For the noise canceling system y and the output signal of the adaptive filter 35b for the reference signal x _n are minimized.
It operates so that the difference between the output of the cancellation propagation system 33 for _n and the output signal of the adaptive filter 36b for the noise cancellation signal y _n becomes zero. Eventually, finally h ″ = h,
The coefficients of the adaptive filters 35b and 36b are determined so that c ″ = c. The transfer characteristic c ″ of the noise canceling sound propagation system identified above is set in the signal processing filter 31c, and thereafter, the transfer function c Noise cancellation processing is performed using "".

(C) In the conventional online identification method in which the number of taps of the first application example h of the present invention is 1, the number of taps of c is 1, and the number of taps of w is 1, it is assumed that w _n = w = constant. , The correlation matrix is

[Formula 19] And the first and last matrices on the right hand side are singular matrices. Therefore, it is not always possible to correctly identify h and c. Therefore, in order to make the correlation matrix a regular matrix, the first and last matrices are

[Equation 20] Is replaced by a regular matrix.

Therefore, in the present invention, the number of taps of the noise canceling adaptive filter 31b is set to 2, and w _n = [w
_0n , w _1n ],

[Equation 21] Therefore, if w ₁ ≠ 0, the first and last matrices on the right side are regular matrices. Therefore, h and c can be correctly identified. From the above, when both h and c have one tap, the adaptive filter has two taps and the final tap w ₁
The unknown system (h, c) can be accurately estimated by controlling so that the convergence value of does not become zero.

FIG. 3 is an explanatory view of the reason why h and c cannot be obtained by the conventional identification method. In the system of FIG.

[Equation 22] Becomes Therefore,

[Equation 23] Is only obtained. E [] represents the expected value,
E [x_ne_n], E [x_n ²] Is x_nAnd e_nCross-correlation function of,
And x_n, Which represents the autocorrelation function of
Knowledge. The system in Fig. 3 is the total system (x_nEnter the
e_nIf you see it as a system that outputs
System. Therefore x_n, Y_n, E _nSeeking from
Only the total gain (g) is given. When
This gain (g) depends on w, h and c.
,

[Equation 24] Is. Therefore, in this case, h and c cannot be determined.

FIG. 4 is an explanatory diagram of the reason that h and c can be obtained by the identification method of the present invention. In the system of FIG.

[Equation 25] Becomes Therefore,

[Equation 26] Therefore, the system of FIG. 4 is a 2-tap FIR system when viewed as a total system.

Since the input / output characteristic of this system can be determined from x _n and e _n , the two tap _coefficient values (g ₀ ,
g ₁ ) can be obtained. And these are w,
depends on h and c,

[Equation 27] Is. Therefore, in this case, if w ₁ ≠ 0, h and c can be uniquely determined.

(D) If the number of taps in the second application example h of the present invention is 1, the number of taps in c is 1, and the number of taps in w is 3,

[Equation 28] Becomes Therefore, the correlation matrix is

[Equation 29] Becomes

If w ₁ = 0, the above equation is

[Equation 30] Therefore, if w ₂ ≠ 0, the first and last matrices are both regular matrices. When w ₂ = 0,

[Equation 31] Next, w₁If ≠ 0, the first and last matrices are both positive
It becomes a rule matrix. That is, w₁Or w₂One of
Uniquely sets the unknown (h, c) if is not at least 0
You can ask. In other words, at least one
It may be controlled so that the other value becomes a value other than 0. or,
w₁, W₂If none of the two are 0, then two unknowns (h,
Three equations hold for c). In this case
However, since the correlation matrix is regular, the unknowns (h, c) are
If estimated by an adaptive filter, E [ε _n ²] Is the minimum
The optimum estimation can always be performed.

FIG. 5 is an explanatory diagram of the reason why h and c can be obtained by the identification method of the present invention. The system of FIG. 5 is a 3-tap system when viewed as a total system,

[Equation 32] Holds. Therefore,

[Expression 33] Becomes Since g _{0 to} g ₂ can be obtained and w _{0 to} w ₂ are also known, the unknown number (h, c) can be uniquely determined as the least squares solution.

(E) A method of determining the number of taps of w when the number of taps of the third application example h of the present invention is 4 and the number of taps of c is 3 will be described. Unknown number is 4 + 3
= 7, so 7 independent equations are needed. To do so, a system that includes 7 times (7-tap FIR system)
Must be made up of subordinate connections of w and c. Since c is a 3-tap (secondary) system and the 7-tap system is a 6th-order system, w must be at least a 4th-order system (5-tap FIR type system). Let us consider the regularity of the correlation matrix when w is 5 taps.

[0042]

[Equation 34] Is.

Therefore, the correlation matrix

[Equation 35] Becomes a regular matrix if W ₄ ≠ 0, and unknowns (h, c)
Is required. 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.

[0044]

As described above, according to the present invention, if the propagation characteristic h of the noise propagation system is specified by K tap coefficients, the number of taps of the adaptive filter that outputs the noise cancellation signal is set to K + 1 or more, and the K + 1th Since at least one coefficient after that is controlled to be non-zero, the propagation characteristic h of the noise propagation system and the propagation characteristic c of the cancel sound propagation system can be uniquely determined. Further, according to the present invention, it is possible to improve the sound deadening effect by performing adaptive signal processing based on the Filtered-X LMS algorithm using the identified transfer characteristic. Furthermore, according to the present invention, even if the transfer characteristics h and c change, they can be identified online and noise can be canceled.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a noise canceling system of the present invention.

FIG. 2 is a configuration diagram of a tap coefficient control unit.

FIG. 3 is an explanatory diagram of a reason why h and c cannot be obtained by the conventional identification method, and is an example in the case where h, c and w are 1 tap.

FIG. 4 is an explanatory diagram of the reason that h and c can be obtained by the identification method of the present invention, and is an example when h and c have 1 tap and w has 2 taps.

FIG. 5 is another explanatory diagram of the reason that h and c can be obtained by the identification method of the present invention, and is an example when h and c have 1 tap and w has 2 taps.

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

FIG. 7 is a configuration diagram of an adaptive filter.

FIG. 8 is a configuration diagram of a filter that generates a reference signal for adaptive processing (filtered reference signal).

FIG. 9 is a block diagram of a noise cancellation system expressed using a primary sound and a secondary sound propagation system.

FIG. 10 is an explanatory diagram of a first conventional online identification method.

FIG. 11 is an explanatory diagram of a second conventional online identification method.

FIG. 12 is a configuration diagram of a noise canceling system using a second online identification method.

FIG. 13 is a configuration diagram of a noise canceling system using a second online identification method, and is an example in the case where h, c, and w are 1 taps.

[Explanation of symbols]

31 .. Noise canceling controller 31b .. Adaptive filter 32 .. Noise propagation system 33 .. Canceling sound propagation system 35 .. First identification unit 36 for identifying the transfer characteristic of the noise propagation system. Second to identify characteristics
Identification unit 37 ... Calculation unit 38 ... (k + 1) tap coefficient determination unit

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G10K 11/178 F01N 1/00 H03H 21/00

Claims (2)

(57) [Claims] 1. A cancel sound generation unit for outputting a cancel sound for canceling noise at a noise cancel point,
A sensor that detects an error signal that is a combined sound of noise and cancellation sound at a noise cancellation point, a reference signal generation unit that generates a reference signal according to the noise generated from a noise source, and a cancellation sound propagation from the cancellation sound generation unit to the sensor A filter for generating a reference signal for adaptive processing by convolving the propagation characteristics in the system with a reference signal, and a noise canceling unit for generating a noise canceling signal by applying predetermined filtering to the reference signal output from the reference signal generating unit A noise canceling system comprising: an adaptive filter to be input to an error signal; and an adaptive signal processing unit that determines a coefficient of the adaptive filter so as to cancel noise at a noise canceling point by adaptive signal processing using an error signal and a signal adaptive reference signal. The adaptive characteristics of the noise propagation system from the noise source to the noise cancellation point First identifying means for identifying the noise propagation system by the signal processing, second identifying means for identifying the propagation characteristics in the cancellation sound propagation system by adaptive signal processing, and the case of identifying the propagation characteristics of the noise propagation system by K tap coefficients, The number of tap coefficients of the adaptive filter that outputs the noise canceling signal is set to K + 1 or more, and a coefficient control unit that controls the coefficient so that at least one tap coefficient after the K + 1th is non-zero is provided, and the canceling sound is generated online. A noise cancellation system characterized by identifying the propagation characteristics of a propagation system and the propagation characteristics of a noise propagation system. 2. An arithmetic unit for synthesizing an output signal of the first identifying means and an output signal of the second identifying means, and computing a difference signal between the synthetic signal and the error signal, the first identifying means. An adaptive signal processing unit that performs adaptive signal processing using the reference signal and the difference signal; and an adaptive filter that performs predetermined filtering on the reference signal using the coefficient determined by the adaptive signal processing and outputs the reference signal, The second identifying means performs an adaptive signal processing unit that performs adaptive signal processing using the noise cancellation signal and the difference signal, and a predetermined filtering process on the noise cancellation signal using the coefficient determined by the adaptive signal processing. The noise cancellation system according to claim 1, further comprising an adaptive filter for outputting.