JPH06259083A - Noise canceling system - Google Patents

Abstract

PURPOSE:To perform highly accurate noise control with a small number of operations by selecting an optimum sampling frequency and tap length for each harmonics. CONSTITUTION:When plural harmonic components (second, fourth harmonic components) out of harmonic components caused by rotation of an engine are canceled, and the lowest common multiple of the order of each harmonic components to be canceled is assumed as J and the upper limit frequency of harmonic components to be canceled is assumed as fH, sampling frequency Fs is decided so as to satisfy 2.fH<=Fs, also the number of a coefficient for convolution of a propagation characteristic is made integral multiple of the lowest common multiple and stored in a coefficient memory 53. And when the upper limit frequencies of a second and a fourth harmonic components are assumed as fH2, fH4, a second and a fourth harmonic cancel processing section 51, 52 decide (n), (m) so as to satisfy respectively 2.fH2<=Fs/n and 2.fH4<=Fs/ m, and adaptive signal processing is performed by using the coefficient for convolution of a propagation characteristic for every (n), (m) pieces, and by using Fs/n, Fs/m as sampling frequencies.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise canceling method, and more particularly to a noise canceling method for effectively canceling a plurality of harmonic components of engine speed.

[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. 2 is a block diagram of a conventional noise canceling apparatus, which is an example in which there is one noise source, one canceling sound source (speaker), and one noise canceling point (observation point). . Reference numeral 11 is an engine that is a noise source, 12 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 xn. Is. 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 4-cylinder engine, the periodic noise generated in the passenger compartment is dominated by the second harmonic of the engine rotation speed, and the rotation speed is 600 rpm (10 rps).
At this time, the frequency of noise generated in the vehicle compartment is 20 Hz, and when the rotation speed is 6000 rpm (100 rps), the frequency of noise generated in the vehicle compartment is 200 Hz. The reference signal generation 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 xn. 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 denotes a noise canceling controller, which receives the reference signal xn generated from the reference signal generating section 13 and outputs 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 en, and adaptive signal processing is performed so that the error signal is minimized, and a noise cancel signal yn is output. The noise cancellation controller 14 convolves the adaptive signal processing unit 14a, the adaptive filter 14b having a digital filter configuration, and the reference signal xn with the propagation characteristics of the cancellation sound propagation system from the speaker to the noise cancellation point to obtain a filtered X signal (signal). Filtered X to create processing reference signal) rn
Signal creation filter (propagation characteristic convolution filter) 1
4c. Reference numeral 15 is a DA converter for converting the adaptive filter output (noise cancel signal yn) into an analog noise cancel signal, 16 is a power amplifier for amplifying the noise cancel signal, 17 is a cancel speaker for radiating the noise cancel sound Sc, 18 Is located at the noise canceling point, detects a synthesized sound of the noise Sn and the cancel sound Sc, and outputs the synthesized sound signal as an error signal en.
Microphone, 19 is an amplifier for amplifying the error signal en, 20
Is a low-pass filter for removing noise signals outside the band of periodic noise, and 21 is an AD converter for converting the output of the low-pass filter into digital form.

The adaptive signal processing unit 14a receives the error signal en at the noise cancellation point and the signal processing reference signal (filtered X signal) rn input through the propagation characteristic convolution filter 14c, and uses these signals. Adaptive signal processing is performed so as to cancel noise at the noise cancel point, and the coefficient of the adaptive filter 14b is determined. For example, the adaptive signal processing unit 14a determines the coefficient of the adaptive filter 14b so that the error signal en input from the error microphone 18 is minimized according to a well-known filtered X LMS (Least Mean Square) adaptive algorithm. The adaptive filter 14b performs digital filter processing on the reference signal xn according to the coefficient determined by the adaptive signal processing unit 14a, outputs a noise cancellation signal yn, and cancels noise. It should be noted that the reference signal xn must be a signal having a high correlation with the noise Sn that is desired to be erased, and a sound having no correlation with the reference signal is not erased.

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 coefficient w ₁ (n), w ₂ (n), w for each delay element output
₃ (n) ... W _N (n) multiplication units ML, ML, ...
And adder units AD, AD ...
・ It is realized by. That is, the reference signal at the current time n · Ts is xn, and the coefficient of each multiplier at that time is w ₁ (n), w
₂ (n), w ₃ (n) ・ ・ ・ w _N (n), output (noise cancellation signal)
Let yn be the adaptive filter 14b

[0007]

[Equation 1] Then, the noise cancellation signal yn is output.

The propagation characteristic convolution filter 14c is shown in FIG.
As shown in, it is composed of FIR type digital filter,
For example, delay elements DL, DL, ... Which sequentially delay the input signal by one sampling time, and coefficients c ₁ ,
c _2, c ₃ ··· c _M is multiplied by a multiplication unit ML, ML, ···
And adder units AD, AD ...
・ It is realized by. The coefficients c ₁ , c ₂ , c ₃ ... c _M are determined so as to simulate the propagation characteristics of the secondary sound propagation system (system from the speaker to the observation point), and are stored in the coefficient memory (not shown) in advance. Has been done. Outputs reference signal xn at time n · Ts
If the (filtered X signal) is r (n), the propagation characteristic convolution filter 14c executes the operation of the following equation and outputs the filtered X signal r (n).

[0009]

[Equation 2]

The adaptive signal processing unit 14a has the coefficients w ₁ (n + 1), w ₂ (n + 1) and w ₃ of the adaptive filter 14b at the next time (n + 1) · Ts after one sampling time Ts. (n + 1) ・ ・ ・ w
_N (n + 1) is the coefficient at the current time n · T and the error signal en
And the filtered X signal rn, the following formula (coefficient update formula)
Determined by

[0011]

[Equation 3]

However, the j-th filter coefficient updating formula is given by w _j (n + 1) = w _j (n) + μ · r (n-j + 1) · en (4). In equation (3), (n) is the value at the current sampling time, (n + 1) is the value one sampling time later, and (n-1) is 1
The value before the sampling time, (n-2) means the value before the two sampling times, .... Further, μ is a constant (step size parameter) of 1 or less that determines the step of updating the coefficient of the adaptive filter, and is set to an appropriate value according to the noise cancellation system. In the noise cancellation, the operations of the above equations (1), (2) and (3) are performed within one sampling time, and the noise cancellation signal yn is output. Assuming that the number of taps of the propagation characteristic convolution filter 14c is M, the number of calculations (the number of sums of products) for outputting the noise cancellation signal yn is M times of sums of products in the calculation of r (n) in the equation (2). Is required, and at least M times of operations are required to update the coefficient of one tap by the equation (4). Therefore, the adaptive filter 1
Assuming that the number of taps in 4b is N, at least MN calculations are required to output the noise cancellation signal. still,
Generally, the number of taps M of the filter 14c required for good noise reduction is several tens to several hundreds of taps, and the adaptive filter 1
Similarly, the number N of taps of 4b is several tens to several hundreds of taps.
It is necessary to perform product-sum calculation at least 1,000 times or more within the sampling time.

By the way, the engine sound contains a harmonic component of the engine speed as described above. Therefore, the dominant second-order harmonic component and the fourth-order or sixth-order harmonic component are canceled at the same time. FIG. 5 is a configuration diagram of a noise canceling system that simultaneously cancels second and fourth harmonic components, and the same parts as those in FIG. 2 are denoted by the same reference numerals. 2 is different from the DSP shown in FIG. 2 in that it includes a noise canceling processor 14 'for the second harmonic and a noise canceling processor 14 "for the fourth harmonic.
A noise canceling controller 14 having a configuration is provided. The reference signal generating unit 13 generates reference signals xn ₂ and xn ₄ of the second and fourth harmonics of the engine speed, and the noises of the corresponding harmonics are generated. elimination processing unit 14 ', a point input to the 14 ", the adder 14d is provided, that the output as noise cancellation signal yn by adding the noise cancellation controller output yn _2, yn _4, detected by the error microphone 18 synthesis The sound signal (error signal) en is converted into noise canceling processing units 14 'and 14 ".
This is the point of feedback to.

A noise canceling processing unit 14 'for each harmonic,
14 ″ are the reference signals xn ₂ and xn ₄ and the synthetic sound signal e, respectively.
Using n and the step size parameter μ, the above-mentioned adaptive signal processing is performed by the coefficient updating equation (3), and the coefficient of each adaptive filter is determined. Further, the reference signals xn ₂ and xn ₄ are input to the respective adaptive filters, and the noise cancellation signals yn ₂ and yn ₄ are output based on the equation (1). Adder 14
d is the output y of each noise cancellation processing unit 14 ', 14 "
DA is added as the noise cancellation signal yn by adding n ₂ and yn _4.
It is input to the converter 15, and the DA converter 15 converts it into an analog noise canceling signal and inputs it to the speaker to output a noise canceling sound. By the way, when a plurality of harmonic components are removed, the sampling frequency is determined according to the higher harmonic component, and in the example of FIG. 5, the sampling frequency is determined by the fourth harmonic component. Each time the sampling pulse SP is generated as shown in FIG. 6, the noise elimination processing unit 14 ', 14 "performs adaptive signal processing takes in the error signal en fetches a reference signal xn _2, xn ₄ respectively , Noise cancel signals yn ₂ and yn _4. That is, every time the sampling pulse SP is generated, the DSP performs noise cancel processing for canceling the second harmonic component and outputs the noise cancel signal yn ₂ . At the same time, the noise canceling process for canceling the fourth harmonic component is similarly performed to output the noise canceling signal yn ₄ .

[0015]

When the frequency band of noise to be silenced becomes wider, the sampling frequency fs needs to be increased according to its upper limit frequency. For example,
If the upper limit frequency is f _H , it is necessary to determine so that 2 · f _H ≦ fs. However, if the sampling frequency is increased, the resolution is lowered, and noise close to the lower limit frequency cannot be effectively silenced. That is, the resolution η in noise cancellation by digital adaptive signal processing is determined by the following equation η = fs / N (Hz) (5) fs: sampling frequency, N: number of taps of adaptive filter, so that the sampling frequency fs becomes high. , The controllable frequency interval becomes rough, and the muffling effect near the lower limit frequency decreases. Therefore, if the sampling frequency fs becomes higher, the number of taps N may be lengthened, but the number of calculation processes increases, which is not preferable.

Particularly, when a plurality of noises (harmonic components) having a wide frequency band such as engine sound are removed,
Since the sampling frequency is determined in accordance with the upper limit frequency of the higher order harmonic component, the resolution of the lower order harmonic component is greatly reduced, and the silencing effect near the lower limit frequency is considerably reduced. From the above, an object of the present invention is to provide a noise canceling method capable of simultaneously muting a plurality of noises (engine sounds) having a wide frequency band, and further improving the muting effect near the lower limit frequency. Another object of the present invention is a noise canceling method in which an optimum sampling frequency can be selected for each harmonic component and a memory for storing the coefficient of a propagation characteristic convolution filter can be provided in common for each harmonic component. Is to provide.

[0017]

According to the present invention, the upper limit frequency of the harmonic components of the engine sound to be canceled is f _H , and the least common multiple of the orders of the harmonic components to be canceled is J. Sampling frequency Fs
For satisfying 2 · f _H ≦ Fs, means for holding all the coefficients by setting the number of coefficients of the propagation characteristic convolution filter as an integral multiple of the least common multiple, and for each harmonic component, the harmonic component When the upper limit frequency of is f _Hi , 2 · f _Hi ≦
It is achieved by means for determining n that satisfies Fs / n, and means for performing adaptive signal processing by using the coefficient for every n pieces and every n sampling pulses.

[0018]

When a plurality of harmonic components of the engine speed are canceled, the least common multiple of the orders of the harmonic components to be canceled is J, and the upper limit frequency of the harmonic components to be canceled is f _H. , The sampling frequency Fs is determined so as to satisfy 2 · f _H ≦ Fs,
Further, the number of coefficients of the propagation characteristic convolution filter is held in one memory as an integral multiple of the least common multiple. Then, for each harmonic component, the upper limit frequency of the harmonic component is set to f _Hi
Then, n that satisfies 2 · f _Hi ≦ Fs / n is defined, and
Adaptive signal processing is performed using the above n coefficients and every n sampling pulses, in other words, with Fs / n as the sampling frequency. By doing this, the optimum sampling frequency can be selected for each harmonic component, and
Multiple noises (engine sounds) with a wide frequency band can be silenced at the same time, and the silencing effect can be improved. Further, a memory for storing the coefficient of the propagation characteristic convolution filter can be provided in common for each harmonic component.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Overall Configuration FIG. 1 is a configuration diagram of a noise canceling controller according to the present invention, which is an embodiment applied in the case of simultaneously canceling second-order and fourth-order harmonic components included in engine sound. The noise cancellation controller has a digital signal processor (DSP) configuration, and is provided commonly to the second harmonic cancellation processing unit 51, the fourth harmonic cancellation processing unit 52, and each harmonic cancellation processing unit,
A coefficient memory 53 for storing the propagation characteristics convolution coefficients _{c 1, c 2, c 3} ··· c M, a sampling pulse for generating a sampling pulse having a predetermined frequency Fs corresponding to the upper limit frequency of the harmonic component is muted target The noise cancel signal yn is generated by adding the noise cancel signals y2n and y4n output from the generation unit 54 and the harmonic cancellation processing units 51 and 52.
And an adder 55 for outputting as. The sampling pulse generator 54 generates a sampling pulse Ps having a frequency Fs that satisfies the following equation 2 · f _H ≦ Fs (6) when the upper limit frequency of the harmonic components to be canceled is f _H. The coefficient memory 53 has J · i (i is a positive integer) propagation characteristic convolution coefficients c ₁ , c ₂ , c _3, ... When the least common multiple of the order of each harmonic component to be canceled is J.
Store c _M (M = J · i). In the example, the least common multiple is 4.

Second-order harmonic cancellation processing unit The second-order harmonic cancellation processing unit 51 receives the reference signal x2n corresponding to the second-order harmonic of the engine sound generated from the reference signal generation unit (not shown). , The synthesized sound signal of the noise at the noise canceling position in the vehicle interior and the canceling sound is input as an error signal en, and adaptive signal processing is performed so that the second harmonic component included in the error signal is minimized. The cancel signal y2n is output. The second-order harmonic cancellation processing unit 51 includes an adaptive signal processing unit 51a.
And an adaptive filter 51b having a digital filter configuration and a filtered X by convolving the reference signal x2n with the propagation characteristics of the cancellation sound propagation system from the speaker to the noise cancellation point.
A filtered X signal creation filter (propagation characteristic convolution filter) 51c that creates a signal (reference signal for signal processing) r2n, and a self sampling pulse generator 51d that generates a sampling pulse Ps ₂ for second harmonic cancellation processing. have.

The self-sampling pulse generator 51d has two
Assuming that the upper limit frequency of the second harmonic component is f _H2 , n that satisfies the following equation 2 · f _H2 ≦ Fs / n (7) is determined, and the sampling pulse Ps of the frequency Fs is divided by 1 / n to obtain the frequency Fs. / N sampling pulse Ps ₂ is generated. Propagation characteristic convolution filter 51c
Is a sum-of-products calculating unit 51c-1 for calculating the reference signal r2n for signal processing by the equation (2), and a coefficient for extracting propagation characteristic convolution coefficients from the coefficient memory 53 for every n and inputting to the sum-of-products calculating unit. It has a take-out section 51c-2. Since the coefficient memory 53 M (= J · i) pieces of transmission characteristic convolution coefficients _{c 1, c 2, c 3} ··· c M are stored, the coefficient extraction unit 51c-2 are sampling pulses Ps ₂ Whenever, the n-th coefficient c ₁ , c _{1 + n} , c _{1 + 2n} , ... Is taken out and input to the product-sum operation unit 51c-1.

Fourth-order harmonic cancellation processing unit The fourth-order harmonic cancellation processing unit 52 receives the reference signal x4n corresponding to the fourth-order harmonic of the engine sound generated from the reference signal generation unit (not shown) and , The synthesized sound signal of the noise and the cancel sound at the noise cancel position in the passenger compartment is input as an error signal en, and adaptive signal processing is performed so that the fourth harmonic component included in the error signal is minimized. The cancel signal y4n is output. The fourth harmonic cancellation processing unit 52 includes an adaptive signal processing unit 52a.
, An adaptive filter 52b having a digital filter configuration, and a filtered X by convolving the reference signal x4n with the propagation characteristics of the cancellation sound propagation system from the speaker to the noise cancellation point.
A filtered X signal creation filter (propagation characteristic convolution filter) 52c that creates a signal (reference signal for signal processing) r4n, and a self sampling pulse generator 52d that generates a sampling pulse Ps ₄ for fourth harmonic cancellation processing. have.

The self sampling pulse generator 52d has four
If the upper limit frequency of the second harmonic component is f _H4 , m that satisfies the following equation 2 · f _H4 ≦ Fs / m (8) is determined, and the sampling pulse Ps of frequency Fs is divided by 1 / m to obtain frequency Fs. / M sampling pulse Ps ₄ is generated. In the example, m = 1 because the fourth order is the highest order. Propagation characteristic convolution filter 52c
Is a sum-of-products calculating unit 52c-1 for calculating the reference signal r4n for signal processing by the equation (2), and a coefficient for extracting propagation characteristic convolution coefficients from the coefficient memory 53 for every m and inputting them to the sum-of-products calculating unit. It has a take-out section 52c-2. Since the coefficient memory 53 M (= J · i) pieces of transmission characteristic convolution coefficients _{c 1, c 2, c 3} ··· c M are stored, the coefficient extraction unit 52c-2 are sampling pulses Ps ₄ Whenever, the m-th coefficient c ₁ , c _{1 + m} , c _{1 + 2m} , ... Is taken out and input to the product-sum operation unit 52c-1.

When the entire engine rotates, a reference signal generator (not shown) outputs reference signals x2n and x4n of the second harmonic and the fourth harmonic corresponding to the engine speed to the second and fourth harmonics, respectively. Input to the wave cancellation processing units 51 and 52. At this time, the engine sound generated from the engine propagates through the air having a noise propagation system having a predetermined transfer function and reaches a noise cancellation point.
The propagation characteristic convolution filter 52c of the fourth harmonic cancellation processing unit 52 takes in the reference signal x4n of the fourth harmonic every time the sampling pulse Ps ₄ is generated, and at the same time stores m coefficients c ₁ and c from the coefficient memory 53. _{Take out 1 + m} , c _{1 + 2m} , .... The multiply-accumulate operation unit 52c-1 fetches the reference signal x4
The reference signal r4n for signal processing is calculated by the equation (2) using n, some reference signals in the past, and propagation characteristic convolution coefficients c ₁ , c _{1 + m} , c _{1 + 2m} , .... Adaptive signal processing unit 52
a is the coefficient w ₁ (n), w of the adaptive filter 52b that is obtained by performing LMS adaptive signal processing according to equation (3) using the error signal en at the noise cancellation point and the reference signal r4n for signal processing.
₂ (n), w ₃ (n) ... W _N (n) are calculated. Adaptive filter 5
1b is a coefficient w ₁ (n), w determined by the adaptive signal processing.
₂ (n), w ₃ (n) ... w _N (n) is used as the reference signal x4n (2)
Noise cancellation signal y4n
Is output.

Further, the propagation characteristic convolution filter 51c of the second-order harmonic cancellation processing section 51 takes in the reference signal x2n of the second-order harmonic every time the sampling pulse Ps ₂ is generated, and at the same time every n units from the coefficient memory 53. The coefficients c ₁ , c _{1 + n} , c _{1 + 2n} , ... Are taken out. The product-sum calculation unit 51c-1 fetches the reference signal x2
A reference signal r2n for signal processing is calculated by the equation (2) using n and some past reference signals and coefficients c ₁ , c _{1 + n} , c _{1 + 2n} , for propagation characteristic convolution. Adaptive signal processing unit 51
a is the coefficient w ₁ (n), w of the adaptive filter 51b, which is obtained by performing LMS adaptive signal processing according to equation (3) using the error signal en at the noise cancellation point and the reference signal r4n for signal processing.
₂ (n), w ₃ (n) ... W _N (n) are calculated. Adaptive filter 5
1b is a coefficient w ₁ (n), w determined by the adaptive signal processing.
₂ (n), w ₃ (n) ... w _N (n) is used as the reference signal x2n (1)
Noise cancellation signal y2n
Is output.

The adder 55 is provided for each harmonic cancellation processing section 5
Noise cancellation signals y2n, y4n output from 1, 52
Is added and input to a speaker (not shown) as a noise cancellation signal yn. As a result, the noise canceling sound is output from the speaker, reaches the noise canceling point via the secondary sound propagation system, and acts to cancel the noise.
Thereafter, the above operation is repeated and the noise is promptly canceled. In the case of the example, the fourth harmonic cancellation processing unit 52 performs noise cancellation processing for each sampling frequency Fs / m (Fs if m = 1), and the second harmonic cancellation processing unit 51 determines the sampling frequency Fs / m. n (n = 2
Then, the noise canceling process is performed every Fs / 2).

In this case, the fourth harmonic cancellation processing unit 5
2, the tap length of the propagation characteristic convolution filter 52c is J · i / m, and the tap length of the propagation characteristic convolution filter 51c in the second harmonic cancellation processing unit 51 is J · i / m.
・ It is i / n. Therefore, the resolution η ₂ in the second harmonic cancellation processing is η ₂ = (Fs / n) / (J · i / n) = Fs / J · i, and the resolution η ₄ in the fourth harmonic cancellation processing is
Is equal to η ₄ = (Fs / m) / (J · i / m) = Fs / J · i. Therefore, by appropriately setting the integer value i so that a predetermined resolution can be obtained, accurate noise cancellation control can be performed. Further, according to the above configuration, the optimum sampling frequency and tap length can be selected for each harmonic, and the number of calculations can be reduced. Further, it suffices to provide one propagation characteristic convolution coefficient memory that must be held for each sampling frequency in common for each harmonic, and the number of storage elements (ROM) can be reduced. Above,
Although the case of canceling the two harmonic components of the second order and the fourth order has been described, the present invention is not limited to two and can be similarly applied to the case of canceling three or more harmonic components. is there. 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.

[0028]

As described above, according to the present invention, the optimum sampling frequency and tap length can be selected for each harmonic, the resolution in each harmonic can be made the same, and the silencing control with high accuracy can be performed with a small number of calculations. it can. Further, according to the present invention, it is sufficient to provide one propagation characteristic convolution coefficient memory that must be held for each sampling frequency in common for each harmonic component, and the number of storage elements (ROM) can be reduced.

[Brief description of drawings]

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

FIG. 2 is a configuration diagram of a conventional noise canceling device.

FIG. 3 is a configuration diagram of an adaptive filter.

FIG. 4 is a configuration diagram of a filter for generating a filtered X signal.

FIG. 5 is a configuration diagram of a conventional noise canceling device that cancels each harmonic component included in engine sound.

FIG. 6 is a time chart for explaining a conventional operation.

[Explanation of symbols]

 51 ... Second harmonic cancellation processing unit 51d ... Self sampling pulse generation unit 52 ... Fourth harmonic cancellation processing unit 52d ... Self sampling pulse generation unit 53. Coefficient memory 54 ... Sampling pulse generation unit 55.・ Adding part

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H03H 17/04 A 7037-5J 21/00 7037-5J

Claims (1)

[Claims] 1. A speaker that outputs a cancel sound for canceling an engine sound at a noise cancel point, a microphone that detects a combined sound of the engine sound and the cancel sound at the noise cancel point, and a reference signal corresponding to the engine sound. When generated, a reference signal generation unit, a propagation characteristic convolution filter that convolves the propagation characteristic of the cancel sound propagation system from the speaker to the microphone to the reference signal to generate a signal processing reference signal, and the reference signal generation unit outputs the reference signal. The adaptive filter for generating a noise canceling signal by applying a predetermined filtering process to the reference signal to be input to each speaker, and the noise at the noise canceling point by using the synthesized sound signal at the noise canceling point and the signal processing reference signal. And an adaptive signal processing unit that determines the coefficient of the adaptive filter so as to cancel. In the noise canceling method of the noise canceling system, when canceling a plurality of harmonic components of the engine speed, the least common multiple of the orders of each harmonic component to be canceled is J, and the upper limit frequency of the harmonic component to be canceled is f. _H
Then, the sampling frequency Fs is determined so as to satisfy 2 · f _H ≦ Fs, and the number of coefficients of the propagation characteristic convolution filter is set to an integral multiple of the least common multiple, and the harmonic component When the upper limit frequency of the wave component is f _Hi , n that satisfies 2 · f _Hi ≦ Fs / n is determined, and adaptive signal processing is performed using the above n coefficient and every n sampling pulse. Noise canceling method.