JP3002049B2 - Silencer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silencer using active noise control in a noisy environment.

[0002]

2. Description of the Related Art In recent years, there has been proposed an active noise control method for outputting a control sound from a speaker by using digital signal processing technology to mitigate environmental noise at a listening position.

Hereinafter, a conventional silencer will be described with reference to the drawings. FIG. 10 is a block diagram of a conventional silencer. In FIG. 10, reference numerals 1 a and 1 b denote microphones, 2 denotes an adaptive acyclic digital filter (hereinafter abbreviated as an AFIR filter), 3 denotes an acyclic digital filter (hereinafter abbreviated as an FIR filter), and 4 denotes The LMS calculator 5 is a speaker.

[0004] The operation of the thus configured silencer will be described below. Microphone 1a
The noise signal detected by the AFIR filter 2 and the FIR
Input to filter 3. The signal processed by the AFIR filter 2 is reproduced by the speaker 5. Then, the reproduced sound and the noise from the noise source interfere with each other, and the interference sound is detected by the microphone 1b. The detected signal is input to the LMS calculator 4. On the other hand, FIR filter 3
The noise signal subjected to the signal processing is also input to the LMS calculator 4. Here, a transfer function C from the speaker 5 to the microphone 1b is set in the FIR filter 3 in advance. Therefore, the LMS computing unit 4 uses the two signals r (n) and e (n) shown in FIG.
The coefficient of the AFIR filter 2 is calculated so that (n) is minimized, and the coefficient of the AFIR filter 2 is updated.

[0005]

(Equation 1)

As a result, the noise signal is adaptively controlled by the AFIR filter 2 and reproduced from the speaker 5, so that the error signal at the microphone 1b is reduced and the noise is attenuated.

[0007] A method using the FIR filter 3 is called a Filtered-x LMS algorithm,
The AFIR filter 2, the FIR filter 3, and the LMS calculator 4 constitute a so-called adaptive filter.

[0008]

However, in the above configuration, when the noise of the noise source is colored as shown in FIG. 6, the noise signal and error signal detected by the microphones 1a and 1b are not detected. In the case where the characteristics are as shown in FIG. 6, there is a problem that the sound extinction varies depending on the frequency band and the convergence time is delayed as shown by the dotted line in FIG. 6.

The present invention has been made to solve the above-mentioned problem. Even when the noise signal and the error signal are colored,
An object of the present invention is to provide a muffling device that eliminates the influence and shortens the convergence time, and also provides a muffling device that can obtain the same muffling volume in a control band.

[0010]

In order to achieve this object, a first aspect of the present invention provides a noise reduction device for detecting noise from a noise source, and noise control by controlling the frequency characteristics of the detected noise signal. A frequency characteristic adjustment circuit for whitening (frequency flattening) within a band, an adaptive filter for adaptively controlling the output of the frequency characteristic adjustment circuit, a speaker for reproducing the output of the adaptive filter, and And an error detector for controlling the coefficient of the adaptive filter based on the interference sound generated by the interference between the reproduced sound and the noise from the noise source.

According to another aspect of the present invention, there is provided a muffler comprising: a noise detector for detecting noise from a noise source; an adaptive filter for adaptively controlling the detected noise signal; The frequency characteristic of the output of the adaptive filter is white within the noise control band.
A frequency characteristic adjusting circuit for converting (frequency flattening), a speaker for reproducing an output of the frequency characteristic adjusting circuit, and an interference sound generated by interference between a reproduced sound from the speaker and noise from a noise source. And an error detector for controlling the coefficient of the adaptive filter.

According to a third aspect of the present invention, there is provided a muffler comprising: a noise detector for detecting noise from a noise source; an adaptive filter for adaptively controlling the detected noise signal; A speaker that reproduces the output of the adaptive filter, an error detector that detects an interference sound between the reproduced sound from the speaker and noise from a noise source,
Noise frequency characteristics for the output from the error detector
A frequency characteristic adjusting circuit for whitening (frequency flattening) in the control band and controlling the coefficient of the adaptive filter based on the adjustment signal.

Further, in order to achieve the above object, a noise suppressor according to a fourth aspect of the present invention includes a noise detector for detecting noise from a noise source, and a noise control band for the detected noise signal. Whitening within (flat frequency)
A first frequency characteristic adjusting circuit, an adaptive filter for adaptively controlling the output of the first frequency characteristic adjusting circuit, a speaker for reproducing the output of the adaptive filter, a reproduced sound and a noise source from the speaker An error detector for detecting an interference sound with noise from the apparatus, and a frequency characteristic of an output from the error detector within a noise control band.
And a second frequency characteristic adjustment circuit for controlling the coefficient of the adaptive filter based on the adjustment signal.

Further, in order to achieve the above object, according to a fifth aspect of the present invention, there is provided a muffler comprising: a noise detector for detecting noise from a noise source; an adaptive filter for adaptively controlling the detected noise signal; The frequency characteristics of the output of the adaptive filter are white in the noise control band.
A first frequency characteristic adjustment circuit for colorization (frequency flattening), a speaker for reproducing the output of the first frequency characteristic adjustment circuit, and an interference sound between a reproduced sound from the speaker and noise from a noise source. An error detector to be detected, and a frequency characteristic of an output from the error detector within a noise control band.
And a second frequency characteristic adjustment circuit for controlling the coefficient of the adaptive filter based on the adjustment signal.

[0015]

According to the configuration of the first invention, the convergence speed can be increased by whitening the noise signal detected by the noise detector in the frequency characteristic adjusting circuit.

According to the configuration of the second invention, the control sound from the speaker detected by the error detector is whitened, so that the convergence speed can be increased.

According to the configuration of the third aspect, the error signal detected by the error detector is whitened in the frequency characteristic adjusting circuit, so that the convergence speed can be increased. Can be obtained.

Since the configuration of the fourth invention is a combination of the configurations of the first and third inventions, the respective effects can be obtained more reliably.

Since the configuration of the fifth invention is a combination of the second and third configurations, the respective effects can be obtained efficiently.

[0020]

An embodiment of the first invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a muffler according to an embodiment of the first invention. In FIG. 1, reference numerals 1a and 1b denote microphones, 2 denotes an AFIR filter, 3 denotes an FIR filter, 4 denotes an LMS calculator, and 5 denotes a speaker, which are the same as those in the above-described conventional example. This embodiment is characterized in that an equalizer 6 is provided at the inputs of the AFIR filter 2 and the FIR filter 3.

The operation of the thus configured silencer will be described below. Microphone 1a
If the noise signal detected in step (1) is a signal having the characteristic shown in FIG. 7, the equalizer 6 has the characteristic shown in FIG. Thus, the noise signal from the microphone 1a has a flat characteristic as shown in FIG. 9 by the equalizer 6 (FIG. 9), is adaptively controlled by the AFIR filter 2, and is reproduced from the speaker 5. Then, the reproduced sound and the noise from the noise source interfere with each other, and the interference sound is detected by the microphone 1b as an error signal.

Next, the error signal is input to the LMS calculator 4, which also receives the output of the equalizer 6 that has been signal-processed by the FIR filter 3. Where F
The transfer function from the speaker 5 to the microphone 1b is identified in the IR filter 3 in advance. The LMS calculator 4 calculates a coefficient based on the error signal and the output signal of the FIR filter 3 so as to minimize the error signal, and transfers the coefficient to the AFIR filter 2. The AFIR filter 2 performs the next signal processing using the coefficient, and by repeating this, the error signal is reduced and the noise is attenuated. The attenuation speed is high because the input of the AFIR filter 2 is whitened. By the way, this is generally called Filt
The ered-x LMS algorithm is used.

As described above, according to this embodiment, by whitening the noise signal using the equalizer 6, it is possible to quickly mute a desired band of the colored noise signal.

Next, an embodiment of the second invention will be described with reference to the drawings. FIG. 2 shows a block diagram of a muffler according to an embodiment of the second invention.
The configuration shown in FIG. 2 is a modification of the configuration in FIG. 1 and the configuration requirements are the same, but the equalizer 6 is connected to the AFI.
The difference is that it is connected to the output of R2.

The operation of the muffler configured as described above will be described below. Microphone 1a
Is adaptively controlled by the AFIR filter 2, the output of which is adjusted in frequency characteristics by the equalizer 6, and reproduced from the speaker 5. The reproduced sound from the speaker 5 and the noise from the noise source cancel each other, and the microphone 1b
Is detected as an error signal. And the error signal and F
The LMS calculator 4 updates the coefficient using the signal from the IR filter 3. Thus, the noise at the microphone 1b is attenuated. Here, the equalizer 6 can obtain the same effect as the embodiment of the first invention by making the characteristics from the speaker 5 to the microphone 1b flat so as to correct the characteristics.

Next, an embodiment of the third invention will be described with reference to the drawings. (FIG. 3) shows a block diagram of a muffler according to an embodiment of the third invention.
The configuration shown in FIG. 3 is a modification of the configuration of FIG. 1 and has the same configuration requirements, but differs in that the equalizer 6 is connected to the output of the microphone 1b.

The operation of the muffler configured as described above will be described below. Microphone 1a
Is adaptively controlled by the AFIR filter 2, and its output is reproduced from the speaker 5. The reproduced sound from the speaker 5 and the noise from the noise source cancel each other, and are detected by the microphone 1b as an error signal as shown in FIG. The error signal is whitened as shown in FIG. 9 by an equalizer 6 having the characteristics shown in FIG.
It is input to the arithmetic unit 4. The LMS calculator 4 is an equalizer 6
From the output signal of the FIR filter 3
Update the coefficient of filter 2. As a result, control is performed to minimize the error signal, and as a result, noise at the microphone 1b is attenuated.

Here, by making the error signal flat characteristics by the equalizer 6, the same effect can be obtained, and the same silencing volume can be obtained at each frequency as shown by the dotted line in FIG.

Next, an embodiment of the fourth invention will be described with reference to the drawings. (FIG. 4) shows a block diagram of a muffler according to an embodiment of the fourth invention.
In FIG. 4, 1a and 1b are microphones, 2 is A
An FIR filter 3, an FIR filter 3, an LMS calculator 4, a speaker 5, and equalizers 6a and 6b.

The operation of the thus configured silencer will be described below. Microphone 1a
If the noise signal detected in step (1) is a signal having characteristics as shown in FIG. 7, the equalizer 6a has characteristics as shown in FIG. The noise signal from the microphone 1a has a flat characteristic as shown in FIG.
The signal is adaptively controlled by the IR filter 2 and reproduced from the speaker 5. Then, the reproduced sound and the noise from the noise source interfere with each other, and the interference sound is detected as an error signal as shown in FIG. 7 by the microphone 1b. The error signal is whitened as shown in FIG. 9 by the equalizer 6b having the characteristic shown in FIG. The LMS calculator 4 updates the coefficient of the AFIR filter 2 from the output signal of the equalizer 6b and the output signal of the FIR filter 3. As a result, control is performed to minimize the error signal, and as a result, noise at the microphone 1b is attenuated.

As described above, according to the present embodiment, the desired band of the colored noise signal can be quickly silenced by whitening the noise signal using the equalizer 6a. Further, by whitening the error signal using the equalizer 6b, the same silencing volume can be obtained at each frequency as shown by the dotted line in FIG.

Further, by combining the first and third inventions, the effects can be obtained simultaneously and reliably.

Next, an embodiment of the fifth invention will be described with reference to the drawings. (FIG. 5) shows a block diagram of a muffler according to an embodiment of the fifth invention.
In FIG. 5, 1a and 1b are microphones, 2 is A
An FIR filter 3, an FIR filter 3, an LMS calculator 4, a speaker 5, and equalizers 6a and 6b.

The operation of the thus configured silencer will be described below. Microphone 1a
Is adaptively controlled by the AFIR filter 2, the output of which is adjusted in frequency characteristics by the equalizer 6a and reproduced from the speaker 5. Here, the equalizer 6a has a characteristic for correcting the characteristic from the speaker 5 to the microphone 1b flat. The reproduced sound from the speaker 5 and the noise from the noise source cancel each other, and are detected by the microphone 1b as an error signal as shown in FIG. The error signal is whitened as shown in FIG. 9 by the equalizer 6b having the characteristic shown in FIG. The LMS operation unit 4 outputs the output signal of the equalizer 6b and the signal FI.
The coefficient of the AFIR filter 2 is updated from the output signal of the R filter 3. As a result, control is performed to minimize the error signal, and as a result, noise at the microphone 1b is attenuated.

As described above, according to the present embodiment, by using the equalizer 6a to flatten the characteristics from the speaker 5 to the microphone 1b, the desired band of the colored noise signal can be quickly silenced. Further, by whitening the error signal using the equalizer 6b, the same silencing volume can be obtained at each frequency as shown by the dotted line in FIG.

Further, by adopting a configuration in which the second and third inventions are combined, the effects can be obtained simultaneously and reliably.

In the above-described first to fifth inventions,
In the example, the equalizer is used to adjust the frequency characteristic, but a filter having an A-curve characteristic, for example, may be used. Also, instead of adjusting the frequency characteristic over the entire band as described in the present embodiment, if it is desired to control only a band with noise, the characteristic may be adjusted to increase only the level of the band. .

[0039]

As described above, according to the first aspect of the invention, the noise signal is whitened by using the frequency characteristic adjusting circuit, whereby the desired band of the colored noise signal can be quickly silenced. A silencer can be realized.

Further, the second invention obtains the same effects as the first invention by correcting the characteristics from the loudspeaker to the error detector by using the frequency characteristic adjusting circuit after the adaptive filter. Can be.

According to the third aspect of the present invention, a desired band of a colored noise signal can be quickly silenced by whitening an error signal using a frequency characteristic adjusting circuit. Thus, it is possible to realize an excellent silencer capable of obtaining the same silencing volume.

According to a fourth aspect of the present invention, the noise signal is whitened by providing the first frequency characteristic adjusting circuit before the adaptive filter, and the error signal is whitened by the second frequency characteristic adjusting circuit. Since the effects of the first and third inventions can be simultaneously and reliably obtained,
An excellent silencer capable of efficiently silencing can be realized.

Further, in the fifth invention, a first frequency characteristic adjusting circuit is provided after the adaptive filter to correct the characteristic from the speaker to the error detector, and the error signal is further converted to white by the second frequency characteristic adjusting circuit. With this configuration, the effects of the second and third aspects of the present invention can be simultaneously and reliably obtained, so that an excellent silencer capable of silencing efficiently can be realized.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment of the first invention.

FIG. 2 is a block diagram of one embodiment of the second invention.

FIG. 3 is a block diagram of one embodiment of the third invention.

FIG. 4 is a block diagram of an embodiment of the fourth invention.

FIG. 5 is a block diagram of one embodiment of the fifth invention.

FIG. 6 is a sound pressure frequency characteristic diagram of a noise signal or an error signal.

FIG. 7 is a sound pressure frequency characteristic diagram of a noise signal or an error signal.

FIG. 8 is an amplitude frequency characteristic diagram of the equalizer.

FIG. 9 is an amplitude frequency characteristic diagram of a noise signal or an error signal corrected by an equalizer.

FIG. 10 is a block diagram showing a conventional silencer.

[Explanation of symbols]

 1a, 1b microphone 2 AFIR filter 3 FIR filter 4 LMS calculator 5 speaker 6, 6a, 6b equalizer

Continued on the front page (72) Inventor Hironari Ogata 6-2-61 Imafukunishi, Joto-ku, Osaka-shi, Osaka Inside Matsushita Seiko Co., Ltd. (72) Inventor Chie Yano 6-2, Imafukunishi, Joto-ku, Osaka-shi, Osaka No. 61 Matsushita Seiko Co., Ltd. (56) References JP-A-3-274997 (JP, A) JP-A-3-274895 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G10K 11/178

Claims (5)

(57) [Claims] 1. A noise detector for detecting noise from a noise source, and a noise control band for detecting a frequency characteristic of the detected noise signal.
A frequency characteristic adjustment circuit for whitening (frequency flattening) within the range, an adaptive filter for adaptively controlling the output of the frequency characteristic adjustment circuit, a speaker for reproducing the output of the adaptive filter, and reproduction sound and noise from the speaker An error detector for controlling a coefficient of the adaptive filter based on an interference sound generated by interference with noise from a source. 2. A noise detector for detecting noise from a noise source, an adaptive filter for adaptively controlling the detected noise signal , and whitening a frequency characteristic of an output of the adaptive filter in a noise control band. (frequency
A frequency characteristic adjusting circuit for performing number flattening), a speaker for reproducing the output of the frequency characteristic adjusting circuit, and the adaptive filter based on an interference sound generated by interference between a reproduced sound from the speaker and noise from a noise source. And an error detector for controlling a coefficient of the noise reduction device. 3. A noise detector for detecting noise from a noise source, an adaptive filter for adaptively controlling the detected noise signal, a speaker for reproducing an output of the adaptive filter, and a reproduced sound from the speaker. An error detector for detecting an interference sound with noise from a noise source; and a frequency control band for a frequency characteristic of an output from the error detector.
And a frequency characteristic adjusting circuit for controlling the coefficient of the adaptive filter based on the adjustment signal. 4. A noise detector for detecting noise from the noise source, its frequency characteristic with respect to the detected noise signal noisy
1st whitening (frequency flattening) within the sound control band
A frequency characteristic adjustment circuit, an adaptive filter that adaptively controls the output of the first frequency characteristic adjustment circuit, a speaker that reproduces the output of the adaptive filter, and a reproduction sound from the speaker and noise from a noise source. An error detector for detecting interference sound , and whitening the frequency characteristic of an output from the error detector in a noise control band.
And a second frequency characteristic adjustment circuit for controlling the coefficient of the adaptive filter based on the adjustment signal (frequency flattening) . 5. A noise detector for detecting noise from a noise source, an adaptive filter for adaptively controlling the detected noise signal , and whitening the frequency characteristic of an output of the adaptive filter in a noise control band. (frequency
A first frequency characteristic adjusting circuit for performing number flattening);
A speaker that reproduces the output of the frequency characteristic adjustment circuit, an error detector that detects an interference sound between the reproduced sound from the speaker and the noise from the noise source, and a frequency characteristic of the output from the error detector. Whitening within noise control band
And a second frequency characteristic adjustment circuit for controlling the coefficient of the adaptive filter based on the adjustment signal (frequency flattening) .