JPH05216485A - Silencer - Google Patents

Abstract

(57) [Abstract] [Purpose] The present invention relates to a silencer that uses active noise control, and in particular, it silences a desired band quickly by adaptively controlling an adaptive filter with a whitened signal by a frequency characteristic adjustment circuit. Provide the device. [Configuration] Microphone 1 for detecting noise from a noise source
a, an equalizer 6 that adjusts the frequency characteristics of the detected noise signal, and an AFI that adaptively controls the output of the equalizer 6.
The R filter 2, the FIR filter 3 which also processes the output of the equalizer 6, the speaker 3 which reproduces the output of the AFIR filter 2, the microphone 1b which detects noise at the evaluation point, the output from the microphone 1b and the FIR
It is composed of an LMS calculator 4 for updating the coefficient of the AFIR filter 2 by the output from the filter 3.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art In recent years, an active noise control method has been proposed in which a control sound is output from a speaker by using a digital signal processing technique to mute environmental noise at a listening position.

A conventional silencer will be described below with reference to the drawings. FIG. 10 is a block diagram of a conventional silencer. In FIG. 10, 1a and 1b are microphones, 2 are adaptive acyclic digital filters (hereinafter abbreviated as AFIR filters), 3 are acyclic digital filters (hereinafter abbreviated as FIR filters), 4 are LMS calculator 5 is a speaker.

The operation of the muffler having the above structure will be described below. Microphone 1a
The noise signal detected by the
It is input to the 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 that has been signal-processed by is also input to the LMS calculator 4. Here, the transfer function C from the speaker 5 to the microphone 1b is preset in the FIR filter 3. Therefore, the LMS calculator 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) becomes the minimum, 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 by the speaker 5, whereby the error signal in the microphone 1b is reduced and the noise is attenuated.

The 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 chromatic as shown in (FIG. 6), that is, the noise signal and the error signal detected by the microphones 1a and 1b are not detected. When the characteristic as shown in (FIG. 6) is used, there are problems that the volume of sound is different depending on the frequency band and the convergence time is delayed as shown by the dotted line in (FIG. 6).

The present invention solves the above problems, and when the noise signal and the error signal are chromatic,
An object of the present invention is to provide a muffling device that eliminates the influence thereof and shortens the convergence time, and also to provide a muffling device that can obtain a similar muffling volume within a control band.

[0010]

In order to achieve this object, a silencer of the first invention is a noise detector for detecting noise from a noise source, and a frequency characteristic of the detected noise signal is set to an arbitrary value. A frequency characteristic adjusting circuit for adjusting the frequency characteristic,
An adaptive filter that adaptively controls the output of the frequency characteristic adjusting circuit, a speaker that reproduces the output of the adaptive filter, and an interference sound generated by interference between a reproduced sound from the speaker and noise from a noise source. And an error detector that controls the coefficient of the adaptive filter.

Also, in order to achieve the above object, a silencer of the second invention is a noise detector for detecting noise from a noise source, an adaptive filter for adaptively controlling the detected noise signal, and A frequency characteristic adjusting circuit for adjusting the frequency characteristic of the output of the adaptive filter to an arbitrary frequency characteristic, a speaker for reproducing the output of the frequency characteristic adjusting circuit, a reproduced sound from the speaker and noise from a noise source. The error detector controls the coefficient of the adaptive filter based on the interference sound generated by the interference.

Also, in order to achieve the above object, a silencer of the third invention is a noise detector for detecting noise from a noise source, an adaptive filter for adaptively controlling the detected noise signal, and A speaker that reproduces the output of the adaptive filter, and an error detector that detects an interference sound between the reproduced sound from the speaker and the noise from the noise source,
The frequency characteristic adjusting circuit adjusts the frequency characteristic of the output from the error detector to an arbitrary frequency characteristic and controls the coefficient of the adaptive filter based on the adjustment signal.

Further, in order to achieve the above-mentioned object, the silencer of the fourth invention further comprises a noise detector for detecting noise from a noise source and a frequency characteristic of the detected noise signal at an arbitrary frequency. A first frequency characteristic adjusting circuit for adjusting the characteristics, 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, and a reproduced sound and noise from the speaker. An error detector that detects an interference sound with noise from a source, adjusts the frequency characteristic of the output from the error detector to an arbitrary frequency characteristic, and controls the coefficient of the adaptive filter based on this adjustment signal. And a second frequency characteristic adjusting circuit.

Further, in order to achieve the above-mentioned object, the silencer of the fifth invention further comprises a noise detector for detecting noise from a noise source, an adaptive filter for adaptively controlling the detected noise signal, and A first frequency characteristic adjusting circuit that adjusts the frequency characteristic of the output of the adaptive filter to an arbitrary frequency characteristic, a speaker that reproduces the output of the first frequency characteristic adjusting circuit, and a reproduced sound and noise from the speaker. An error detector that detects an interference sound with noise from a source, adjusts the frequency characteristic of the output from the error detector to an arbitrary frequency characteristic, and controls the coefficient of the adaptive filter based on this adjustment signal. And a second frequency characteristic adjusting circuit.

[0015]

According to the structure of the first aspect of the present 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 convergence speed can be increased by whitening the control sound from the speaker detected by the error detector.

According to the configuration of the third invention, the error signal detected by the error detector is whitened in the frequency characteristic adjusting circuit, so that the convergence speed can be increased and the frequency is substantially the same at any frequency within the control band. You can get the silence volume of.

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

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

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the first invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a silencer according to an embodiment of the first invention. In FIG. 1, 1a and 1b are microphones, 2 is an AFIR filter, 3 is a FIR filter, 4 is an LMS calculator, and 5 is a speaker, which are the same as those in the conventional example described above. The feature of this embodiment is that an equalizer 6 is provided at the input of the AFIR filter 2 and the FIR filter 3.

The operation of the muffler having the above structure will be described below. Microphone 1a
When the noise signal detected in step S1 has a characteristic as shown in FIG. 7, the equalizer 6 has the characteristic as shown in FIG. As a result, the noise signal from the microphone 1a has a flat characteristic as shown in FIG. 9 by the equalizer 6, is adaptively controlled by the AFIR filter 2, and is reproduced by the speaker 5. The reproduced sound and the noise from the noise source interfere with each other, and the interference sound is detected as an error signal by the microphone 1b.

Next, the error signal is inputted to the LMS calculator 4, and the output of the equalizer 6 which has been signal-processed by the FIR filter 3 is also inputted to the LMS calculator 4. Where F
The transfer function from the speaker 5 to the microphone 1b is previously identified in the IR filter 3. The LMS calculator 4 calculates a coefficient by 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 following signal processing using the coefficient, and by repeating this, the error signal becomes smaller 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, the desired band of the colored noise signal can be quickly silenced by whitening the noise signal using the equalizer 6.

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

The operation of the muffler having the above structure will be described below. Microphone 1a
The noise signal detected in 1 is adaptively controlled by the AFIR filter 2, the output of which is adjusted in frequency characteristic 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 out, 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. As a result, the noise in the microphone 1b is attenuated. Here, the equalizer 6 has the characteristic of flatly correcting the characteristic from the speaker 5 to the microphone 1b, so that the same effect as that of the first embodiment of the present invention can be obtained.

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

The operation of the muffling device having the above structure will be described below. Microphone 1a
The noise signal detected in 1 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. Then, the error signal is whitened as shown in FIG. 9 by the equalizer 6 having the characteristics of FIG.
It is input to the calculator 4. The LMS calculator 4 is an equalizer 6
AFIR from the output signal of the FIR filter and the output signal of the FIR filter 3
The coefficient of the filter 2 is updated. As a result, the error signal is controlled so as to be minimized, and as a result, the noise in the microphone 1b is attenuated.

Here, by making the error signal have a flat characteristic by the equalizer 6, the same effect can be obtained, and as shown by the dotted line (FIG. 7), the same sound volume can be obtained at each frequency.

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

The operation of the muffler having the above structure will be described below. Microphone 1a
When the noise signal detected in step (1) has a characteristic as shown in FIG. 7, the equalizer 6a has the characteristic as shown in FIG. The noise signal from the microphone 1a has a flat characteristic as shown in FIG.
It is adaptively controlled by the IR filter 2 and 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 as an error signal as shown in FIG. Then, the error signal is whitened as shown in FIG. 9 by the equalizer 6b having the characteristic of FIG. 8 and input to the LMS calculator 4. 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, the error signal is controlled so as to be minimized, and as a result, the noise in the microphone 1b is attenuated.

As described above, according to this 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 by using the equalizer 6b, the same sound volume can be obtained at each frequency as shown by the dotted line in FIG.

Further, by adopting the constitution in which the first and third inventions are combined, it is possible to obtain those effects simultaneously and surely.

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

The operation of the muffling device having the above structure will be described below. Microphone 1a
The noise signal detected in 1 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 flatly correcting the characteristic from the speaker 5 to the microphone 1b. 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. Then, the error signal is whitened as shown in FIG. 9 by the equalizer 6b having the characteristic of FIG. 8 and input to the LMS calculator 4. The LMS calculator 4 outputs the FI and the output signal of the equalizer 6b.
The coefficient of the AFIR filter 2 is updated from the output signal of the R filter 3. As a result, the error signal is controlled so as to be minimized, and as a result, the noise in the microphone 1b is attenuated.

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

Further, by adopting the constitution in which the second and third inventions are combined, it is possible to obtain those effects simultaneously and surely.

Although the equalizer is used for adjusting the frequency characteristic in this embodiment, a filter having an A curve characteristic may be used instead. Further, instead of adjusting the frequency characteristic over the entire band as described in the present embodiment, when it is desired to control only the noisy band, the characteristic may be adjusted so that only the level of the band is increased. ..

[0039]

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

Further, the second aspect of the invention has the same effect as the first aspect of the invention, since the frequency characteristic adjusting circuit is used after the adaptive filter to correct the characteristic from the speaker to the error detector. You can

In the third aspect of the invention, the desired band of the colored noise signal can be quickly silenced by whitening the error signal using the frequency characteristic adjusting circuit, and each frequency within the control band can be suppressed. It is possible to realize an excellent silencer capable of obtaining the same silence volume.

According to a fourth aspect of the invention, the first frequency characteristic adjusting circuit is provided in front of the adaptive filter to whiten the noise signal, and further the error signal is whitened by the second frequency characteristic adjusting circuit. Since the effects of the first and third inventions can be obtained simultaneously and reliably,
It is possible to realize an excellent muffling device that can efficiently muffle sound.

Further, in the fifth invention, the 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 made white by the second frequency characteristic adjusting circuit. With this configuration, the effects of the second and third aspects of the invention can be obtained at the same time and surely, so that it is possible to realize an excellent muffling device that can effectively muffle the sound.

[Brief description of drawings]

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

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

FIG. 3 is a block diagram of an embodiment of a third invention.

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

FIG. 5 is a block diagram of an 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

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical display location H04R 1/30 B 8946-5H (72) Inventor Hironari Ogata 6 Imafuku Nishi, Joto-ku, Osaka City, Osaka Prefecture 2-61, Matsushita Seiko Co., Ltd. (72) Inventor, Chie Yano 6-61, 2-61, Imafuku Nishi, Joto-ku, Osaka City, Osaka Prefecture Matsushita Seiko Co., Ltd.

Claims (5)

[Claims] 1. A noise detector for detecting noise from a noise source, a frequency characteristic adjusting circuit for adjusting the frequency characteristic of the detected noise signal to an arbitrary frequency characteristic, and an output of the frequency characteristic adjusting circuit is adapted. An adaptive filter to control, a speaker that reproduces the output of the adaptive filter, and an error detection that controls the coefficient of the adaptive filter based on an interference sound generated by interference between a sound reproduced from the speaker and noise from a noise source. A silencer equipped with a container. 2. A noise detector that detects noise from a noise source, an adaptive filter that adaptively controls the detected noise signal, and the frequency characteristic of the output of the adaptive filter is adjusted to an arbitrary frequency characteristic. A frequency characteristic adjusting circuit, a speaker that reproduces the output of the frequency characteristic adjusting circuit, and a coefficient of the adaptive filter based on an interference sound generated by interference between a reproduced sound from the speaker and noise from a noise source. A silencer comprising an error detector. 3. A noise detector that detects noise from a noise source, an adaptive filter that adaptively controls the detected noise signal, a speaker that reproduces the output of the adaptive filter, and a reproduced sound from the speaker. An error detector that detects an interference sound with noise from a noise source, the frequency characteristic of the output from the error detector is adjusted to an arbitrary frequency characteristic, and the coefficient of the adaptive filter is adjusted based on this adjustment signal. A silencer comprising: a frequency characteristic adjusting circuit for controlling. 4. A noise detector for detecting noise from a noise source, a first frequency characteristic adjusting circuit for adjusting the frequency characteristic of the detected noise signal to an arbitrary frequency characteristic, and the first frequency characteristic adjusting circuit. An adaptive filter that adaptively controls the output of the frequency characteristic adjusting circuit, a speaker that reproduces the output of the adaptive filter, an error detector that detects an interference sound between a reproduced sound from the speaker and noise from a noise source, and And a second frequency characteristic adjusting circuit for adjusting the frequency characteristic of the output from the error detector to an arbitrary frequency characteristic and controlling the coefficient of the adaptive filter based on the adjusted signal. Silencer. 5. A noise detector that detects noise from a noise source, an adaptive filter that adaptively controls the detected noise signal, and the frequency characteristic of the output of the adaptive filter is adjusted to an arbitrary frequency characteristic. A first frequency characteristic adjusting circuit; a speaker that reproduces an output of the first frequency characteristic adjusting circuit; an error detector that detects an interference sound between a reproduced sound from the speaker and a noise from a noise source; And a second frequency characteristic adjusting circuit for adjusting the frequency characteristic of the output from the error detector to an arbitrary frequency characteristic and controlling the coefficient of the adaptive filter based on the adjusted signal. Silencer.