JPH0511772A - Noise canceling system - Google Patents

Abstract

PURPOSE:To stop the noise canceling operation when the noise is so small as to be masked by the audio sound. CONSTITUTION:The signal according to the noise generated from a noise source is received as a reference signal SN and a synthesized signal of the noise SN at a noise canceling point and a canceling sound SC is received as an error signal Er by a noise canceling controller 21. A noise canceling signal NC is outputted so that the error signal may be minimized, and a comparative part 28 makes a comparison between an audio signal AS' outputted by an audio circuit 11 and the noise canceling signal N,, and a stopping order SPC of the noise canceling processing is outputted to the noise canceling controller 21 when the audio sound is so large as mask the noise, while an order of continuation and restarting of the noise canceling processing is made when masking can not be made.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise canceling system, and more particularly to a noise canceling system capable of canceling noise and listening to comfortable audio audio.

[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 low, 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 a speaker to reduce the noise (active control) has been in the limelight and has been put to practical use in a part of indoor space such as a factory or an office. At the same time, a method has been proposed in which noise is reduced by active control even in the passenger compartment of an automobile.

[0004]

In the conventional active control for reducing noise in a room provided with an audio device, such as a passenger compartment of an automobile, a constant noise canceling process (regardless of audio audio level) is performed. For example, the adaptive algorithm processing) is performed to generate a noise canceling signal and the canceling sound is emitted from the speaker. As described above, since the conventional noise canceling system always operates, there is a problem that the power consumed on the canceling system side becomes large, and moreover, the canceling system components,
In particular, there has been a problem that the loudness of a speaker that emits a low-frequency canceling sound increases.

In a space where noise and audio sound are mixed, when the audio sound level is considerably higher than the noise level, the noise is masked by the audio sound and cannot be heard. When the noise is masked by the audio sound as described above, the noise is not perceptually sensed even if the noise canceling system is not activated. Further, when noise has only frequency components within a certain band, in order to make a large contribution to masking, it is a component in the same band as the noise among the frequency components included in the audio signal.

The present invention has been made in view of the above points, and an object thereof is to stop the noise canceling operation when the noise is small enough to be masked as compared with the audio voice. It is to provide a noise cancellation system.

Another object of the present invention is to provide a noise canceling system which can reduce the operating time of the noise canceling system and save power consumption, and further reduce the consumption of the speaker or the like to prolong the life of the noise canceling system. It is to be.

Still another object of the present invention is to provide a noise canceling system capable of accurately detecting the masking state and stopping the noise canceling operation.

[0009]

According to the present invention, there is provided a noise canceling controller for outputting a noise canceling signal to reduce noise, an audio device for outputting audio sound, and an audio device. This is achieved by a comparison unit that compares the magnitudes of the Dio signal and the noise cancellation signal and a filter having a noise frequency band.

[0010]

The noise canceling controller receives the signal corresponding to the noise generated from the noise source as the reference signal and the synthesized sound signal of the noise at the noise canceling point and the canceling sound as the error signal, and the error signal is minimized. The noise canceling signal is output so that the comparison unit compares the size of the audio signal and the noise canceling signal, or compares the size of the audio signal and the noise signal at the noise canceling point. When the noise is large enough to be masked, the noise canceling controller is instructed to stop the noise canceling process, and when the masking cannot be performed, the noise canceling process is restarted.

As described above, when noise is masked by audio sound, if the canceling process is stopped so that the canceling sound is not output, the operating time of the noise canceling system is reduced and the power consumption is saved. In addition, the degree of wear of the speaker or the like can be reduced and the service life can be extended.

Further, a filter having a noise frequency band is provided, and the size of the audio signal that has passed through the filter and the noise cancellation signal are compared by a comparison unit, and audio audio components within the noise frequency band are noisy. When it is large enough to mask, the noise canceling controller is instructed to stop the noise canceling process. If you do this,
It is possible to prevent the situation in which the noise canceling operation is stopped despite the insufficient masking, and it is possible to accurately detect the masking state and stop the noise canceling operation.

[0013]

【Example】

(a) Overall configuration of the first embodiment of the present invention FIG. 1 is a configuration diagram of an embodiment of the noise canceling system of the present invention, which is an example in the case of reducing the noise in the passenger compartment. In the figure, reference numeral 11 denotes an audio circuit for applying various processing (frequency characteristics, volume, sound quality adjustment, etc.) to the input audio signal As, and 12 an audio signal output from the audio circuit. A power amplifier for amplifying As', and 13 is an audio speaker for radiating an audio sound Sa. still,
The audio device is constructed as described above.

21 is generated from a noise source (eg engine)
The signal corresponding to the noise that is generated is the reference signal S _NIs entered as
Along with noise cancellation points in the passenger compartment (for example, the driver's ear
Near the source) A synthesized message of noise Sn and cancellation sound Sc
Signal is input as an error signal Er, and the error signal is
Noise cancellation processing is performed to reduce the noise.
With a noise cancellation controller that outputs the cell signal Nc
is there. The reference signal S_NIs close to the engine, for example
It is a noise signal detected by the sensor provided,
The sound Sn is at the noise cancellation point due to the engine rotation.
It will occur.

Reference numeral 22 is a power amplifier for amplifying the noise canceling signal Nc, 23 is a canceling speaker for radiating the noise canceling sound Sc, and 24 is arranged at the noise canceling point to detect a synthesized sound of the noise Sn and the canceling sound Sc. Then, the error microphones 25 and 26 respectively output the synthesized sound signal (error signal) Er, the gain adjusters, and the reference numeral 28 compares the audio signal As' and the noise canceling signal Nc to determine the audio voice. Is large enough to mask noise, the noise cancel controller 21 outputs a stop command SPC for the noise cancel processing.

Noise Canceling Operation The noise canceling controller 21, as shown in FIG.
It has an adaptive algorithm processing section 21a, an adaptive filter 21b having a digital filter configuration, and a DA converter 21c for converting the output of the adaptive filter into an analog noise canceling signal Nc. Adaptive algorithm processing unit 21a
Determines the coefficient of the adaptive filter 21b so that the error signal Er input from the error microphone 24 is minimized according to a well-known LMS (Least Mean Square) adaptive algorithm, and the adaptive filter 21b follows the determined coefficient. The reference signal S _N is digitally processed, and the DA converter 21c outputs a noise cancellation signal N _C having a predetermined phase, gain, band, and the like. It should be noted that the reference signal S _N must be a signal having a high correlation with the noise Sn to be erased, and a sound having no correlation is not canceled.

[0017] noise source (engine) 31 noise cancellation controller 21 as noise signal is the reference signal S _N which is detected by the reference microphone 32 when noise (periodic noise) occurs shown in Fig. 3 (a) having a periodicity from Is entered. At this time, the noise generated from the noise source 31 propagates through the air having a predetermined transfer function to reach the noise canceling point, and the noise Sn at the point is slightly weakened in level and delayed, as shown in FIG. As shown.

First, the noise canceling controller 21 detects, for example, a noise canceling signal Nc whose phase is opposite to that of the reference signal S _N.
And the cancel speaker 23 outputs the cancel sound Sc shown in FIG. 3 (c). However, since the noise Sn is out of phase with the noise Sn, the noise is not canceled by the cancel sound Sc, and the error signal Er is generated. The noise canceling controller 21 performs adaptive algorithm processing so that the error signal is minimized, and the adaptive filter 21
The coefficient of b is determined, and in the ideal case, the phase of the cancel sound Sc shown in FIG. 3 (d) is finally made opposite to the phase of the noise Sn, and the levels are matched to cancel the noise.

Structure of Comparing Section (1) First Example of Comparing Section The comparing section 28 is, as shown in FIG. 4, an audio signal As'.
Absolute value output unit 28a for outputting the absolute value of x and the average value x of the absolute values output from the absolute value output unit 28a within a predetermined time
A time averaging unit 28b that outputs a, an absolute value output unit 28c that outputs the absolute value of the noise cancellation signal Nc, and a time that the average value xc of the absolute values output from the absolute value output unit 28c within a predetermined time period is output. It has an averaging unit 28d, a computing unit 28e for computing the difference between the average value xa and the average value xc, and a determining unit 28f.

Based on the difference (xa-xc) between the average value xa and the average value xc, the judging section 28f determines whether or not the audio sound is in a state of masking noise (masking state). If it is determined that the masking state is present, a noise canceling process stop command SPC is output to the noise canceling controller 21, and if the masking state is not detected, the noise canceling process is continued / restarted. For example, if the set value is r, the masking state is set when the state of (xa-xc) ≧ r continues for a certain time or more, and the masking state is set when the state of (xa-xc) <r continues for a certain time or more. Determine not.

The reason for comparing the audio signal As 'with the noise canceling signal Nc without comparing the audio signal As' with the noise signal at the noise canceling point in judging the masking state is that the noise is This is because the noise Sn and the cancel sound Sc are similar in level in the cancel system. As shown by the dotted line in FIG. 1, a characteristic changing unit 29 simulating the transfer function from the noise source to the noise canceling point is provided, and the characteristic changing unit 29 has a reference signal (noise signal).
It is also possible to input S _N , regard the output signal of the characteristic changing unit 29 as a noise signal at the noise cancellation point, and compare the noise signal with the audio signal to detect the masking state.

(2) Second Embodiment of Comparing Unit FIG. 5 is another block diagram of the comparing unit 28, which includes a power spectrum calculating unit 28a 'for calculating the power spectrum of the audio signal As'. Power spectrum calculation unit 28
a power average calculating unit 28b 'which outputs an average value xa' of a power spectrum output from a'in a predetermined time,
A power spectrum calculating unit 28c 'for calculating the power spectrum of the noise cancellation signal Nc, and a power average calculating unit for outputting an average value xc' of the power spectrum output from the power spectrum calculating unit 28c 'within a predetermined time. It has a unit 28d ', a computing unit 28e' for computing the difference between the average value xa 'and the average value xc, and a judging unit 28f'.

The determination unit 28f 'determines whether or not the masking state is present based on the difference (xa'-xc') between the average value xa 'and the average value xc'. A stop command SPC for the noise canceling process is output to the cancel controller 21, and a command for restarting the noise canceling process is issued if it is not in the masking state. For example, if the set value is r ', the masking state is set when the state of (xa'-xc') ≥r 'continues for a certain time or more, and the state of (xa'-xc') <r 'is set for a certain time. When the above operation is continued, it is determined that the masking state is not established.

Overall Operation The audio circuit 11 includes an audio source (the video source, not shown).
Audio signal As from a deck, CD player, AM / FM tuner, etc.), the audio signal is subjected to sound quality, volume, equalizing processing, etc., and input to the power amplifier 12. -The audio speaker Sa emits the audio sound Sa.

On the other hand, the noise cancellation controller 21 uses the error signal Er detected at the noise cancellation point to set L
The MS adaptive algorithm process is performed to determine the coefficient of the adaptive filter. Then, using the coefficient, a signal (reference signal) S _N corresponding to the noise generated from a noise source such as an engine is adaptively filtered to create a noise cancellation signal Nc, which is input to the power amplifier 22. Cancellation
A cancel sound Sn is emitted from the mosquito 23.

The error microphone 24 detects the synthesized sound of the newly emitted cancel sound Sc and noise Sn, and uses the synthesized sound signal as an error signal Er to cancel the noise cancellation controller 21.
To enter. The noise cancellation controller 21 performs the same processing as described above based on the input error signal Er, and outputs the noise cancellation signal Nc so that the error signal is minimized. After that, the error detection and the noise cancel signal output processing are performed at predetermined time intervals, and finally the noise is canceled by the cancel sound.

In this state, the comparison unit 28 compares the audio signal As' and the noise cancel signal Nc to determine whether they are in the masking state, and if the noise cancel controller 21 instructs the noise cancel controller 21 to stop the noise cancel process.
Is output and the noise canceling process is stopped. Therefore, in the masking state, the cancel sound is not output from the cancel speaker 23.

On the other hand, if it is not in the masking state, the execution of the noise canceling process is instructed, and the noise canceling process is continued or restarted. The gain adjusters 25 and 26
By adjusting the gain, it is possible to adjust the difference between the audio signal and the noise canceling signal, which are judged to be in the masking state, and an appropriate gain is set according to the operator's preference.

(B) Second Embodiment of the Present Invention FIG. 6 is a block diagram of a second embodiment of the present invention, in which the same parts as those in FIG. 1 are designated by the same reference numerals. In FIG. 6, 31 is a microphone for detecting the level of the audio sound Sa output from the audio speaker 13, and 32 is a microphone for detecting the level of the cancel sound Sc output from the cancel speaker 23. . The comparison unit 28 includes the microphones 31 and 3
The two output signals are regarded as the audio signal As 'and the noise canceling signal Nc, respectively, and the masking state is judged based on the magnitude of both signals As', Nc to cancel the noise canceling process by stopping, continuing or restarting. Controller 2
Instruct 1.

(C) Third Embodiment of the Present Invention FIG. 7 is a block diagram of a third embodiment of the present invention, in which the same parts as those in FIG. 1 are designated by the same reference numerals. 7 is different from FIG. 1 in that (1) the power amplifier and the speaker on the noise canceling side are deleted, and the power amplifier 12 and the speaker 13 on the audio side are shared. 2) A synthesizer 41 for synthesizing the audio signal As' which is the output of the audio circuit 11 and the noise canceling signal Nc which is the output of the noise canceling controller 21 is provided, and the synthetic signal AN is input to the power amplifier 12. , A point at which the audio sound Sa and the cancel sound Sc are emitted from the speaker 13. According to the third embodiment, the expensive power amplifier and the loudspeaker on the noise canceling side can be removed, and the device can be downsized and the cost can be reduced.

(D) Fourth Embodiment of the Present Invention FIG. 8 is a block diagram of a fourth embodiment of the present invention, in which the same parts as those in FIG. 1 are designated by the same reference numerals. 8 is different from FIG. 1 in that the filter 5 having the same frequency band as the noise band between the audio circuit 11 and the gain adjuster 25.
1, and the comparison unit 28 compares the audio signal As ″ that has passed through the filter with the noise cancellation signal Nc.
The point is to judge the masking state based on the magnitude of both signals As ″, Nc, and to instruct the noise canceling controller to stop, continue or restart the noise canceling process.

FIG. 9 is an explanatory diagram of the frequency band of the filter 51, where f _CL is the low cutoff frequency, f _CH is the high cutoff frequency of the filter, f _L is the lower limit frequency of the noise band, and f _H Is the upper limit frequency of the noise band, f _CL , f _CH
Is set to f _CL = f _L −120 (Hz) f _CH = f _H +120 (Hz) based on the critical bandwidth of pure tone.

When the noise has only the frequency component within the predetermined band, it is the component in the same band as the noise among the frequency components included in the audio signal that is significantly involved in the masking. In the first to third embodiments, the noise level is compared with the overall level in all frequency bands of audio voice without considering such masking effect. For this reason, the noise canceling operation may be stopped when it is determined that the masking state is set in spite of the insufficient masking.

However, in the fourth embodiment of FIG. 8, the level of the noise and the same band component of the frequency components included in the audio signal are compared with the noise level, so that masking is performed accurately. It is possible to control the stop, continuation, and restart of the noise cancellation processing by judging the state. In FIG. 8, a characteristic changing unit 29 may be provided as in FIG. 1, and the comparing unit 28 may compare the output of the characteristic changing unit and the filter output to determine the masking state.

(E) Fifth Embodiment of the Present Invention FIG. 10 is a block diagram of the fifth embodiment of the present invention, in which the same parts as those in FIG. 8 are designated by the same reference numerals. In FIG. 10, 6
Reference numeral 1 is a microphone for detecting the level of the audio sound Sa output from the audio speaker 13, and reference numeral 62 is a microphone for detecting the level of the cancel sound Sc output from the cancel speaker 23. The comparison unit 28 uses each microphone 6
The output signals of 1, 62 are respectively the audio signals As',
Considered as noise cancellation signal Nc, audio signal As'
Is input to the filter 51, and the output signal As ″ of the filter is input.
Then, the masking state is judged based on the magnitude of the noise canceling signal Nc, and the noise canceling controller 21 is instructed to stop, continue or restart the noise canceling process.

(F) Sixth Embodiment of the Present Invention FIG. 11 is a configuration diagram of a sixth embodiment of the present invention, in which the same parts as those in FIG. 8 are designated by the same reference numerals. 11 is different from FIG. 8 in that (1) the power amplifier and the speaker on the noise canceling side are deleted, and the power amplifier 12 on the audio side is removed.
And the speaker 13 is shared, (2) Audio circuit 1
1 and the audio signal As' which is the output of 1 and the noise canceling signal Nc which is the output of the noise canceling controller 21.
A synthesizer 71 for synthesizing the sound signal is provided, the synthesized signal AN is input to the power amplifier 12, and the audio sound S is output from the speaker 13.
This is the point at which a and the cancel sound Sc are emitted.

According to the sixth embodiment, the masking state can be accurately determined, and the expensive power amplifier and speaker on the noise canceling side can be removed, so that the apparatus can be downsized and the cost can be reduced. Become. 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.

[0038]

As described above, according to the present invention, when the noise is masked by the audio sound, the canceling process is stopped and the canceling sound is not output. Therefore, the operating time of the noise canceling system is reduced. Thus, it is possible to save power consumption, reduce the consumption of the speaker, etc., and prolong the service life.

Further, according to the present invention, a filter having a noise frequency band is provided, and the size of the audio signal that has passed through the filter is compared with that of the noise cancellation signal in the comparison unit,
When the audio component in the noise frequency band is large enough to mask noise, the noise cancel controller is instructed to stop the noise cancel processing, so the masking state can be detected accurately. The noise canceling operation can be stopped.

Further, according to the present invention, there are provided a detecting section for detecting the level of the cancel sound output from the cancel speaker and a detecting section for detecting the level of the audio sound output from the audio speaker. The noise canceling signal and the audio signal are output from the respective detecting units, and the comparing unit compares the sizes of the audio signal and the noise canceling signal, and the audio sound is large enough to mask noise. At this time, since it is configured to instruct the noise cancellation controller to stop the noise cancellation processing,
It is possible to accurately judge the masking state based on the actual noise at the noise canceling point and the signal corresponding to the audio sound, and stop the noise canceling operation.

[Brief description of drawings]

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

FIG. 2 is a configuration diagram for explaining a noise canceling operation.

FIG. 3 is a waveform diagram for explaining the operation of the noise canceling controller.

FIG. 4 is a configuration diagram of a first embodiment of a comparison unit.

FIG. 5 is a configuration diagram of another embodiment of the comparison unit.

FIG. 6 is a configuration diagram of a second embodiment of the present invention.

FIG. 7 is a configuration diagram of a third embodiment of the present invention.

FIG. 8 is a configuration diagram of a fourth embodiment of the present invention.

FIG. 9 is an explanatory diagram of a band of a filter.

FIG. 10 is a configuration diagram of a fifth embodiment of the present invention.

FIG. 11 is a configuration diagram of a sixth embodiment of the present invention.

[Explanation of symbols]

11 ... Audio circuit 21. Noise canceling controller 24 ... Error microphone 28 ... Comparison section 51 ... Filter

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shunichi Imanishi             1-8 Nishigotanda, Shinagawa-ku, Tokyo             Within Lupine Co., Ltd. (72) Inventor Satoshi Yoshida             1-8 Nishigotanda, Shinagawa-ku, Tokyo             Within Lupine Co., Ltd.

Claims (3)

[Claims] 1. A signal corresponding to noise generated from a noise source is input as a reference signal, and a composite sound signal of noise and a cancel sound at a noise cancel point is input as an error signal, and the error signal is minimized. The noise cancellation controller that outputs the noise cancellation signal so that the audio signal is output based on the audio signal, and the audio device that outputs the audio sound based on the audio signal are compared with each other.
Alternatively, the audio signal and the noise signal at the noise cancellation point are compared in magnitude, and when the audio sound is large enough to mask the noise, a comparison unit for instructing the noise cancellation controller to stop the noise cancellation process is provided. A noise canceling system characterized by being equipped. 2. The noise canceller according to claim 1, wherein a filter having a noise frequency band is provided, and the comparison unit compares the audio signal passed through the filter with the noise canceling signal. system. 3. A detection unit for detecting the level of a cancel sound output from the speaker and a detection unit for detecting the level of audio sound output from the speaker are provided, and the output of each detection unit is set. The noise cancellation system according to claim 1 or 2, wherein the noise cancellation signal and the audio signal are respectively used.