JPH06276599A - Impulsive sound suppressing device - Google Patents

Abstract

PURPOSE:To suppress impulsive sound inputted in a hearing aid, etc., by detecting impulsive sound, switching a switch and outputting delay impulsive sound via an LPF (low pass filter). CONSTITUTION:The instantaneous value of an input signal 210 or the instantaneous value after the only high frequency components of the signal 210 are filtered exceeds a threshold, impulsive sound is detected by an impulsive sound detection means 230 and the switch 72 of an impulsive sound suppression circuit 710 is switched by a temporary holding circuit 250. A delay input signal through a delay circuit 280 is outputted via an LPF (low pass filter) 730 and impulsive sound inputted in a hearing aid, etc., is suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shock noise suppressor for an audio device such as a hearing aid.

[0002]

2. Description of the Related Art The general characteristics of impact noise will be described before describing the conventional art. FIG. 13 shows a general signal waveform diagram of an impact sound. For general characteristics of impact sound, see “Effect of some physical parameters of impact sound on off sound on it's loudness”.
impact sound on its loudoness) (J. Acoust. Soc.Jp
n. (E) 2,1 (1981)). According to this material, the impact noise is 1 to 15 ms / 60 as shown in FIG.
The steep envelope rising characteristic of 10 dB and 60 to 1
It has a gradual and exponential envelope fall characteristic 20 of 000 ms / 60 dB. Further, the sound pressure at the maximum instantaneous sound pressure point 30 is very large, for example, 120 dBSPL or more when the juice can is dropped. The duration tl of the impact sound is 61 to 1015 ms, which varies greatly depending on the impact sound. The perceived loudness of the impact sound is hardly affected by the rise time, and the higher the sound pressure at the maximum instantaneous sound pressure point, the longer the fall time is perceived as a loud sound.

As a conventional shock noise suppressing device for suppressing the shock noise as described above, there are an automatic gain control circuit and a limiter circuit.

FIG. 14 shows a block diagram of a conventional automatic gain control circuit used for removing impact noise. In FIG.
Reference numeral 110 denotes a short-time average amplitude extraction means, which is composed of an absolute value conversion means 120 composed of a detector and the like and an integration means 130 composed of an integrator and the like. 140 is a gain control amplifier, and 150 and 160 are a signal input terminal and a signal output terminal, respectively.

In the conventional automatic gain control circuit configured as described above, the integrating means 130 is charged with a relatively short time constant (several ms) and a long time constant (several tens to 100 m).
s) is set to discharge, a fast attack,
It realizes the characteristic called slow release. When the amplitude of the input signal becomes large, the integrating means 130 is charged in a relatively short time, and the gain of the gain control amplifier 140 is prevented from decreasing in a short time to prevent an excessive output. Further, when the amplitude of the input signal becomes small, the integrating means 130 discharges for a relatively long time, the gain of the gain control amplifier 140 gradually increases, and the gain suddenly increases due to a pause time during conversation. It didn't stop.

[0006]

If the automatic gain control circuit of FIG. 14 is used to eliminate the impulsive sound as shown in FIG. 13, the impulsive sound rises quickly with the time constant of the conventional automatic gain control circuit, so that the impulsive sound rises. When reaches the maximum sound pressure point, the gain is not sufficiently lowered. Therefore, in order to cope with the impact noise, the charging time constant of the integrating means 130 must be shortened to 1 ms or less. However, if the time constant is shortened, noise tends to cause malfunction, and the envelope of the rising part of the output signal has a constant amplitude due to the automatic gain control circuit, which reduces the naturalness of the sound. Had. Also, once the impact sound is input, the integrating means 130 is charged with a very high voltage. Therefore, there is a problem that the gain is lowered and the output signal of a sufficient level cannot be obtained until the integrating means 130 discharges sufficiently even after the impact noise disappears. If the discharge time of the integrating means 130 is shortened in order to improve this problem, discharge is performed even during pauses between talks, the gain increases after the pauses, and abnormalities occur at the beginning of the next voice. It had a problem that it was greatly amplified and the conversation became unnatural. In addition, in a hearing aid that emphasizes high frequencies very much, FIG.
14 is applied, since the gain is determined based on the average amplitude of the frequency components of all bands in the circuit of FIG. 14, the high frequency components exceed the user's discomfort threshold and the user feels uncomfortable. There was also a problem that it had a negative effect on feeling and residual hearing.

Further, when the limiter is used, a signal having an amplitude equal to the output limit value of the limiter is output for several to several hundred ms while the amplitude of the impact sound exceeds the input limit value.
Voice has a peak factor of 12 dB. It is also necessary to set a margin in the output limit value of the limiter so that the input voice is sufficiently passed. When the impact sound is passed through the limiter with the output limit value set as described above, the average energy of the impact sound becomes 20 dB or more higher than the average energy of the sound, and it is perceptually perceived as an excessive sound.
I had a problem.

Further, there is a problem that the impact sound is suppressed and at the same time other sounds are also suppressed.

On the other hand, the impulsive sound is an important clue to detect danger and the like, and if it cannot be perceived, it is life-threatening, and it is not always good to completely suppress it.

In view of the above points, an object of the present invention is to provide an impact sound suppressing device that reliably suppresses impact noise and does not reduce the naturalness of voices other than impact noise.

Further, there is provided a shock noise suppressing device which does not cause the user to feel uncomfortable due to the shock noise, adversely affect the hearing, or conversely suppress the shock noise so that the shock noise cannot be heard and poses a risk to life. The purpose is to

Another object of the present invention is to make it possible to listen to other sounds that are simultaneously generated while suppressing the impact sound.

[0013]

[Means for Solving the Problems] Means for delaying an input signal, impact sound detection means for determining an impact sound when the amplitude of the input signal exceeds a certain threshold, and impact sound detection means for detecting the impact sound. If so, means for measuring a fixed time after that, and shock noise suppressing means for suppressing and outputting the output signal of the delay means during the fixed time, and otherwise outputting the output signal of the delay means as it is. The shock noise suppression device provided is configured.

[0014]

According to the above construction, the input signal delayed is suppressed for a certain period of time after the impact sound is detected, so that the impact sound can be reliably removed.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram of a shock noise suppressing device according to a first embodiment of the present invention, and FIG. 2 is each of (a), (b), (c) and (d) of FIG. FIG. 8 is a signal waveform diagram at a point. In FIG. 1, 210 and 220 are signal input terminals and signal output terminals. The impact sound detection circuit 230 is composed of a threshold value judgment means 240. Threshold value judging means 240
The threshold value of is set to a value slightly larger than the maximum amplitude of normal voice as shown in FIG. Threshold value judging means 24
0 outputs a control signal at the moment when the input signal exceeds the threshold value. The temporary holding means 250 holds and outputs the input control signal for a fixed time (several to 1000 ms) after the input control signal rises. The impact sound suppressing means 260 is composed of a gain control amplifier 270. The delay means 280 gives a delay of the maximum rise time of the impact sound of about 15 ms to the input signal. The gain control amplifier 270 has a control terminal 29.
This is a shock noise suppression device that reduces the amplification factor while a control signal is input to 0.

The operation of the shock noise suppressor of this embodiment constructed as above will be described below. When the impact sound is input to the signal input terminal, the instantaneous maximum sound pressure of the impact sound has a larger maximum sound pressure value than that of the other sounds.
As shown in (a), the threshold value is exceeded and detected by the threshold value judging means 240. At that time, a control signal is output from the threshold value judgment circuit 240, and as shown in FIG.
At 50, the control signal is held for a fixed time. On the other hand, FIG.
The input signal is delayed by the delay unit 280 as shown in (c). Finally, in the output signal, as shown in FIG.
As shown in, the impact sound is suppressed from rising to falling.

As described above, according to the present embodiment, the impact sound in the input signal is detected by the magnitude of the instantaneous value, and the delayed input signal is attenuated for a certain period of time according to the result of the determination, so that the impact sound is generated. It is possible to suppress from rising to falling.

FIG. 3 is a block diagram of a shock noise suppressor in a second embodiment of the present invention, and FIG. 4 is a signal waveform diagram at points (a) and (b) in FIG. In FIG. 3, the same elements as those of FIG. 3 differs from the embodiment of FIG. 1 in that a high-pass filter 320 is added to the impact sound detecting means 230.

The operation of the embodiment of FIG. 3 constructed as above will be described. The impact sound is 1 as shown in FIG.
It has a steep envelope rising characteristic of ˜15 ms / 60 dB. Therefore, the rising portion of the impact sound contains a large amount of high-frequency energy components as compared with normal sound. FIG. 4A shows an input signal, and FIG. 4B shows an output signal of the high pass filter 320. Comparing FIGS. 4A and 4B, it is clear that the output signal of the high-pass filter 320 has a larger difference in the amplitude level between the voice section and the impact sound, and the impact sound can be detected reliably.

As described above, according to this embodiment, the input signal is input to the high-pass filter, the impact noise is detected by the magnitude of the output signal, and the delayed input signal is fixed according to the determination result. By suppressing the time, it becomes possible to more reliably suppress the impact sound from the rising edge to the falling edge.

FIG. 5 is a block diagram of a shock noise suppressor in a third embodiment of the present invention, and FIG. 6 is each of (a), (b), and FIG.
It is a signal waveform diagram in (c), (d), (e), (f) point. 5, the same components as those in FIGS. 1 and 3 are designated by the same reference numerals for description. In FIG. 5, 280 is a delay means similar to that in FIG. 1, and 270 is a gain control amplifier. Reference numeral 410 is an envelope extraction means, which can be composed of a detector and an integrator having a short charge / discharge time. Reference numeral 420 denotes a threshold value determination means, which outputs a control signal while the input signal exceeds the threshold value. Reference numeral 430 is a time axis expansion means, which expands the time length of the input control signal by three times and outputs it.

The operation of the shock noise suppressor of the present embodiment constructed as above will be described below. Figure 6
As shown in (a), it is assumed that impact sounds having different falling characteristics are input to the signal input terminal. The envelope detecting means 410 extracts the envelope, and the signal shown in FIG. 6B is input to the threshold determining means 420. Threshold value determination means 4
20 outputs the control signal while the input signal exceeds the threshold value as shown in FIG. 6 (c). At that time, the time axis expansion means 430 outputs a control signal having a time length three times as long as the input control signal, as shown in FIG. On the other hand, as shown in FIG. 6E, the input signal is delayed by the delay means 280. Then, the output signal of the delay means is amplified by the gain control amplifier whose gain is controlled by the output signal of the time axis expansion means 430. The gain of the gain control amplifier is very low while the control signal is output from the time axis expanding means 430.
Therefore, the impact sound is suppressed in the output signal as shown in FIG. In this embodiment, unlike the embodiment of FIGS. 1 and 3, the time during which the gain of the gain control amplifier 270 is low changes according to the length of time that the envelope of the impact sound exceeds the threshold value, so that the impact sound with a long duration is changed. However, it can be surely suppressed, and at the same time, the period for suppressing sounds other than the impact sound is shortened.

As described above, according to this embodiment, the impact sound is reliably suppressed by adjusting the time for attenuating the delayed input signal according to the time when the impact sound in the input signal exceeds the threshold value. At the same time, it is possible to shorten the period for suppressing sounds other than the impact sound.

FIG. 7 is a block diagram of a shock noise suppressor according to a fourth embodiment of the present invention. 7, FIG. 1, FIG.
The same components as those in FIG. 5 will be described with the same reference numerals. In FIG. 7, the high-pass filter 320 and the threshold determination 24
0, the delay means 280, and the gain control amplifier 270 are the same components as those shown in FIG. Envelope extraction means 41
0, the time axis expansion means 430 is the same component as that in FIG. The fall detection means 510 generates a control signal when the input signal goes below the threshold value. The control signal generation means 520 outputs the control signal from the time when the control signal is output from the threshold value judgment circuit 240 until the time when the fall detection means 510 outputs the control signal.

The operation of the shock noise suppressor of this embodiment having the above-described structure will be described below. The high-pass filter 320 and the threshold determination circuit 240 detect the rise of the impact sound. Next, the envelope extraction means 410 and the fall detection means detect when the magnitude of the impact sound falls below the threshold as a fall. The control signal from the rising edge to the falling edge is the control signal generating means 52.
It is output from 0. After that, as in the embodiment of FIG. 5, the time axis expansion means 430 expands the time length of the control signal in time and outputs it. Then, the output signal of the delay means 280 is amplified by the gain control amplifier 270 whose gain is controlled by the output signal of the time base expansion means 430, so that the time base expansion means 4 is obtained.
While the control signal is being output from 30, the gain of the gain control amplifier is very low. Therefore, the impact sound of the output signal is suppressed. In this embodiment as well, as in the embodiment of FIG. 5, the time during which the gain of the gain control amplifier 270 is low changes according to the time length from the rise to the fall of the impact sound, so the impact sound is reliably suppressed. At the same time, the period for suppressing sounds other than the impact sound is shortened. Moreover, similarly to the embodiment of FIG. 3, the rising of the high-pass filter 320 can be detected more reliably by the function of the high-pass filter 320.

As described above, according to this embodiment, the impact sound is suppressed at the same time as the impact sound is suppressed by adjusting the time for attenuating the delayed input signal according to the time when the impact sound in the input signal exceeds the threshold value. , It is possible to shorten the period for suppressing sounds other than the impact sound.

FIG. 8 is a block diagram of a shock noise suppressing device according to the fifth embodiment of the present invention. In FIG. 8, the same components as those of FIG. In FIG. 8, the absolute value converting means 610 and the integrating means 62 having a charging / discharging time sufficiently longer than the rising and falling of the impact sound.
0, a constant generation means 630, and a threshold value determination means 650 composed of an adder 640 are added, which is a difference from the embodiment of FIG.

The operation of the embodiment of FIG. 8 constructed as above will be described. The absolute value converting means 610 and the integrating means 620 determine the average amplitude level of the output signal of the high pass filter 320, and the value generated by adding the constant generated by the constant generating means 630 by the adder 640 is the threshold value of the threshold value judging circuit 240. Output as. By setting the threshold value as described above, an appropriate threshold value can be automatically set even if the level of the input voice changes.

As described above, according to the present embodiment, by setting the threshold value of the threshold value judging means by using the threshold value deciding means for setting the average amplitude of the input signal of the threshold value judging means as the reference, It is possible to automatically set an appropriate threshold value for sound detection.

FIG. 9 shows a block diagram of the shock noise suppressor in the sixth embodiment of the present invention, and FIG. 10 shows points (a), (b), (c) and (d) of FIG. 3 is a signal waveform diagram in FIG. 9, the same components as those in FIGS. 1 and 3 are designated by the same reference numerals for description. In FIG. 9, 210, 22
0 is a signal input terminal and a signal output terminal, respectively. 25
Reference numeral 0 is a temporary holding means and 280 is a delay means. Reference numeral 230 is an impact sound detecting means for detecting an impact sound and outputting a control signal. Reference numeral 710 is an impact noise suppressing unit including a changeover switch 720 and a low-pass filter 730. A contact of the changeover switch 720 is connected to the terminal (A) side only while the temporary holding unit 250 holds the control signal, and to the terminal (A) side otherwise.

The operation of the embodiment of FIG. 9 constructed as above will be described. It is assumed that a signal as shown in FIG. 10A is input. The signal is delayed by the function of the delay unit 280 for a fixed time, and has a signal waveform as shown in FIG. 10B at the point in FIG. On the other hand, when an impact sound is detected, a control signal is output from the impact sound detecting means 230, and the control signal shown in FIG.
As shown in (c), the temporary holding means 250 holds the control signal for a certain period of time. While the control signal is held, the changeover switch 730 is switched to the contact (A) side, and the delayed input signal is input to the low pass filter 730. Eventually, the output signal becomes as shown in FIG. 10 (d), the high frequency component of the impact sound portion is removed, and the instantaneous maximum sound pressure of the impact sound is reduced by the amount that the sharp rise is alleviated. Moreover, the signal passes through the low-pass filter only while the control signal of the temporary holding circuit is held, and the sound quality of the other part of the audio signal does not change. The impact sound passes through the low-pass filter 730 and can be perceived as an easily audible sound with the high frequency removed, and it is possible to perceive the impact sound without feeling discomfort and perceive a danger.

As described above, according to the present embodiment, the impact sound in the input signal is detected, and the delayed input signal is filtered by the low-pass filter for a certain time after the detection. It is possible to obtain an impact sound suppressing device capable of perceiving an impact sound with a sound quality and a volume that does not cause a pleasant sensation.

FIG. 11 is a block diagram of the shock noise suppressor in the seventh embodiment of the present invention. 11, the same components as those of FIG. 9 are designated by the same reference numerals for description. 11 is different from the embodiment of FIG. 10 in that an impact sound suppressing device including a changeover switch 810 and a warning sound generating means 830 is present instead of the impact sound suppressing means 710.

In the shock noise suppressor configured as described above, the control signal is output from the temporary holding means 250 for a certain period of time after the shock noise is detected, and the contact of the changeover switch 810 is switched to the (a) side during that time. To be While the changeover switch 810 is switched to (A),
A warning sound that is completely different from the impact sound is output from the signal output terminal 22.
It is output to 0.

As described above, according to the present embodiment, the impact sound in the input signal is detected, and the warning sound is output to the signal output terminal only for a certain time after the detection. It is possible to obtain an impact sound suppressing device that can perceive an impact sound with a favorite sound different from the sound.

FIG. 12 is a block diagram of the shock noise suppressor in the eighth embodiment of the present invention. In FIG. 12, 910,
Reference numerals 920 and 930 denote unidirectional microphones directed in different directions, and 940, 950, and 960 each detect an impact sound in an input signal, and a fixed period including a period in which the impact sound is generated, It is the shock noise suppressor as described in the embodiment of FIG. 1 in which the gain between the input and output terminals is made lower than usual. 970 adder and 980 are signal output terminals.

The operation will be described in the embodiment of FIG. 12 configured as above. While the impact sound is not detected, the audio signals input from the microphones 910, 920, and 930 are directly applied to the impact sound suppressors 940 and 95.
0, 960, the adder 970 adds them, and the signal is output from the signal output terminal. Therefore, the microphone 910,
All the sounds from the directions in which 920 and 930 are facing are output from the signal output terminal 980 as audio signals. Next, assume that an impact sound is generated in the direction in which the microphone 910 is directed. In this case, the shock noise suppressor 94
0 suppresses the impact sound. However, the microphone 920,
The audio signals input from the respective 930 are output from the shock noise suppressors 950 and 960 as they are, added by the adder 970, and output from the signal output terminal 980. Therefore,
Only the signal from the direction of impact sound is suppressed for a certain period,
It is possible to listen to the sound coming from the other direction as it is.

As described above, according to the present embodiment, a plurality of microphones each having its directivity directed in different directions and the impact sound suppressing device connected to each microphone are provided. By adding the output signals, it is possible to obtain a shock sound suppressing device that suppresses only the sound in the direction in which the shock sound arrives for a certain period of time, and can hear the sound from other directions even when the shock sound is generated.

In the embodiment of FIG. 1, the delay time of the delay means may be any length as long as it is longer than the symmetrical rise time of the impact sound. A difference circuit or the like may be used in place of the high pass filter in the embodiment of FIG.
It goes without saying that the expansion rate of the time axis expansion means 430 in the embodiment of FIG. 4, FIG.
It goes without saying that the shock noise suppressing means shown in FIGS. 9 and 11 may be used instead of the shock noise suppressing means shown in FIGS.

[0040]

According to the present invention, it is possible to obtain an impact sound suppressing device that reliably suppresses impact noise and does not reduce the naturalness of voices other than impact noise. In addition, it is possible to obtain an impact sound suppressing device that does not cause discomfort to the user due to the impact sound, adversely affects the hearing, or conversely suppresses the impact sound so that the impact sound cannot be heard and poses a risk to life. . Further, it is possible to obtain an impact sound suppressing device capable of listening to the sound generated at the same time as the impact sound, and its practical effect is great.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a shock noise suppressor according to a first embodiment.

FIG. 2 is a signal waveform diagram at points (a), (b), (c), and (d) in FIG.

FIG. 3 is a configuration diagram of a shock noise suppressor according to a second embodiment of the present invention.

FIG. 4 is a signal waveform diagram at points (a) and (b) in FIG.

FIG. 5 is a configuration diagram of an impact sound suppressing device according to a third embodiment of the present invention.

FIG. 6 is a signal waveform diagram at points (a), (b), (c), and (d) in FIG.

FIG. 7 is a block diagram of a shock noise suppressor according to a fourth embodiment of the present invention.

FIG. 8 is a configuration diagram of a shock noise suppressor according to a fifth embodiment of the present invention.

FIG. 9 is a configuration diagram of an impact sound suppressing device according to a sixth embodiment of the present invention.

FIG. 10 is a signal waveform diagram at points (a), (b), (c), and (d) in FIG.

FIG. 11 is a configuration diagram of an impact sound suppressing device according to a seventh embodiment of the present invention.

FIG. 12 is a configuration diagram of an impact sound suppressing device according to an eighth embodiment of the present invention.

FIG. 13 is a general signal waveform diagram.

FIG. 14 is a block diagram of a conventional automatic gain control circuit.

[Explanation of symbols]

 210 signal input terminal 220 signal output terminal 230 shock noise detecting means 240 threshold value judging means 250 temporary holding means 260 shock noise suppressing means 270 gain control amplifier 280 delay means 290 gain control terminal 310 shock noise detecting means 320 high pass filter 410 envelope Line extracting means 420 Threshold determining means 430 Time axis expanding means 510 Falling detecting means 520 Control signal generating means 610 Absolute value converting means 620 Integrating means 630 Constant generating means 640 Adder 650 Threshold value determining means 710 Impact noise suppressing means 720 Changeover switch 730 Low-pass filter 810 Changeover switch 820 Warning sound generating means 830 Impact sound suppressing means

Claims (11)

[Claims] 1. A means for delaying an input signal, an impact sound detecting means for determining an impact sound when the amplitude of the input signal exceeds a certain threshold value, and an impact sound detecting means for detecting an impact sound after that. And a shock noise suppressing unit that suppresses the output signal of the delay unit during the constant time and outputs the output signal, and otherwise outputs the output signal of the delay unit as it is. Shock noise suppressor characterized by. 2. A means for delaying an input signal, an impact sound detecting means for extracting a high frequency component of the input signal and determining an impact sound when the amplitude thereof exceeds a certain threshold value, and an impact sound by the impact sound detecting means. And a shock noise suppression that suppresses and outputs the output signal of the delay means during the constant time, and otherwise outputs the output signal of the delay means as it is. And a shock noise suppression device. 3. Means for extracting the envelope of the input signal, and means for measuring the length of time that the envelope exceeds a threshold value,
A means for determining a second time length according to the time length, and a shock for suppressing the output signal of the delay means for the second time length and otherwise outputting the output signal of the delay means as it is. An impact sound suppressing device comprising: a sound suppressing unit. 4. The impulsive sound according to claim 3, wherein the means for determining the second time length is to add a constant time length to a constant multiple of the time when the envelope exceeds the threshold value. Suppressor 5. An impact sound rise determination means for extracting a high frequency component of an input signal and determining that it is a rise of an impact sound when its amplitude exceeds a certain threshold value, and an envelope curve of the input signal is extracted and the envelope curve is a threshold value. Means for detecting the falling time of the impact sound as a falling time, a means for measuring the time length from the rising edge to the falling edge, and a second means according to the time length from the rising edge to the falling edge. And a shock noise suppressor that suppresses the output signal of the delay unit during the second time length and outputs the output signal of the delay unit as it is in other cases. A characteristic shock noise suppressor. 6. The impact according to claim 5, wherein the means for determining the second time length is to add a constant time length to a constant multiple of the time from the rise of the impact sound to the fall thereof. Sound suppressor 7. An impact sound detecting means comprising a threshold value determination circuit for inputting an input signal or a signal obtained by processing the input signal and determining an impact sound when the input signal or the signal obtained by processing the input signal exceeds a threshold value. And a threshold value determining unit that sets the threshold value of the threshold value determining unit with reference to an average amplitude of an input signal of the threshold value determining unit within a certain period of time. 8. The shock noise suppressor according to claim 7, wherein the threshold value determining means sets a value obtained by adding a constant to the average amplitude within a constant time as a threshold. 9. A means for delaying an input signal for a fixed time,
An impact sound detecting means for detecting an impact sound in the input signal; and when the impact sound is detected by the impact sound detecting means, a high frequency component of the output signal of the delay means is attenuated to a level higher than usual, and otherwise. An impact sound suppressing device comprising an impact sound suppressing means for outputting as it is. 10. A means for delaying an input signal for a predetermined time, and an impact sound detecting means for detecting an impact sound in the input signal,
When the impact sound is detected by the impact sound detection means, which is an alternative to the impact sound, the signal from the warning sound generation means is output instead of the output signal of the delay means, and in other cases. Is an impact sound suppressing device, which is provided with an impact sound suppressing means for outputting the output signal of the delay means as it is. 11. A plurality of directional microphones, and a plurality of impact sound suppressing devices connected to each of the microphones,
An impact sound suppression device comprising an adder for adding the output signals of the impact sound suppression device, and using the output signal of the adder as an output signal.