JP2010011270A - Howling suppression device and microphone - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a howling suppression device capable of continuously detecting a frequency band, that causes howling, and suppressing the relevant frequency band. <P>SOLUTION: A pseudo noise superimposing part 7 superimposes pseudo noise (M sequences) onto audio collected by a microphone element 11 and outputs the audio to an amplification system. An arithmetic unit 5 calculates a correlation between the audio collected by the microphone element 11 and the pseudo noise. The arithmetic unit 5 calculates reception timing to collect again the pseudo noise output to the amplification system and calculates a delay time of a closed loop from a difference between the relevant reception timing and transmission timing. By calculating the delay time, a frequency band that causes howling is calculated and the relevant frequency band is suppressed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a howling suppression device that suppresses howling.

Conventionally, there exists a thing like patent document 1 as what suppresses an echo. The apparatus of Patent Document 1 includes a measurement mode in which a reference signal having white noise or the like is transmitted to the outside. The delay of the loop system is measured by measuring the delay time from the output of the reference signal to the input to the microphone. It measures time. The echo can be suppressed by measuring the delay time of the loop system and suppressing the frequency band corresponding to the delay time.
JP 2007-214976 A

  However, the delay time of the loop system changes every moment due to a change in the position of the microphone. In particular, in the case of a loudspeaker system such as a presentation or live performance, the position of the microphone often moves, and even if the measurement as in Patent Document 1 is performed, the delay time of the loop system changes each time, and howling is suppressed. I couldn't. As a result, in practical use, strong band limitation was performed in a wide band at the expense of sound quality.

  Moreover, even if the configuration as in Patent Document 1 can be incorporated in the amplifier device in advance, it has been extremely difficult to incorporate it later in the existing amplifier device.

  Furthermore, even in an amplifier device incorporating the above-described configuration, when a plurality of microphones are connected, it is necessary to remove the feedback signal for a single signal that integrates the input signals of all the microphones. The feedback signals input to the microphones cannot be individually handled, and it has been difficult to suppress howling.

  Therefore, an object of the present invention is to provide a howling suppression apparatus that can continuously detect a frequency band that is a basis of howling and suppress the frequency band.

  A howling suppression apparatus according to the present invention includes a sound collection unit that collects an audio signal, a noise generation unit that generates pseudo noise, and an external amplification by superimposing the pseudo noise on the audio signal collected by the sound collection unit. Based on the superimposition unit that outputs to the system, the correlation calculation unit that obtains the correlation between the sound signal collected by the sound collection unit and the pseudo noise generated by the noise generation unit, and the peak of the correlation value calculated by the correlation calculation unit Calculating a reception timing at which the pseudo-noise output to the amplification system is collected from the sound collection unit, and calculating a delay time of the closed loop from the difference between the reception timing and the transmission timing; And a howling suppression unit that suppresses a frequency band corresponding to the delay time from a signal output to the system.

  In this way, the pseudo-noise is superimposed on the sound picked up by the microphone, and the correlation calculation is performed to calculate the closed-loop delay time. When the correlation peak is calculated, it can be determined that the pseudo noise has returned to the microphone. Therefore, by obtaining the delay time from the output of the pseudo noise to the calculation of the correlation peak, the frequency band that is the basis of howling is obtained and the frequency band is suppressed. Since the closed-loop delay time can be continuously obtained before howling occurs, it is possible to suppress howling even when the position of the microphone often moves such as in presentations and live performances. . In addition, in order to obtain the closed-loop delay time at the previous stage of the amplification system (microphone unit or mixer) and suppress its frequency band, it is possible to perform feedback regardless of whether it is an existing amplifier device or a plurality of microphones connected. Can be suppressed.

  In the above invention, the noise generation unit may be configured to control the level of pseudo noise according to the sound collection level of the sound collection unit.

  In this case, by adjusting the level of the pseudo noise according to the sound collection level, it is possible to output a sound with no sense of incongruity in hearing. That is, if the sound collection level is high, the noise level is increased to increase the accuracy of correlation calculation, and if the sound collection level is low, the noise level is reduced so that the listener cannot hear it.

  In the above invention, the noise generation unit may be configured to increase the period of the pseudo noise when the correlation calculation unit cannot calculate a correlation value.

  In this case, the S / N ratio is not secured by increasing the level of the pseudo noise, but the S / N ratio is secured by increasing the period of the pseudo noise, so that a sense of incongruity does not occur.

  In the above invention, the noise generation unit may be configured to increase the period of the pseudo noise and lower the level after the correlation calculation unit calculates the correlation value. is there.

  In this way, when the delay time can be measured, the pseudo noise is not completely turned off, but the pseudo noise period is lengthened to lower the level while ensuring the SN ratio. Therefore, the delay time can be continuously measured.

  Further, in the above invention, the noise generation unit can be configured to generate a plurality of patterns of pseudo noise. By generating multiple patterns of pseudo noise, for example, it is possible to switch the pattern of pseudo noise for each of a plurality of microphones. In this case, the correlation can be calculated with high accuracy without mutual interference of pseudo noises. Moreover, since the closed-loop delay time can be calculated individually for each microphone, howling can be suitably suppressed even when a plurality of microphones are used simultaneously.

  Moreover, the aspect of incorporating the said howling suppression apparatus in a microphone is also possible. By incorporating in the microphone, howling can be suppressed regardless of which amplifier device is connected, and ideal howling can be suppressed according to the closed loop system for each microphone.

  According to the present invention, since the delay time of the closed loop can be continuously obtained before the howling occurs, the howling can be performed even in the case where the position of the microphone often moves such as in a presentation or a live performance. Can be suppressed. In addition, in order to obtain the closed-loop delay time at the previous stage of the amplification system (microphone unit or mixer) and suppress its frequency band, it is possible to perform feedback regardless of whether it is an existing amplifier device or a plurality of microphones connected. Can be suppressed.

  FIG. 1 (A) is a block diagram showing the overall configuration of the loudspeaker of this embodiment, and FIG. 1 (B) is a block diagram showing the configuration of a microphone unit incorporating the howling suppression device of the present invention. In the description of this embodiment, the audio signals are all digital signals, and the configurations of A / D conversion and D / A conversion are omitted.

  The microphone unit 1 includes a calculation unit 5 and a pseudo noise superimposing unit 7 for inputting a sound signal picked up by the microphone element 11. The pseudo noise superimposing unit 7 superimposes pseudo noise on the audio signal picked up by the microphone element 11 and outputs it to the outside.

  The audio signal output from the microphone unit 1 is amplified by the amplifier device 2 and emitted from the speaker 3. The sound emitted from the speaker 3 returns to the microphone unit 1 to form a closed loop.

  The microphone unit 1 measures the closed-loop delay time in the arithmetic unit 5. A frequency band in which howling is expected is calculated according to the measured delay time. The microphone unit 1 suppresses the frequency band calculated by the calculation unit 5 by a howling suppression unit such as a notch filter and outputs the result to the subsequent amplification system (amplifier device 2).

  As shown in FIG. 1B, the microphone unit 1 includes a microphone element 11, an LPF 12, a notch filter 13, a superposition unit 14, an HPF 15, a correlation calculation unit 16, an M-sequence generator 17, an N-times oversampling unit 18, and an HPF 19. A timer 20 and a howling frequency calculation unit 21.

  The calculation unit 5 includes an M-sequence generator 17, an HPF 15, a correlation calculation unit 16, a timer 20, and a howling frequency detection unit 21. The pseudo noise superimposing unit 7 includes an LPF 12, a superimposing unit 14, an M sequence generator 17, an N-times oversampling unit 18, and an HPF 19.

  The audio signal picked up by the microphone element 11 is input to the LPF 12 and the HPF 15. The configuration and function of the pseudo noise superimposing unit 7 will be described with reference to FIG. The lower column of each component shows the waveform of the signal output by each component.

  An audio signal picked up by the microphone element 11 is input to the LPF 12 of the pseudo noise superimposing unit 7. The LPF 12 cuts the high frequency from the collected audio signal and outputs it to the notch filter 13 (see the lower waveform of the LPF 12 in the figure).

  The notch filter 13 suppresses the frequency band set by the howling frequency detection unit 21 from the output signal of the LPF 12 and outputs it to the superposition unit 14. Details will be described later.

  The M-sequence generator 17 generates a signal having high autocorrelation such as a PN code (M-sequence) as pseudo noise, and outputs the signal to the N-times oversampling unit 18 (the lower column of the M-sequence generator 17 in FIG. Refer to the waveform. However, the waveform in the bottom column represents the time axis). The level and period of the pseudo noise are set according to the sound collection level of the microphone element 11 and the correlation calculation result of the correlation calculation unit 16, but are set to a weak level that does not cause a sense of incongruity. Details will be described later. In addition, you may use other random numbers, such as not only M series but Gold series.

  The N-times oversampling unit 18 oversamples the pseudo noise. For example, 16 times oversampling is performed, the code period of each bit of the PN code is expanded, and the pseudo noise length is 16 times (refer to the lower waveform of the N times oversampling unit 18 in FIG. Represents the time axis). The N-times oversampling unit 18 outputs the oversampled signal to the HPF 19.

  The HPF 19 cuts the low frequency range of the signal input from the N-times oversampling unit 18 (refer to the lower waveform of the HPF 19 in the figure, where the waveform in the lowermost column represents the time axis). The cut-off frequency is determined corresponding to the LPF 12, but is set to 10 kHz, for example.

  Note that LPF 12 and HPF 19 are not essential. However, since the sound other than the high frequency of the pseudo noise is cut by the HPF 19, even if the sound is emitted from the speaker 3, there is no sense of incongruity in hearing (noise is difficult to hear). In addition, since the signal input from the microphone element 11 is mainly composed of components of 10 kHz or less, such as the human voice range, the high frequency is cut by the LPF 12 and the band of the pseudo noise is divided to calculate correlation described later. Accuracy can be improved. Further, the LPF 12 and the HPF 19 prevent the high-frequency pseudo-noise once input to the microphone from being output again to the amplification system, thereby suppressing the pseudo-noise loop phenomenon. When the LPF 12 and the HPF 19 are omitted, the pseudo noise component may be subtracted from the audio signal picked up by the microphone element 11 and then output to the amplification system to suppress the loop phenomenon.

  Note that oversampling by the N-times oversampling unit 18 is not essential in the present invention. However, by performing oversampling, the temporal redundancy of pseudo noise increases, and the accuracy of correlation calculation can be improved. In practice, the presence or absence of oversampling may be set according to the required accuracy and the length of pseudo-noise (time for outputting one cycle).

  The signal output from the HPF 19 (pseudo noise) and the signal output from the notch filter 13 (sound collected sound signal) are superimposed by the superimposing unit 14 and output to the external amplification system (amplifier device 2).

  Next, the configuration and function of the calculation unit 5 will be described with reference to FIG. The lower column of each component shows the waveform of the signal output by each component. The M-sequence generator 17 outputs the same pseudo noise as that output to the N-times oversampling unit 18 to the correlation calculation unit 16 (refer to the lower waveform of the M-sequence generator 17 in FIG. Represents the axis). Further, after outputting the pseudo noise, a signal indicating the output timing (timing signal) is transmitted to the timer 20. When receiving the timing signal, the timer 20 starts time counting and transmits a timer signal indicating the counting time to the howling frequency detection unit 21.

  The microphone element 11 picks up the superimposed signal shown in FIG. 2 and external audio (speech voice or the like). An audio signal picked up by the microphone element 11 is input to the HPF 15 of the calculation unit 5. The HPF 15 cuts the low frequency from the collected audio signal and outputs it to the correlation calculator 16 (refer to the lower waveform of the HPF 15 in the figure, where the waveform represents the frequency axis). The cut-off frequency is determined corresponding to the HPF 19 and is set to 10 kHz, for example.

  The correlation calculation unit 16 obtains the correlation between the pseudo noise input from the M-sequence generator 17 and the output signal of the HPF 15. Since the M-sequence code has a very high autocorrelation, if the same M-sequence pseudo noise is included in the output signal of the HPF 15, as shown in the waveform of FIG. A peak (a peak having a level equal to or higher than a predetermined threshold value) appears. The correlation calculation unit 16 transmits the timing (reception timing) at which this peak is calculated to the howling frequency calculation unit 21.

  When receiving the peak calculation timing, the howling frequency detection unit 21 refers to the timer signal from the timer 20 and obtains the difference from the timing at which the peak is calculated from the timing at which the pseudo noise is output. This timing difference corresponds to the delay time of the closed loop.

  As described above, the calculation unit 5 measures the delay time of the closed loop. The howling frequency detector 21 sets the frequency band of the notch filter 13 so as to suppress the frequency band corresponding to the measured delay time. Any method of suppressing the notch filter 13 may be used. For example, only the measured frequency band (fundamental tone) may be suppressed, or higher harmonics such as second harmonics and third harmonics may be suppressed. You may set as follows. The intensity of the notch filter 13 is set according to the peak intensity of the correlation obtained by the correlation calculation unit 16. When the peak intensity of the correlation is strong, it is determined that the probability of howling is high, and the suppression of the frequency band is set strongly.

  Thus, by superimposing pseudo noise on the sound collected by the microphone and performing correlation calculation, the delay time of the closed loop can be calculated, and the frequency band that is the basis of howling can be obtained. Therefore, it is possible to continuously suppress the closed-loop acoustic path before howling occurs, so that even when the microphone position often moves such as in presentations and live performances, howling is suitably suppressed. can do. Further, since a closed loop delay time is obtained by the microphone unit and its frequency band is suppressed, howling can be suppressed even in the case of an existing amplifier device or a case where a plurality of microphones are connected.

  A plurality of pseudo noise patterns generated by the M-sequence generator 17 may be prepared, and these patterns may be switched. For example, by switching the pseudo noise pattern for each microphone, even if a plurality of microphones are used simultaneously, the correlation can be calculated with high accuracy without mutual interference of pseudo noise. Since the closed loop delay time can be calculated individually for each microphone, howling can be suitably suppressed even when a plurality of microphones are used simultaneously.

  In particular, when a Gold sequence is used as the pseudo-noise, it is possible to generate many types of code sequences by switching the tap position of the code generation circuit (shift register), so that it is compatible with a large-scale PA system. be able to.

  Next, FIG. 4 is a flowchart showing the operation of the howling suppression apparatus. When the microphone unit is turned on, the arithmetic unit 5 and the pseudo noise superimposing unit 7 perform the operation shown in this flow.

  First, the M-sequence generator 17 of the pseudo noise superimposing unit 7 checks the microphone input level (s11) and generates an M-sequence code (s12). Further, a timing signal is transmitted to the timer 20 (s13).

  That is, the M-sequence generator 17 determines the pseudo noise level according to the microphone input level. If the microphone input level is high, the pseudo noise level is increased to increase the accuracy of correlation calculation, and if the microphone input level is low, the pseudo noise level is decreased so that the listener cannot hear it. Note that when the level of the pseudo noise is reduced, the period of the pseudo noise may be lengthened accordingly. By increasing the period of the pseudo noise, the SN ratio is improved, and the accuracy of correlation calculation is improved.

  Thereafter, the correlation calculation unit 16 of the calculation unit 5 obtains the correlation between the signal input from the microphone element 11 and the input signal from the M-sequence generator 17, and determines whether or not to calculate the peak (s14). If the peak cannot be calculated even after a predetermined time has elapsed (s15 → N), it is determined that the detection level of the pseudo noise cannot be secured in a noisy environment, and the M-sequence generator 17 The period of noise is lengthened (s16), and pseudo noise is output again (s12).

  When calculating the correlation peak, the correlation calculation unit 17 transmits the timing (reception timing) at which the peak is calculated to the howling frequency calculation unit 21. The howling frequency detector 21 refers to the timer signal from the timer 20 (s17). The howling frequency detection unit 21 obtains a time difference between the timing at which the pseudo noise is output and the timing at which the peak is calculated, calculates a closed loop delay time, and obtains a howling occurrence frequency (s18). Then, the frequency band of the notch filter 13 is set to suppress the frequency band corresponding to the measured delay time (s19).

  Thereafter, the calculation unit 5 does not turn off the pseudo noise, but lengthens the period of the pseudo noise (s20), and repeats the processing from s11. By increasing the period of the pseudo noise, the SN ratio is improved and the accuracy of correlation calculation is improved. At this time, the pseudo noise level may be set to be lowered. By increasing the period of the pseudo noise, the level can be lowered while ensuring the SN ratio, and the delay time can be continuously measured.

  If the period of the pseudo noise is increased, the time until the correlation calculation is increased. Therefore, in the process of s11, when the microphone input level is increased, the period of the pseudo noise is shortened again until the correlation calculation. You may make it attach importance to suppression of howling generation | occurrence | production shortening time.

  In this manner, pseudo noise superimposition and correlation calculation are continued even while the microphone is being used, and the frequency band setting of the notch filter 13 is continuously performed. Howling can be suitably suppressed.

  Note that the arithmetic unit 5 and the pseudo noise superimposing unit 7 may be incorporated in each channel of the mixer instead of the microphone unit. In any case, it suffices if it is provided before the amplification system such as an amplifier device. It is also possible to configure an adapter incorporating the arithmetic unit 5 and the pseudo noise superimposing unit 7 and apply the howling suppression device of the present invention to an existing microphone unit and amplifier device.

It is the block diagram which showed the structure of the howling suppression apparatus. It is the block diagram which showed the structure and process content of the pseudo noise superimposition part. It is the block diagram which showed the structure and processing content of the calculating part. It is the flowchart which showed operation | movement of the howling suppression apparatus.

Explanation of symbols

1-microphone unit 2-amplifier device 3-speaker 5-calculation unit 7-pseudo-noise superimposing unit

Claims (6)

A sound collection unit for collecting an audio signal;
A noise generator that generates pseudo noise;
A superimposing unit that superimposes the pseudo noise on the audio signal collected by the sound collecting unit and outputs the signal to an external amplification system;
A correlation calculation unit for obtaining a correlation between the sound signal collected by the sound collection unit and the pseudo noise generated by the noise generation unit;
Based on the peak of the correlation value calculated by the correlation calculation unit, the reception timing at which the pseudo noise output to the amplification system is collected from the sound collection unit is calculated, and from the difference between the reception timing and the transmission timing, a closed loop is calculated. A delay time calculation unit for calculating the delay time of
From a signal output to the amplification system, a howling suppression unit that suppresses a frequency band corresponding to the delay time;
A howling suppression device comprising:   The howling suppression apparatus according to claim 1, wherein the noise generation unit controls a level of pseudo noise according to a sound collection level of the sound collection unit.   3. The howling suppression apparatus according to claim 1, wherein the noise generation unit increases a period of the pseudo noise when the correlation calculation unit cannot calculate a peak of a correlation value.   4. The howling suppression apparatus according to claim 1, wherein the noise generation unit increases the period of the pseudo noise and lowers the level after the correlation calculation unit calculates a correlation value. 5.   The howling suppression apparatus according to claim 1, wherein the noise generation unit generates a plurality of patterns of pseudo noise.   A microphone incorporating the howling suppression device according to any one of claims 1 to 5.

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