JP2010226403A - Howling canceler - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a howling canceler capable of suppressing howling by accurately detecting a frequency band, in which howling may occur, without incurring howling in an acoustic space actually. <P>SOLUTION: A loudspeaker 1 changes over switches to form a first loop (speaker SP, microphone M, impulse response measuring section 11) and a second loop (filter 16, FIR filter 12). The loudspeaker 1 sets the FIR filter 12 simulating a transfer function of an acoustic feedback system from the speaker SP to the microphone in the first loop, detects a frequency band in which howling may occur by generating a measuring signal in the second loop, and sets the filter 16 suppressing a gain of the frequency band. The loudspeaker 1 changes over the switches to form a third loop (microphone M, amplifier 14, filter 16, speaker SP) and outputs an audio signal inputted to the microphone M to the speaker SP via the filter 16. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a howling canceller used for a loudspeaker or the like.

  Conventionally, various howling cancellers that suppress howling based on a return sound generated in an acoustic feedback system from a speaker to a microphone have been proposed (see, for example, Patent Document 1).

  For example, a howling canceller described in Patent Document 1 includes a delay circuit that delays a residual signal and an adaptive filter. The howling canceller sets the delay amount of the delay circuit and the number of taps of the adaptive filter according to the power spectrum of the impulse response of the acoustic feedback system from the speaker to the microphone.

JP 2006-270368 A

  Since the howling canceller described in Patent Document 1 measures the howling frequency based only on the power spectrum of the impulse response, even in an environment where no howling occurs (for example, an environment where the power spectrum is strong but the phase is different) If howling occurs, it will be falsely detected. For this reason, the howling canceller described in Patent Document 1 has a problem in that the gain in the frequency band where no howling is suppressed and the sound quality is deteriorated. Therefore, the present invention provides a howling that can accurately detect a frequency band in which howling is generated by performing simulation without actually generating howling in an acoustic space and suppress howling in the frequency band. Provide a canceller.

  The howling canceller of the present invention includes suppression means (for example, a notch filter, a dip filter, an all-pass filter, etc.) that suppresses howling caused by an acoustic feedback system from the speaker to the microphone. The howling canceller measures the impulse response of the acoustic feedback system and configures a pseudo loop system that simulates the impulse response. This pseudo loop system does not include an acoustic feedback system, and is configured by an electric circuit, software, or the like.

  The howling canceller switches between an acoustic feedback system and a pseudo loop system as a path of an audio signal. When the path of the audio signal is switched to the pseudo loop system, the howling canceller generates a measurement signal (for example, an impulse signal) and passes the measurement signal to the pseudo loop system a plurality of times. Since the impulse response is convoluted when the measurement signal passes through the pseudo loop system, the intensity of the frequency band in which howling occurs increases by passing through the pseudo loop system multiple times. Thus, howling is generated in a pseudo manner by passing the measurement signal through the pseudo loop system a plurality of times. Then, the howling canceller sets a parameter for suppressing the pseudo-generated howling in the suppression unit. That is, the howling canceller sets a parameter for suppressing howling that would occur in the acoustic feedback system in the suppression means.

  Accordingly, the howling canceller can accurately detect the frequency band in which howling occurs by generating howling internally without actually generating howling in the acoustic space. The howling canceller can suppress howling in the frequency band. Therefore, when the howling canceller of the present invention is applied to a loudspeaker, sound can be emitted without deteriorating sound quality.

  Further, the howling canceller of the present invention changes how much the measurement signal is amplified stepwise to generate pseudo howling, and stores the amplification amount and the parameter of the suppression means in association with each other. The howling canceller may be configured to switch the setting of the suppression unit in accordance with the amount of amplification with respect to the audio signal input to the microphone.

  Thereby, the howling canceller can suppress the howling which changes according to the amplification amount of the audio signal.

  Furthermore, the howling canceller of the present invention detects the occurrence of howling even when the path of the audio signal is an acoustic feedback system (that is, when the audio signal input from the microphone is emitted from the speaker). The configuration may further suppress the howling.

  As a result, even if howling occurs, it can be immediately suppressed.

  The howling canceller of the present invention can accurately detect the frequency band in which howling occurs without actually generating howling in the acoustic space, and suppress howling in the frequency band. That is, the howling canceller of the present invention can prevent howling from occurring in advance.

2 is a block diagram showing the function and configuration of the loudspeaker 1. FIG. It is a figure which shows an example of the suppression aspect table. It is a block diagram which shows the function and structure of a loudspeaker at the time of initialization. It is a flowchart which shows the flow of the process at the time of filter setting. It is a block diagram which shows the function and structure of a loudspeaker at the time of utilization.

  A loudspeaker 1 according to an embodiment of the present invention will be described with reference to the drawings. The loudspeaker 1 corresponds to a howling canceller of the present invention. The loudspeaker 1 is installed in a living room, a lecture hall, or the like by a user and is initially set. In this initial setting, the filter 16 that suppresses howling of the audio signal input from the microphone M is set by simulating howling. Thereafter, the loudspeaker 1 emits the sound input from the microphone M from the speaker SP via the filter 16.

  First, the function and configuration of the loudspeaker 1 will be described with reference to FIGS. FIG. 1 is a block diagram showing the function and configuration of the loudspeaker 1. As shown in FIG. 1, the loudspeaker 1 includes a microphone M, a speaker SP, a control unit 10, an impulse response measurement unit 11, an FIR filter 12, a measurement signal generation unit 13, an amplifier 14, an adder 15, and a filter 16 (present invention). ), A howling detection unit 17, a filter coefficient generation unit 18, and switches SW1 to SW4 (corresponding to the switching unit of the present invention).

  The microphone M picks up surrounding sounds and generates a sound signal. The speaker SP emits sound based on the input sound signal.

  The control unit 10 includes a memory (not shown), and controls the configuration of the loudspeaker 1 based on an input from the operation unit (not shown). The memory stores a suppression mode table shown in FIG. FIG. 2 is a diagram illustrating an example of a suppression mode table. In the suppression mode table, a suppression mode (filter coefficient of the filter 16) is registered for each amplification amount of the amplifier 14. The suppression mode of the suppression mode table is registered by the control unit 10 at the time of initial setting and is referred to when used. Details of the processing of the control unit 10 will be described later.

  The impulse response measuring unit 11 measures an impulse response of an acoustic feedback system from the speaker to the microphone. The impulse response measuring unit 11 outputs a test signal (for example, a signal including all frequencies such as a TSP signal and a white noise signal) to the speaker SP and emits sound from the speaker SP. In addition, when a test signal picked up by the microphone M is input, the impulse response measurement unit 11 obtains a cross-correlation coefficient between the test signal and the test signal output to the speaker SP, and measures the impulse response. To do.

  In the FIR filter 12, the impulse response measured by the impulse response measuring unit 11 is set as a filter coefficient. Therefore, the FIR filter 12 becomes a filter that simulates a transfer function of an acoustic feedback system from the speaker to the microphone.

  The measurement signal generator 13 generates a measurement signal (for example, an impulse signal) when the filter coefficient of the FIR filter 12 is set. In addition, the measurement signal generation unit 13 includes a counter. A method of using this counter will be described later.

  The amplifier 14 amplifies the input audio signal. The amount of amplification is set by the measurement signal generator 13.

  The adder 15 outputs the measurement signal from the measurement signal generator 13 and the output signal from the amplifier 14 to the filter 16. Immediately after the measurement signal generator 13 generates the measurement signal, the adder 15 receives the measurement signal from the measurement signal generator 13 but does not receive the output signal from the amplifier 14. Output. Otherwise, since the measurement signal is not input from the measurement signal generator 13 to the adder 15, the output signal from the amplifier 14 is output to the filter 16.

  The filter 16 is, for example, a notch filter or a dip filter, and suppresses a gain in a frequency band where howling occurs from the output signal of the adder 15.

  The howling detection unit 17 detects whether or not howling has occurred. Specifically, the howling detection unit 17 performs analysis such as instantaneous frequency analysis, zero cross counter coefficient, or FFT analysis on the input signal, and determines whether each frequency band exceeds a predetermined intensity. Thus, the presence or absence of howling is detected. A frequency band exceeding the predetermined intensity is set as a frequency band in which howling occurs. When detecting howling, the howling detection unit 17 outputs a frequency band in which howling has occurred to the filter coefficient generation unit 18.

  The filter coefficient generation unit 18 sets the filter coefficient of the filter 16 so as to suppress the gain with respect to the frequency band input from the howling detection unit 17.

  The switches SW1 to SW4 are switches that switch the loop path. The switch SW1 switches the connection destination of the speaker SP to the impulse response measuring unit 11 and the switch SW3. The switch SW2 switches the connection destination of the microphone M to the impulse response measuring unit 11 and the switch SW4. The switch SW3 switches the connection destination of the filter 16 to the FIR filter 12 and the switch SW1. The switch SW4 switches the connection destination of the howling detection unit 17 and the amplifier 14 to the FIR filter 12 and the switch SW2.

  Next, the operation of the loudspeaker 1 and the flow of processing will be described with reference to FIGS. First, the initial setting of the loudspeaker 1 will be described with reference to FIGS. FIG. 3 is a block diagram showing the function and configuration of the loudspeaker at the time of initial setting. FIG. 4 is a flowchart showing the flow of processing when setting a filter.

  As illustrated in FIG. 3, the control unit 10 switches the switch SW1 to connect the impulse response measurement unit 11 to the speaker SP, and switches the switch SW2 to connect the impulse response measurement unit 11 to the microphone M. As a result, the loudspeaker 1 forms a first loop by the speaker SP, the microphone M, and the impulse response measuring unit 11. The first loop is an open loop without a signal path for outputting the test signal collected by the microphone M to the speaker SP again. For this reason, even when the test signal is emitted from the speaker SP into the acoustic space, howling does not occur in the first loop.

  Further, the control unit 10 switches the switch SW3 to connect the FIR filter 12 to the filter 16 and switches the switch SW4 to connect the FIR filter 12 to the howling detection unit 17 and the amplifier 14. As a result, the loudspeaker 1 forms a second loop (corresponding to the pseudo loop system of the present invention) by the filter 16 and the FIR filter 12.

  First, as a first step, the loudspeaker 1 sets an FIR filter 12 that simulates a transfer function of an acoustic feedback system from the speaker SP to the microphone M in the first loop. Specifically, the impulse response measurement unit 11 outputs a test signal to the speaker SP based on an instruction from the control unit 10. The speaker SP emits a test signal. The microphone M picks up the test signal and outputs it to the impulse response measuring unit 11. The impulse response measurement unit 11 measures the impulse response based on the cross-correlation coefficient between the test signal collected by the microphone M and the test signal output to the speaker SP, and outputs the impulse response to the FIR filter 12. The FIR filter 12 sets the impulse response as its filter coefficient. As described above, the loudspeaker 1 completes the setting of the FIR filter 12.

  Next, as a second step, the loudspeaker 1 sets a filter 16 that suppresses the gain of the frequency band in which howling occurs in the second loop. The second loop is a closed loop realized by an electric circuit or software. For this reason, the howling generated in the second loop is pseudo and does not generate howling in the acoustic space.

  Specifically, as shown in FIG. 4, the measurement signal generation unit 13 generates a measurement signal based on an instruction from the control unit 10, and outputs the measurement signal to the second loop by the adder 15 (S11). At this time, the measurement signal generator 13 resets the counter (counter t = 0) (S12). This counter is used to count the number of times the measurement signal passes through the second loop.

  The filter 16 filters the measurement signal output to the second loop (S13). Then, the FIR filter 12 performs FIR processing (convolution of the impulse response measured by the impulse response measuring unit 11) on the measurement signal input from the filter 16 (S14). The filter 16 is set with a filter coefficient that outputs the input signal as it is until the howling detection unit 17 detects howling.

  The howling detection unit 17 detects whether or not howling has occurred in the measurement signal that has passed through the FIR filter 12 (S15). At this time, the howling detection unit 17 also detects a frequency band in which howling occurs.

  When the howling detection unit 17 detects the occurrence of howling (S15: Yes), the filter coefficient generation unit 18 sets a filter coefficient for suppressing the gain of the frequency band in which howling is generated in the filter 16 (S16). Then, the measurement signal generator 13 resets the counter (counter t = 0) (S17), and proceeds to the process of S19. That is, when detecting the occurrence of howling, the loudspeaker 1 resets the counter and continuously detects the presence or absence of howling.

  When the howling detection unit 17 does not detect howling (S15: No), the measurement signal generation unit 13 counts up the counter (counter t = counter t + 1) (S18), and the process of S19 is performed. move on.

  In S19, the measurement signal generator 13 checks whether or not the counter exceeds an upper limit value (for example, 10). If the counter does not exceed the upper limit (for example, 10) (S19: No), the process proceeds to S13. That is, the loudspeaker 1 passes the measurement signal into the second loop until the counter exceeds the upper limit value (repeated a plurality of times), and detects whether or not howling has occurred.

  In addition, when the counter of the measurement signal generator 13 exceeds the upper limit value (S19: Yes), the controller 10 stores the filter coefficient of the filter 16 in the memory of the controller 10 (S20). The measurement signal generator 13 amplifies the gain of the measurement signal with the amplifier 14 (S21). Then, the measurement signal generator 13 checks whether or not the amplification amount exceeds the upper limit value (S22). When the amount of amplification of the measurement signal does not exceed the upper limit (S22: No), the process proceeds to S12. That is, the loudspeaker 1 amplifies the measurement signal stepwise until the measurement signal amplification amount exceeds the upper limit value, passes the measurement signal through the second loop, detects whether or not howling has occurred, and increases the amplification amount. The filter coefficient of the filter 16 in each stage is stored.

  Moreover, the measurement signal generation part 13 will complete | finish a process, if the amplification amount of a measurement signal exceeds an upper limit (S22: Yes). For example, the measurement signal generator 13 amplifies the measurement signal step by step by 1 dB, and ends the process when the measurement signal is amplified to 12 dB.

  As described above, the loudspeaker 1 first measures the impulse response of the acoustic feedback system from the speaker to the microphone. Then, the loudspeaker 1 uses the measured impulse response to detect a frequency band in which howling occurs inside the apparatus, and sets the filter 16 to suppress the gain of the frequency band. As a result, the loudspeaker 1 can accurately detect the frequency band in which howling occurs by performing simulation without actually generating howling in the acoustic space and generating howling internally.

  Further, the loudspeaker 1 detects the occurrence of howling, sets the filter coefficient, resets the counter, and redetects the presence or absence of howling. If the filter coefficient is set in the filter 16 so as to suppress the gain in the frequency band in which howling occurs, the phase near the frequency band in which the gain is suppressed rarely changes and new howling may occur. Therefore, the loudspeaker 1 resets the counter and detects the occurrence of howling again in order to detect new howling even after setting the filter coefficient. Thereby, the loudspeaker 1 can detect the frequency band in which howling occurs more accurately.

  Furthermore, the loudspeaker 1 passes the measurement signal into the second loop until the counter exceeds the upper limit (repeated a plurality of times). This is because when the measurement signal passes through the FIR filter, the impulse response is convoluted, and when the measurement signal passes through the FIR filter a plurality of times, the intensity of the frequency band in which howling occurs increases. The loudspeaker 1 can accurately detect the frequency band in which howling has occurred by passing the measurement signal through the FIR filter (in the second loop) a plurality of times.

  In addition, the loudspeaker 1 amplifies the measurement signal in stages until the amplification amount of the measurement signal exceeds the upper limit value, and detects a frequency band in which howling occurs. And the loudspeaker 1 memorize | stores the filter coefficient of the filter 16 in each step. Thereby, the loudspeaker 1 can appropriately set the filter coefficient of the filter 16 according to the amplification amount of the audio signal input from the microphone, and appropriately suppress the gain of the frequency band in which howling occurs. Can do.

  Next, a method of using the loudspeaker 1 will be described with reference to FIG. FIG. 5 is a block diagram showing the function and configuration of the loudspeaker during use.

  As illustrated in FIG. 5, the control unit 10 switches the switch SW1, connects the switch SW3 to the speaker SP, switches the switch SW3, and connects the switch SW1 to the filter 16. Further, the loudspeaker 1 switches the switch SW2, connects the switch SW4 to the microphone M, switches the switch SW4, and connects the switch SW2 to the howling detection unit 17 and the amplifier 14. As a result, the loudspeaker 1 forms a third loop by the microphone M, the amplifier 14, the filter 16, and the speaker SP. The third loop is a closed loop including an acoustic feedback system from the speaker SP to the microphone M.

  As a third step, when the audio signal is input from the microphone M, the loudspeaker 1 amplifies the audio signal by the amplifier 14. And the loudspeaker 1 suppresses the gain of the frequency band in which howling is generated by the filter 16 and emits sound based on the sound signal from the speaker SP. At this time, the loudspeaker 1 refers to the suppression mode table, acquires a suppression mode (a filter coefficient of the filter 16) according to the amplification amount of the audio signal, and sets a frequency band to be suppressed based on the suppression mode.

  The audio signal input from the microphone M is also input to the howling detection unit 17. That is, the loudspeaker 1 detects whether or not howling has occurred based on the audio signal input from the microphone M. Then, the loudspeaker 1 sets a filter 16 that suppresses the gain of the frequency band in which howling has occurred. Since the loudspeaker 1 always detects whether or not howling has occurred, even if howling occurs, it can be immediately suppressed.

  In the above-described embodiment, the filter 16 is a notch filter or a dip filter that suppresses the gain of the frequency band in which howling occurs. However, howling may be suppressed by using an all-pass filter that rotates the phase of the frequency band in which howling occurs as the filter 16. The loudspeaker 1 can control the gain characteristic or phase characteristic of the filter 16 to suppress the closed loop gain of the second loop or the third loop and prevent the occurrence of howling.

  In the above-described embodiment, the frequency band in which howling is generated by detecting the amplification amount of the measurement signal stepwise is detected. However, howling is performed by gradually decreasing the amplification amount of the measurement signal from the upper limit value. The generated frequency band may be detected. Normally, when the acoustic engineer performs howling detection manually, the measurement signal is amplified in stages. For this reason, it is preferable that the loudspeaker 1 amplifies the measurement signal stepwise so that the acoustic engineer manually performs howling detection, and can obtain a result equivalent to the howling detection manually performed by the acoustic engineer.

  DESCRIPTION OF SYMBOLS 1 ... Loudspeaker, 10 ... Control part, 11 ... Impulse response measurement part, 12 ... FIR filter, 13 ... Measurement signal generation part, 14 ... Amplifier, 15 ... Adder, 16 ... Filter, 17 ... Howling detection part, 18 ... Filter coefficient generation unit, M ... microphone, SP ... speaker, SW1 to SW4 ... switch

Claims (3)

A howling canceller equipped with suppression means for suppressing howling caused by an acoustic feedback system from a speaker to a microphone,
Measuring means for measuring the impulse response of the acoustic feedback system;
A switching means for switching the pseudo-loop system simulating the impulse response measured by the measuring means and the acoustic feedback system in the path of the audio signal;
The acoustic feedback system is switched to the pseudo loop system by the switching means to generate a measurement signal, and a pseudo howling generation means for generating the howling by passing the measurement signal through the pseudo loop system a plurality of times;
Control means for setting a parameter for suppressing loop gain according to the frequency band of howling generated by the pseudo howling generating means in the suppressing means,
Howling canceller with Amplifying means for amplifying the audio signal supplied to the suppressing means;
Storage means for storing parameters of the suppression means,
The control unit changes the amplification amount of the amplification unit stepwise to cause the pseudo howling generation unit to generate pseudo howling, and the storage unit associates the suppression amount with the amplification amount of the amplification unit. Memorize the parameters of the means,
The howling canceller according to claim 1, wherein a parameter stored in the storage unit is set in the suppression unit in accordance with an amplification amount of the amplification unit. A detection means for detecting howling;
When the detection means detects howling after the path of the audio signal is switched to the acoustic feedback system by the switching means, the control means sets a parameter for further suppressing howling in the detected frequency band to the suppression means. The howling canceller according to claim 1 or claim 2 to be set.

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