JP2560923B2 - Howling cancel device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a howling canceling device which has a reproducing speaker and a sound collecting microphone and is applied to an acoustic system in which an acoustic signal input to the microphone is output from the speaker.

[0002]

2. Description of the Related Art As an acoustic system having a speaker and a microphone of this kind, there is an acoustic system for concerts, lectures and conferences, and a sound room system (SRS) described in, for example, JP-A-61-257099. . The SRS was obtained by collecting the performance sound with a microphone in order to give the presence of being in a different acoustic space such as a hall when playing a piano or other musical instrument in a room of a general household. This is a sound field control device in which a signal of a reflected sound or a reverberation sound (hereinafter referred to as a reflected sound signal) is added by digital signal processing using the signal as a source signal, and the signal is reproduced from a speaker.

[0003]

However, in such a sound field control device, since the sound reproduced from the speaker is fed back to the microphone, the sound on which the echo is superposed is reproduced, and the sound field effect is not produced. When the reproduction volume is increased to raise the volume, an oscillation phenomenon called howling occurs. Note that an acoustic system that has a speaker and a microphone in this way and in which an acoustic signal input to the microphone is output from the speaker is referred to as a speaker-microphone system, and howling is caused by feedback from the speaker to the microphone. Collectively. When such howling occurs, naturally not only the intended sound field reproduction cannot be performed, but
It will be very difficult to hear.

An object of the present invention is to solve the above-mentioned conventional problems and to provide a howling canceling device which can effectively prevent howling due to feedback in a speaker-microphone system.

[0005]

A howling canceling device according to the present invention has at least one reproducing speaker and at least one sound collecting microphone, and an acoustic signal input to the microphone is output from the speaker. In a howling canceller that prevents howling from occurring in a system, a coefficient is determined based on an impulse response of an acoustic system, and a first calculation means performs a convolution calculation of an input signal to a speaker based on this coefficient, and a second calculation is performed. The output signal of the microphone and the output signal of the first calculation means are phase-inverted and added by the arithmetic means to obtain an input signal to the speaker. First
The calculation means of, for example, FIR (finite impulse response)
) A filter, and the second arithmetic means is composed of, for example, a digital signal processing circuit (DSP).

In the present invention, it is desirable that the coefficient used in the first calculation means is determined by averaging the impulse responses obtained a plurality of times. Detects the temperature of the acoustic system in the present invention, the output signal of the microphone in response to the detection result to control the sampling frequency for converting A / D, and more specifically the temperature
If the temperature rises, increase the sampling frequency
If is falling, lower the sampling frequency
The first feature is to control. Further , according to the present invention, a volume gay that determines the output volume from the speaker
Controlling the output level of the first arithmetic means in accordance with the emission
Is the second feature .

[0007]

The output of the first calculation means obtained by convoluting the coefficient determined based on the impulse response of the acoustic system with the input signal to the speaker corresponds to the feedback component from the speaker to the microphone. Therefore, if the output signal of the first calculating means is added to the output signal of the microphone in the second calculating means in an opposite phase to each other, the feedback component contained in the output signal of the microphone is removed and howling cancellation is performed. .

If the impulse response of the acoustic system is obtained a plurality of times and the coefficients are averaged by averaging them to determine the coefficient in the first calculating means, the impulse response S / N due to the fluctuation of the acoustic system results. Coefficient error is reduced, and howling is canceled more accurately.

Further, by controlling the sampling frequency for the output signal A / D conversion of the microphone in response to the temperature detection result of the acoustic system, the impulse response due to the speed of sound varies with temperature changes in the acoustic system The effect of changes in is corrected. As a result, accurate howling cancellation is possible even with changes in temperature.

Furthermore, if the output volume of the speaker is changed,
Since the loop gain of the acoustic system changes and the amplitude of the feedback component also increases accordingly, a cancellation error of the feedback component occurs when the gain of the first calculation means is constant. By controlling the output level of the first calculation means input to the second calculation output according to the output volume, such a cancel error does not occur, and correct howling cancellation is performed regardless of the change in the output volume.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the howling canceling device of the present invention is applied to a sound field control device having a speaker-microphone system will be described below. FIG. 1 is a block diagram showing a schematic configuration of a single-channel sound field control device according to an embodiment of the present invention.

This sound field control device includes a reproduction speaker 1, a sound pickup microphone 2, and a microphone mixing circuit (MIX).
3, input volume 4, low-pass filter (LPF)
5, A / D converter 6, digital signal processing circuit (DS
P) 7, FIR filter 8, D / A converter 9, low-pass filter 10, output volume 11, amplifier 12, temperature sensor 13, temperature compensation circuit 14, wireless remote controller 1
5, a remote control interface (I / F) 16, a microcomputer 17 and a ROM 18.

The reproducing speaker 1 is for reproducing the reflected sound and is installed at an appropriate position in the room. The sound pickup microphone 2 is for picking up a sound of a musical instrument or the like, and its output is amplified by the microphone mixing circuit 3 and, if necessary, mixed with other source signals at a desired ratio, The signal level is adjusted by the input volume 4. The low-pass filter 5 is for removing unnecessary high-frequency components (frequency components that are twice or more the sampling frequency of the A / D converter 6), and its output is sampled by the A / D converter 6 and digitally output. After being converted into a signal, it is input to the digital signal processing circuit 7.

The digital signal processing circuit 7 is a circuit for performing a specified process under the control of the microcomputer 17, and specifically, it can selectively program an impulse response measurement mode and a reflected sound reproduction mode, which will be described later. Is configured. The output of the digital signal processing circuit 7 is converted into an analog signal by the D / A converter 9, further smoothed by the low-pass filter circuit 10 to remove unnecessary high frequency components, and then, through the output volume 11 and the amplifier 12. Are supplied to the speaker 1.

The ROM 18 has a digital signal processing circuit 7 for imparting a frequency characteristic to a reflected sound parameter and a reflected sound parameter obtained in advance for various acoustic spaces such as a hall.
The frequency characteristic parameters of the digital filter and the program of the digital signal processing circuit 7 and the like are stored. Then, according to the operation of the wireless remote controller 15, a reflected sound parameter of a predetermined hole or the like, a frequency characteristic parameter or a program is read from the ROM 18 by the microcomputer 17.

Under the control of the microcomputer 17, this sound field control device measures the transmission characteristics (impulse response) of the system of the speaker 1 to the microphone 2 including the characteristics of the room on the same digital signal processing system. Two operation modes can be selected: response measurement mode and reflected sound reproduction mode. Therefore, the error due to the difference in the transmission characteristics of the system in both modes can be minimized. Hereinafter, each of these operation modes will be described.

(1) Impulse Response Measurement Mode FIG. 2 is a diagram showing a state in the impulse response measurement mode. Note that FIG. 2 shows only the main part of FIG. In this mode, the microcomputer 1
A program for impulse response measurement is loaded from the ROM 18 by 7. When this program is loaded, a pulse voltage (impulse) is output from the digital signal processing circuit 7 and reproduced from the speaker 1 through the D / A converter 9, the low pass filter 10, the output volume 11 and the amplifier 12.

The pulse output from the speaker 1 is picked up by the microphone 2 after being reflected directly and in the room. The output of the microphone 2 is the microphone mixing circuit 3,
A / via the input volume 4 and low-pass filter 5
The digital signal is converted by the D converter 6 and input to the digital signal processing circuit 7. The digital signal processing circuit 7 takes in the input signal as an impulse response measurement result showing the transmission characteristic including the characteristic of the room from the speaker 1 to the microphone 2 and stores it in a built-in RAM (not shown).

By the way, since the impulse response is not stable due to the fluctuation of the sound field (room), an accurate impulse response measurement result cannot be obtained by only one measurement. Therefore, in order to improve the S / N of the measured impulse response, the above-described impulse response measurement operation is randomly repeated a plurality of times, and the results of the plurality of measurements are averaged (averaging) to obtain the final impulse response. It is regarded as the response measurement result. The final impulse response measurement result is transferred to the FIR filter 8 in the backward direction and set in the FIR filter 8 as coefficient data, whereby the impulse response measurement mode ends.

(2) Reflected Sound Reproducing Mode FIG. 3 is a diagram showing a state in the reflected sound reproducing mode. Note that FIG. 3 shows only the main part of FIG. In this mode, the microcomputer 17 first sets the ROM
A reflected sound reproduction program is loaded from 18. When this program is loaded, in the digital signal processing circuit 7, the microphone 2 to the microphone mixing circuit 3, the input volume 4, the low-pass filter 5 and the A /
The reflected sound signal is generated by the reflected sound generation circuit 23 based on the source signal input through the D converter 6.

The method of generating the reflected sound signal may be basically the same as the method described in, for example, JP-A-61-257099. Since the details thereof are described in the publication, a brief description will be given. First, a reflected sound parameter (delay time and gain data) designated by the user is read from the ROM 18 through the wireless remote controller 16.
It is once transferred to a RAM (parameter memory, not shown) provided in the reflected sound generation circuit 23. In the reflected sound generation circuit 23, a signal group having various delay times and amplitude levels is created from the source signal using the output signal of the A / D converter 6 as a source signal based on the reflected sound parameter held in the RAM. , The reflected sound signal is generated by synthesizing them by the convolution operation.

The frequency characteristic of a digital filter (not shown) provided in the digital signal processing circuit 7 for imparting a frequency characteristic to the reflected sound signal is stored in the ROM 18
It is controlled according to the frequency characteristic parameter designated by the user through the wireless remote controller 16 read from the. The frequency characteristic parameter read from the ROM 18 is temporarily transferred to the RAM (not shown).
The frequency characteristic parameter stored in the RAM can be adjusted by the user through the wireless remote controller 16 according to his / her preference.

The reflected sound signal thus generated is D / A
After being converted into an analog signal by the converter 9, it is supplied to the speaker 1 through the low-pass filter 10, the output volume 11 and the amplifier 12, and the reflected sound is reproduced. on the other hand,
The reflected sound signal from the reflected sound generation circuit 23 is
It is also input to the filter 8. The output signal of the FIR filter 8 is supplied to the adding circuit 22 via the phase inverting circuit 21 and added to the output signal of the A / D converter 6. The output signal of the adder circuit 22 is input to the reflected sound generation circuit 23.

Here, the impulse response measurement result including the characteristics of the room of the system from the speaker 1 to the microphone 2 in the impulse response measurement mode is set in the FIR filter 8 as a coefficient. Therefore, the reflected sound signal obtained through the FIR filter 8 is the reflected sound generated from the speaker 1
After being picked up by, the signal becomes almost the same as the signal obtained through the microphone mixing circuit 3, the input volume 4, the low pass filter 5 and the A / D converter 6. Therefore, by adding the anti-phase signal of the output signal of the FIR filter 8 to the output signal of the A / D converter 6 using the phase inverting circuit 21 and the adding circuit 22, the sound reproduced from the speaker 1 enters the microphone 2. As a result, the feedback component (echo component) generated in the output of the A / D converter 6 is canceled and the howling is controlled.

Next, the principle of howling cancellation in one channel (one speaker and one microphone) in this embodiment will be described in more detail with reference to FIG. In FIG. 4, y (t) is the input signal of the microphone 2, R (t) is the output of the speaker 1, and s (t) is the sound source. ER (t) is the initial reflected sound sequence output from the reflected sound generation circuit 23, and h (t) is the speaker 1 including the characteristics of the room.
To the microphone 2 impulse response of the system,
Let h ′ (t) be the coefficient of the FIR filter 8 which is the measurement result of this impulse response h (t), K is a constant, C
When (t) is the output of the FIR filter 8, the following relational expression is obtained. However, * indicates a convolution operation.

[0026]

## EQU00001 ## y (t) = s (t) + h (t) * R (t) (1) R (t) = {y (t) -K.C (t)} * ER (t) (2 ) C (t) = R (t) * h '(t) (3)

By modifying this, the output R of the speaker 1
(T) can be rewritten as follows.

[0028]

[Equation 2] R (t) = s (t) * ER (t) + [{h (t) -K · h '(t)} * R (t)] * ER (t) (4)

Here, the first term on the right side of the equation (4) is the original output of the speaker 1, and the second term is the so-called echo component and FI in which the output of the speaker 1 returns to the microphone 2 again.
This is the output of the R filter 8. Impulse response h
If the output of (t) and the output of the FIR filter 8 are added in opposite phases, and the constant K is set to an appropriate value, the second term on the right side of the equation (4) can be made zero. This is the principle of echo cancellation in the present invention, that is, howling cancellation, and it is possible to reproduce only the original reflected sound that does not include an echo component.

The constant K is considered to be the ratio of the loop gain when the impulse response is measured and when the reflected sound is reproduced, and its value is usually 1. If the output volume (input volume 4) of the microphone 2 is constant during impulse response measurement and reflected sound reproduction, h (t) and h '
It is almost equal to (t). In addition, the howling phenomenon occurs when the loop gain of the speaker 1-microphone 2 system is increased, but by changing the value of K according to the loop gain, the second term on the right side of the equation (2) can be eliminated, and howling Can be controlled.

Next, temperature compensation will be described. Generally, the speed of sound propagating in air, that is, the speed of sound, changes depending on the temperature of the place. The temperature dependence of the speed of sound is expressed by the following equation.

[0032]

[Equation 3] C = 331.45 + 0.6 · θ (m / s) (5) C: Sound velocity θ: Celsius temperature

That is, when the temperature changes by 1 ° C., about 0.6
The sound arrival distance will differ by the amount corresponding to m / s. As described above, when the impulse response from the speaker 1 to the microphone 2 including the characteristics of the room is measured by the digital signal processing and howling cancellation is performed, ideally the room temperature is the same during measurement and during reproduction. is necessary. If the room temperature at the time of measurement is different from that at the time of reproduction, the impulse response waveform will differ depending on the difference in sound velocity. The difference in sound velocity can be roughly estimated from the equation (5).

Here, for example, the sampling frequency fs in the A / D converter 6 (= conversion clock frequency in the D / A converter 9) is 44.1 kHz, and the sound velocity C during measurement is 340 m /
If the temperature is changed by 1 ° C, the A / D converter 6
Output signal (input signal of digital signal processing circuit 7)
Is 44,100 × 0.6 / 34 per second during measurement and during playback
The waveform will shift by 0 ≈ 77 samples. This is illustrated in FIG. When howling cancellation is performed by using the digital signal processing circuit 7 and the FIR filter 8 as in this embodiment, which of the waveforms of the input signal of the digital signal processing circuit 7 during measurement and reproduction as described above is howling canceling operation. It causes an error of, and becomes a problem. Therefore, at the time of howling cancellation, some kind of temperature compensation is necessary in order to prevent the influence of the difference in the sound velocity due to the temperature change at the time of the reproduction during the measurement.

The time length of the FIR filter 8 is generally finite, but when it is used for howling cancellation, a length corresponding to the reverberation time (RT) of the room may be used. For example, for a room with less reverberation at RT = 0.2 seconds or less, the time length of the FIR filter 8 is experimentally 70 msec.
A sufficient howling canceling effect can be obtained in the time width of. For rooms with reverberation times longer than this, FI
This can be dealt with by further increasing the time length of the R filter 8. Based on this matter, a method of temperature compensation in howling cancellation will be described below.

First, when the reverberation time of the room is short, since the time length of the FIR filter 8 is short, it can be dealt with by delaying the output signal waveform of the FIR filter 8 by several samples according to the temperature change.

FIG. 6 is a diagram showing an embodiment provided with the temperature compensating means based on the first method, in which the delay circuit 24 is provided on the input side of the output signal from the FIR filter 8 in the digital signal processing circuit 7. Has been inserted. Since the delay circuit 24 handles digital data, a RAM (random access memory) is suitable, for example. On the other hand, the output from the temperature sensor 13 is supplied to the temperature detection circuit 25, where it is converted into temperature data and input to the microcomputer 17. The microcomputer 17 knows the temperature change between the impulse response measurement and the reproduction from the input temperature data, and accordingly, the delay time of the delay circuit 24, that is, the output signal of the microphone 2 (A / D converter 6).
Of the output signal of the FIR filter 8 with respect to the output signal of the. That is, when the temperature rises and the speed of sound becomes faster during reproduction than during measurement, the timing of the output waveform of the A / D converter 6 becomes relatively faster than the output signal waveform of the FIR filter 8, so that the delay circuit 8 Shorten the delay time, and increase the delay time when the temperature drops.

As a second method of temperature compensation, there is a method of varying the sampling frequency fs in response to a change in sound velocity due to a change in temperature. As described with reference to FIG. 5, the impulse response waveform, which is the coefficient of the FIR filter 8 for howling cancellation, is constant during digital signal processing unless the sampling frequency changes. On the other hand, when the temperature of the room changes at the time of reproduction from that at the time of measuring the impulse response, the impulse response waveforms of the speaker 1 and the microphone 2 system differ in a stretched form. This causes an error in the cancel waveform when performing howling cancellation.

In such a case, A
By changing the sampling frequency fs of the / D converter 6 (the conversion clock frequency of the D / A converter 9), the apparent impulse response waveform becomes the same. For example, when the temperature rises during the reproduction from the impulse response measurement, the impulse response waveform component contained in the output signal of the A / D converter 6 can be measured by raising the sampling frequency fs by an appropriate amount corresponding to the temperature rise. It becomes the same as that at the time, and howling can be canceled correctly. If the temperature drops from the time of measurement, the sampling frequency fs may be decreased.

The temperature compensating circuit 14 in FIG. 1 is a circuit for compensating the temperature by the second method, for example, FIG.
It is configured as shown in. In FIG. 7, the temperature sensor 1
The output of 3 is converted into a DC voltage by the DC amplifier 31,
It is applied to the clock generation circuit 32. In the clock generation circuit 32, the bias voltage CV to the varicap VC is generated by the resistors R1, R2, the variable resistor RV and the capacitor C1 based on the DC voltage from the DC amplifier 31. The variable resistor RV is used for setting the reference value of the sampling frequency. The capacitance value of the varicap VC is determined by the bias voltage CV, and as a result, the ceramic vibrator XL, the capacitors C2 and C3, and the resistor R3.
The oscillation frequency of the oscillation circuit formed by the inverters I1 and I2 is determined. The oscillation output of this oscillation circuit is output from the clock generation circuit 32 as a system clock and supplied to each part of the system, and at the same time, the frequency dividing circuit 3
The frequency is divided by 3 to obtain the sampling frequency fs.

FIG. 8 shows a change f / fo (fo: fo) of the output frequency f of the clock generation circuit 32 with respect to the bias voltage VC.
An example of the center frequency) is shown. Within the change range as shown in FIG. 8, it is easy to create the sampling frequency fs proportional to the sound velocity fluctuation due to the temperature change.

The temperature dependence of the sound velocity is as shown in the above equation (3), but the sampling frequency f
FIG. 9 shows the result of back-calculation of how much s should be changed from the sampling frequency at the time of impulse response measurement to achieve temperature compensation. However, the ambient temperature θ during measurement should be 15
C. and the sampling frequency fs was 44.1 kHz.
The room temperature during playback is ± 2 at most compared to the temperature during measurement.
Considering the increase or decrease of about ° C, it is sufficient from Fig. 9 that the change of the sampling frequency fs is about ± 0.35%. This is a sufficiently realizable range from FIG. Further, if the center frequency fo is set according to the season or the current room temperature, the temperature compensation as described above is possible unless the room temperature changes significantly.

FIG. 10 shows another configuration example of the temperature compensation circuit 14 according to the second method. This example is the same as that of FIG. 7 in principle, but a VCO (voltage controlled oscillator)
34 is used to directly generate the sampling frequency fs. On the other hand, the system clock is generated by inputting the output of the VCO 34 to a PLL (phase lock loop) 36 and appropriately multiplying the frequency.

By the way, when the output volume from the speaker 1 is increased by the output volume 11 in order to increase the effect of the sound field reproduction, the loop gain of the speaker 1 and the microphone 2 system becomes large, so that the feedback component (echo Component) also has a larger amplitude. Therefore, in this embodiment, as shown in FIG. 3, for example, the gain of the phase inverting circuit 21 is controlled in association with the output volume 11, and the output level of the phase inverting circuit 21, that is, FIR, is controlled according to the output volume from the speaker 1. The output level of the filter 8 is controlled. As a result, howling can be correctly canceled even when the amplitude level of the feedback component changes due to the change in output volume.

Next, an embodiment of the multi-channel sound field control device will be described. FIG. 11 is a diagram showing a schematic configuration of a 4-channel sound field control device according to the present invention. The same parts as those of the single-channel sound field control device shown in FIG. explain.

In the four-channel sound field control device shown in FIG. 11, the reproduction speaker 1 is a front left (FL) channel, a front right (FR) channel, a rear left (RL) channel, and a rear right (RR) channel. 4 speakers are arranged, and correspondingly four digital signal processing circuits 7, FIR filters 8, low-pass filters 10, output volumes 11 and amplifiers 12 are also provided. The output signals of the four FIR filters 8 are commonly input to the digital signal processing circuit 8 via the adder 19.

This sound field control device performs measurement independently for each channel in the impulse response measurement mode, transfers the coefficient individually to the FIR filter 8 of each channel, and adds in the reflected sound reproduction mode. Bowl 19
Then, the sum of the output signals of the FIR filter 8 of each channel is calculated, and this is summed up
Howling is canceled by inputting in common.

Next, the principle of howling cancellation in four channels (four speakers and one microphone) in this embodiment will be described in more detail with reference to FIG.

When there are two or more speakers 1 (two channels), it is considered that the impulse response of the room due to the speaker reproduction of the other channels affects each other. As a procedure for howling cancellation in this case, first, impulse responses are measured independently for each channel, and these are used as coefficients of the FIR filter 8 for each channel. Next, all the convolution operation results of the FIR filter 8 of each channel are added by the adder 19,
By canceling the echo component of the signal from the microphone 2 with the added signal, howling cancellation can be performed when a multi-channel speaker is used.

In FIG. 12, y (t) is the input signal of the microphone 2, R _FL (t), R _FR (t), R _RL (t) and R _RR (t) are the outputs of the speaker 1 of each channel, s (t) is a sound source. ER _FL (t), ER _FR (t), ER _RL (t), and ER _RR (t) are the initial reflected sound sequence output from the reflected sound generation circuit 23 of each channel, h _FL (t), h _FR ( t), h _RL (t), h _RR (t) is output from the speaker 1 of each channel, the impulse response of the system from the speaker 1 to the microphone 2 including the characteristics of the room, h ′ _FL (t), Let h ′ _FR (t), h ′ _RL (t), h ′ _RR (t) be the convolver coefficient of the FIR filter 8 of each channel as the measurement result of these impulse responses, and K
_{When FL} , K _FR , K _RL , and K _RR are constants, and C (t) is the output of the adder 19 which is the sum of the outputs of the FIR filters 8 of all channels, the following relational expression is obtained. However, * indicates a convolution operation.

[0051]

[Formula 4] y (t) ＝ s (t) ＋ h _FL (t) ＊ R _FL (t) ＋ h _FR (t) ＊ R _FR (t) ＋ h _RL (t) ＊ R _RL (t) ＋ h _RR (t ) * R _RR (t) R _FL (t) = {y (t) -K _FL・ C (t)} * ER _FL (t) R _FR (t) = {y (t) -K _FR・ C ( t)} * ER _FR (t) R _RL (t) = {y (t) −K _RL・ C (t)} * ER _RL (t) R _RR (t) = {y (t) −K _RR・C (t)} * ER _RR (t) C (t) = h ' _FL (t) * R _FL (t) + h' _FR (t) * R _FR (t) + h ' _RL (t) * R _RL ( t) ＋ h ′ _RR (t) ＊ R _RR (t)

By transforming these, each speaker output R
By rearranging _FL (t), R _FR (t), R _RL (t), and R _RR (t), the following relational expression is obtained.

[0053]

[Formula 5] R _FL (t) = s (t) * ER _FL (t) + [{h _FL (t) -K _FL · h ' _FL (t)} * R _FL (t) + {h _FR ( t) −K _FL・ h ′ _FR (t)} * R _FR (t) + {h _RL (t) −K _FL・ h ′ _RL (t)} * R _RL (t) + {h _RR (t) −K _FL・ h ′ _RR (t)} * R _RR (t)] * ER _FL (t) (6) R _FR (t) ＝ s (t) ＊ ER _FR (t) + [{h _FR (t ) −K _FR・ h ′ _FR (t)} * R _FR (t) + {h _FL (t) −K _FR · h ′ _FL (t)} * R _FL (t) + {h _RR (t) − K _FR・ h ′ _RR (t)} * R _RR (t) ＋ {h _RL (t) −K _FR・ h ′ _RL (t)} * R _RL (t)] * ER _FR (t) (7) R _RL (t) = s (t) * ER _RL (t) + [{h _RL (t) -K _RL · h ' _RL (t)} * R _RL (t) + {h _RR (t) -K _{RL · h 'RR (t)} } * R RR (t) + {h FL (t) -K RL · h' FL (t)} * R FL (t) + {h FR (t) -K RL · h ′ _FR (t)} * R _FR (t)] * ER _RL (t) (8) R _RR (t) = s (t) * ER _RR (t) + [{h _RR (t) −K _RR・ H ′ _RR (t)} * R _RR (t) + {h _RL (t) −K _RR・ h ′ _RL (t)} * R _RL (t) + {h _FR (t) −K _RR · h ′ _FR (t) ＋ ＊ R _FR (t) ＋ {H _FL (t) -K _RR・ h ′ _FL (t)} ＊ R _FL (t)] ＊ ER _RR (t) (9)

Here, the first right side of each of the equations (6) to (9)
The term is the output signal to be originally reproduced. (6)-(9)
The second term on the right-hand side of each equation is the echo component and the convolver output of each channel that influence each other on the speaker output of each channel. Also in this case, this second term can be made zero if the conditions at the time of measurement and at the time of reproduction are made constant. That is, by setting all the brackets {} in each expression to zero, each speaker output becomes only the signal output to be originally reproduced. Therefore, howling cancellation can be performed as in the case of the previous single channel.

In order to simplify the howling cancel operation, in the case of two channels R and L,
This will be described using the actual observed waveform shown in FIG. FIG.
Shows the waveform of each part for the impulse signal,
(A) and (b) are output waveforms with respect to the pulse input of the FIR filter 8 having impulse responses of R and L channels as coefficients, and (c) is an output signal of the adder 19 in which these (a) and (b) are added. It is a waveform. In addition, FIG.
In (d), when impulses are simultaneously output from the reflected sound generation circuit 23, L and R are reproduced from the speaker 1,
It is an output signal waveform of the A / D converter 6 when the room response (echo component) is fed back to the microphone 1.
The output signal of the adder 19 shown in FIG. 13C is reversed in phase by the phase inversion circuit 21 in the digital signal processing circuit 7 shown in FIG. 3, and then added by the adder circuit 22 shown in FIG. A
When added to the output signal of the / D converter 6, the result is as shown in FIG. It can be seen that the waveform in FIG. 13E is the original output of the speaker 1 in which the echo component is canceled, and howling is canceled by this.

In this embodiment, the phase inverting circuit 21 in the digital signal processing circuit 7 for each channel may be provided in common for each channel. Further, also in this embodiment, the phase inversion circuit 21 according to the output volume 11
It is possible to obtain a correct howling canceling effect regardless of the output volume by controlling the gain of the output signal and controlling the output level of the phase inversion circuit 21 according to the output volume of the speaker 1. In the above-described embodiment, the case where the number of the microphones 2 is one has been described. However, when a plurality of microphones 2a to 2n are used as shown in FIG. , A /
It may be input to the D converter 6.

Although the present invention is applied to the sound field control device in the above embodiments, the present invention is also applicable to other acoustic systems in concert halls, lectures, conferences and the like.

[0058]

As described above, according to the present invention, in a howling cancel device that prevents howling that occurs in an acoustic system having a speaker and a microphone, the coefficient determined based on the impulse response of the acoustic system is used as the speaker. It is possible to remove feedback components and cancel howling by calculating the feedback component from the speaker to the microphone by convolution with the input signal to the microphone and adding this with the output signal of the microphone in opposite phase. Become.

[Brief description of drawings]

FIG. 1 is a block diagram of a single-channel sound field control device using a howling cancel device according to an embodiment of the present invention.

FIG. 2 is a block diagram schematically showing a state at the time of impulse response measurement of the example.

FIG. 3 is a block diagram schematically showing a state at the time of reproducing a reflected sound of the embodiment.

FIG. 4 is a diagram for explaining the principle of howling cancellation in the embodiment.

FIG. 5 is a diagram for explaining the difference in impulse response at the time of measurement and at the time of reproduction due to temperature change in the present invention.

FIG. 6 is a block diagram showing a configuration of a sound field control device to which the first temperature compensation method according to the present invention is applied.

FIG. 7 is a circuit diagram showing a configuration example of a temperature compensation circuit to which a second temperature compensation method according to the present invention is applied.

8 is a diagram showing changes in the output frequency of the clock generation circuit with respect to the bias voltage of the varicap in FIG.

9 is a diagram showing a control amount of a sampling frequency necessary for a temperature change in FIG.

FIG. 10 is a circuit diagram showing another configuration example of the temperature compensating circuit to which the second temperature compensating method according to the present invention is applied.

FIG. 11 is a block diagram of a 4-channel sound field control device using a howling cancel device according to another embodiment of the present invention.

FIG. 12 is a diagram for explaining the principle of howling cancellation in the example.

FIG. 13 is a waveform diagram for explaining howling cancel operation in the embodiment.

FIG. 14 is a diagram showing an embodiment in the case of a plurality of microphones.

[Explanation of symbols]

1 ... Playback speaker, 2 ... Sound pickup microphone, 3 ... Microphone mixing circuit, 4 ... Input volume, 5, 10 ...
Low-pass filter, 6 ... A / D converter, 7 ... Digital signal processing circuit, 8 ... FIR filter, 9 ... D / A converter, 11 ... Output volume, 12 ... Amplifier, 13 ... Temperature sensor, 14 ... Temperature compensation circuit , 15 ... Wireless remote control, 16 ... Remote control interface, 17 ... Microcomputer, 18 ... ROM.

Claims (2)

(57) [Claims] 1. A howling canceling device having at least one reproducing speaker and at least one sound collecting microphone for preventing howling of an acoustic signal input to the microphone from occurring in an acoustic system output from the speaker. Coefficient determining means for determining a coefficient based on the impulse response of the acoustic system; first computing means for convoluting the input signal to the speaker based on the determined coefficient; the microphone output signal; the output signal of the first calculating means adds to phase inversion to one another, and a second arithmetic means for obtaining an input signal to the speaker, and a temperature detecting means for detecting a temperature of said acoustic system, in the temperature detecting means If the detected temperature rises,
Sampler for A / D conversion of the microphone output signal
Temperature detected by the temperature detection means
If is decreased, the sampling frequency will be decreased.
And a means for controlling so that a howling cancellation device. 2. A howling canceling device having at least one reproducing speaker and at least one sound collecting microphone for preventing howling of an acoustic signal input to the microphone from occurring in an acoustic system output from the speaker. Coefficient determining means for determining a coefficient based on the impulse response of the acoustic system; first computing means for convoluting the input signal to the speaker based on the determined coefficient; the microphone output signal; The second arithmetic means for obtaining the input signal to the speaker by phase-inverting and adding the output signal of the first arithmetic means and the volume gain for determining the output volume from the speaker.
For controlling the output level of the first computing means according to
A howling canceling device comprising a step .