JPH03237899A - Howling suppression device - Google Patents

Abstract

PURPOSE:To easily adjust an optimum acoustic characteristic in a short period by attenuating the output level of a frequency band including a howling frequency of a prescribed level or over when the howling frequency of a prescribed level or over is detected. CONSTITUTION:A digital signal processor 7e converting an input data Ds into a spectrum level for each frequency component detects a frequency of a spectrum level being a preset threshold level or over and outputs a signal representing it. A sound volume control circuit 7g varies a 1st control signal so as to increase the sound volume level gradually when no howling frequency is detected and varies a 1st control signal so as to be sequentially increased at a smaller step after the sound volume level is decreased by a prescribed quantity when the howling frequency is detected and adjusts a 2nd control signal so as to decrease a signal level of the frequency band including the howling frequency when the howling frequency is again detected. Thus, an optimum acoustic characteristic is adjusted easily in a short period.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a howling suppression device for suppressing howling in an acoustic system installed in, for example, a concert hall or the like.

"Prior Art" FIG. 6 is a block diagram showing an example of a conventional howling suppression device. In this figure, M, = Mn is a microphone, and l-1-1-N are microphones M, =
This is a preamplifier that amplifies and outputs a small voltage signal output from Mn. 2 is an adder that adds input signals and outputs the result. 3 is a volume that adjusts the volume level, and 4 is a graphic equalizer that boosts or cuts a specific frequency band of the input signal and outputs it, and is a band pass filter (hereinafter abbreviated as BPF).
481 to 4a-N, volumes 4b-1 to 4b-N, and an adder 4c. This BPF・4a-1~4a
-N passes signals in respective preset frequency bands. 5 is a noise generator that generates and outputs a white noise signal in an audible frequency band. The output signal of the noise generator 5 is input to the adder 4c via the switch SW. 6 is a power amplifier that amplifies the power of an input signal and outputs it, and SP is a speaker.

For example, when adjusting the acoustic characteristics of a concert hall or the like using a howling suppression device with such a configuration,
First, the adjuster closes the switch SW to input the white noise signal to the adder 4c, and outputs the white noise sound from the speaker SP.

Next, the adjuster gradually increases the output level of the volume 3, and while listening to this white noise sound, adjusts the level of each frequency band of the graphic equalizer 4 so that howling does not occur. The acoustic characteristics of the concert hall thus obtained are flat frequency characteristics without howling.

``Problems to be Solved by the Invention'' However, even if a flat frequency characteristic is obtained through the above-mentioned adjustment, howling may still occur due to the gain characteristics of the preamplifiers 1-1 to 1-N, the reverberation characteristics of the concert hall, etc. There is a certain frequency band, and such a frequency band cannot be identified unless howling actually occurs.

Incidentally, there are cases in which the acoustic characteristics are adjusted while actually causing howling, but this adjustment is difficult even for experts and has the disadvantage that unpleasant howling sounds are generated over a long period of time.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a howling suppression device that can easily adjust optimal acoustic characteristics within a short time.

"Means for Solving the Problem" The invention according to claim 1 includes a volume that adjusts a volume level in accordance with a first control signal, and an acoustic signal output from the volume that is transmitted in a plurality of frequency bands. an adjusting means for adjusting the signal level of each band according to a second control signal supplied for each band; and detecting frequency components of the acoustic signal and having a frequency component of a predetermined level or higher. The control means includes a detection means for detecting a howling frequency, and a control means for outputting first and second control signals according to an output signal of the detection means, and the control means is configured to detect a howling frequency when the howling frequency is not detected. Changing the first control signal so that the volume level increases sequentially in a first step, and once decreasing the volume level by a predetermined amount when the howling frequency is detected,
The first control signal is changed so as to increase sequentially in steps smaller than the first step, and when the howling frequency is detected again, the second control signal is changed so that the signal level of the frequency band including the howling frequency is decreased. It is characterized by adjusting the control signal.

Further, in the invention as set forth in claim 2, the detection means detects the howling frequency based on the signal of each frequency band output from the adjustment means as 4I fine.

"Operation" According to the present invention, the volume level is adjusted to the first level until a howling frequency having a frequency component equal to or higher than a predetermined level is detected.
When the howling frequency is detected, the volume level is once decreased by a predetermined amount, and then increased in steps smaller than the first step. Then, when the howling frequency is detected again,
The second control signal is adjusted so that the signal level of a frequency band including the howling frequency is reduced. This suppresses howling.

"Embodiment" Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a howling suppression device which is an embodiment of the present invention. In this figure, parts corresponding to those in Fig. 6 are given the same reference numerals.
The explanation will be omitted.

In FIG. 1, Vol is composed of shift registers, analog switches, etc., and volume control data C, which will be described later.
It is an electronic volume that changes the resistance value according to v.

In addition, V-1 to V- in the graphic equalizer 4
N is also a similar electronic volume, and receives equalizer control data Vs and =Vsn, which will be described later, to adjust the level. 7 is a howling suppression circuit, whose configuration is shown in the second
Illustrated in the figure.

In FIG. 2, 7a is a CPU (central processing unit) that controls each part in the howling suppression circuit 7. 7b is a ROM in which the control program is written, 7c is a CP
This is a RAM used as a work area for U7a.

7d is an AD converter that converts the output signal S of the electronic volume V01 into digital data Ds and outputs it.

7e executes the fast Fourier transform program stored in itself and converts the input data Ds into spectral levels for each frequency component. It is a digital signal processor (DSP). This DSP 7e detects a frequency at a spectral level that is above a preset threshold level, and outputs a signal representing this frequency.

7f is an equalizer control circuit that receives control data from the CPU 7a and outputs the above-mentioned equalizer control data Vs, -Vsn. 7g is a volume control circuit that receives control data from the CPU 7g and outputs the above-mentioned volume control data Cv. 7h receives control data from the CPU 7a and outputs a white noise signal W in the audible frequency band.
This is a noise generator that generates and outputs h. This white noise signal wh is sent to the adder 4C as shown in FIG.
is input.

Next, an adjustment operation using the howling suppression device having the above configuration will be explained with reference to FIGS. 3 and 4. First, when the power is turned on to this howling suppression device, the C
The PU 7a loads a control program written in the ROM 7b and starts the program. Then, it waits until a number parameter N that defines the number of adjustment operations is input. Here, for example, when the operator 5 inputs the number of times parameter N as r3J (Pi adjustment operation 3 times) from a numeric keypad (not shown), the CPU 7a executes step S! of the flowchart shown in FIG. Proceed to.

In step S1, the counting parameter i for counting the number of adjustment operations is reset to zero, and the electronic volume Vol is set to the minimum level, and the process proceeds to the next step S2. In step S2, a white noise signal wh of a constant level is outputted from the white noise generator 7h, and the process proceeds to the next step S3. In step S3, the electronic volume Vol is increased by 6 minutes, and white noise sound is generated from the speaker SP. Next, in step S4, it is determined whether the DSP 7e has detected a spectrum level equal to or higher than the threshold level. If no peak is detected at this point, the judgment result is "NO".
Then, the process proceeds to step SI3.

In step S13, it is determined whether or not the electronic volume Vol is set to the maximum level, but since the electronic volume Vol has only been increased by Δ at this point, the determination result is "NO" and step Return to S2. Thereafter, the determination result in step S4 is rYEs.
Sequentially adjust the level of the electronic volume Vol by Δ until it reaches J.
Increase the volume level of the white noise sound by increasing the volume level by minutes. In this way, the electronic volume Vol is sequentially increased until howling occurs.

Now, for example, if the electronic volume Vol is set to the volume level "A" shown in Figure 4 (A), and at this time the DSP 7e detects a howling frequency as shown by the broken line in Figure 4 (B), The determination result in step S4 is rYESJ, and the process advances to the next step S5. In step S5, the level of the electronic volume Vol is once lowered from "A" by Δ.

Then, in the next step S6, the electronic volume V
The level of ol is increased by Δ° (Δ'=Δ/10).

Next, in step S7, the same judgment as in step S4 described above is made, and the electronic volume Vol.
Increase by Δ゛. In this way, the electronic volume Vol is finely adjusted to make it easier to determine the level at which howling occurs.

Here, the level of the electronic volume Vol is shown in Figure 4 (a).
When the DSP 7e reaches point B shown in the figure and detects the howling frequency as shown by the solid line in the figure (b), the judgment result of step S7 becomes rYEsJ, and the next step S
Proceed to step 8. In step S8, a frequency band above a threshold level is detected from the output data of the DSP 7e, and in the above example, frequency bands f1 to fr are detected. Next, in step S9, the level of the graphic equalizer 4 corresponding to the detected frequency band is lowered by δ. For example, when the above-mentioned frequency bands f and -f correspond to the band of BPF 4a-2, the level of the electronic volume V-2 that adjusts the output level is lowered by δ. This results in
Howling in the frequency band is suppressed. Next? In step SIO, the zf number parameter i is incremented by rlJ, and the process advances to the next step Sll. Step Sll
Now, it is determined whether or not the counting parameter i and the number of times parameter N match, that is, whether or not the prescribed number of times has been adjusted.At this point, it is still the first adjustment, so this determination result is rNOJ, and the process returns to step S2. Then, when the above-mentioned adjustment is repeated up to a predetermined number of times, the determination result in step Sll becomes "YESJ" and the process proceeds to step S12.

Meanwhile, the electronic volume Vol.
When is set to the maximum level, the determination result in step S13 becomes rYEsJ, and the process advances to step S12. In step S12, the white noise signal wh is cut,
Finish the adjustment. Then, the operator recognizes that the adjustment has been completed when the white noise sound disappears.

In the embodiment described above, the howling frequency component is suppressed by the graphic equalizer 4, but instead of this, a multi-stage verametric equalizer may be used. In this case, the parametric equalizer has a filter characteristic in which the center frequency fS, depth d, and width Q can be adjusted as shown in Fig. 5, so the center frequency f is adjusted to the howling frequency, and the It becomes possible to set the optimum depth d and width Q.

In addition, in the embodiment described above, the electronic volume Vo
The presence or absence of howling is detected from the output signal of l, but
Instead of this, the presence or absence of howling may be detected from each output signal of the BPFs 4a-1 to 4a-N. In this case, howling is suppressed by lowering the volume level of the bandpass filter that detected howling.

In addition, according to the above-described embodiment, natural Pack-Grandland noise is transmitted to the microphone M without using a white noise signal.
Adjustment can also be made by howling caused by layering in I-M n.

``Effect of the invention'' As explained above, is this invention? According to this, when a howling frequency higher than a predetermined level is detected, the output level of the frequency band that includes that frequency is quickly attenuated, so that the optimum acoustic characteristics can be easily adjusted within a short time. can.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a howling suppression device according to an embodiment of the present invention, FIG. 2 is a block diagram showing the configuration of the howling suppression circuit 7 in the same embodiment, and FIG. 3 is a flowchart showing the operation of CP07a. , FIG. 4 is a diagram for explaining the operation of the same embodiment, FIG. 5 is a diagram for explaining a modified example, and FIG. 6 is a diagram for explaining a conventional example. Vol...Electronic volume, 4...Graphic equalizer, 7...Howling suppression circuit.

Claims (2)

[Claims] (1) A volume that adjusts the volume level according to a first control signal, and a second volume that divides the audio signal output from the volume into a plurality of frequency bands, and that is supplied for each frequency band.
adjusting means for adjusting the signal level of each band according to the control signal of the acoustic signal; and detecting the frequency component of the acoustic signal;
a detection means for detecting a howling frequency having a frequency component equal to or higher than a predetermined level; and a control means for outputting first and second control signals in accordance with an output signal of the detection means, the control means comprising: If the howling frequency is not detected, the first control signal is changed so that the volume level increases sequentially in a first step, and if the howling frequency is detected, the volume level is once decreased by a predetermined amount. After that, the first control signal is changed so as to increase sequentially in steps smaller than the first step, and when the howling frequency is detected again, the signal level of the frequency band including the howling frequency is decreased. A howling suppression device, characterized in that the second control signal is adjusted to . (2) The howling suppression device according to claim 1, wherein the detection means detects the howling frequency based on the signals of each frequency band output from the adjustment means.