JP3067409B2 - Anti-howling processor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a loudspeaker system for amplifying an audio signal input from a microphone and uttering a loudspeaker, and relates to a howling prevention processor for preventing howling.

[0002]

2. Description of the Related Art In a loudspeaker system for amplifying an audio signal from a microphone and generating a loudspeaker sound from a speaker,
When the loud sound emitted from the speaker is picked up again by the microphone, the amplification system oscillates under a certain condition, causing so-called howling. As a method for preventing such howling, there is a method in which an equalizer or a compressor is provided in an amplification system and these are manually adjusted. FIG.
0 is a block diagram showing a conventional howling prevention processor for realizing such a method. The audio signal generated by the microphone 10 is transmitted through the preamplifier 12 to the equalizer 1.
4 and its output signal is provided to a compressor 16. The output signal of the compressor 16 is the power amplifier 1
8 to one or more speakers 20 for loudspeaking.

According to the conventional howling prevention method shown in FIG. 10, the compressor 16 first sufficiently compresses the audio signal so that the speaker 20 is not damaged. Next, the volume is increased by manually operating a volume control element (not shown) to cause howling. In this state, the frequency and gain of the equalizer 14 are adjusted to stop howling. Next, howling is generated by increasing the volume again, and the same operation is repeated. This is because howling often occurs at a plurality of frequencies, and it is necessary to provide sufficient attenuation at these frequencies. As the equalizer 14, a graphic equalizer may be used. Even if the signal is considerably compressed by the compressor 16, if the signal exceeds the howling start level, howling occurs, so that further measures are required.

FIG. 11 is a graph showing the operation of the compressor 16 in the apparatus shown in FIG. In this graph, when the input signal level becomes equal to or higher than the operation start level (compression start level) of the compressor 16, the volume (solid line) when the compressor 16 is not operated is input by performing compression as shown by a dotted line. The signal level margin increases by P, but if the volume exceeds the howling start level, a howling state is set. If the compression is performed as shown by the one-dot chain line in the figure, howling does not occur, but the loudspeaker volume cannot be sufficiently increased. The equalizer 14 shown in FIG. 10 corrects the peak value of the frequency component included in the howling sound to a flat frequency characteristic. This correction can improve the howling start level by about 3 dB. As described above, as a conventional general countermeasure against howling, an equalizer and a compressor are used in combination.

[0005]

In the above-mentioned conventional method, it is necessary to distinguish the peak frequency causing the howling by ear and to determine the peak frequency, and to operate the equalizer.
It required skill. Also, howling start level is 3dB
Since the equalizer always operates to raise the level, the frequency characteristic is changed unnecessarily even for an input signal of a normal level lower than the howling start level. There was a problem that would change. Further, in order to further increase the howling margin, it is necessary to increase the level compression amount by a compressor as shown by the one-dot chain line in FIG. 11. In this case, there is a problem that the loud sound loses a sense of volume.

Accordingly, the present invention does not require skill in discriminating howling frequencies, does not inadvertently change the frequency characteristics of an input signal having a normal level lower than the howling start level, and impairs the sense of volume of a loud sound. It is an object of the present invention to provide a howling prevention processor which does not have any problem.

[0007]

In order to achieve the above object, the present invention has the following arrangement. That is,
By providing the howling frequency detecting means for automatically detecting the peak frequency of howling in the howling state, skill for discriminating the howling frequency is not required, and at the time of operation, the graphic equalizer and the compressor are operated according to the input signal level. Controlling the amount of compression, preventing changes in tone by not changing the frequency characteristics for low-level input signals that do not produce howling, and ensuring that the amount of compression of the compressor is not unnecessarily large. , The sound volume is maintained as much as possible.

Therefore, according to the present invention, an attenuator for attenuating an input signal level and a frequency component set when the output signal of the attenuator is equal to or higher than a predetermined level are compressed. An equalizer / compressor having a flat frequency characteristic, a linear compression compressor for linearly compressing the output signal of the equalizer / compressor against its level, and a frequency component having the highest level in response to the output signal of the attenuator And howling frequency components detected in response to the output of the howling frequency detecting means are controlled to be compressed by the equalizer / compressor means, and during normal operation, the attenuator is controlled. According to the output signal level of Howling prevention processor and a control means for controlling them by calculating the serial equalizer compressor means and the amount of compression of the polygonal line compression-type compressor is provided. If a parameter such as a howling start level or howling peak frequency or a plurality of peak frequencies is stored in a memory, howling can be prevented in accordance with a unique howling generation mode determined by the location of a venue, microphones and speakers, and the like. Can be automatically set.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a howling prevention processor of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing one embodiment of the present invention. An input audio signal from a microphone (not shown) is supplied to an attenuator (ATT) 22 in FIG. 1 via a mixer and a preamplifier as necessary. An output signal from the attenuator 22 includes a first equalizer / compressor (EQC1) E1, a variable bandpass filter (BPF) 26, and a second A / D converter 32.
Respectively. The output signal of the first equalizer / compressor E1 is supplied to the similar second to fourth equalizer / compressors E2, E3, E4 which are sequentially connected in series, and the output signal of the last fourth equalizer / compressor E4 is the polygonal line type compressor. (Polyline COMP) 24
And the output signal is supplied to a power amplifier (not shown).

The output signal of the variable BPF 26 is supplied to a first A / D converter 28, and becomes a digital signal to
(Central processing unit) 30. The digital signal from the second A / D converter 32 is similarly supplied to the CPU 30. Reference numeral 34 denotes an operation switch connected to the CPU 30, which is used for automatically detecting a howling frequency. A memory 36 is connected to the CPU 30. The memory 36 is for writing data as needed, and a ROM containing a program for the operation of the CPU 30 is not shown. The dotted line in FIG.
PU30 to ATT22, variable BPF26, first to fourth
Equalizer / compressor E1-E4, compressor 2
4 shows a control signal line provided to the control signal line 4. Each of the equalizer / compressors E1 to E4 is a circuit having both functions of a graphic equalizer and a compressor.
As shown in (1), the equalizer attenuates the set frequency component above the howling start level, but has a flat frequency characteristic with respect to a normal signal level, and does not change the tone. The broken line compression type compressor 24 is not a direct compression in which the output signal level is proportional to the input signal, but has a broken line relationship as shown by a solid line in FIG. This solid line is a broken line compression type compressor 24.
Only characteristics are shown. The dotted lines in FIG. 2 show how each of the equalizer / compressors E1 to E4 operates to compress the howling frequency and perform the polygonal line compression by the polygonal line compression type compressor 24. Since the compression for the howling frequency is sufficiently performed, the howling of the full swing does not occur. In addition, since the equalizers / compressors E1 to E4 have flat characteristics for frequencies other than the howling frequency,
The compression characteristic is shown by the solid line in FIG. In FIG. 2, Q indicates an increase in the sense of volume when the howling is suppressed as compared with the normal compression state.

Next, the operation of the circuit of FIG. 1 will be described with reference to the graph of FIG. 3, the flowcharts of FIGS. 4 and 5, and FIGS. During use, the howling processor is connected between a microphone (not shown) (via a preamplifier if necessary) and a power amplifier (not shown), and the output signal of the power amplifier is connected to a speaker (not shown). Next, an automatic detection of a howling frequency is performed before a normal operation for preventing howling starts. Howling is manually generated for this automatic detection. That is,
The ATT 22 is set once to -4 dB, and the amount of attenuation is reduced by 1 dB (or point) as shown in the graph of FIG. When the operation switch 34 is operated with the occurrence of howling as a measurement start point, the signal level input to the CPU 30 via the second A / D converter 32 is taken as the howling start level and stored in the memory 36 (step in FIG. 4). S1). In the next step S2, it is determined whether or not the input signal level detected via the A / D converter 32 exceeds the howling start level stored in the step S1, and if YES, the pass band of the variable BPF 26 is changed in a step S3. The input signal level in each pass band is read by sequentially changing. As the pass band, for example, 280-360 Hz, 360-450H
z, 450-560 Hz, 560-700 Hz, 700
~ 900Hz, 900 ~ 1100Hz, 1100 ~ 14
00Hz, 1400-1800Hz, 1800-220
0Hz, 2200-2800Hz, 2800-3600
Hz, 3600-4500Hz, 4500-5600H
z There are 14 frequency bands from 5600-7000 Hz.
In the next step S14, a frequency band indicating the maximum level is detected and stored in the memory 36. Variable BP in Fig. 1
F26, the first A / D converter, and the CPU 30 constitute a howling frequency automatic detection unit.

In the next step S5, it is determined whether or not the frequency band detected in step S14 has changed from that detected last time. If there is no change and there is a peak of howling in a certain band, in the next step S6, a control signal is sent to operate the first equalizer / compressor E1 in that frequency band. Thereafter, the process returns to step S2 to execute steps S3 to S5. When a change occurs in the detection band, the process goes to step S7, ATT22 is set to -3 dB, and the second step is performed through steps similar to steps S2 to S6.
It controls the equalizer / compressor E2. In the following steps S8 and S9, similarly to step S7, the attenuation of the ATT 22 is reduced by 1 dB, and the third and fourth steps are performed in the same manner.
This controls the equalizer / compressors E3 and E4. The control frequency of each of the equalizer / compressors E1 to E4 is stored in the memory 36. Finally, step S10
Then, the ATT 22 is set to -4 dB, which is a normal level, and the howling frequency automatic detection flow ends.

The actual howling prevention operation is performed according to the normal operation flow shown in FIG. First, in step S11, the input signal level is read from the output signal of the second A / D converter 32. In the next step S12, the compressor 2
4 determines whether it is currently operating. As a judgment method,
The state of the flag that is set when the compressor 24 is operating is checked. In the case of NO, it is determined in step S13 whether or not the input signal level is equal to or higher than the compression start level of the compressor 24 shown in FIG.
Calculates the amount of compression of the compressor 24 and the amount of compression of each of the equalizer / compressors E1 to E4 from the input signal level, and stores them in the memory 36. As shown in FIG. 6, when the input signal level is C and D (C <D), the compression ratio X of the compressor 24 and the compression ratio Y of each of the equalizer compressors E1 to E4 are different as shown in FIG. ing. When the input signal level exceeds the immediately preceding level (for example, B → C, C → D, etc.), the respective compression amounts are recalculated, but when the level decreases (for example, C → B), the latest calculation is performed. The value is held, and the control is performed using the value. In the next step S15, the compressor 24 and the first to fourth equalizer / compressors E1 to E4 are controlled to operate using the respective compression amounts calculated in step S14, and the process returns to step S11.

If it is determined in step S12 that the compressor 24 is operating, the flow advances to step S16 to determine whether the input signal level is equal to or lower than the level M corresponding to the compression stop level of the compressor 24 shown in FIG. Is done.
If step S16 is YES, it is determined in step S17 whether or not this state exceeds a predetermined time (compressor hold time). If YES, step S17 is performed.
At 18, a restoration process for setting the compression amount by the compressor 24 to 0 dB is started. On the other hand, if the compressor hold time is not reached in step S17, step S1
Return to 1. Here, the compressor hold time is such that the compression amount of the equalizer / compressors E1 to E4 and the compressor 24 does not change frequently due to the level change of the input signal, and the compression amount is fixed for, for example, about 1 second as shown in FIG. It is for doing. FIG. 7 shows the return process.
As shown in R, if the compression amount is returned to 0 dB instantaneously, the volume changes unnaturally and it is unpleasant.
This is for returning to 0 dB over a certain period of time.

FIG. 8 is a block diagram showing an example in which the howling prevention processor 38 of the present invention is applied. By setting the speaker position and the delay amount of the delay circuits 40A and 40B, the sound image can be localized in the direction of the speaker so that a sufficient volume feeling can be obtained. This circuit configuration is suitable for lectures and speeches.

FIG. 9 is a block diagram showing another application example. In this application example, a plurality of howling processors 3 respectively responding to input signals from a plurality of microphones 10
By using the compression state in 8, a fader with a motor, a VCA (volume adjustment attenuator) and the like in the mixer 42 for synthesizing the output signal are controlled. With this control, the volume of all microphones can be automatically reduced to a level close to the normal level, regardless of the position of the microphone, and an automation system that completely prevents howling can be realized. Conventionally, even if it is possible to automate which microphone is output to which speaker and at what volume, an unmanned system cannot cope with unexpected situations such as changing the microphone position. However, in this application example, unmanned operation is possible. Therefore, this application example is useful in banquet halls, conference halls, and the like where an unspecified number of people use microphones.

[0017]

As is apparent from the above description, according to the anti-howling processor of the present invention, the howling frequency is automatically detected, so that no skill is required for the judgment and the input signal is not required. Since the compression is performed in accordance with the level, the frequency characteristics of an input signal having a normal level lower than the howling start level are not changed, so that the timbre has no unnaturalness. Further, since two stages, an equalizer compressor and a polygonal line compression type compressor, are provided in advance, it is possible to perform compression beyond the howling start level, and the loudness of the loud sound is not impaired. In addition, by storing howling start levels and parameters for controlling each equalizer / compressor in a memory, control for howling prevention corresponding to a specific howling pattern based on the positional relationship between a microphone and a speaker at a predetermined venue is automatically performed. Can be done Further, when the state where the input signal level is equal to or lower than the predetermined value continues for a predetermined time or more, a means for reducing the compression amount of the compressor to 0 over a predetermined time by the operation of the CPU 30 prevents an unnatural change in volume. be able to.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a howling prevention processor according to the present invention.

FIG. 2 is a graph for explaining the operation of the embodiment of FIG. 1;

FIG. 3 is a graph showing how the attenuator is manually adjusted to cause howling in the embodiment of FIG. 1;

FIG. 4 is a flowchart illustrating an operation of a CPU for automatically detecting a howling frequency in the embodiment of FIG. 1;

FIG. 5 is a flowchart showing an operation of a CPU for performing a normal operation for preventing howling in the embodiment of FIG. 1;

FIG. 6 is a graph illustrating steps for calculating a compression amount in FIG. 5;

FIG. 7 is a signal level diagram for explaining the operation of the latter half of FIG. 5;

FIG. 8 is a block diagram showing a configuration of an example to which the howling prevention processor of the present invention is applied.

FIG. 9 is a block diagram showing a configuration of another application example of the howling prevention processor of the present invention.

FIG. 10 is a block diagram of a loudspeaker system for explaining a conventional howling prevention method.

11 is a graph showing the operation of the compressor in the conventional device shown in FIG.

[Explanation of symbols]

Reference Signs List 10 microphone 12 preamplifier 14 equalizer 16, 24 compressor (COMP) 18 power amplifier 20 speaker 22 attenuator (ATT) 26 variable bandpass filter 28, 32 A / D converter 30 CPU (control means) 34 operation switch 36 memory (storage means) 38 Howling prevention processor 40A, 40B Delay circuit 42 Mixer E1, E2, E3, E4 Equalizer compressor (EQC)

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04R 3/02 H03G 5/16 H03G 11/04

Claims (3)

(57) [Claims] An attenuator for attenuating an input signal level, and a frequency component set when an output signal of the attenuator is equal to or higher than a predetermined level;
In response to the output signal of the attenuator, the equalizer / compressor means having a flat frequency characteristic when the level is less than the predetermined level, the linear compression type compressor for linearly compressing the output signal of the equalizer / compressor means with respect to the level. A howling frequency detecting means for detecting a frequency component having the highest level, and a control for compressing the howling frequency component detected in response to an output of the howling frequency detecting means by the equalizer / compressor means. A howling prevention processor comprising: control means for calculating and controlling the amount of compression of the equalizer / compressor means and the polygonal line compression type compressor according to the output signal level of the attenuator during operation. 2. A storage means for storing an output signal level of the attenuator when a howling occurs when the attenuation of the attenuator is reduced and howling starts, and for storing the howling frequency. Anti-howling processor. 3. When the output signal level of the attenuator is equal to or less than a predetermined value for a predetermined time or more, a means for reducing the amount of compression of the equalizer / compressor means and the polygonal line compressor to 0 over a predetermined time. The anti-howling processor of claim 1, further comprising: