JPS612497A - Device for suppressing howling - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a howling suppression device for automatically suppressing howling in a public address system.

2. Description of the Related Art Structures and Problems In recent years, with the development of conference systems and teleconference systems, there has been a need for a public address system that can provide clear and natural sound amplification. A conventional howling suppression device of this loudspeaker will be explained below.

FIG. 1 is a block diagram of a conventional howling suppression device. In Fig. 1, 1 is a microphone, 2 is a microphone amplifier, and 11 to 1n are n bandpass filters (B
, P, F), 21 to 2nld
n energy detecting sections that detect the energy of the output of this band dividing section, and n attenuation sections 31 to 3n that increase the amount of attenuation of the attenuation section described later when the output of the energy detecting section exceeds a certain threshold. An amount control section, 41 to 4n are n attenuation sections that are controlled by this attenuation amount control section and attenuate the output of the broom area division section, and 3 is an addition section that adds the frequency band signals of the attenuation section outputs. , 4I′i speaker amplifier, and 5 is a speaker.

Regarding the howling suppression device configured as above,
The operation will be explained below.

First, the output signal of the microphone 1 is amplified by the microphone amplifier 2, and is input to a band division section composed of band pass filters 11 to 1n each having n frequency bands different from each other. Now, if we pay attention to the bandpass filter 11, its output is transmitted to the attenuation section 41 and the energy detection section 21.
is input.

The energy detection section 21 detects the energy of this frequency band signal and sends it to the attenuation amount control section 31, and when this attenuation amount control section 31 determines that this energy is equal to or higher than a set threshold, the attenuation amount of the attenuation section 41 is adjusted. increase.

The above operation is performed in the same way for all frequency bands constituted by the bandpass filter 1i, the energy detection section 2i, the attenuation amount control section 3i, and the attenuation section 41 when i = 1 to ni. The signals of the respective bands output from the attenuators 41 to 4n are added by the adder 3, and then sent to the speaker amplifiers 4. The sound is amplified by speaker 5.

When howling is not occurring, the energy of the collected sound is distributed over a wide frequency band, so the energy of the output of the bandpass filters 11 to 1n, which are band division units, is relatively small, and the attenuation amount control unit The threshold value set inside 31 to 3n is not exceeded. Conversely, this threshold value needs to be set in advance so that normal voice energy does not exceed this value under conditions where the above-mentioned howling does not occur. As a result, no command to increase the attenuation amount is sent from the attenuation amount control sections 31 to 3n to the attenuation sections 41 to 4n, and the addition section 3 adds up any frequency band signals without attenuating them.

Now consider the case where howling occurs. As is well known, howling is a phenomenon in which a relatively high-energy sound similar to a pure tone is generated. Therefore, when howling occurs, the frequency band signal of any of the bandpass filters 11 to 1n is becomes extremely large. Assuming that the frequency band signal of the bandpass filter 11 includes a howling signal, the energy detected by the energy detection section 21 will exceed the threshold set inside the attenuation amount control section 31, and as a result, the attenuation section 41 will Attenuates frequency band signals. Noh Woo-ring is on microphone 1. amplification system,
Speaker 5. The signal circulates in the loop of microphone 1,
Since this is a phenomenon in which a signal at a certain frequency is amplified at an accelerated rate, the amplification factor at this frequency is reduced. That is, by attenuating the signal in this frequency band, the knowing ring can be eliminated. In amplification with howling suppressed in this way, the output of the adder 3, that is, the sound amplified from the speaker, becomes a sound that lacks a certain frequency band signal where howling was occurring, but If the number of divisions is increased to a certain extent, the deterioration in sound quality will be hardly noticeable.

However, in the conventional configuration described above, howling noise is suppressed only when the energy of the howling sound exceeds a certain threshold, so the howling sound is still amplified, albeit for a short time.

Furthermore, since the slight --uling does not exceed the threshold, there is a problem in that the suppressing effect against this is insufficient.

OBJECTS OF THE INVENTION The present invention solves the above-mentioned conventional problems, and aims to provide a howling suppression device that suppresses howling before it occurs and is highly effective in suppressing even slight howling.

Structure of the Invention The present invention includes a band division section that divides an input signal into a plurality of frequency bands, an attenuation section that attenuates each frequency band signal divided by the band division section by a certain amount, and a signal that is attenuated by the attenuation section. an adding section that adds the respective frequency band signals; a phase control section that changes the phase of the output of the adding section over a range of approximately 360 degrees at a constant cycle; and a phase control section that divides this one period into multiple time periods. , a switch unit that time-divides each of the frequency band signals for each time period in synchronization with the phase control unit; An energy detection section detects the average energy, and in each frequency band, the ratio of the minimum value and the maximum value of the average energy is determined, and when this ratio exceeds a certain threshold, the first attenuation section is controlled to reduce the amount of attenuation. It focuses on the fact that in the frequency band immediately before howling occurs, the phase of the amplification system has a large effect on the energy of the signal in that frequency band. This howling suppression device is capable of suppressing howling in advance by determining that there is a risk of howling occurring in a frequency band where energy fluctuates above a certain threshold and attenuating the signal in that frequency band.

DESCRIPTION OF EMBODIMENTS FIG. 2 shows a block diagram of a howling suppression device according to embodiments of the present invention. In Figure 2, 11
is microphone, 12I'i, microphone amplifier, 1
11 to 11n are band dividing units each composed of n bandpass filters having different frequency bands; 121
~12n are n switch units 131 to 13 that perform time division of frequency band signals in synchronization with the phase control unit 140 cycles;
n means n average energy detecting sections 14 for detecting the average energy of the nine time-division signals outputted from the switch sections 121 to 12n over a period sufficiently longer than the above-mentioned period;
1 to 14n calculate the ratio between the highest value and the lowest value of the average energy sent from the average energy detection units 131 to 13n, and when this ratio exceeds a threshold value, the attenuation units 141 to 14
n attenuation control units 151 to 16n perform control to increase the attenuation of n;
13 is an addition section, 14 is a phase control section that completely changes the phase at a constant cycle, 15 is a speaker amplifier, and 16 is a speaker.

The operation of the howling suppression device of this embodiment configured as described above will be explained below. First, the signal from the microphone 11 is transmitted to the microphone amplifier 12.
and n bandpass filters 111 to 11.
The signal is input to a band division section composed of n. Now focusing on the bandpass filter 111, its output is output from the attenuation section 161.
and is sent to the switch section 121. The switch section 121 time-divides this frequency band signal in synchronization with the cycle of the phase control section 140. For example, the phase change width of the phase control unit 14 is 3600
If the amount of phase change is controlled in a triangular waveform with a period of T seconds, and the number of time divisions in one period is 8, the time division time is T.
/ If set to a second, □Q~900.900~180o
, 18o0~27oO227oO~3600 can be separated. This will be explained with reference to FIGS. 3 and 4. FIG. 3 shows the switch section 121 of FIG. 2 more specifically.

In FIG. 3, 201 is an input terminal of the switch section 121 connected to the bandpass filter 111, and 211 to 214 are the input terminals of the switch section 121 connected to the average energy detection section 131.
1 is the output terminal, 202 is the center terminal of the switch section 121,
203 to 210 are peripheral poles of the switch section 121, and 215 is a connecting piece of the switch section 121. The connection piece 216 of the switch section 121 is synchronized with the phase control section 14 so that it rotates once in the period T of the phase control section 14, and T/s.
As time passes, it connects to the surrounding poles one by one while rotating counterclockwise in the figure. FIG. 4 shows the signals of each part of the switch section 121 and the open/closed state of the switch section 121, and 301 indicates the time dependence of the amount of phase change of the phase control section 14. In FIG. 4, all horizontal axes are shown with equal time axes. 302
3o3 is a signal input to the input terminal 201 of the switch section 121, and 3o3 is a connection state between the input terminal 201 and the output terminal 211.

304 is the connection state between the input terminal 201 and the output terminal 212;
305 is the connection state between the input terminal 201 and the output terminal 213;
306 is the connection state between the input terminal 201 and the output terminal 214;
307 is the signal of the output terminal 211, 308 is the output terminal 21
2, 309 is a signal at the output terminal 213, and 310 is a signal at the output terminal 214. In Figure 3, o −T
/a, the connecting piece 216 is connected to the surrounding pole 203, and during the time T/8 to 2T/8, the connecting piece 215 is connected to the surrounding pole 203.
04, and the connection pieces 215 are synchronized so that they move in the same manner.

As described above, according to this embodiment, only the signal when the phase changes from 00 to 90 degrees is extracted from the signal 307 at the output terminal 211, and from the signal 308 at the output terminal 212 is extracted from the phase change from 900 to 180 degrees.
Only the signal at the time of phase change of o is extracted and sent to the output terminal 213.
Only the signal when the phase changes from 1800 to 27oO is extracted as the signal 309 of the output terminal 214, and the signal 310 of the output terminal 214 has the
Only the signal when the phase changes from 700 to 36o0 is extracted. The signal 302 at the input terminal 201 is assumed to be just before howling occurs; in this case, as shown in the example of the signal 302, by changing the phase, the energy of the signal changes significantly. Therefore signals 307-310
What can be detected is a large energy difference. The average energy detector 131 and the attenuation amount controller 141 shown in FIG. A section 141 compares these energies to determine the ratio between the highest value and the lowest value, and when the ratio exceeds a certain threshold, the attenuation amount of the attenuation section 161 is increased. The above operation is carried out by the bandpass filters 111. to i=1 to n. Switch section 121° Average energy detection section 131. This is done in the same way for all the bands constituted by the attenuation amount control section 141 and the attenuation section 15i. The frequency band signals processed in this way are added by the adder 13, and then the phase is changed at a constant cycle by the phase controller 14 as described above, and the sound is amplified by the speaker amplifier 16° speaker 16. Since the human ear is insensitive to changes in the phase of sound, there is no deterioration in sound quality even if the phase of the amplified sound is changed in this way.

Note that in the above example, the amount of phase change is controlled in the form of a triangular wave, but even if it is controlled in a sine wave or other form, the same effect can be obtained by changing the time setting of time division and weighting the average energy. Needless to say, you can obtain

Effects of the Invention The present invention includes a phase control section that changes the phase of a loudspeaker system at a constant cycle, a switch section that processes a frequency band signal obtained by dividing a microphone output signal into frequency bands, an average energy detection section, and an attenuation amount. By providing a control section and an attenuation section, it is possible to detect and suppress no-ring before it occurs.
This makes it possible to realize a no-wring suppression device with an extremely high wring-suppressing effect.

[Brief explanation of drawings]

Figure 1 is a block diagram of a conventional howling suppression device, and Figure 2 is a block diagram of a conventional howling suppression device.
The figure is a block diagram of a no-ring suppression device according to an embodiment of the present invention, FIG. 3 is a configuration diagram of the switch section in FIG. 2, and FIG. FIG. 111-11n... Bandhus filter, 12
1~12n...-switch section, 131~13n・
...Average energy detection section, 141 to 14n...
...Attenuation amount control section, 151 to 15n... Attenuation section, 13... Addition section, 14... Phase control section. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 3
Figure 4

Claims (1)

[Claims] a band dividing section that divides the input signal into multiple frequency bands;
an attenuation section that attenuates each frequency band signal divided by the band division section by a certain amount; an addition section that adds the respective frequency band signals attenuated by the attenuation section; and a phase adjustment section of the output of the addition section. Approximately 360° at a constant cycle
a phase control unit that changes the frequency within a range of 1 to 1000 kHz, and a switch unit that divides this one cycle time into a plurality of time zones and time-divides the respective frequency band signals for each time zone in synchronization with the phase control unit. and an energy detection unit that detects the average energy for a time sufficiently longer than the period of each time-division signal of each frequency band time-divided by the switch unit, and a maximum value of the average energy in each frequency band. and an attenuation amount control section that determines a ratio between the minimum value and the minimum value, and controls the attenuation section to increase the amount of attenuation when this ratio exceeds a certain threshold value.