JPS59194597A - Howling preventing system - Google Patents

Abstract

PURPOSE:To prevent a howling by providing a means for detecting plural frequency components having a large coupling quantity, which are coupled acoustically to a microphone from a loudspeaker, and suppressing the components concerned, on a sound signal transmitting side of the microphone. CONSTITUTION:Before using a voice remote conference device, a noise is generated from a noise generator 20 by turning on switches SW1, SW2. This noise is outputted from loudspeakers 13, 14, goes round to microphones 1, 2, is amplified by a microphone coupling circuit 3, and its output synchronizes with frequency of a frequency automatic switching oscillator 19 and is inputted to a frequency variable BPF16. The BPF16 makes frequency of a passing band pass through, for instance, by varying it to ten kinds, and it is inputted to a round- in component detector 17. The detector 17 varies digitally the frequency components of the ten kinds concerned, for instance, selects five kinds in order of a larger component, and they are sent out to a frequency variable rejector 15 through a controlling circuit 18. The rejector 15 inserts a filter for rejecting this frequency component between the circuit 3 and a circuit 4, by the frequency components of the five kinds concerned.

Description

Detailed Description of the Invention (a) Technical Field of the Invention The present invention relates to a method for preventing howling caused by sound from a speaker entering the microphone in an audio remote conference system using a microphone and a speaker in the same conference room. This relates to improvements in prevention methods.

(b) Background of the technology An audio teleconferencing system is a system that connects remotely located conference rooms using a communication line. Each conference room has a microphone and a speaker. A conference is held between people in a remote conference room by listening to the sound through a loudspeaker. Such an audio teleconference system requires a howling prevention method that prevents howling that often occurs when sound from a speaker enters a microphone.

(C) Prior Art and Problems An example of a conventional howling prevention method will be described below.

FIG. 1 is a block diagram showing the circuit configuration of main parts of a conventional audio teleconferencing device.

In the figure, reference numeral 1.2 indicates a microphone, representing n microphones. 3 is a microphone coupling amplifier, 4.5 is an automatic loss adjuster, 6 and 7 are amplifiers, 8 and 9 are rectifiers, 10.
11 is a voltage detector, 12 is a subtracter, 13 and 14 are speakers 7, and the audio signals from the n/a microphones represented by microphones 1 and 2 are sent to the microphone coupling amplifier 3. After passing through an automatic loss adjuster 4 using a variable element (F'ET? etc.) with linearity so as not to cause disconnection at the beginning and end of the conversation, the signal is amplified by a amplifier 6. The signal is then sent to the other party via a transmission line, passed through an automatic loss adjuster 5 on the other party, is amplified by an amplifier 7, and is outputted as sound from speakers 13 and 14. In this case, it is necessary to prevent the sound from the speakers 13, 14 from being transmitted to the microphone 1, 2, and the feedback caused by this. For this purpose, the output level and reception level of the microphone coupling circuit 3 are rectified by rectifiers 8 and 9 to obtain DC voltages V 1 and V 2, and subtracted by a subtracter 12. When v2 is larger than vl (receiving side When vl is larger than v2 (when a voice signal is input), it is detected by the voltage detector 10, and when vl is larger than v2 (when a person is detected at the microphone), the voltage detector 11 detects it, and the automatic loss adjusters 4 and 5 respectively detect it. An automatic loss adjuster that increases the loss appropriately and does not increase the loss prevents howling (while maintaining a low loss state).

However, the loss of the automatic loss adjuster cannot be made infinite in order to prevent truncating the beginning and end of the speech. Therefore, the sound from the speakers 13 and 14 is reflected by the walls of the room, etc., and is felt by all the n microphones installed, and is amplified by the microphone coupling amplifier 3 and rectified by the rectifier 10. The DC voltage v1 may be equal to the DC voltage v2 obtained by rectifying the audio signal on the receiving side by the rectifier 9. When the voltage becomes equal, the voltage detectors 10 and 11 do not detect the voltage instantly, and the automatic loss adjuster 4.5
The loss remains small and howling occurs.

Conditions that cause such howling vary depending on environmental changes such as the size of the room, the number of microphones and speakers, and the volume of the speakers. Therefore, it would be better to set these environmental conditions to conditions that do not cause howling, but this is not easy to do. Therefore, the conventional audio teleconferencing device using an automatic loss adjuster or the like has the drawback of causing howling as described above.

(d) Purpose of the Invention In view of the above drawbacks, the purpose of the present invention is to provide a howling prevention method that can easily prevent howling without changing the environmental conditions when a large amount of sound from a speaker enters a microphone. It is in.

(e) Structure of the Invention In order to achieve the above-mentioned object, the present invention has the following objectives: In an initial state where the speaker is acoustically coupled to the microphone and howling occurs, the audio teleconferencing is performed using frequency components with a large amount of acoustic coupling. Focusing on the point where the loop of the system becomes an oscillating state, multiple frequency components with a large coupling amount that are acoustically coupled from the speaker to the microphone are detected in the audio teleconferencing device using a conventional automatic loss adjuster etc. The method is characterized in that the method includes means for suppressing a plurality of frequency components detected by the microphone on the audio signal transmitting side of the microphone to prevent howling.

(f) Examples of the invention An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is a block diagram showing the circuit configuration of the main parts of the audio teleconferencing device according to the embodiment of the present invention.

Components in the figure that have the same functions as those in FIG. 1 are indicated by the same symbols.

15 is a frequency variable rejector, 16 is a frequency variable bandpass R wave generator, 17 is a interference component detector, 18 is a control circuit, 19 is an automatic frequency switching oscillator for the audio frequency band, 20 is a noise generator, SWI, SW2 indicates a switch.

A sound is generated, and this noise is output from the speakers 13 and 14, goes around to the microphones 1 and 2, and is amplified by the microphone coupling circuit 3. For example, the frequency of the pass band of the variable frequency band pass P-wave device 16 that changes the frequency of the pass band in synchronization with 10 types of frequencies) is changed, for example, by 10 types, and is input to the interference component detector 17. In the SUM wrap-around component detector 17, the frequency i variable band pass f
The volumes of the 10 types of frequency components that have passed through the transducer 16 are converted into digital signals, read by a microcomputer, and the five largest components are selected, for example, and sent to the variable frequency rejector 15 via the control circuit 18.

The variable frequency rejector 15 includes, for example, an R-wave device that rejects 10 types of frequencies, and an R-wave device that rejects these frequency components according to signals of 5 types of frequency components sent from the control circuit 18. is inserted between the microphone coupling circuit 3 and the automatic loss adjuster 4. In this way, it is possible to suppress frequency components having a high degree of acoustic coupling from the speakers 13 and 14 to the microphone, and the switches SWI and SW2 are opened to use the audio teleconferencing device. If this is done, frequency components with a high possibility of causing wring will not appear in the output of the variable frequency nozzle 15, so that the speaker 13,
Even if the amount of input into the microphones 1 and 2 is larger than that of 14, howling can be easily prevented without changing the environmental conditions.

The operation of the ring prevention circuit by the automatic loss adjusters 4 and 5 is the same as that shown in FIG.

(g) Effects of the Invention As explained in detail above, according to the present invention, the amount of feedback from the speaker to the microphone is large, and howling cannot be prevented by the conventional howling prevention method using an automatic loss adjuster or the like. It has the effect of easily preventing this without changing the environment.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the circuit configuration of the main part of a conventional audio teleconference device, and FIG. 2 is a block diagram showing the circuit configuration of the main part of the audio teleconference device according to the embodiment of the present invention. In the figure, 1 and 2 are microphones, 3 is a microphone coupling amplifier, and 4
, 5 is an automatic loss adjuster, 6, 7 is an amplifier, 8.9 is a rectifier, 10.11 is a voltage detector, 12 is a subtracter, 13, 1
4 is a speaker, 15 is a variable frequency rejector, 16 is a variable frequency bandpass f-wave device, 17 is an MA interference component detector,
18 is a control circuit, 19 is an automatic frequency switching oscillator, 20 is a noise generator, SWI, and 8W2 is a switch.

Claims (1)

[Claims] In an audio teleconferencing system that uses a microphone and a speaker in the same conference room, the method includes means for detecting a plurality of frequency components having a large amount of acoustic coupling from the speaker to the microphone; A method for preventing howling, characterized in that means for suppressing a plurality of frequency components is provided on the audio signal transmitting side of a microphone to prevent howling.