JPS58200690A - Howling preventive circuit - Google Patents

Abstract

PURPOSE:To make simpler the operation, by providing a voice signal level comparator, variable load controlling part and voice signal adder to a howling preventive circuit to perform the centralized comparison of voice signal level by a comparator located at one place so that the adjustment is centralized. CONSTITUTION:Microphone 10A-10C for a conference room are connected to a many-attendance conference unit 14 with upward transmission lines 12A-12C belonging to each of microphones. Speakers 11A-11C of the conference room are connected to the unit 14 with downward transmission lines 13A-13C. The respective voice levels of the transmission lines 12A-12C are inputted to a voice signal level comparator 15. The comparator 15 performs centralized comparison of the input, and the output of the comparator 15 is inputted to a variable load controlling part 16. The controlling part 16 controls variable loads 17A-17C which make input the voice signal out of the transmission lines 12A-12C. The voice signals from the transmission lines 12A-12C are added by voice signal adders 18A-18C through the loads 17A-17C, and voice signals come outside the conference room are added for each conference room to simplify the operation by realizing the centralization of adjustment.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a howling prevention device that prevents the resonance phenomenon (wringing) of voices caused by acoustic coupling between microphones and speakers in each conference room in multi-site voice conferences. It is something.

Conventionally, systems for conducting conferences by connecting remote points with audio transmission lines have been centered on systems between two locations. FIG. 1 shows the configuration of a conventional audio system for conferences held between two locations.

Conference room A has microphone lA and speaker 2A.

Conference room B has a transmitting amplifier 3^ and a receiving amplifier 4A.
Includes microphone IB, speaker 2B, and transmitter 3B.
and a receiving amplifier 4B. Audio from conference room A is collected by microphone 1A, amplified by transmission amplifier 3A, and then transmitted to conference room B through transmission line 5.

This audio signal is amplified by the receiving amplifier 4A and reproduced as audio in the conference room B by the speaker 2B.

A part of this audio signal is collected by the microphone IB on the conference room B side as shown by the arrow CB, and transmitted to the conference room A through the transmitting amplifier 3B and the transmission line 6. A portion of this sound is collected by the microphone IA in the conference room A indicated by the arrow CA and transmitted to the conference room B again.

In this way, a closed loop for audio signal transmission is formed between conference rooms A and B, but if the gain of the transmitting/receiving amplifiers in one round of this system becomes greater than l, howling will occur.

Figure 2 shows a circuit that has been considered in the past to prevent this phenomenon.In conference rooms A and B, there are audio signal level comparators 7A and 7B, and transmitter side variable loads 8A and 8.
For example, the signal level of microphone IA in conference room A is compared with the audio signal level sent from conference room B, and the signal level from microphone IA is determined as that of conference room B. If the audio signal level is lower than the level of the audio signal sent from the
Load amount, ;:・ ,.

is increased to lower the output level of the audio signal from the microphone LA, or is cut off to reproduce only the sound 7ji signal from the conference room B. Conversely, if the signal level from microphone IA is higher than the sound signal level from conference room B, the load amount on variable load lid 9A on the receiving side is increased, and the audio signal from conference room B is reproduced and output. reduce or block.

The same applies to meeting room B9111.

In this way, the gain of one round of the closed loop of the audio signal is 1
In order to prevent noise caused by acoustic coupling between the microphone and the speaker, the following methods were used, or at one time, the audio signal was only transmitted in one direction.
This method had the disadvantage that the terminals were expensive because a ring prevention circuit was installed in each conference room.

Figure 3 is intended to explain the mechanism by which ringing occurs in a so-called multi-party conference system in which three or more conference rooms are interconnected by audio transmission lines.Here, conference rooms A,
Figure 1 shows the case of a three-party meeting between B and C.
IC, 2A, 2B, 2C, and J indicate the microphones and speakers provided in each conference room, as explained in Figures 1 and 2.

In this case, Ll + L2 * t between each conference room,
3...There are a large number of audio signal loops as shown in L4, and if this is handled by an expanded form of the method shown in Figure 2 above, a large amount of variable load is required. In addition, at present, there is no known effective method for inserting the audio level comparator even if there are two positions for inserting the audio level comparator.

The present invention eliminates these drawbacks and allows...
The purpose of this drawing is to effectively and economically realize the Uring Defense IF, and the drawings will be described in detail below.

FIG. 4 is a block diagram of an embodiment showing the configuration of a multi-party audio conference to which the anti-woofer circuit of the present invention is applied.
．． 1O1 (i-A, B, . . . C1 and below) is the microphone of conference room l, lli is the speaker of conference room 1, and 12i and 131 are the upstream and downstream speakers of conference room i, respectively. 14 is a multi-party conference device with a no-ring prevention circuit; 15 is an audio level comparator; 16 is a variable load amount controller; 17i is variable load paper in conference room i; 18i
indicates the audio signal adder in conference room i.

Next, howling prevention operation in a multiparty conference will be explained.

During the progress of the meeting, each conference room A, B, etc.
・The key voice from C is from each microphone IOA and I
OB.

・・・・・・・・・Converted into a signal by IOc, transmission line 12A
, 12B, . . . 12C.

Here, the audio signal level comparator 15 extracts the a-angle signals of each conference room and ranks them according to the magnitude of the audio signal level. It is clear that the circuit that compares the levels of the plurality of audio signals and determines the ranking can be easily constructed using existing circuit technology, so the explanation thereof will be omitted here.

Next, the variable load amount control section 16 sets the value of the variable load amount 17i inserted into each audio transmission path to a predetermined value based on the audio signal level ranking information.

That is, the variable load amount 17 inserted into the transmission path 12i that transmits the audio signal level 1=the loudest signal level among the audio signals sent out from each microphone 10i.
The value of i is made the smallest, and the variable load 117j inserted into the transmission line 12J of the second audio signal level is made the second smallest load amount. Thereafter, depending on the order of the sound 7ji signal levels, the amount of insertion load to the corresponding transmission path is increased sequentially.

The audio signal adder 18i is a circuit that adds (mixes) audio signals from other than the conference room i and sends it to the conference room i.This allows each conference room to listen to the audio from conference rooms other than its own through the speaker lli. I can do it.

As a result, in each conference room, the voice of the conference room where the loudest speaker is speaking can be heard the loudest (emphasized), and the voice of the second or lower voice level can be heard in a suppressed manner.

At this time, the ratio of the insertion load amount for the speaking voice with the highest audio level and the insertion load amount assigned to the second and subsequent audio level signals is adjusted, and the transmission path is configured to connect each conference room. The gain for closed loop audio signals is 1
Below, it becomes ↓ If you do this, you can 't' prevent ulling.

That is, the amplification gain of the audio signal based on the insertion of the variable load value corresponding to the order of the sound signal level is Pi.

P2. PJ......, the sound level reproduced in each conference room is the sum of the audio loops including that conference room, and is expressed by the following equation.

ΣC4CrP, P, -)ΣC1CrC3PiPjPk
10Σc9crcsctp, p, 1 p, + ・=
(t) (++ J '-4,"'n) (s J -
１

・・・・・・・・・ is F%, Pj, ・・・・・・・・・
is the degree of acoustic coupling between the microphone and speaker in the assigned conference room.

Here, the amplification gain P1 for the largest audio signal and the amplification gain P2 for the second and subsequent audio signals. P3・・・・・・・・・
If the ratio of ... is taken large, the dominant term in equation (1) becomes the first
Item only c9crp, P26 or c, c parrot P2
+cq('rP1P3, and other terms can be ignored.

Therefore, in order to prevent howling from occurring, p, , I12. Pl...
By determining ..., it becomes possible to easily prevent howling.

In this case, 'Q' cr, C'q, (if ' is the same value (the degree of coupling between the microphone and speaker in each room is the same), tf Pl.

Well, p3 may be a preset value, and if it is non-uniform, it will be adaptively controlled.

As explained above, the howling prevention circuit according to the method of the present invention concentrates the level comparators in one place and compares the voice signals, so it is different from the conventional howling prevention circuit for two-party conferences. Compared to a method expanded for multi-person conferences (a method in which terminals are distributed and installed in each conference room), the number of howling prevention 1'J paths is smaller, and signal levels can be compared uniformly, ensuring equality for each conference room. In addition to ensuring the following, operations are simplified by centralizing adjustments. It also has the advantage of simplifying the design of the variable load amount.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the configuration of the sound system 1 in a conventional conference between two parties, Fig. 2 is an explanatory diagram of a howling prevention circuit in a conventional two-party conference, and Fig. 3 is a diagram showing a multi-party conference! FIG. 4 is an explanatory diagram of the howling generation mechanism in the Il/stem. FIG. 4 is a block diagram of an embodiment showing the configuration of a multi-party voice conference to which the howling prevention circuit of the present invention is applied. to l IB, IC, loi... Microphone% 2A, 2B. 2C, 11i...Speaker, 3A,
3B......Transmission amplifier, 4A, 4B...
・・・・・・Receiving amplifier・5・6"°゛Transmission line 7
, 15...... sound 1if signal level comparator,
8, 9.17i......Variable load amount, 12
1......Uplink transmission line, 13i...
. . . Downward transmission line, 14 . . . Multi-party conference device, 16 . . . Variable load amount control unit, 1
8i...Audio signal adder. Figure 3 L4 Figure 4 4 488-

Claims (1)

[Claims] In a system that connects at least three or more conference rooms with each other through audio transmission paths and conducts multi-party conferences using audio, the system has a network configuration that concentrates the audio transmission paths from each conference room in one place, and A circuit that compares and ranks the signal levels of conference audio signals to be transmitted, and based on that ranking, sets the magnitude of the variable load to be inserted into the corresponding transmission path to a predetermined value or to each conference room. A circuit that adaptively sets a value depending on the degree of acoustic coupling between a microphone and a speaker, and adds and transmits audio signals from conference rooms other than that conference room to each conference room. What is claimed is: 1. A no-wring prevention circuit comprising: