JPS61200755A - Echo cancelling type conference talking equipment - Google Patents

Abstract

PURPOSE:To prevent deterioration of S/N when plural microphones are in use by controlling only the attenuation of a variable loss circuit in the highest level channel to 0dB and others to a prescribed attenuation. CONSTITUTION:A respective output signal at the sending side of the 1st-3rd echo cancelling circuits 10-12 is fed to variable loss circuits 17-19 provided respectively and the output at sending side of the 1st-3rd echo cancelling circuits 10-12 is detected and compared. Only the attenuation of the variable loss circuits 17-19 of a channel of the highest output level is controlled to 0dB and the other attenuation of the variable loss circuits 17-19 of the other channels is controlled to a prescribed value. Then outputs of the variable loss circuits 17-19 are added by an adder circuit 23 and sent to the remotest end and the 4th echo cancelling circuit 24 cancels a detour signal produced by a 2/4-wire converting circuit 25.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field to Which the Invention Pertains] The present invention relates to an echo-canceling conference call device that is applied to a conference call using a microphone and a speaker.

[Prior art]

This is a generally well-known conference call device.

As shown in Fig. 2, echo canceling circuits 3 and 4 are connected between the transmitting side and the receiving side connected to the 2-wire to 4-wire conversion circuit 5 to prevent the signal from going around due to acoustic coupling. There is something. This type of conference call device is suitable for a small number of people, and
Although it is suitable for an indoor conference room that is not very large, if a large number of people are using it in a fairly large indoor conference room, it becomes necessary to prepare a plurality of microphones M. but.

In such cases, with conventional equipment, as the number of microphones increases, room noise is added through the microphones, and this room noise reaches the speaker of the conference call device on the far end speaker's side. . For example, n
If you use a book speaker, 101 ogn(d
B) The noise increases, and conversely, the S/N ratio with respect to the signal S to be transmitted deteriorates to about 101 ogn (dB).

[Objective of the Invention] The purpose of the present invention is to solve the problem of deterioration of the S/'N ratio even though it is used in a large meeting room, etc. with a large number of people, which is impossible to apply with the above-mentioned conventional technology. An object of the present invention is to provide an echo-canceling conference call device with high call quality without any interference.

[Structure of the invention]

The echo canceling conference call device according to the present invention includes a plurality of microphones for inputting audio signals of near-end speakers, a plurality of amplification circuits for amplifying output signals of these microphones, and a plurality of amplifier circuits for amplifying the output signals of these microphones. a speaker for outputting an incoming audio signal, and an output side of the D amplifier circuit and an input side of the amplifier circuit for driving the speaker, respectively, in order to eliminate a loop signal due to acoustic coupling from the speaker to the microphone. a plurality of echo canceling circuits each connected between the echo canceling circuits, a plurality of loss circuits respectively connected to the transmission output sides of these echo canceling circuits, and a plurality of loss circuits connected to the output sides of these loss circuits; an adding circuit for adding the output signals of the plurality of echo canceling circuits, a plurality of detection circuits each connected to the transmission output side of the plurality of echo canceling circuits and detecting the transmission output levels of these circuits, and a plurality of detection circuits for receiving the output signals of these detection circuits. a comparison circuit that compares the magnitude relationship of transmitting side output levels of the plurality of echo cancellation circuits; a plurality of loss control circuits that respectively control attenuation amounts of the plurality of loss circuits based on output signals of the comparison circuits; The output side of the adder circuit is connected to the transmission input terminal, and the reception output terminal is connected to the input side of the amplifier circuit for driving the speaker. s-4@conversion circuit and 2! s-
In order to eliminate the loop signal that affects the 4-wire conversion circuit,
K between the transmission input side and the reception output side of the 2-wire to 4-wire conversion circuit.

The present invention is characterized by comprising an echo canceling circuit connected so that an output signal on the receiving side is given to the driving amplifier circuit of the speaker.

[Embodiments of the invention]

Next, an embodiment according to the present invention will be described with reference to the schematic diagram of FIG. In the figure, audio signals from near-end speakers are provided from microphones 26-28 connected to respective microphone amplifier circuits 6-8. On the other hand, the audio signal from the far end speaker is amplified by the speaker amplifier circuit 9.

A speaker 29 is also obtained. In this case, traps and first to third echo canceling circuits 10 to 12 are respectively arranged to cancel the feedback signals caused by the acoustic coupling between the microphones 26 to 28 and the speaker 29. In this way, When multiple microphones are installed, the apparent room noise on the near-end speaker side increases.Therefore, the output signals on the transmitting side of each of the first to third echo canceling circuits 10 to 12 are individually adjusted. The variable loss circuits (loss circuits 17 to 19 and loss control circuits 20 to 22) provided in After controlling only the attenuation of the variable loss circuit on the highest level communication path to OdB and giving a predetermined attenuation to the variable loss circuit on the other communication paths, these variable loss The output signals of the circuits are added by the adding circuit 23. By doing this,
Only one microphone is actually used,
Deterioration of SA will be prevented.

The transmitting side output levels of the first to third echo canceling circuits 10 to 12 are detected by level detection circuits 13 to 15, respectively. These detected outputs are supplied to a level comparison circuit 16 and compared therein in order to determine the magnitude of the transmitting side output levels of the first to third echo cancellation circuits 10 to 12.

The level comparison circuit 16, which has determined the input of the highest output level, uses the output to control the first to third loss control circuits 20 to 22.
, and the $ and attenuation amount of the first to third loss circuits 17 to 19 are respectively controlled as described above.

In this way, the transmitting side output signals of the first to third echo canceling circuits 10 to 12 added by the adding circuit 23 are 2-4 wires.
While being transmitted to the far end side via the line conversion circuit 25,
υ2 line-14 line conversion circuit 2 by the fourth echo cancellation circuit 24
The wrap-around signal generated at 5 is eliminated. , it should be noted that the microphone amplifier circuits 6 to 1 connected to the microphone amplifier circuits
It is also possible to connect up to multiple units, provided some S/N deterioration is tolerated.

〔Effect of the invention〕

As is clear from the above explanation, 9 According to the present invention, when a large number of people use multiple microphones for a conference call, the apparent increase in room noise during no calls is suppressed compared to the conventional method. This makes it possible to improve the clarity of calls to the far-end talker side, and also to eliminate loop signals and two-wire signals due to acoustic coupling between the microphone and speaker.
It is highly effective in that it can sufficiently eliminate the loop signals caused by the 4-wire conversion circuit, thereby improving call quality and achieving good simultaneous call performance between near-end and far-end talkers. .

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of an embodiment of the present invention, and FIG. 2 is a diagram showing an example of the configuration of a conventional conference call device. In this figure, 1, 2
．． 6-8 are microphone amplifier circuits, 3, 4.10-1
2.24 is an echo cancellation circuit, 5.25 is a 2-wire to 4-wire conversion circuit, 9 is a speaker amplifier circuit, and 13 to 15 are level detection circuits. 16 is a level comparison circuit, and 17 to 19 are loss circuits. 20 to 22 are loss control circuits, and 23 is an addition circuit. M, 26-28 are Microho 7. L, 29 is a speaker.

Claims (1)

[Claims] 1. A plurality of microphones for inputting the voice signals of near-end speakers, a plurality of amplification circuits for amplifying the output signals of these microphones, and a plurality of amplifier circuits for outputting the voice signals sent from the far-end side. a plurality of speakers connected between the output side of each of the amplifier circuits and the input side of the amplifier circuit for driving the speaker, in order to eliminate a loop signal due to acoustic coupling from the speaker to the microphone; an echo canceling circuit, a plurality of loss circuits each connected to the transmission output side of these echo canceling circuits, and an adder circuit connected to the output side of these loss circuits and adding the output signals of these loss circuits. , a plurality of detection circuits each connected to the transmission output side of the plurality of echo cancellation circuits and detecting the transmission output level of each of the plurality of echo cancellation circuits; a comparison circuit that compares the magnitude relationship between output levels on the transmitting side; a plurality of loss control circuits that respectively control attenuation amounts of the plurality of loss circuits based on output signals of the comparison circuit; and an output side of the adder circuit connected to the transmission input terminal. a 2-wire to 4-wire conversion circuit connected to the 2-wire to 4-wire conversion circuit whose reception output end is connected to the input side of the driving amplifier circuit of the speaker; It is characterized by comprising an echo cancellation circuit connected between the transmission input side and the reception output side of the line-to-four-wire conversion circuit so that the output signal on the reception side is given to the amplifier circuit for driving the speaker. An echo-canceling conference call device.