JPS5924582B2 - conference call method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a speaker-microphone conference telephone system in which a plurality of terminal devices are connected to a central device via a four-wire telephone line or a private telephone line. It is.

Conventionally, this type of conference telephone system, as shown in Figure 1,
A conference bridge circuit 1 is placed at a center station, and n conference telephone terminal devices 2-1 to 2-n are connected to the conference bridge circuit 1 via n four-wire telephone lines.

As shown in FIG. 2, this terminal device 2 is connected to a transmitting side T of a telephone line via a microphone 4, a microphone amplifier 3a, a variable transmission loss circuit 3b, and a lamp amplifier 3c. On the other hand, the receiving side R of the telephone line is connected to a speaker 5 via a receiving variable loss circuit 3d and a speaker amplifier 3e. The output of the microphone amplifier 3a and the receiving line R are also connected to the audio switch control circuit 3f. Now, when an input is applied to the microphone 4, the microphone output signal is amplified by the microphone amplifier 3a and given to the audio switch control circuit 3f. The voice switch circuit 3f uses its DC control voltage to minimize the loss in the transmitting variable loss circuit 3b (sending line on state), and at the same time minimizes the loss in the receiving variable loss circuit 3d (hereinafter referred to as large loss Lv). (reception path off state). Conversely, when an input signal is applied to the receiving line R, the loss of the receiving variable loss circuit 3d becomes minimum, and the loss of the sending variable loss circuit 3b becomes maximum. In this way, by providing a large loss Lv to either the transmitting path or the receiving path, it is possible to prevent the occurrence of howling due to acoustic coupling loss between the speaker and the microphone.

In the sending path or receiving path of a terminal device, this large loss Lv corresponds to the level difference when the speaking path is on and off, and is generally the same value for both the sending path and the receiving path. Set. In order to prevent howling, the larger the loss Lv is, the better; however, due to limitations on call quality, if it is set too high, the beginning of the word will disappear as the sound is turned on and off with a large level difference. The quality of the call deteriorates as the beginning of the conversation is cut off and it becomes difficult to make a call. For this reason, it is generally necessary to keep the large loss Lv to 35 dB or less from the viewpoint of speech quality. On the other hand, as the number n of stations participating in a conference increases, the acoustic coupling between the speakers and microphones of each station increases, making it easier for howling to occur, which increases the input loss Lv of each terminal. Therefore, it is necessary to prevent howling from occurring, and as mentioned above, the quality of the call inevitably deteriorates.

The influence of this number of participating stations n on the input loss is 1010
g10(n-1) (n=2, 3,...)
It is expressed as For example, when n=30, Lv=35dB
is required, then L=35-1010 for n-5
g10(29-4)=21 dB. When designing a conference telephone system, the input loss L of the audio switch circuit of each terminal must be set to a value that does not cause howling in accordance with the maximum number of participating stations Nmax. However, from an actual operational point of view, meetings are often held with the participation of fewer stations than all stations. However, since the input loss is set to the maximum value of Lv corresponding to the maximum number of stations Nmax, if a conference is actually held with stations below NrrlaX,
Even though it is possible to make a better call with a smaller input loss, the conference has to be held with a large input loss, and the conference has to be held with poor call quality. It is also possible to manually set the input loss L on each terminal according to the number of participating stations, but this would not only be time-consuming, but also
Incorrect settings may cause confusion in the meeting.
SUMMARY OF THE INVENTION An object of the present invention is to provide a loudspeaker conference telephone system that eliminates the above-mentioned drawbacks and allows conferences to be held with good call quality at all times, depending on the actual number of conference participants.

According to the present invention, a speaker using an audio switch circuit
A microphone-type terminal device is provided for each of the plurality of stations, and each of the plurality of terminal devices is connected to the center station via a 4-wire telephone line or a private telephone line, and the communication between the plurality of stations is In a conference telephone system in which a conference call is made using loudspeaker, each control signal transmitted from a conference participating station among the plurality of stations is received by the device of the center station, and the number of the control signals is counted. By creating a control signal corresponding to the number of stations participating in the conference, and sending the control signal to the plurality of terminal devices, the plurality of terminal devices can generate optimal audio according to the number of stations participating in the conference. A conference telephone system characterized by setting the input loss of the switch circuit is obtained.

Next, one embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 3 shows a simplified block diagram of the conference telephone type terminal device according to the present invention.
The signal is applied to the transmitting voice gate circuit 13 which is turned on and off depending on the DC output voltage of the voice control circuit 22.

The output side of the outgoing voice gate circuit 13 is connected via a line amplifier 15 to a outgoing end terminal 16 of a four-wire telephone line. On the other hand, the input side of the receiving side terminal 17 of the 4-wire telephone line is connected to the receiving audio gate circuit 18 which is turned on and off by the audio control circuit 22, and the output side of this terminal is connected to the receiving audio gate circuit 18 via the speaker amplifier 20. 21. The switch 23 represents a switch or contact provided to be operated by the terminal device, and is connected to drive the multi-frequency oscillator 24. The output side of the multi-frequency oscillator 24 is connected to the transmitting side terminal 16 via a buffer amplifier 25. The receiver terminal 17 is also connected to a multifrequency receiver 26 , the output of which is applied to a loss control circuit 27 .
A transmitting auxiliary variable loss circuit 14 and a receiving auxiliary variable loss circuit 19 are connected to the input and output terminals of the transmitting audio gate circuit 13 and the receiving audio gate circuit 18, respectively. It is controlled by the DC output voltage of the loss control circuit 27. FIG. 4 is a block diagram showing the center equipment installed in the center office of the conference telephone system according to the present invention. The talking side is connected to terminal 1T, the receiving side of the 2nd line is connected to terminal 2R, and the sending side is connected to terminal 2T.
connected to.

Similarly, the receiving side of the black n circuit is connected to the terminal NR, and the transmitting side is connected to the terminal NT, and one of each of these n four-wire telephone lines is accommodated in the conference bridge circuit 51. The multi-frequency receivers 52-1 to 52-n are connected to the receiving end of n sets of four-wire telephone lines, and their outputs are given to an OR circuit 53.

The output 61 of the OR circuit 53 is added to the n-ary counter 54, which outputs parallel outputs 62-1 to 62-n each consisting of n bits. These outputs are connected to a multi-frequency oscillator control circuit 55, and 16 types of control signals extracted through the output lead wires 63-1 to 63-16 are supplied to the multi-frequency oscillator 56. The output 64 of the multi-frequency oscillator 56 is connected to the transmitting side of n sets of four-wire telephone lines via buffer amplifiers 591 to 59-n, respectively. On the other hand, the output 61 of the OR circuit 53 is given to a timer circuit 57, and its output is added to the input of the multi-frequency oscillator 56 in order to drive it.
The switch 58 is a key of the center device and is connected to the input of the n-ary counter 54. Next, the overall operation of the terminal device and center device that constitute the conference telephone system according to the present invention will be explained.

First, in FIG. 3, the switch 23 operates in conjunction with when the user of the terminal device turns on the power, or
It works by pressing a separate activation key. switch 2
3 closes, the multi-frequency oscillator 24 is started, and the multi-frequency signal common to each specific terminal is emitted for a certain period of time, for example, 100
mS, and is sent to the transmitting side terminal 16 of the telephone line via the buffer amplifier 25. This end inactivation signal is the same multi-frequency signal with a certain time interval from each terminal of the participating stations of the system via the 4-wire telephone line to the terminals 1R, 2R, . . . of the center equipment, respectively. ...,N
given to R. These multi-frequency signals are received and detected by multi-frequency receivers 52-1 to 52-n corresponding to each telephone line, and a single pulse signal is guided to these outputs 60-1 to 60-n, respectively. It is added to the OR circuit 53. Control signals from each terminal are generally received at certain time intervals since the probability that each terminal issues an activation signal at the same time is very low. Therefore, if the number of participating stations is i, the same number i pulse trains appear at the output of the OR circuit 53 and are input to the n-ary counting circuit 54. Further, the output 61 of the OR circuit 53 is a pulse of a certain time width (for example, 100
msec), so that every time a pulse is applied to the input of the timer circuit 57, a single pulse of 100 msec is generated at the output, thereby causing the multifrequency oscillator 56 to generate a single pulse of 100 msec. to drive.
Counter circuit 54 of n lines 62-1 to 62
A pulse corresponding to the number of stations participating in the conference (1) appears at -n. When these outputs are given to the multi-frequency oscillator control circuit 55, one of the 16 outputs 63-1 to 63-16 corresponds to the count value of the counter 54, that is, the number of participating stations is 1, The logic becomes "O" level, and one of the 16 sets of two-frequency oscillation circuits in the multi-frequency oscillation circuit 56 is selected.As described above, the multi-frequency oscillation circuit 56 receives control pulses from each terminal. It is driven by a timer circuit 57 that generates a 100 msec pulse every time the station is connected, and its output 64 contains a multi-frequency signal (100 msec pulse) corresponding to the number of participating stations (1).
) is extracted. This signal is transmitted to all n terminals via n buffer amplifiers 59-1 to 59-n.
Sending side terminals of wire telephone line 1T, 2T,...
..., are sent out all at once via NT. Since the multi-frequency oscillation circuit 56 can generate 16 types of two-frequency combination signals,
If each two-frequency combination signal is associated with the input loss L of the terminal device described above on a one-to-one basis, 16 types of input loss Lv can be controlled depending on the number of participating stations.

In reality, Lv-6, 8, 10, etc.
, it is sufficient to be able to set it in steps of 36 dB. Further, when the conference ends, the counter circuit 54 is reset by pressing the center device reset key 58. On the other hand, as described above, the input loss control signal (two-frequency signal) sent simultaneously to each terminal is applied to the terminal 17 of the terminal device shown in FIG. 3 via a four-wire telephone line.

This control signal is received and detected by the multi-frequency receiver 26. At the output 28 of the multi-frequency receiver 26, a code corresponding to the received two-frequency signal is obtained. The loss control circuit 27 receiving this output code generates a DC voltage corresponding to the code. This control output 29 is transmitted through a transmitting auxiliary variable loss circuit 14 and a receiving auxiliary variable loss circuit 19 consisting of FET diodes and the like.
The loss L is controlled to be set according to the control DC voltage. The transmitting voice gate circuit 13 and the receiving voice gate circuit 18 are turned on and off by the output DC voltage of the voice control circuit 22 composed of FETl diodes, etc., and when the transmitting (or receiving) is on, the receiving (or Or 2e!! Shout:=:=J circuit 19 is connected in parallel to transmitting voice gate circuit 13 and receiving voice gate circuit 18, respectively, so these losses give the above-mentioned input loss loss L. It turns out.

According to the present invention, as described above, the input loss of the audio switch of each terminal can be automatically set by the control signal from the center according to the number of stations participating in the conference out of the number of installed stations. This makes it possible to always have conference calls with good amplification under the best conditions.

To explain with an example, the number of stations in a conference telephone system is Nm.
Assuming ax-30, when using a normal conference room, the input loss Lv of each terminal needs to be set to 23 dB or more in order for this system to not cause howling. L
If you set it to -25dB, the beginning of the conversation will be cut off, etc.
Call performance is not satisfactory. However, in a system where up to 30 stations can be connected, if the number of stations participating in the conference is 5, in order to prevent howling, the noise loss Lv of the audio switch circuit of each terminal should be set to 14 dB. Good, if it is L-14dB, the communication path is on.
Since there is little difference in the off level, there is almost no noticeable disconnection at the beginning of the conversation, and high-quality calls are possible. In the system according to the present invention, even if Lv is set to -25 dB when the number of stations is 30, when the actual number of participating stations is 5, it is automatically set to Lv -14 dB by a control signal from the center. Therefore, conference calls with good voice quality can be made. If the input loss Lv of a terminal does not change according to the number of participating stations as in the present invention, in the above example, the maximum number of stations would be 30 even though the number of participating stations was 5. You will have to make a call at 25dB below the supported Lv, so you cannot expect a high-quality conference call. As explained above, the present invention allows the input loss of the audio switch circuit of each terminal to be automatically set according to the number of conference participating stations using the control signal from the center. The effect obtained is significant in that conference calls can be made with the best call quality depending on the number of conference calls.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram showing an example of a conventional conference telephone system;
1 is a block diagram showing an example of a terminal device according to the method of FIG. 1, FIG. 3 is a block diagram of a conference terminal device for explaining an embodiment according to the present invention, and FIG. FIG. 2 is a block diagram of a conference call center device for explaining one embodiment. In the figure, 11 is a microphone, 13 is a transmitting audio gate circuit, 14 is a transmitting auxiliary variable loss circuit, 18 is a receiving audio gate circuit, 19 is a receiving auxiliary variable loss circuit, 21 is a speaker, 22 is an audio control circuit, 24 is a multi-frequency oscillator, 26
is a multi-frequency receiver, 27 is a loss control circuit, 51 is a conference bridge circuit, 52-1 to 52-n are multi-frequency receivers, 53
is an OR circuit, 54 is an n-ary counter, 55 is a multi-frequency oscillator control circuit, and 56 is a multi-frequency oscillation circuit.

Claims (1)

[Claims] 1 A speaker-microphone type terminal device using an audio switch circuit is installed at each of a plurality of stations, and each of the plurality of terminal devices is connected to the center station via a four-wire telephone line or a private telephone line. In a conference telephone system in which a loudspeaker conference call is made between the plurality of stations, each control signal sent from a conference participating station among the plurality of stations is received by the device of the center station. Then, by counting the number of control signals, creating a control signal corresponding to the number of stations participating in the conference, and transmitting the control signal to the plurality of terminal devices, the plurality of terminal devices A conference telephone system characterized by setting the optimum input loss of a voice switch circuit according to the number of stations participating in the conference.