JPS62154839A - Conference telephone equipment - Google Patents

Abstract

PURPOSE:To improve the SN ratio and articulation of a transmitting signal by reducing only the loss quantity of a variable loss circuit and suppressing the reduction of the loss quantity of variable loss circuits in other terminal equipments when a detecting output signal is supplied to a flip flop (FF) as a reset signal. CONSTITUTION:At first, voice is initially reached and inputted to a transmitter 5 connected to a terminal equipment 4 arranged on the nearest position to the initial speaker, an output signal from a sound switch circuit 19 is turned to the 'L' level and a pre-FF 23 and a post-FF 23 are simultaneously inverted to the reset state. Consequently, the loss quantity of the variable loss circuit 16 is controlled from 10dB e.g. to 0dB, a control signal line 12 is turned to the 'L' level and all pre-FFs 22 and post-FFs 23 in other terminal equipments are turned to the reset state.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a conference call device used for a telephone conference between a plurality of people who are located apart from each other through a telephone line.

Conventional technology) By installing a plurality of terminals 81 to which conventional transmitting microphones are connected in one conference room, etc., and adding the transmitting signals picked up by each microphone and transmitting the sum to the telephone line, There was a conference call device that was designed to communicate with terminal devices installed in a conference room or the like.

(Problem to be Solved by the Invention) However, as the noise level collected by each of the plurality of microphones is added and accumulated, the S of the transmission signal is
/ The N ratio was poor.Also, the paths of sound waves reaching multiple microphones installed in the same room at a distance from the sound source (speaker) are different, and there is not only direct sound but also reflected sound. Since sound is also collected, simply adding up these audio signals with phase and time differences results in a transmitted signal with large echoes and reverberations, reducing clarity and making it difficult for the receiver to hear the exact content of the transmitted message. There was a problem with that.

(Means for Solving the Problems) The present invention has been made to solve the above conventional problems, and its purpose is to substantially reduce the number of microphones that operate simultaneously among a plurality of microphones. By reducing the S/N ratio of the transmitting signal and the brightness [IF1
! A meeting that can improve the &? The purpose of the present invention is to provide an iTi talking device.

The present invention will be described in detail below based on the embodiments shown in the drawings. FIG. 1 is a system configuration diagram of a conference telephone device, in which a plurality of terminal devices 4 are sequentially connected to one device [2] connected to a telephone line 1 with a connecting cable 3, and each terminal device 4 has two A transmitter 5 consisting of a pair of bidirectional microphones is attached, and four receivers 6 consisting of earphones or speakers are connected.

As shown in FIG. 2, the main device 2 includes a 2-wire 4-wire conversion circuit 7,
A receiving signal amplifier 8 and a transmitting signal mixing amplifier 9 are connected to this. The connection cable 3 has a reception signal line 10 connected to the output side of the amplifier 8, a transmission signal line 11 connected to the input side of the mixing amplifier 90, and a control signal line 12. The devices @4 are commonly connected in parallel. The terminal device 4 includes a switch 14 that controls on/off operation of a transmitter 5 disposed on the same side as the receiver 6 in conjunction with connecting or disconnecting the receiver 6 to the connection terminal 13; 5 differential amplifier 15, a variable loss circuit 16 composed of FETs, etc., for varying the loss M of the transmission signal, and an output amplifier 17 for sending the transmission signal to the transmission signal line 11, A mixing resistor 18 is connected in series. Then, the output id of the differential amplifier 15 is rectified and smoothed to create a threshold value.
The audio switch circuit 19 outputs an active level signal when the level exceeds the level, and the loss amount of the variable loss circuit 16 is determined according to the state of this output signal and the control signal supplied from the control signal line 12. and a #11 control circuit 20 for controlling the control signal of the control signal line. In addition, you can adjust the volume! The listening volume of the handset 6 is individually adjusted at step a21.

As shown in FIG. 3, the control circuit 20 reduces the loss of the variable loss circuit 16 of the terminal device 4 closest to the sound source by using R3 type flip-flops 22 and 23 connected in two stages.
Other terminal equipment v! The output side of the audio switch circuit 19 is connected to the set signal input terminal S of the first stage flip-flop 22 via a pull-up resistor 24. and the control signal line 12 is connected to the reset signal input terminal R.
is connected. This i, II if circuit 20 may be of positive logic, but it may be negative logic, that is, the signal is "L°'(low)".
An example is shown in which the active operating state is reached at the level. The output terminals Q and Q of the first stage flip-flop 22 are connected to the input terminals R and S of the second stage flip-flop 23, respectively, and the output terminal Q of the second stage flip-flop is connected to the control signal line 12 via an inverter transistor 25 and a resistor 26. The loss amount control signal is supplied to the variable loss circuit 16. The second stage flip-flop 23 may be omitted and the first stage flip-flop 22 may be used alone.

With this structure, a plurality of terminal devices 4 are installed on a desk in the same room depending on the number of participants in the conference, the size of the conference room, etc. In Figure 3,
In the initial state where there is no audio input to the transmitter 5 of any terminal device 20, the first stage flip-flop 22 is in a reset state, that is, the terminals 10 and 1 are at the 'l-1' level and the terminal Q is at the 'L' level. level, the subsequent flip-flop 23 is in a reset state, that is, the terminals 100 and Q are at the ``L°'' level, the terminals 100 and Q are at the ``tobi'' level, and the loss amount of the variable loss circuit 16 is, for example, 10 dB, and the collector electrode of the transistor 25 is in the reset state. The control signal line 12 and the terminal R of the first stage flip-flop 22 are both at the 1'' level. First, the voice first reaches and is input to the transmitter 5 connected to one terminal device 4 located at the position closest to the first speaker, that is, the sound source, and the output signal of one of the voice switch circuits is ゛L. At the same level, both the first-stage flip-flop 22 and the second-stage flip-flop 23 are inverted to the set state. As a result, the amount of loss of the variable loss circuit 16 is, for example, 10d.
B to OdB, the control signal line 12 goes to L'' level, and all of the first-stage flip-flops 22 and second-stage flip-flops 23 of the other terminal devices 4 are reset. In step 4, the voice signal and noise signal picked up by the transmitter 15 are attenuated by the variable loss circuit 16, and almost no input is sent to the transmitter signal line 11. The terminal K El −' of the flip-flop 22
When the L level is at the w-L level, both the terminals Q and Q are at the "1-de level", so the subsequent flip-flop 23 is not reset. Then, a signal only from the transmitter 5 connected to the terminal device 4 closest to the first person who initiated the transmission is detected, selected preferentially, and sent to the transmission signal line 11, and transmitted to the other terminal devices 4. The noise signals from the connected transmitters 5 are hardly added and accumulated.Therefore, as the number of transmitters 5 that are turned on at the same time is substantially reduced, the S/N ratio of the transmitted signal is reduced. At the same time, the clarity of the transmitted signal is improved by reducing reverberation and anti-W sound.

Next, when the audio input to the transmitter 5 during transmission is stopped, the output signal of one audio switch circuit of the terminal device 4 becomes H" level, and all the flip-flop circuits 22 and 23
returns to its original initial state and becomes ready for interrupt calls from any terminal @4.

(Effects of the Invention) As described above, according to the present invention, it is possible to reduce the loss in the variable loss circuit of the terminal device located closest to the transmitter among the plurality of transmitters installed in the same room. By automatically controlling the variable loss circuits of other terminal devices to a high-loss state, the number of handsets in the on state can be substantially reduced, improving the S/N ratio and intelligibility of the transmitted signal. This has the remarkable effect of improving the

[Brief explanation of drawings]

FIG. 1 is a system configuration diagram of a conference telephone device embodying the present invention, FIG. 2 is a circuit diagram of the main device and terminal device, and FIG.
The figure is also a circuit diagram of the control circuit of the terminal device. DESCRIPTION OF SYMBOLS 1... Telephone line, 2... Main device, 3... Connection cable, 4... Terminal device, 5... Transmitter, 6... Receiver, 10... Receiving signal line, 11... Transmission signal line,
12... Control signal line, 16... Variable 1Ω loss circuit, 1
9... Audio switch circuit, 20... Control circuit, 22
・23...Flip-flop. Figure 2

Claims (1)

[Claims] In a conference telephone system using a plurality of terminal devices connected in parallel to a common control signal line with a transmitter connected thereto, each of the terminal devices has a variable loss transmitter inserted into the output signal path of the transmitter. a voice switch circuit for detecting the output signal level of the transmitter, and a flip-flop to which the detection output signal of the voice switch circuit is supplied as a set signal, and the output signal of the flip-flop is used to detect the variable loss. In addition to controlling the loss amount of the circuit, a control signal is supplied to the control signal line and a reset signal of the flip-flop is supplied, so that the detection output signal from the audio switch circuit is sent to the flip-flop as a set signal at the earliest time. When the flip-flop is supplied to the control signal line, the loss amount of only the variable loss circuit of the terminal device to which this flip-flop belongs is reduced, and at the same time, the loss amount of the variable loss circuit of the other terminal devices is not reduced by the control signal of the control signal line. conference telephone equipment.