JPH021464B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a conference call noise insertion device for time division multiplexed PCM signals.

The conference call is for n participants participating in the conference call.
of other channels except for the own channel's PCM signal.
This is achieved by adding and combining PCM signals and distributing the resulting PCM signals to the receiving sections of each subscriber. In this case, simply adding the PCM signals of other channels other than the own channel will not be enough, for example, when all channels are silent, each subscriber will be able to listen to the noise level at the time of no calls heard on a normal telephone. This means that the user will hear a noise that is approximately √-1 times as large as , and this cannot be said to satisfy the transmission quality above a certain level required for public telephone lines.

Conventionally, for example, an audio power comparison method selects and adds k channels (k<n) in descending order of audio power.
Alternatively, the number of channels to be added can be reduced by adopting an audio power pre-emption priority method that focuses on the presence or absence of audio power and selects and adds k channels (k<n) in the order of those with audio power. It suppressed the rise in levels. However, in both of the above methods, when the k channel is fully used, the speech is not transmitted immediately, and furthermore, depending on the difference between the two methods, the speech is inevitably transmitted with the beginning of the speech being cut off. It had the disadvantage of being This undermined the original format of conferences, in which when one person speaks, all other conference participants must be able to hear it immediately.

Therefore, as a method to solve the drawbacks of the voice power comparison method or the voice power preemption priority method, the present applicant et al. ” (“Conference Telephone Noise Suppression Device” filed on the same day as the present application). According to this proposal, the increase in noise during no calls can be suppressed, and the purpose of not outputting noise during no calls can be achieved. However, each conference participant is forced to listen to a DC 0-level signal, which creates dead silence and makes the listeners feel unnatural.

SUMMARY OF THE INVENTION An object of the present invention is to provide a conference call noise insertion device that can ensure the same level of call quality as in a normal conference call when all channels of the conference call are idle.

In order to achieve the above object, the conference call noise insertion device according to the present invention resets a plurality of channels respectively assigned to a plurality of subscribers participating in a conference call with a frame pulse of a frame constituted by a PCM signal which is time-division multiplexed. and a flip-flop that is set by a voice detection signal indicating that there is voice power in the channel, and a conference telephone device whose input signal is the input PCM signal when there is voice power, and the "0" code when there is no voice power. an all-channel no-call monitoring circuit consisting of a delay circuit that gives a delay amount equivalent to the absolute delay time of , a noise generation circuit, and a time division multiplexed signal output from the conference telephone device by the output of the delay circuit, or the noise generation circuit. a noise insertion circuit consisting of a multiplexing circuit for selecting one of the outputs, and configured to send noise to all channels of the conference telephone device output when there is no audio output on all channels of the time division multiplexed signal. It has been done.

According to the above configuration, it is possible to provide the same level of noise as a normal telephone without entering the actual conference telephone device which performs the conference telephone function itself, and the object of the present invention is completely achieved.

Hereinafter, the present invention will be explained in more detail with reference to the drawings and the like. FIG. 1 is a circuit block diagram showing an embodiment of a conference telephone noise insertion device according to the present invention.

Time division of each subscriber's audio signal inserted into the channel assigned to each subscriber participating in the conference call
The PCM signal a is input to the noise suppression device 1-2.
The voice detection signal c output from the noise suppression device 1-2 is input to the all-channel no-call monitoring circuit 1-3, and the output signal e of the all-channel no-call monitoring circuit 1-3 is applied to the noise insertion circuit 1-4. be done. On the other hand, the delayed signal b of the time-division multiplexed PCM signal passed between the noise suppression device 1-2 is input to the conference telephone device 1-1, where the time-division multiplexed PCM signal is subjected to predetermined processing. Signal output d is noise insertion circuit 1
-4, and a time division multiplexed PCM signal controlled by the conference telephone noise insertion device according to the present invention is output from the output of the noise insertion circuit 1-4. If there is no audio output on any channel of the time-division PCM signal a, the noise suppression device 1-2 applies a PCM code of "0" to those channels, and on the other hand, if there is audio output on any channel, It is configured to output the time-division PCM signal and audio detection signal of that channel.

The conference telephone device 1-1 receives time-division multiplexed PCM signals from n conference telephone subscribers, and
It is configured to output a PCM signal obtained by adding and combining PCM signals of other channels except for the PCM signal.

FIGS. 4a and 4b are diagrams showing examples of input and output frame formats of the conference telephone device 1-1. In the figure a, TS ₀ , TS ₁ , ...TSi,
TSn is the time slot corresponding to each channel, and TS ₀ , TS ₁ , ...TSi, TSn in FIG. ing. The conference telephone device 1-1 is, for example, disclosed in Japanese Patent Application Laid-Open No.
25508, and the like. The conference telephone device according to this application includes the above-mentioned time division multiplexed PCM as one embodiment.
A first gate that gates the signal by a communication line, and a PCM signal that passes through this gate and this gate.
An adder that adds the second gate output that outputs the sum of the PCM signals input until just before the PCM signal is input, a c-bit first shift register that holds the PCM signal added by the adder, and a clear a second gate for gating the summed PCM signal held by the c-bit first shift register by a line; and a second register for holding the PCM signals of all channels summed by the adder. , 1st
Sequentially hold the PCM signal which is the gate output of n
An example is shown in which the circuit is comprised of a third register of xc bits and a subtracter that sequentially subtracts the PCM signal of the third register from the addition PCM signal held by the second register and outputs the result.

Figures 2 and 3 show the all channel no-call monitoring circuit.
FIG. 3 is a circuit diagram showing details of each noise insertion circuit. In each figure, the signal lines connecting each circuit are parallel signals. The following processing assumes time-division processing corresponding to input time-division signals.

In FIG. 2, the flag circuit 3-1 is R-S
It is composed of a flip-flop circuit,
It is RESET by the frame pulse FP located at the beginning of the frame shown in FIG. 4c, and is SET by the output signal c of the silence detector 2-1. R-S flip-flop circuit 3-1 operated with such wiring
The meaning of the signal output from is the beginning frame pulse.
It is set to "L" in FP, which indicates the state "L" in which there is no audio power in all channels, and then if there is audio power in one channel or more than one channel, there is audio power in one or more channels at the end of the frame pulse. Since this shows the state "H", it is determined at the end of the frame pulse whether there is no sound on all channels or not in that frame pulse. This output is then given a delay time equivalent to the absolute delay time of the conference telephone device 1-1 by a delay circuit 3-2. Conference telephone device 1
Since -1 is time division multiplexed, the input/output delay difference is an integral multiple of the frame, so this delay circuit is constituted by a shift register using the frame pulse FP as a clock. The connections in FIG. 2 show this situation.

In the noise insertion circuit 1-4 shown in FIG.
3. According to the instruction of the output e, either the output d of the conference telephone device 1-1 or the output of the noise generator 4-2 is selectively output. The selection criteria is: All channel no-call monitoring circuit 1
-3 is "H", that is, when there is audio power for one or more channels, the conference telephone device 1-1 output is selected, and when it is "L", that is, when there is no audio power for all channels, the noise generator 4 -2 outputs are selected. In the latter case, the conference telephone device 1-
1 Output d is supposed to be "0" for all channels due to the effect of noise suppression, and if this is sent as is to the receiving section of each conference participant, each conference participant will hear a DC 0 level signal. This gives a dead silence and makes the listener feel unnatural. For this purpose, the noise signal from the noise generator 4-2 is sent to all channels of the corresponding frame. The noise generator 4-2 is composed of a pseudo-random sequence generation circuit, and its noise level is set to correspond to the background noise level in a normal telephone. Further, the multiplexing circuit 4-1 is one in the commercially available MSI family.

As described above in detail, according to the present invention,
If the time-division multiplexed PCM signal input to the conference phone device does not contain audio power, the PCM signal of that channel is set to 0 code, so it is possible to suppress the increase in the noise level within the conference phone device. ,
Furthermore, when all channels become silent, it is configured to send out a signal that serves as an appropriate background noise, so it provides call quality comparable to that of a regular telephone line without causing unnatural silence. This effect can be obtained.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of a conference telephone noise insertion device according to the present invention, FIGS. 2 and 3 are block diagrams showing details of an all-channel no-call monitoring circuit and a noise insertion circuit, respectively. 1 is a diagram showing an example of a frame format and a frame pulse of an input/output signal of a conference telephone device to which the present invention is applied; FIG. 1-1...Conference telephone device, 1-2...Conference telephone noise suppression device, 1-3...All channel non-call monitoring circuit, 1-4...Noise insertion circuit, 3-1...Flag circuit, 3 -2... Delay circuit, 4-1... Multiplexing circuit, 4-2... Noise generator, a... Input signal, b... Noise suppression circuit output signal, c... Voice detector output signal, d ...Conference telephone device output signal, e
...All channels no-call monitoring circuit output signal, f...
Output signal, FP...frame pulse.

Claims (1)

[Claims] 1 PCM that time-division multiplexes multiple channels assigned to multiple subscribers participating in a conference call.
The flip-flop is reset on the frame pulse of the frame constituted by the signal and is set on the audio detect signal indicating that audio power is present on the channel and the input of audio power, if present.
An all-channel no-call monitoring circuit consisting of a delay circuit that gives a PCM signal a delay equivalent to the absolute delay time of a conference telephone device that takes a "0" code as an input signal when there is no audio power; a noise generation circuit; a noise insertion circuit consisting of a multiplexing circuit that selects either the time division multiplexed signal output from the conference telephone device or the output of the noise generation circuit according to the output of the delay circuit, A conference telephone noise insertion device characterized in that the conference telephone noise insertion device is configured to send noise to all output channels of the conference telephone device when there is no audio output.