JPS6094572A - Conference telephone system - Google Patents

Abstract

PURPOSE:To transmit voice of all conference participants at a uniform level by inserting a variable gain circuit to a transmission line and a reception line between an exchange trunk and a conference use bridge. CONSTITUTION:Variable gain circuits As1-Asn for transmission and variable gain circuits AR1-ARn for reception controlled by a talker voice signal are provided to input/output transmission lines and a reception line of the conference use bridge B. Then each talker voice signal is controlled automatically so that the average level of the signal at an output point from the conference use bridge B to the exchange trunk C is made uniform. Thus, the loss of transmission lines L1-LN from subscriber telephone sets to the conference use exchange trunk C being in variation to various values is adjusted to a prescribed value, the result is added and distributed to the conference use bridge B so that the voice of all the conference participants is transmitted to other conference participants at a uniform level.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention utilizes a telephone line in which a plurality of subscriber telephones are simultaneously configured by a bridge 11 to form an af-L conference telephone system. According to K, when making a telephone call, at a conference bridge that connects the telephone lines of subscribers of 3 Å or more in a conference exchange trunk, the voices of all subscribers are added up and distributed to all subscribers except for oneself. configured. The addition and distribution methods of actual conference bridges have conventionally been the above-mentioned full addition method, the maximum value method that distributes only the voice of the speaker with the largest voice, and the method that adds the voices of an appropriate number of speakers starting from the voice with the largest voice power. Various methods have been proposed to deal with problems such as deterioration of sound quality and level increase due to addition, and deterioration of naturalness due to switching.

On the other hand, in general public telephone lines, the transmission path loss to the conference exchange trunk where the conference bridge is installed is not uniform due to the fact that the distance from the subscriber to the telephone center varies. Therefore, the actual situation is that the audio level of each subscriber varies widely depending on the conference bridge input. In such a normal telephone line, no matter which of the above-mentioned conference bridge addition and distribution methods is used, a fair telephone conference cannot be established for all subscribers. That is,
The speaker's voice is dominated by transmission path loss and is not transmitted to other conference participants at a uniform level, and the addition of the conference bridge has a level of superiority or inferiority depending on the magnitude of transmission path loss, making it impossible to make a fair conference call. There were disadvantages such as the loss of information.

[Purpose of the invention]

The present invention eliminates the above-mentioned disadvantages, and allows the audio of all conference participants to be added and distributed to the conference bridge regardless of the transmission path loss from the various subscriber telephones to the conference exchange trunk, so that the audio of all conference participants is at a uniform level. The purpose of the present invention is to provide a conference telephone system that allows a fair and natural telephone conference in which the number of conference participants is overwhelmed.

[Features of the invention]

The present invention provides a conference telephone system in which subscriber telephones of three or more parties are connected to each other by a conference bridge via one telephone line. a variable gain circuit controlled by the speaker audio signal, the variable gain circuit being automatically controlled to equalize the average level of each speaker audio signal at its output point from the conference bridge to the switched trunk; It is characterized by

[Explanation based on examples]

Embodiments of the present invention will be described with reference to the drawings. 1st
The figure is a block diagram of the main parts of a device related to a conference telephone system according to an embodiment of the present invention. In FIG. 1, subscriber telephone 81
The input and output of ~SN are connected to hybrid circuits H1 to HN, respectively. The outputs and inputs of the hybrid circuits H4 to HN are respectively connected to the exchange trunk C, and audio is transmitted to and received from the exchange trunk C.

The feature of the present invention is the variable gain circuit surrounded by a dashed line. That is, each output of the exchange trunk C is connected to a variable gain circuit for sending speech As+ to ASN and a level detector to DN. The outputs of the transmitting variable gain circuits As+ to ASN are connected to the conference bridge B, respectively.
connected to each input of

Each output of the conference bridge B is connected to variable gain circuits ART to ARN for reception, respectively. Outputs of variable gain circuits AR1 to ARN for receiving calls are connected to respective inputs of switched trunk C, respectively. Level detection circuit.

-DN are connected to variable gain circuits A81-80N for transmitting and variable gain circuits AR4-ARN for receiving, respectively.

The conference telephone system is comprised of one subscriber unit S, .about.SN, a hybrid circuit H, .about.H1□, a switched trunk C1, a conference bridge B, and the variable gain circuit of the present invention.

The operation of the conference type 5-pack system having such a configuration will be explained. In FIG.
are connected to each other at a conference bridge B of a conference exchange trunk via transmission lines with transmission line losses L1 to LN that vary in various ways. At the input/output points of the conference bridge B of each subscriber, there are variable gain circuits for transmission, As+ to ASN, whose gains are varied by control signals from level detection circuits J]1 to DN, respectively.

Variable gain circuits ARI to A'RN for receiving calls are inserted. Previous value i: I Kusaki Yoro 1 trigram upper r do tatami as: En-douyojil
It ear n ridge Δ-Δ-H A speaker who detects the magnitude of the input level of the conference bridge B of each subscriber's voice and outputs control information for the gain of the variable gain circuit A8 and AR for sending and receiving. The level detection circuit of the level is controlled by ~DN.

In this configuration, each of the level detection circuits D1 to DN detects the average level equivalent to the speaking time of each speaker, and based on this detection information, the variable gain circuits for transmitting and receiving that are inserted in the transmitting path and the receiving path A8, set the AR gain. That is, the detected average level of the speaker is compared with a preset reference level, and the gains of the transmitting and receiving variable gain circuits A8 and AR are varied to compensate for the difference. Alternatively, the transmitting variable gain circuit As is adjusted so that the average value of the speaker input level to the conference bridge B is adjusted to a predetermined constant value, and at the same time, the receiving variable gain circuit AR is also adjusted to the transmitting variable gain circuit. The gain is controlled to be similar to that of gain circuit A8. The above predetermined reference value may be, for example, a level value that can ensure an appropriate communication level between the subscriber telephones of the three parties.

With the above configuration and operation, each subscriber telephone 8. ~ The variation in transmission path loss between the SN and the conference bridge 9 is adjusted to a roughly constant value by the variable gain circuits A8 and AR for transmitting and receiving. To this end, adjustments are made only after each subscriber speaks in a manner that causes the transmitting and receiving variable gain circuits A8 and AR to operate appropriately. In order to set the gain of the variable gain circuit A8 and AR for transmitting and receiving, a time is required to detect the average value of the voice level, and generally the number is expressed by the equation 1.
It can be detected in about 0 milliseconds to several seconds and can be adjusted in a short time. In an actual conference-type episode, for example, conference R
This can be done by having each conference participant introduce themselves just before the start of the session. Even during a conference, the adjustment of the variable gain circuits A8 and AR for sending and receiving calls is slowly controlled by the time constants of the level detection circuits D1 to DN at the speaker level.

FIG. 2 is a block diagram of a variable gain circuit for a conference telephone system according to the present invention. In FIG. 2, the output of an exchange trunk C (not shown) is connected to a variable gain circuit AB for transmission and a level detector D.
'rK connected. The output of the transmitting variable gain circuit A8 is connected to a conference bridge B (not shown). The output of conference bridge B (not shown) is connected to variable gain circuit AR for receiving calls,
The output of the variable gain circuit AR for reception is connected to an exchange trunk (not shown). The output of the level detector DT is connected to a comparison circuit OPM and a comparison circuit CPM2. A voice presence/absence threshold THo is also input to the comparison circuit OPM. The reference level THm is also input manually to the comparison circuit CPM2. The outputs of the comparison circuits OFM, , OPM2 are:
Each is connected to a timer circuit T. The output of the timer circuit T is the variable gain circuit A8 for transmitting and the variable gain circuit A8 for receiving.
and R, respectively.

The operation of the variable gain circuit having such a configuration will be explained. In FIG. 2, the speaker's voice is detected by a level detection circuit, and then a comparison circuit C! detects the presence or absence of voice.
At PM, it is compared with the voice presence/absence threshold THo and at the same time 1
It is input to a comparator circuit CPM2 which compares it with a reference level THm. The output of the comparison circuit OFM 2 is input to the timer circuit T, and then sent to the variable gain circuits A8 and AR for transmitting and receiving.
is inputted with appropriate operating time constants and residual time constants. Further, the operation of the timer circuit T is based on the comparison circuit O.
According to the output information of PM, it is possible only during the sound period, and does not operate during the silent period. The voice presence/absence threshold THo is set to a sufficiently low level and at a level that detects the noise level from the subscriber transmission path. Generally, a level of -40 to -50 dBm is appropriate.

Each of the transmitting and receiving variable gain circuits A8 and AR is realized by, for example, a step variable gain circuit. Comparison circuit OP
The output of M2 adjusts the steps of the transmitting and receiving variable gain circuits A8 and AR by the difference from the reference level.

FIG. 5 is a block diagram of another embodiment of the variable gain circuit. In FIG. 6, as shown by the broken line, the transmitting voice m
The level is detected from the output of the variable gain circuit A8, and the variable gain circuits A8 and AR for transmitting and receiving are adjusted so that the output level of the variable gain circuit A8 for transmitting becomes a predetermined constant level.

The embodiments of the present invention shown in FIGS. 1, 2, and 5 are as follows:
Although an example in which switched trunk C is configured with an analog switched trunk is shown, even in a case where switched trunk C is configured with a digital time-division switch and conference bridge B is implemented on a digital multiplexing basis, it is possible to It is well known that the receiving variable gain circuits A8 and AR can be constructed in a similar manner using digital multiplexing.

〔Effect of the invention〕

As explained above, the present invention inserts a variable gain circuit into the sending and receiving paths between the switching trunk and the conference bridge to maintain a constant variation in loss in the transmission path between each subscriber telephone and the conference bridge. By adjusting the value, each subscriber's voice is transmitted to other conference participants at roughly the same level, even on a single-phone line where transmission path loss varies widely, making it possible to create a conference call that is close to a fair natural conference. It has great effects.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the main parts of a device related to a conference telephone system according to an embodiment of the present invention. FIG. 2 is a block diagram of a variable gain circuit for a conference telephone system according to the present invention. FIG. 3 is a block diagram of another embodiment of the variable gain circuit. AR...variable gain circuit for receiving calls, A8...variable gain circuit for sending calls, B...conference bridge, O...exchange trunk, OPM,, OPM2...comparison circuit, D... Level detection circuit, DT: Level detector, H: Hybrid circuit, S: Subscriber telephone, T: Timer circuit, THm: Reference level, THo: Voice presence/absence threshold. Patent Applicant NEC Corporation Representative Patent Attorney Takashi Ide 1121

Claims (1)

[Scope of Claims] (In a conference telephone system in which subscriber telephones of three or more parties are interconnected via a telephone line by a conference bridge, It includes a variable gain circuit controlled by the talker audio signal, which variable gain circuit automatically equalizes the average level of each talker audio signal at its output from the conference bridge to the switched trunk. A conference telephone system characterized by being controlled.