JP2603955B2 - Audio conference equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a voice conference apparatus for conducting a conference by a loudspeaker call via a telephone line or a dedicated line using a speaker and a microphone. .

2. Description of the Related Art Conventionally, as shown in the block diagram of FIG. 2, this type of audio conference apparatus uses a two-wire / four-wire conversion circuit 2 connected to a wired line 1 to transmit to a conference partner. The speech signal and the reception signal received from the other party are separated, and the reception signal is converted into a first echo canceling circuit 3, a variable gain amplifier 4,
The signal is input to an amplifier circuit 6 via a second echo canceling circuit 5, and the received signal is amplified by the amplifier circuit 6 so as to have a predetermined volume level. The transmission signal input from the microphones 8 assigned to all or several persons is amplified by the amplifying circuit 9 and then passed through the second echo canceling circuit 5 and the first echo canceling circuit 3 to the two wires 4. The signal is input to the line conversion circuit 2 and transmitted from the wired line 1 through the circuit 2.

The first echo canceling circuit 3 eliminates a sneak signal from the transmission signal path to the reception signal path of the two-wire / four-wire conversion circuit 2 as shown by a broken line, and is, for example, an adaptive type such as an adaptive finite impulse response filter. Consists of a filter. The second echo canceling circuit 5, as shown by a dashed line, eliminates a sneak signal due to acoustic coupling between the speaker 7 and the microphone 8, and uses an adaptive filter or the like as in the first echo canceling circuit 3. Be composed.

Further, the variable gain amplifier 4 controls the receiving sound volume according to the level of the control signal VOL.

With such a configuration, the conference can be proceeded by voice call with the conference partner.

(Problems to be Solved by the Invention) However, in the first and second echo canceling circuits 3 and 5, the levels that can be eliminated are limited by the relationship between the noise level of the wired line and the indoor noise level. For this reason, in the configuration in which the variable gain amplifier 4 is inserted in the reception signal path as shown in FIG. 2, when the reception sound volume is set to be higher than a predetermined value, the acoustic coupling between the speaker 7 and the microphone 8 and the two-wire / four-wire conversion circuit There is a possibility that so-called howling may occur due to an increase in loop gain due to the loop-around in 2, and therefore, the receiving volume is limited, and the volume of the speaker 7 decreases when a line having a large loss such as a public line is used. There has been a problem that the listening of the content becomes insufficient.

An object of the present invention is to provide an audio conference apparatus that can generate a sound from a speaker having a sufficient volume even when a lossy wired line is used and can smoothly proceed with a conference.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the present invention relates to a speech signal which is connected to a line and transmitted from a conference partner via the line. A separation circuit that outputs the line to the reception side and outputs the transmission voice signal transmitted through the voice signal transmission path to the conference partner side; and a reception section that transmits the voice signal reception path. A speaker that generates an audio signal as an audible sound, a microphone that inputs audio for a conference call, converts the audio into the transmission audio signal, and outputs the audio signal to the audio signal transmission path, and the audio signal reception path A first echo canceling circuit connected between the audio signal transmitting path and the audio signal transmitting path, for canceling a loop signal in the separation circuit; and a first echo canceling circuit connected between the audio signal receiving path and the audio signal transmitting path. , The speaker and the micro A second echo canceling circuit for canceling a loop signal caused by acoustic coupling between the first and second echo canceling circuits in the audio signal transmission path between the first echo canceling circuit and the second echo canceling circuit. A first variable loss element provided; an amplification circuit and a second variable loss element provided in the audio signal receiving path between the first echo canceling circuit and the second echo canceling circuit; The loss of the second variable loss element is controlled in response to the volume setting signal for the speaker, and when the volume setting signal exceeds a predetermined value, the first variable And a volume control circuit for increasing the loss of the first variable loss element and increasing the loss of the second variable loss element when the transmission state is in effect. And

(Operation) When the volume setting signal for the speaker exceeds a predetermined value set in advance, the loss of the first variable loss element is increased in the receiving state and the first variable loss element is in the transmitting state. The loss of the loss element is reduced and the second
The loss of the variable loss element is increased, thereby reducing the howling caused by the so-called loop gain due to the sneak in the separation circuit and the sneak due to the acoustic coupling between the loudspeaker and the microphone even when the volume setting for the speaker is increased.

FIG. 1 is a block diagram showing one embodiment of the present invention.
2 are indicated by the same symbols. FIG. 1 differs from the conventional configuration of FIG.
And a variable gain amplifier circuit 10 comprising a fixed gain amplifier circuit 10a and a variable loss element 10b, and a variable transmission amplifier between the second echo canceler circuit 5 and the first echo canceler circuit 3. A loss element 11 is provided.
That is, a volume control circuit 12 for controlling 0 and 11 is provided.

Here, the input signal of the amplification circuit 6,
The TSO, the output signal TS of the amplifier circuit 9, the transmission input signal RSO of the 2-wire 4-wire conversion circuit 2, the reception output signal RS, and the volume control signal VOL are input.

In the above configuration, when the volume setting value indicated by the volume control signal VOL is equal to or less than the predetermined value, there is no possibility that howling occurs. Therefore, the volume control circuit 12 sets only the reception volume from the speaker 7 with the control signal VOL. A loss corresponding to the set volume is inserted into the variable loss element 10b in order to control the volume to the set level.

However, when the volume setting value indicated by the volume control signal VOL is equal to or higher than a predetermined value (for example, 20 dB or higher), howling may occur if the loss amounts of the variable loss elements 11 and 10b in the transmission and reception paths are simply reduced. There is. Therefore, in the present embodiment, when it is determined that the volume setting value indicated by the volume control signal VOL is equal to or greater than a predetermined value, the volume control circuit 12 controls the loss control of the variable loss elements 11 and 10b according to the transmission state and the reception state. To reduce howling. First, when the volume control circuit 12 determines that the volume has been set to a predetermined value or more, it determines whether it is in the transmission state or the reception state based on the transmission signal input TS and the reception input signal RS. When it is determined that the receiving state is set, the volume control circuit 12 performs loss control (gain control) based on the volume control signal VOL to reduce the loss of the variable loss element 10b in the receiving signal path. As a result, the volume of the received voice becomes large according to the set value. At this time, the volume control circuit 12 is controlled to increase the loss of the variable loss element 11 in the transmission signal path so that the howling hardly occurs even when the loss of the variable loss element 10b controlled based on the volume control signal VOL is reduced. I do. In other words, in the receiving state when the volume setting is equal to or higher than the predetermined value, the loss reduction on the receiving side is offset by increasing the loss on the transmitting side, and the loop gain is controlled so that howling does not occur. I have.

Conversely, if it is determined that the telephone is in the transmitting state, the volume control circuit 12
Performs loss control (gain control) based on the volume control signal VOL to reduce the loss of the variable loss element 11 in the transmission signal path. As a result, the volume of the transmission becomes large according to the set value. At this time, the volume control circuit 12 controls to increase the loss of the variable loss element 10b in the reception signal path in order to prevent howling from occurring even when the loss of the variable loss element 11 controlled based on the volume control signal VOL is reduced. . In other words, in the transmitting state when the volume setting is equal to or higher than the predetermined value, the loss reduction on the transmitting side is offset by increasing the loss on the receiving side from a value based on the voice control signal VOL, and howling is reduced. The loop gain is controlled so as not to occur. Variable loss element 10 in transmission state and reception state
The loss control for preventing howling of b and 11 is based on the influence of howling on the wraparound of the received signal due to the spatial coupling between the speaker 7 and the microphone 8 and the wraparound of the transmitted signal due to the sidetone of the 2-wire 4-wire conversion circuit 2. It is set in view of it.

By the way, in the present embodiment, the volume control circuit 12 detects these transition states to smoothly transition from the transmission state to the reception state or vice versa from the reception state to the transmission state, and performs variable loss elements 10b, 11b. Control is performed smoothly to reduce discomfort. The detection of such a transition state is performed by the volume control circuit 12, and the transition from the transmission state to the reception state is performed by the transmission signal input TS.
The transition from the receiving state to the transmitting state is detected based on the receiving input signal RS and the transmitting input signal RSO.

In addition, since the loss inserted in the receiving signal path and the transmitting signal path is only for the prevention of howling when the receiving sound volume is set high, the deterioration of the communication quality is small, and the receiving Sufficient call quality can be ensured even when the volume is increased.

It is needless to say that the echo canceling circuits 3 and 5, the variable loss element 11 and the variable gain amplifying circuit 10 can all be replaced by digital signal processing circuits. In this case, the circuit scale can be further reduced. Further, in the present embodiment, the state detection of the transmission / reception is performed based on the transmission signal input TS and the reception input signal RS, but may be performed based on the output of the echo canceling circuit 3 and the transmission signal input TS. Alternatively, it may be performed based on the input signal TSO and the transmission signal input TS.

[Effects of the Invention] As described above, in the present invention, when the receiving sound volume is set to be large, the minimum loss required for preventing howling is inserted into the receiving signal path and the transmitting signal path, so that the loss is reduced. When a public telephone line with a large volume is used, howling can be avoided even when the reception volume must be set high, and a smooth conference call can be proceeded by voice generated at a sufficient volume from the speaker.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a block diagram showing a configuration of a conventional voice conference apparatus. 1 ... wired line, 2 ... 2-wire 4-wire conversion circuit, 3 ... first
5, a second echo canceling circuit, 7 a speaker, 8 a microphone, 10 a variable gain amplifying circuit, 10a a fixed gain amplifying circuit, 10b and 11 a variable loss element, 12 ... Volume control circuit.

 ──────────────────────────────────────────────────続 き Continued on front page (72) Inventor Hiroshi Oikawa 1-2356 Take, Yokosuka City, Kanagawa Prefecture, Japan Inside Combined Communications Research Laboratories (72) Inventor Takashi Saeki 3-1, Asahigaoka, Hino City, Tokyo 1 Inside the Toshiba Hino Plant (72) Naohisa Kushisu 3-1-1 Asahigaoka, Hino-shi, Tokyo 1 Inside the Toshiba Hino Plant (72) Inventor Shigenobu Minami 70 Yanagimachi, Saiwai-ku, Kawasaki-shi, Kanagawa Prefecture (56) References JP-A-61-66458 (JP, A) JP-A-64-24555 (JP, A) JP-A-63-253759 (JP, A)

Claims (1)

(57) [Claims] An audio signal received from a conference partner through the line is output to an audio signal receiving path, and the transmitted audio signal transmitted through the audio signal transmitting path is connected to the line. A separation circuit that outputs to the line for transmission to the conference partner side; a speaker that generates a reception voice signal transmitted as an audible sound transmitted through the voice signal reception channel; A microphone that converts voice into the transmission voice signal and outputs the voice signal to the voice signal transmission path; connected between the voice signal reception path and the voice signal transmission path; A first echo canceling circuit for canceling, a second echo canceling circuit connected between the audio signal receiving path and the audio signal transmitting path and for eliminating a loop-in signal due to acoustic coupling between the speaker and the microphone; Have A first variable loss element provided in the audio signal transmission path between the first echo canceling circuit and the second echo canceling circuit; and the first echo canceling circuit. An amplifier circuit and a second variable loss element provided in the audio signal receiving path between the second echo canceling circuit and the second echo canceling circuit;
When the volume setting signal exceeds a predetermined value, the loss of the first variable loss element is increased when the apparatus is in the receiving state and the apparatus is in the transmitting state. And a volume control circuit for reducing the loss of the first variable loss element and increasing the loss of the second variable loss element.