JP2635684B2 - Stereo audio transmission system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to a stereo audio transmission system used for a teleconferencing system, for example.

(Prior Art) With the start of the ISDN service, not only voice communication conventionally performed but also data communication or image communication have been realized at low cost via a public network. For example, a teleconferencing system has the potential to spread to medium-sized or small businesses and even ordinary households by interfacing with such ISDN.

FIG. 3 shows a schematic configuration of such a remote conference system. A transmission unit 2 for terminating a transmission line 1 includes an audio unit 3 for encoding and decoding audio data, and an audio unit 3 for encoding and decoding image data. Image unit 43 is connected.

Further, a microphone and a speaker are connected to the audio unit 3 as a man-machine interface,
A television camera, a television monitor, an electronic blackboard, a facsimile and a telewriting device are connected to the image unit 4.

Incidentally, it is desirable that the transmission speed of the transmission line 1 used in such a remote conference system be suppressed to about 64 kbps in consideration of economy.

In this case, in the system described above, it is necessary to secure at least about 48 kbps as the transmission capacity of the image data.
Audio data needs to be compressed to a low transmission capacity of about 16 kbps. For this reason, even if audio data compression technology such as ADPCM is used, it is limited to monaural audio as audio data, and stereo audio is not usually used. That is, when stereo sound is used, the fourth
This is because the configuration is as shown in the figure and the transmission capacity is doubled.

However, in such a communication conference, it is desirable to use stereo sound for a sense of realism and for speaker identification.

For this reason, it is conceivable to set 8 kbps per channel to 26 kbps for two channels on the left and right sides.

It is also conceivable to reduce the transmission capacity of image data from 48 kbps to 32 kbps, but in this case, there is a problem that image quality is significantly deteriorated.

The present inventor has disclosed a technique for solving such a problem as disclosed in
No. 191746 and JP-A-61-82840.

FIG. 5 and FIG. 6 are block diagrams showing the configuration on the communication side and the configuration on the receiving side based on such a technique.

On the transmitting side, as shown in FIG. 5, the signal X input to the left and right microphones 5L and 5R and amplified by the amplifiers 6L and 6R.
A monaural signal X obtained by adding L and XR by the adder 7 is obtained. In addition, each delay time τL, τR until a direct wave of the voice X ((W)) of a single sounder is input to the left and right microphones 5L, 5R.
Τ = τR−τL is detected by the correlator 8. And the multiplexer 9
Thus, additional information, which is the difference τ in delay time, is added to the main information, which is a monaural signal X, and these are transmitted to the transmission line 10.

On the other hand, on the receiving side, as shown in FIG. 6, the signal transmitted from the transmission line 10 is separated by the demultiplexer 11 into main information and additional information. The monaural signal X which is the main information is output from the left speaker 15L via the variable delay unit 12L, the variable attenuator 13L, and the amplifier 14L, and the variable delay unit 12R,
Output from the right speaker 15R via the variable attenuator 13R and the amplifier 14R. The delay time difference τ, which is additional information, is RO
Input to the M table 16. The ROM table 16 stores predetermined information corresponding to τ, which is stored in the variable delay unit 12.
By giving different delays to L and 12R and giving different attenuation ratios to the variable attenuators 13L and 13R, a sense of stereo is generated for the listener.

That is, according to this technology, the additional information is 50 to 100 bps.
Therefore, stereo transmission can be performed in a pseudo manner with a transmission capacity equivalent to a monaural.

By the way, the conference by the above-described system is based on the premise of the opposite communication, and when an attempt is made to realize a similar conference among three or more sets of remote conference systems, on the receiving side,
Although each speaker on each transmitting side can be identified by a sense of presence, there is a problem that speakers on different transmitting sides cannot be identified with a sense of stereo.

(Problems to be Solved by the Invention) As described above, in a case where a conference is to be realized among three or more sets of remote conference systems by the pseudo stereo transmission method described above, the receiving side talks about different transmitting sides. There is a problem that it is not possible to distinguish between persons due to a sense of reality.

SUMMARY OF THE INVENTION It is an object of the present invention to make it possible for a receiving side to distinguish between speakers on different transmitting sides with a sense of reality.

[Constitution of the Invention] (Means for Solving the Problems) The present invention relates to a stereo sound transmission system in which a plurality of terminals each of which can be a transmitting side and a receiving side are connected to a transmission path, Microphone, an amplifier that amplifies the audio signal input to each microphone, an adder that adds the audio signal amplified by each amplifier to generate a monaural signal, and a direct wave of the voice of a single speaker. A correlator that detects each delay time before being input to each of the microphones, and a multiplexer that adds, as additional information, a difference between the delay times detected by the correlator to a monaural signal added and generated by the adder. The receiving side separates the signal transmitted to the transmission line for each terminal on the transmitting side, and further separates these signals into monaural signals and their attachments. A demultiplexer that separates the information into information, an audio bridge that generates a predetermined monaural signal and additional information based on the information from the demultiplexer, and a delay and an attenuation of the predetermined monaural signal based on the additional information. And a speaker connected to each variable delay / attenuator.

(Operation) According to the present invention, it corresponds to the received main audio signal, and
Based on these additional information signals reduced / increased / decreased corresponding to the received main audio signal, an audio signal similar to one or more audio signals of a plurality of channels is synthesized. Speakers can be distinguished by a sense of reality.

(Example) Hereinafter, one example of the present invention will be described.

FIG. 1 is a diagram showing a configuration of a communication system according to this embodiment, which is applied, for example, when three sets of a conventional remote conference system shown in FIG. 3 are connected.

In the figure, reference numerals 17, 18, and 19 denote audio terminals. Note that, here, only the transmission unit is used for the audio terminals 17 and 18,
Although only the receiving unit is shown for the audio terminal 19, each of the audio terminals 17, 18, and 19 actually has a transmitting unit and a receiving unit.

The transmitter of each audio terminal has two sets of microphones, left and right.
L, 20R, amplifiers 21L, 21R which are input to the microphones 20L, 20R and amplify the audio signal, these amplified signals XL,
An adder 22 for adding XR is provided. Further, a correlator 23 for detecting a difference τ = τR−τL between respective delay times τL and τR until a direct wave of the voice X ((W)) of a single sounder is input to the left and right microphones 20L and 20R, A multiplexer 25 is provided for adding additional information as a difference τ in delay time to main information as a monaural signal X added by the device 22.

On the other hand, the receiving unit separates the signal transmitted from the transmission line 26 for each transmitting terminal, and further separates them into main information and additional information, and a predetermined multiplexer based on information from the demultiplexer 27. Monaural signal X
An audio bridge 28 for generating predetermined additional information τc; variable delay / attenuators 29L and 29R for providing a predetermined delay and a predetermined attenuation to the monaural signal X;
L, 30R are provided. Further, there is provided a ROM table 31 which stores predetermined information according to τc and gives different delay / attenuation ratios to the variable delay / attenuators 29L, 29R.

The audio bridge 28 described above is a demultiplexer
An adder 32 which adds the main information for each transmitting terminal transmitted from 27 and makes this a monaural signal X 32, and a power detector which detects the presence or absence of each of the monaural signals XA and XB which is the main information for each transmitting terminal
33A and 33B, multipliers 34A and 34B for multiplying each additional information τA and τB for each transmitting terminal by a coefficient “0.5”, and adders 35A and 34B for adding “−d” to the multiplied value by the multiplier 34A An adder 35B for adding "d" to the multiplied value is provided. However, the added value d is given by an expression of d = τMAX / 2 by the positive maximum value τMAX of the additional information. Further, the audio bridge 28 outputs, as the additional information τc, a signal from the adder 34A, a signal from the adder 34B or a switch 36 for switching to “0”, and detection results VA and VB by the power detectors 33A and 33B. And a control circuit 37 for controlling switching of the switch 36 based on the control signal.

Next, the operation of the communication system configured as described above will be described.

 FIG. 2 is a diagram for explaining this operation.

As shown in the figure, the microphones 20L and 2L of the voice terminal 17
Before 0R, the speakers “A”, “B”, “C”, and “D” are arranged in order from the left, and before the microphones 20L and 20R of the voice terminal 18, the speaker “E” , “F”, “G”, and “H” are arranged in order from the left.

Then, assuming that the speech is performed on the voice terminal 17 side but not on the voice terminal 18 side, only the monaural signal XA of the voice terminal 17 is transmitted to the voice terminal 19 and the voice terminal 18 is output.
Does not transmit the monaural signal XB.

In the audio terminal 19, this is detected by the power detectors 33A and 33B, and the detection results VA and VB are sent to the control circuit 37.

When recognizing that the utterance is being performed only on the voice terminal 17 side, the control circuit 37 switches the switch 36 to output the signal from the adder 35A as the additional information τc (B in the figure).
side).

Therefore, the additional information τc is obtained by adding the additional information τA to the multiplier 34.
A, the value via the adder 35A, that is, τc = τA / 2−d.

The additional information τc is provided to the ROM table 31, and different delay / attenuation ratios are provided to the variable delay / attenuators 29L and 29R.

The monaural signal XA is applied to each of these variable delay / attenuators 29.
The signal is output from speakers 30L and 30R through L and 29R.

As a result, the listeners located in front of the speakers 30L and 30R of the audio terminal 19 can hear the speakers “A”,
It recognizes that there are sound images of “B”, “C”, and “D”.

On the other hand, if it is assumed that the voice terminal 17 is not uttering and the voice terminal 18 is uttering, only the monaural signal XB of the voice terminal 18 is transmitted to the voice terminal 19, and the monaural signal is transmitted from the voice terminal 17. XA is not sent.

By the same operation as described above, in this case, the switch 36 is switched to the B side in the figure.

Therefore, the additional information τc is obtained by adding the additional information τB to the multiplier 34.
B, the value via the adder 35B, that is, τc = τB / 2 + d.

The monaural signal XB passes through each of the variable delay / attenuators 29L and 29R set by such additional information τc, and the speaker 30
Output from L, 30R.

As a result, the listeners located in front of the speakers 30L and 30R of the audio terminal 19 can hear the speakers “E”,
It recognizes that there are sound images of “F”, “G”, and “H”.

In this embodiment, when the voice is being output from both the voice terminals 17 and 18, the switch 36 is switched to the C side in the figure, and the monaural signals XA and XB are output from the speakers 30L and 30R.

As described above, in this embodiment, on the receiving side, a sound image is formed in the left half range for one audio terminal, and a sound image is formed in the right half range for the other audio terminal. Therefore, it is possible to distinguish between speakers on different transmission sides by a sense of realism.

Note that, in this embodiment, the case where the number of voice terminals is three, that is, three grounds, has been described. In this case, if the ground number is m, the delay-limited additional information τ′i for the i-th additional information τi is τ′i = τi / m, and the bias value di is di = −τMAX + τMAX / m + 2τMAX (i -1) / m.

Then, the terminal i having voiced data is referred to as the i-th main information.
xi, and based on the additional information from the terminal, new additional information is generated by the formula of τC = τi '+ di and transmitted to the receiving side.

In this embodiment, the audio bridge circuit (within the dashed line in FIG. 1) is provided on the receiving side. However, the audio bridge circuit is provided separately between transmission and reception. , Additional information may be generated and transmitted to the receiving side.

[Effects of the Invention] As described above, according to the present invention, it is possible to distinguish between speakers on different transmitting sides on the receiving side by sound image localization, and to have a realistic conversation.

[Brief description of the drawings]

1 is a diagram showing a configuration of a communication system according to an embodiment of the present invention, FIG. 2 is a diagram for explaining the operation of the system of the embodiment, FIG. 3 is a diagram showing a configuration of a remote conference system, FIG. 4 is a diagram showing an example in which stereo audio is adopted in the remote conference system, FIG. 5 is a diagram showing a configuration of a transmitting side used for pseudo stereo transmission, and FIG. 6 is a diagram showing a receiving side. 17, 18, 19 ... voice terminal, 20L, 20R ... microphone
21L, 21R: amplifier, 22: adder, 23: correlator, 25
... Mux, 26 ... Transmission path, 27 ... Demultiplexer, 28 ... Audio bridge, 29L, 29R ... Variable delay / attenuator, 30L, 30R ... Speaker, 31 ... ROM table, 32 ... Addition Detector, 33A, 33B ... Power detector, 34A, 3
4B Multiplier, 35A, 35B Adder, 36 Switch
37 Control circuit.

Claims (1)

(57) [Claims] 1. A stereo sound transmission system in which a plurality of terminals, each of which can be a transmission side and a reception side, are connected to a transmission path, wherein the transmission side transmits a plurality of microphones and an audio signal input to each microphone. An amplifier for amplifying each, an adder for adding a voice signal amplified by each amplifier to generate a monaural signal, and a delay time until a direct wave of a single sounder's voice is input to each of the microphones. A correlator for detecting, and a multiplexer for adding, as additional information, a difference between the delay times detected by the correlator to the monaural signal added and generated by the adder, wherein the receiving side is transmitted to the transmission path. And a demultiplexer that separates these signals into monaural signals and their additional information, while separating the signals into transmission-side terminals. An audio bridge that generates a predetermined monaural signal and its additional information based on information from the demultiplexer; and a plurality of variable delay / attenuators that provide respective delays and attenuations to the predetermined monaural signal based on the additional information. And a speaker connected to each variable delay / attenuator.