JPH0758939B2 - Stereo signal transmission method, encoding device and decoding device - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a stereo audio transmission system.

[Technical Background of the Invention and Problems Thereof] In recent years, with the progress of communication technology, a remote conference system capable of conducting a conference even from a remote place has begun to spread.

The conventional remote conference system is mainly a video conference system using a broadband leased line, but if the ISDN network (digital integrated service network) being examined by CCITT etc. is established, it will be based on 64kbps as a public network. The narrow-band digital network will be widely spread, and in the future, it is expected that the remote conference system using the narrow-band network will hold the key to the spread to SMEs and homes.

In a teleconferencing system using such a low transmission rate, for example, a transmission path of 64 kbps, it is necessary to compress a large amount of image and audio information within a range that does not hinder the operation of the conference.

FIG. 3 is a configuration example of a conventional remote conference system, which includes a microphone 1 and a speaker 2 which are man-machine interfaces for voice, a TV camera 3, a TV monitor 4, an electronic blackboard 5 and a fax which are man-machine interfaces for images. 6. Telewriting device 7 and audio data 16kbps
An audio unit 8 for encoding and decoding, a control unit 9 for controlling an image unit described later, and a control unit 9
Control pad 10 for inputting an instruction to, an image unit 11 for encoding and decoding the image signal designated by the control unit 9 into 48 kbps, and transmission of these audio and image signals via a transmission path 12 of 64 kbps and Transmission unit 13 for reception
It is composed of

In teleconferencing systems that use such low-rate channels, even monaural audio, for example ADPCM
It is necessary to compress to a low transmission capacity such as 16 kbps by audio data compression processing such as, and therefore stereo audio is not usually used.

On the other hand, it is well known that in a teleconferencing system, it is desirable to use stereo voice for the purpose of giving a sense of presence and for identifying the speaker who knows who is speaking on the other side.

Now, when trying to introduce stereo audio having such an advantage into a teleconference system using a transmission line of low transmission speed as described above, according to the conventional stereo audio transmission system, as shown in FIG. A stereo audio transmission system is required. In this stereo audio transmission system, the audio information has two channels on the left and right, which requires twice the transmission capacity as in monaural. Therefore, the low transmission rate by the conventional method,
For example, as a method of introducing stereo audio into a teleconferencing system that uses a transmission path of 64 kbps, (a) a method of compressing the transmission information amount of one channel of audio to 8 kbps, It is possible to reduce

However, (a) has a problem that the voice quality is deteriorated, and (b) has a problem that the image quality is deteriorated or the service is deteriorated.

As described above, in the conventional stereo audio transmission system, it is very difficult to introduce stereo audio into the remote conference system using the low transmission speed transmission path.

[Object of the Invention] The present invention has been made based on the above circumstances, and is a stereo audio transmission system that can be used even in a transmission line of a low transmission rate, and that enables high-quality stereo audio transmission at low cost. Is provided.

[Summary of the Invention] The present invention provides a stereo signal transmission method for transmitting signals of a plurality of channels, wherein a transmitting side encodes a signal of at least one channel among the signals of the plurality of channels and transmits the main information as main information. A transfer function between signals of at least two channels of the signals of the plurality of channels is estimated, and one of the signals used for the estimation is input to the estimated transfer function to generate a pseudo stereo signal. The other side of the signals used for the estimation is subtracted from the pseudo stereo signal to generate a residual stereo signal, and the residual stereo signal is encoded and transmitted as additional information. Means for decoding the main information, decoding the received additional information, and the decoded residual stereo signal and the decoded Means for generating a transfer function by synthesizing the signal with the signal, and inputting the decoded signal to the transfer function to generate a pseudo stereo signal.

A second aspect of the present invention is, in the encoding device used in the stereo signal transmission method, means for encoding a signal of at least one channel of the signals of the plurality of channels, and at least one of the signals of the plurality of channels. Two
Means for estimating the transfer function between the signals of one channel,
Means for inputting one of the signals used for the estimation to the estimated transfer function to generate a pseudo stereo signal, and subtracting the other signal of the signals used for the estimation from the pseudo stereo signal and leaving the result. It is characterized by comprising means for generating a difference stereo signal and means for encoding this residual stereo signal.

Further, a third invention is, in the decoding device used for the above-mentioned stereo signal transmission method, a means for decoding at least one encoded signal, and a signal of at least two channels among the signals of the plurality of channels. Of the signals used for the estimation by inputting one of the signals used for the estimation to the estimated transfer function, and the other of the signals used for the estimation from the pseudo stereo signal. Means for decoding the coded residual stereo signal generated by subtracting the signal of, and means for synthesizing the decoded residual stereo signal and the decoded signal to generate a transfer function, Means for inputting the decoded signal to the transfer function to generate a pseudo stereo signal.

Embodiments of the Invention Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic configuration diagram of a teleconferencing stereo audio transmission system that implements the transmission system of an embodiment of the present invention. Note that, in the following description, the transmission method is shown only in one direction for the sake of simplicity. In a normal conference, it is considered that it is rare for multiple speakers (A _{1 to} A ₄ , B _{1 to} B _{4 in} Fig. ₄ ) in _one conference room to speak at the same time. Even if a plurality of speakers speak at the same time, it is considered that the necessity of transmitting these voices in stereo is lower than that in the case where one speaker speaks. For this reason, in the following embodiments, only the case where the single speech that occupies most of the conference is transmitted in stereo is described.

In this stereo audio transmission system, the transmitter has left and right channel microphones 1 _L and 1 _R , a delay circuit 20 for delaying the left channel microphone input audio signal, and a right channel audio signal x.
An estimation circuit 21 for estimating an estimated left channel audio signal (k) in the time domain from (k), a subtractor 22 for subtracting the estimated left channel audio signal (k) from the left channel audio signal y (k), It is composed of an encoding circuit 23 that outputs the positive / negative sign of the residual signal which is the output of this subtractor, and the receiving side estimates left channel audio from left channel audio signals x (k) and right and left channel speakers 2r and 2l signal Is composed of a synthesizing circuit 24 for synthesizing the above. Note that x
(K), y (k) The values at the time of k samples of the respective audio signals of the left and right channels are shown.

In the figure, the voice X (ω) uttered by the speaker A ₁ is the microphone 1
This microphone input signal Y _R (ω), Y
_L (ω) is expressed as follows by the transfer functions F _R (ω) and G _L (ω) that are determined by the propagation delay and the voice characteristics in the room. However, ω is each frequency Y _R (ω) = F _R (ω) X (ω) (1) Y _L (ω) = G _L (ω) X (ω) (2) Furthermore, The left microphone input signal Y _L (ω) undergoes a flat delay of D (ω) in the delay circuit 20 for ensuring the causality in the estimation circuit 21, and the transfer function including the delay circuit 20 is included.
It is expressed by F _L (ω) as follows.

Y _L (ω) = D (ω) G _L (ω) X (ω) = F _L (ω) X (ω) (3) This left channel audio signal Y _L (ω) is sent to the subtractor 22. Is entered.

The estimation circuit 21 also determines that the left and right channel audio signals Y _R
(Ω), Y _L (ω) using the right channel audio signal Y
_R (omega) from obtaining a left channel audio signal Y _L (omega) the transfer function _{G (ω) = F L (} ω) / F R (ω) estimated in ...... (4) to estimate the transfer function G (omega) Generate a transfer function G (ω).

This estimation circuit sequentially updates the adaptive traversal filter 21a for calculating the estimated left channel audio signal (k) in the time domain shown in FIG. 2 (A) and the estimated impulse response (k) of the transfer function G (ω). The adaptive transversal filter 21
a and the correction circuit 21b operate in synchronization with the clock.

The adaptive transversal filter 21a also includes an N-tap shift register 27 and an estimated impulse response (k).
And a multiplier 28 for multiplying each component of the right channel audio signal (k), and an adder 29 for obtaining the sum of the results.

In the estimation circuit 21, first, the right channel audio signal x
(K) is input to the shift register 27 having a delay of one sample per stage, and the time series vector X (k) = (x (k), x (k-1) ... ......, x (k-N + 1) ) ^T (5) ( ^T represents a transposed vector) is generated.

On the other hand, the estimated impulse response obtained by approximating the estimated transfer function (ω) in the time domain is (k) = (h ₁ (k), h ₂ (k), h ₃ (k) ………, h _N (k)) ^T (6), the left channel audio signal y is calculated by the following equation.
An estimate (k) of (k) can be obtained.

(K) = H (k) ^T X (k) (7) At this time, the impulse response sequence H of the transfer function G (ω) is H = (h ₁ , h ₂ , ... ......, h _N ) ^T ...... (8) If the transfer function is estimated well and (k) ≈ H (9), the left channel audio signal estimation unit (k) can be displayed.
Is a good approximation of the actual left channel audio signal y (k).

The estimation of the estimated impulse response (k) in the estimation circuit 21 is performed by sequentially performing the following calculation in the correction circuit 21b.

(K + 1) = (k) + αsign (e (k)) X (k) (10) (where (0) = O) This algorithm is a known sign algorithm. In the expression (10), sign (e (k)) is the sign of the output e (k) = y (k) − (k) (11) of the subtractor 22 in FIG. 1, and α is ( It is a coefficient that determines the convergence speed and stability of equation (10).

After the above operation, as the data on the left channel side, only the 1-bit residual code sign (e (k)) is transmitted.

On the other hand, the receiving side has a synthesizing circuit 22 having the same configuration as that of the estimating circuit 21, and this synthesizing circuit 22 sequentially transmits from the transmitted right channel audio signal x (k) and the residual code sign (e (k)). Side left channel audio signal estimation results tracked,
Left channel audio signal estimated from the following formula (In the frequency domain display To get

(However, Is the estimated tap coefficient sequence in the synthesis circuit, Here, the expressions (12) and (13) on the receiving side are the expressions (7) on the transmitting side,
Since it is the same as (10), it is an estimated value of transmission and reception of the left channel audio signal. Is Becomes Therefore, when the impulse response (k) is estimated in the estimation circuit and (k) = H ... (15), Becomes

When the speaker changes, (k) ≠ H, so it is temporarily Although the sound image is disturbed, the estimation circuit 21 always operates (k) .apprxeq.H immediately, so that the sound image is restored to a stereo transmission.

The delay circuit 20 prevents the adaptive transversal filter 21a of the estimation circuit 21 from synthesizing only the delayed component of the left channel audio signal. When the speaker is at the center of the left and right microphones, h _N / ₂ ( A delay of N / 2 samples is added so that the main tap is located in k).

The estimation circuit 21 and the synthesis circuit 22 of this stereo audio transmission system use an adaptive transversal filter in the time domain, but can be realized by an adaptive filter in the frequency domain.

Although the stereo audio transmission system described above performs stereo audio transmission of two channels, the present invention is not limited to this, and stereo audio transmission of three or more channels can be performed.

[Effects of the Invention] As described above, according to the present invention, only the main audio signal and the residual code are transmitted in stereo transmission. Therefore, it is possible to increase the information of several bits as compared with monaural audio transmission. Stereo transmission becomes possible, and high-quality stereo audio can be transmitted at low cost even on a low-speed transmission path.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic configuration diagram of a stereo voice transmission system for implementing an embodiment of the present invention, FIG. 2 is a configuration block diagram of an estimation circuit of the system, and FIG. 3 is a conventional remote control system. FIG. 4 is a schematic configuration diagram of a conference system, and FIG. 4 is a configuration diagram of a conventional stereo audio transmission system. 21 ... Estimation circuit 22 ... Subtractor 23 ... Encoder 24 ... Synthesis circuit

Claims (3)

[Claims] 1. A stereo signal transmission method for transmitting a signal of a plurality of channels, wherein a transmitting side encodes a signal of at least one channel among the signals of the plurality of channels and transmits it as main information; A transfer function between signals of at least two channels of the signals is estimated, and one of the signals used for the estimation is input to the estimated transfer function to generate a pseudo stereo signal. The other side of the signals used for the estimation is subtracted to generate a residual stereo signal, and means for encoding the residual stereo signal and transmitting it as additional information is provided. A means for decoding, decoding the received additional information, and decoding the decoded residual stereo signal and the decoded signal. Form to generate a transfer function, the stereo signal transmission method characterized by comprising a means for generating a pseudo-stereo signal to input the decoded signal to the transfer function. 2. An encoding device used in a stereo signal transmitting method according to claim 1, wherein the encoding device encodes at least one channel signal among a plurality of channel signals. A means for estimating a transfer function between signals of at least two channels of the signals, and a means for inputting one of the signals used for the estimation to the estimated transfer function to generate a pseudo stereo signal, An encoding device comprising: means for subtracting the other signal of the signals used for the estimation from the pseudo stereo signal to generate a residual stereo signal; and means for encoding the residual stereo signal. . 3. A decoding device used in the stereo signal transmission method according to claim 1, wherein at least one means for decoding the encoded signal and at least two of the signals of a plurality of channels are used. A transfer function between signals of one channel is estimated, one of the signals used for the estimation is input to the estimated transfer function to generate a pseudo stereo signal, and the pseudo stereo signal is used for the estimation. Means for decoding the coded residual stereo signal generated by subtracting the other signal from the signals, and combining the decoded residual stereo signal and the decoded signal to generate a transfer function A decoding device, comprising: means and means for inputting the decoded signal to the transfer function to generate a pseudo stereo signal.