JPH02206272A - Stereo audio conference equipment - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Summary] Regarding a stereo type audio conference device, the purpose of the present invention is to provide a stereo type audio conference device that has a small circuit scale and can improve the quality of reproduced audio. is passed through a first echo canceller and encoded with a first adaptive differential encoder that converts it into a 4-bit code with a sampling frequency of 8 KHz, and the audio signal from the second microphone is passed through a second echo canceller and encoded with an adaptive differential encoder. , the sampling frequency is 8KHz and 4
The second 32-bit code is encoded by an adaptive differential encoder, and the two encoded signals are multiplexed into a signal with a transmission rate of 64 Kbps by a multiplexer and transmitted. , a signal obtained by multiplexing the two sent signals is divided into two first . separating the first signal into a second signal; the first signal is input to a first adaptive differential decoder 32 and decoded to produce an audio signal; the first signal is input to and output from a first speaker;
The second signal is input to the second adaptive differential decoder 32 and decoded to produce an audio signal, which is input to and output from the second speaker. The output of the adaptive differential decoder is added to the second 32 in an adder, and the output of the adaptive differential decoder is added to the first 32. The configuration is such that the signal is input to a second echo canceller to cancel the echo.

[Industrial application field]

The present invention relates to a stereo audio conference device for an audio teleconferencing system that uses a transmission line with a transmission rate of 64 Kbps.

In order to provide a sense of realism as an audio remote conference system,
In recent years, devices that allow audio to be heard in stereo have come into use.

In this case, it is desirable that the voices from the left and right speakers be of good quality.

[Conventional technology]

FIG. 3 is a block diagram of a conventional stereo audio teleconferencing system.

In Figure 3, a transmission line 20.21 with a transmission speed of 64 Kbps is shown.
A stereo audio conference device and a telephone device with the same configuration are connected to both sides of the device via switches 18.18'' and 19.19'. conduct.

At this time, the voice from the telephone [17] is encoded by a PCM encoder 15 that converts it into an 8-bit code with a sampling frequency of 8 KHz, and is then encoded by a switch 18, a transmission line 20 . It is transmitted via switch 18'', decoded into a voice signal by PCM decoder 16°, and received by telephone 17°.

Also, the sampling frequency for audio from a 17” telephone is 8.
The code is encoded by a PCM encoder 15 that converts it into an 8-bit code at KHz, and then passed through a switch 19 and a transmission line 20 . The signal is transmitted via the switch 19, decoded into an audio signal by the PCM decoder 16, and received by the telephone 17.

When holding a meeting or holding an audio conference using this operation, switches 18.18" and 19.19' are switched to the dotted line side.

In this system, microphones 1, 2.1', 2' are placed on the left and right, and speakers 10, 12, 10', 12' are also installed on the left and right in order to conduct a stereo-type audio teleconference.

Next, we will explain the operation of the stereo audio teleconferencing system shown in Figure 3. Even when the left stereo audio conference device is the transmitting side and the right stereo audio conference device is the receiving side, the right stereo audio conference system The operation is the same even if the stereo audio conference device on the left is used as the transmitter and the stereo audio conference device on the left is used as the receiver.
The following explanation assumes that the stereo audio conference device on the right is the receiving side.

The voice received by the microphone 1 (left side) is converted into an electrical signal, converted into a digital signal by an analog-to-digital converter (hereinafter referred to as A/D) 24, and then sent to a 48Kbps encoder 30 via an echo canceller 22. The signal is sent to the subtractor 37 , and is converted into a 6-bit code at a sampling frequency of 8 KHz by the 48 Kbps encoder 30 and input to the multiplexer 34 .

On the other hand, the sound received by the microphone 4 (right side) is converted into an electrical signal, converted into a digital signal by the A/D 26, sent to the subtracter 37 via the echo canceller 23, and combined with the digital signal from the microphone 1 side. The difference is taken and inputted to the 16 Kbps encoder 32, converted to a 2-bit code with a sampling frequency of 8KH2, and inputted to the multiplexer 34.

The multiplexer 34 multiplexes the two input signals and sends them to the switch 18. Transmission line 20. It is sent to the separation section 34' via the switch 18'.

The separation unit 34'' separates the two input multiplexed signals, and the signal encoded by one 48Kbps encoder 30 is sent to the 48Kbps decoder 33'', and the other 16K signal is encoded by the 48Kbps encoder 30.
The signal encoded by the bps encoder 32 is 16Kbp
s decoder 31'.

The signal is sent to a 48Kbps decoder 33" and is decoded,
It is sent to a subtracter 36' and a digital-to-analog converter (hereinafter referred to as D/A) 27', where it is converted into an analog audio signal and sent to speaker 12° (right side), and the audio from microphone 1 is Output.

The signal sent to the 16 Kbps decoder 31' and decoded is input to the subtracter 36', and is input to the 48 Kbps decoder 33'.
The difference with the signal decoded by the D/A 25' is output.
It is converted into an analog audio signal and sent to the speaker 10'.
(left side), and the audio from the microphone 4 is output.

The digital audio signals sent to D/A 25° and 27° are added by an adder 38°, and then sent to the echo canceller 22',
23' (equivalent to echo canceller 22.23), and with this input signal, the speakers 10'' and 12
From ゛, go around microphone 1゛4'', A/D24'
, 26' cancel out the digitized signals to prevent howling.

(Problem to be solved by the invention) However, in the conventional device, the transmission rate is 64Kb.
ps, the left and right encoders/decoders are each different 4
8Kbps, must be 16Kbps, 16K
Problems with significant deterioration of audio quality on the bps side and 16
Since the Kbps side uses a difference signal, a circuit for calculating the difference is required, which poses a problem of increasing the circuit scale.

SUMMARY OF THE INVENTION The present invention aims to provide a stereo type audio conferencing device that has a small circuit scale and can improve the quality of reproduced audio.

[Means to solve the problem]

FIG. 1 is a block diagram of the principle of the present invention.

As shown in FIG. 1, a first microphone 1 converts an audio signal from a first microphone 1 into a 4-bit code at a sampling frequency of 8 KHz through a first echo canceller 2.
2 is encoded by an adaptive differential encoder 3, and the audio signal from the second microphone 4 is passed through a second echo canceller 5 at a sampling frequency of 8 KHz.
The second 32 signals are converted into a 4-bit code by an adaptive differential encoder 6, and the two encoded signals are multiplexed into a signal with a transmission rate of 64 Kbps by a multiplexer 7 and transmitted. .

On the receiving side, the two sent multiplexed signals are
In the separating section 8, two first. The first signal is separated into a second signal.
The signal input to the first 32 is input to the adaptive differential decoder 9 and decoded into an audio signal, which is input to the first speaker 10 and outputted. Vessel 1
1, the input is decoded into an audio signal, and the second speaker 12
input and output it, and also the first one. The adder 13 adds the outputs of the adaptive differential decoders 3 and 11 to the second 32, The signal is input to the second echo canceller 2.5 to cancel the echo.

[For production]

According to the invention, two microphones (left.

Right) The audio signal from 1.4 is sent to adaptive differential encoder 3 at 32.
．． At step 6, the signal is converted into a 4-bit code with a sampling frequency of 8 KHz, and is multiplexed at a multiplexer 7 to become a signal with a transmission rate of 64 Kbps and transmitted.

On the receiving side, a separation unit 8 separates the two input multiplexed signals into two, and an adaptive differential decoder 9,
11, which decodes the input and outputs it as an audio signal, and outputs it to speakers 10,1.
Audio is output from 2 (left, right).

At this time, the audio signal to the speaker 10.12 is sent to the adder 13.
and input to echo canceller 2.5.

In Echo Canceller 2.5, with this human-powered signal,
The signal input from the speakers 10 and 12 to the microphone 1 or 4 is canceled to prevent howling.

That is, in the case of the present invention, microphone 1. Instead of transmitting the difference between the audio signals from 4 to 4, the band of each audio signal is compressed, transmitted through a transmission line with a transmission speed of 64 Kbps, and reproduced on the receiving side. The audio quality is better than that which sends the difference, and since no difference signal is used, there is no need for a circuit for determining the difference, and the circuit size is reduced.

〔Example〕

FIG. 2 is a block diagram of a stereo audio teleconference system according to an embodiment of the present invention.

A meeting was held using a telephone device, and switches 1B, 1
9. Switching between 18° and 19' to conduct an audio conference is the same as that explained in the conventional example, so the explanation will be omitted.

Also, the microphones 1, 4, lo, 4' are placed on the left and right, and the speakers 10, 12, 10'', 12' are also placed on the left and right, as in the conventional example.

Next, we will explain the operation of the stereo audio teleconferencing system shown in Figure 2. Even when the left stereo audio conference device is the transmitting side and the right stereo audio conference device is the receiving side, the right stereo audio conference system The operation is the same even if the stereo audio conference device on the left is used as the transmitter and the stereo audio conference device on the left is used as the receiver.
The following explanation assumes that the stereo audio conference device on the right is the receiving side.

The audio received by microphone 1 (left side) is converted into an electrical signal, and then converted into a digital signal by A/D 24.
Adaptive differential encoder 3 at 32 via echo canceller 4
It is converted into a 4-bit code at a sampling frequency of 8 KHz and input to the multiplexer 7.

On the other hand, the audio received by the microphone 4 (on the right side) is converted into an electrical signal, converted into a digital signal by the A/D 26, and sent to the adaptive differential encoder 6 via the echo canceller 5 at 32, where the sampling frequency is adjusted. The signal is converted into a 4-bit code at 8 KHz and input to the multiplexer 7.

In the multiplexing unit 7, the two input signals of 4 bits with a sampling frequency of 8 KHz are multiplexed, and a transmission rate of 64 Kb with a sampling frequency of 8 KHz and 8 bits is multiplexed.
ps signal, switch 18. Transmission line 20. It is sent to the separation section 8' via the switch 18'.

The separation unit 8° separates the 8-bit signal with a sampling frequency of 8KH2 into 4 bits each, inputs it to the adaptive differential decoders 9'' and 11'' at 32, decodes it, and outputs the audio from the microphones 1 and 4, respectively. It is reproduced into a signal, inputted to the adder 13°, added, inputted to the echo canceller 2'5' (equivalent to echo canceller 2.5), and sent to the D/A 27.
'25 is converted to an analog signal, and each speaker I
O'', 12' is output.

In the echo cancellers 2'' and 5'', this input signal is routed from the speakers 10' and 12° to the microphone 1'' or 4'' and sent to the A/D 26'.

At 24', the signal is converted into a digital signal and the input signal is canceled to prevent howling.

That is, in the case of the present invention, instead of transmitting the difference between the audio signals from microphone 1.4, the band of each audio signal is compressed and transmitted through a transmission line with a transmission speed of 64 Kbps, and the receiving side Since the conventional one transmits the difference, the audio quality is better than the conventional one, and since the difference signal is not used, there is no need for a difference circuit, and the circuit size can be reduced.

It is of course possible to connect the transmission line side of the switches 18 and 19 to the 15DN via an 15DN adapter.

〔Effect of the invention〕

As explained in detail above (according to the present invention, the transmission speed is 6.
This has the advantage that a stereo audio conference device used in a stereo audio remote conference system using a 4Kbps transmission path can have a small circuit scale and provide high quality reproduced audio.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the principle of the present invention, FIG. 2 is a block diagram of a stereo audio teleconferencing system according to an embodiment of the invention, and FIG. 3 is a block diagram of a conventional stereo audio teleconferencing system. In the figure, 1.4.1' and 4' are microphones, and 2.5.2'
, 5", 22.23.22', 23" are echo cancellers, 3.6.3', 6° are adaptive differential encoders at 32, 7.7'
, 34.34' is the multiplexing section, 8.8", 35.35
' is the separation unit, 9.11, 9°, 11° is the adaptive differential decoder at 32, 10
．． 12.10", 12゛ is the speaker, 13.13'
15.15" is an adder, 15.15" is a PCM encoder, 16.16' is a PCM decoder, 17.17" is a telephone, 18.19.18', 19° is a switch, 20.21 is a transmission line, 24. 26, 24°, 26° are analog-to-digital converters,

Claims (1)

[Claims] The audio signal from the first microphone (1) is passed through the first echo canceller (2) so that the sampling frequency is 8.
The audio signal is encoded by a first 32K adaptive differential encoder (3) that converts it into a 4-bit code at KHz, and the audio signal from the second microphone (4) is passed through a second echo canceller (5) to adjust the sampling frequency. is encoded by a second 32K adaptive differential encoder (6) that converts it into a 4-bit code at 8KHz, and the two encoded signals are converted into a signal with a transmission rate of 64Kbps by a multiplexer (7). The multiplexed signals are multiplexed and transmitted, and on the receiving side, the two multiplexed signals sent are separated into two first and second signals in a separating section (8), and the first signal is the first signal. The input signal is input to the 32K adaptive differential decoder (9) and decoded into an audio signal, which is input to and output from the first speaker (10), and the second signal is input to the second 32K adaptive differential decoder (11). The input is decoded into an audio signal, which is input to the second speaker (12) and output, and the outputs of the first and second 32K adaptive differential decoders (3, 11) are sent to the adder (13). 1. A stereo audio conference device characterized in that the sum is added and inputted to the first and second echo cancellers (2, 5) to cancel echoes.