JP2897483B2 - Audio coding device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a speech coding apparatus for setting up a plurality of telephone lines using a communication path having a single fixed transmission rate.

[0002]

2. Description of the Related Art In order to efficiently encode and transmit a voice telephone signal for a plurality of channels by a voice encoder, the following two methods have conventionally been adopted.

(A) Reduce the output speed of a single-channel speech coder.

[0004] (b) Only when the voice is busy, that is, when the voice is active, a communication channel is allocated.

[0005] In the former method, for example, a communication path having a transmission speed of 64 Kbps (kilobits / second) has a transmission speed of 8 Kbps.
In this case, eight channels are intended to be secured by using a speech encoder having the following speed. In the latter method, the voice appearance probability is reduced to about one-half, and the user tries to talk on his / her own channel during a time period when the other channel is not talking.

[0006]

In the former method, it is necessary to set the transmission speed low by the amount of the increase in the number of channels, and the sound quality is reduced accordingly. For example, in the case of the speed of 8 Kbps, 16 Kb
The sound quality deteriorates with respect to a speech encoder of ps or 32 Kbps. In addition, if the speech encoder is set to a low speed once in response to a time period when the demand for the telephone line is at its peak, there is a problem that the sound quality remains degraded even when the demand is small.

Next, in the latter method, when the number of channels is 100
As described above, in a state where the number of channels is relatively large, the section in which each channel becomes active can be well allocated. However, when only a small number of channels are set, for example, eight channels, active channels are inevitably concentrated at a certain time. In this section, the active channels exceed the capacity of the communication path. Would. In this case, some channels are excluded from transmission targets, and as a result, a situation in which speech is interrupted during a call frequently occurs, and a practical speech encoding device cannot be realized.

For this reason, when attempting to encode and transmit speech with a small number of channels, for example, eight channels, the former method must be employed, and the quality of the sound is always degraded. There was a problem that had to be.

SUMMARY OF THE INVENTION An object of the present invention is to provide a speech coding apparatus capable of improving sound quality as much as possible even when the number of channels of a voice telephone signal is relatively small.

[0010]

According to the first aspect of the present invention, a plurality of voice encoders individually prepared for each of a plurality of types of transmission rates for encoding a plurality of voice telephone signals, and a time measuring device. And a selection table circuit indicating a transmission rate to be set in relation to the number of voice telephone signals that can be transmitted simultaneously at each time, and a transmission table indicated by the selection table circuit based on the time indicated by the clock. And a speech encoder selecting means for selecting a speech encoder of a speed.

That is, according to the first aspect of the present invention, a speech encoder is prepared for each transmission rate, and a selection table circuit indicating which transmission rate is set in relation to time is prepared. The object of the present invention is to select a speech encoder having an optimal transmission rate based on the time indicated by a clock, thereby changing the speech transmission rate according to demand and improving sound quality when demand is small. To achieve.

[0012]

[0013]

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to embodiments.

[0015]

FIG. 1 shows the configuration of a speech coding apparatus according to an embodiment of the present invention . Audio input signals of respective channels are supplied to _first to _eighth input terminals 111 to 118 of this device. The input terminals 11 ₁ to 11 _8, 8 Kbps coder (hereinafter. To be abbreviated as 8K encoder) and 12 ₁ to 12 _8, 16 Kbps coder (hereinafter abbreviated as 16K coder.) _{131-134 8} inputs are connected in parallel. These encoders 12 ₁
12 _{8, 131-134 8} input side of the multiplexer circuit (MUX) 14 the output side of the are connected. An audio data output terminal 15 is connected to an output side of the multiplexer circuit 14.

The speech coding apparatus also has a speech decoding circuit. That is, the encoded audio data input from the audio data input terminal 21 is input to the input side of the demultiplexer circuit (DEMUX) 22, and the output side is an 8 Kbps decoder (hereinafter, abbreviated as 8K decoder). and 23 ₁ ~ 23 _8, 16 Kbps decoder (hereinafter,
Abbreviated as 16K decoder. ) 24 _{1 to} 24 ₈ . These decoders 23 ₁ to 23 _8, 24 output of _{1-24 8,} the output terminal 25 21 _to the first to eighth grouped by channel
It is connected to the 5 _8.

A clock 31 is arranged in the speech encoding device. Time information output from the clock 31 is input to the selection table 32. In the selection table 32, data indicating the number of usable channels determined from the utilization of each channel according to each time, and the transmission rate that can be selected by an encoder or a decoder when those channels are used are written. Have been. Channel number data indicating the number of usable channels among them is output to the channel signal terminal 33. This channel signal terminal 33 is connected to an exchange (not shown).

In the speech coding apparatus having such a configuration, the selection table 3 is set in accordance with the time information output from the clock 31.
2 outputs a 4-channel selection signal or an 8-channel selection signal. In the time zone in which the demand reaches a peak or a state close to that for a telephone line, since the 8-channel selection signal from the selection table 32 is output, the audio data multiplexer circuit 14 which is encoded by 8K encoder 12 ₁ to 12 ₈ The selected audio data is output from the audio data output terminal 15 for up to eight channels in total. Also, it supplies the audio data demultiplexer circuit 22 similarly by selecting only 8K decoder 23 _{1-23 8} in this state. As a result, audio data for up to eight channels input from the audio data input terminal 21 is decoded, and the first
~ Corresponding to be output from the terminal of the output terminals 25 ₁ to 25 ₈ of the eighth.

On the other hand, a four-channel selection signal is output from the selection table 32 during a time period when the demand for the telephone line is relatively small. In this case, the multiplexer circuit 14
Selects audio data encoded by 16K coder _{131-134 8,} the audio data of a total of four channels will be output from the audio data output terminal 15 at the maximum.
In this case, for the number of channels exceeding this number, the above-mentioned exchange outputs a busy signal. During this time,
The demultiplexer circuit 22 is likewise a 16K
_{1-13 8} selects four channels at maximum decrypts the audio data thereby.

As described above, in the present embodiment, the number of channels is switched using the clock 31 and the selection table 32, so that the voice quality can be improved in a time zone when there is little demand for telephone lines. During times of high demand, transmissions can be made on as many channels as possible.

[0022]

[0023]

[0024]

[0025]

[0026]

[0027]

[0028]

[0029]

[0030]

As described above, according to the first aspect of the present invention, a clock is prepared in the voice coding apparatus, and the transmission speed of the coded voice is switched according to the time zone. There is an advantage that the transmission speed can be determined by the circuit configuration.

[0031]

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an outline of a circuit configuration of a speech encoding device according to an embodiment of the present invention .

[Explanation of symbols]

12 8K encoder 13 16K encoder 14 Multiplexer 31 Clock 32 Selection table 43 Preliminary selection signal

Claims (1)

(57) [Claims] 1. A speech encoder separately prepared for each of a plurality of transmission speeds for encoding a plurality of speech telephone signals; a clock for measuring time; and speech that can be simultaneously transmitted for each time. A selection table circuit indicating a transmission rate to be set in relation to the number of telephone signals; and a speech encoder for selecting a speech encoder having a transmission rate indicated by the selection table circuit based on the time indicated by the clock. A speech encoding device comprising: a selection unit.