JPH04157817A - Variable rate encoding device - Google Patents

Abstract

PURPOSE:To shorten the time when the SN ratio of an encoded signal decreases when the signal is almost at a threshold value level by doubly setting a border so that the encoding rate control signal varies with specific hysteresis when a status quantity veries in crossing the border. CONSTITUTION:The border between adjacent ranges is set double so that when the status quantity varies crossing the border, the encoding rate control signal varies having the specific hysteresis. When the status quantity varies across the double border between the adjacent ranges, the encoding rate control signal varies having the specific hysteresis and the encoding rate of the output of the variable rate encoding device also varies correspondingly while having the specific hysteresis. Therefore, even when said status quantity varies nearby the border between the adjacent ranges, this invention prevents the encoding rate from being switched frequency.

Description

[Detailed Description of the Invention] (Summary) This invention relates to an encoding device that adaptively varies the encoding rate according to a predetermined state quantity such as an input signal level or S/N, the power level of the input signal, or When the S/N of the encoded signal is at a level around the threshold for switching the encoding rate described above, the S/N of the encoded signal is
In an encoding device that adaptively varies the encoding rate according to a predetermined state quantity with the aim of shortening the time for /N to decrease, the present invention includes a plurality of encoding means, a control means, and a selection means. , and an output means, the plurality of encoding means receives the same input signal in parallel and encodes and outputs each at a different encoding rate, and the selection means is configured to input the same input signal in parallel and output the encoded signal at different encoding rates. receiving the signals output from the means and encoded at different encoding rates, and under the control of the encoding rate control signal outputted by the control means, the signals being encoded at the different encoding rates. (1) Select and output one of the signals, and the output means outputs the signal selected by the selection means and the encoding rate control signal corresponding to the signal in association with each other, The control means includes:
For each of a plurality of ranges of a predetermined state quantity indicating the state of a signal to be encoded in the encoding device, a signal encoding rate to be selected by the selection means corresponding to the range is stored. detects the state quantity and outputs the encoding rate control signal for controlling the selection means so that the selection means selects a signal with a coding rate corresponding to a range that includes the detected state quantity; The plurality of ranges of the state quantity cover possible ranges of the state quantity, and
The boundary between adjacent ranges is configured to be doubly set so that when the state quantity changes across the boundary, the encoding rate control signal changes with a predetermined hysteresis.

[Industrial Application Field] The present invention relates to an encoding device that adaptively varies the encoding rate according to a predetermined state quantity such as an input signal level or S/N.

In recent years, research has been progressing on communication systems such as ATMs that handle multimedia information with different transmission bands, such as voice, images, and other data, in a unified manner, making it possible to flexibly allocate transmission speeds according to subscriber requests. became possible.
C came. In such a network, a variable encoding rate encoding method that adaptively varies the encoding bit rate 1 according to the voice generation situation is effective.

[Prior art and problems to be solved by the invention] Part 4
The figure shows the hardware configuration of a typical example of a variable rate encoding device to which the present invention is applied, which receives and decodes encoded data transmitted from the variable rate encoding device. It is shown together with the configuration. In Figure 4,
111 is a 4-pin I ADPCM encoder, 112 is a 2-pin ADPCM encoder, 12 is a selection control circuit, 13 is a selector, 14 is a multiplexing circuit, 15 is a transmission path, 16 is a demultiplexing circuit on the receiving side, And 17 is 4/2 bit ΔD
It is a PCM decoder.

The 4-bit ADPCM encoder 11n is 8 bits x 8MH
The 2-bit ADPCM encoder 112 receives the PCM signal of z and performs ADPCM encoding with 4 bits of quantization bits, and the 2-bit ADPCM encoder 112 also has 8 bits x 8 M
A PCM signal of Hz is received and encoded using ADPCM with a quantization bit count of 4 bits. Both encoders 11n and 112 always perform ADPCM encoding in parallel at their respective quantization bit rates.

The encoded output of the above 4-bit ADPCM encoder 11n,
and 2) The encoded outputs of the ADPCM encoder 112 are applied to one and the other input terminals of the selector 13, respectively. The selector 13 selects one of the above encoded outputs under the control of the selection control circuit 12, and the selected encoded output is determined whether the selected encoded output is the encoded output of the 4-bit ΔDPCM encoder 11n or not. Or 2 pits) A
D)) ζ transmission line 1 via the multiplexing circuit 14 along with rate information indicating whether it is the encoded output of the CM encoder 11
It is transmitted over 5.

On the receiving side, the encoded output and rate information are separated in the demultiplexing circuit 16, and the encoded output and rate information are separated into 4/2 bit ADP
The cM decoder 17 performs 4-bit or 2-bit decoding processing depending on the rate information.

For example, in the case of audio signals, the control method for variable rate encoding is that when the power level of the input PCM signal is high, the signal contains relatively important information, and when the power level of the input PCM signal is low, the signal contains relatively important information. Considering that the 4t'S code is encoded at a relatively low encoding rate and the 'C has no effect on the audibility of the decoded audio signal, for example,
The power level of the input PCM signal is adjusted for a predetermined period of time (e.g.
As shown in FIG. 5, if the integrated value exceeds a predetermined level, the encoded output of the 4-bit ADPCM encoder 111 is selected, and the integrated value is integrated during one frame of the input PCM signal. 2 if the value does not exceed the predetermined level.
There is a selection of the encoded output of the bit ADPCM encoder 11°.

Alternatively, as another control method, the S/N of the encoded signal may be adjusted for a predetermined period of time (for example, input PCM
If the integrated value exceeds a predetermined level, the 2-bit ADPcM encoder 112
There is a method of selecting the code edge of 4) and selecting the encoded output of the ADPCM encoder lit if the integral value does not exceed the predetermined level.

FIG. 6 shows an example of the timing at which the encoding rate is adaptively switched for each frame by the selection control as described above.

However, in a transmission system using variable rate encoding as described above, multiple encoders are operated in parallel on the transmitting side, so each time the encoding rate is switched,
- There is a problem that the S/N of the temporally encoded signal η decreases. Therefore, in the above control, when the power level of the input signal or the S/N of the encoded signal is at a level around the threshold for switching the encoding rate, the seventh As shown in the figure, there is a problem in that frequent switching of the encoding rate increases the time it takes for sound quality to deteriorate.

The present invention has been made in view of the above-mentioned problems, and it is possible to change the power level of an input signal or the signal speed of an encoded signal.
S/N of the encoded signal when /N is at a level around the threshold for switching the encoding rate described above.
It is an object of the present invention to provide a variable rate encoding device that reduces the time required for the rate to decrease.

[Means to solve the problem]

FIG. 1 is a basic configuration diagram of a variable rate encoding device of the present invention.

In FIG. 1, 11+12+12. are a plurality of encoding means, 2 is a control means, 3 is a selection means, and 4 is an output means.

The plurality of encoding means 15.1□, 12.1 receive the same input signal in parallel, encode it at different encoding rates, and output it.

The selection means 3 selects the plurality of encoding means 11+12+12.
7, each coded at a different coding rate, is received, and the control? Under the control of the encoding rate control signal output by the ff11 means 2, one of the signals encoded at the different encoding rates is selected and output.

The output means 4 outputs the signal selected by the selection means 3;
The signal is associated with the encoding rate control signal and output.

The control means 2 determines the code of the signal to be selected by the selection means 3 corresponding to each of a plurality of ranges of a predetermined state quantity indicating the state of the signal to be encoded in the encoding device. The selection means 3 stores the encoding rate, detects the state quantity, and selects the signal of the encoded rate 1- corresponding to the range in which the detected state quantity is included. The encoding rate control signal is output to control the encoding rate.

According to the present invention, the plurality of ranges of the state quantity cover possible ranges of the state quantity, and according to the present invention, the boundary between adjacent ranges is defined by the range where the state quantity crosses the boundary. When changing, the coding rate control signal is set doubly so that it changes with a predetermined hysteresis.

[1] According to the present invention, the boundary between adjacent ranges is double-layered so that when the state quantity changes across the boundary, the encoding rate control signal changes with a predetermined hysteresis. is set to . That is, considering the case where the first and second ranges are adjacent to each other, the boundary between the first and second ranges has a boundary on the first range side and a boundary on the second range side. It will be established.

As a result, when the state quantity changes from the first range to the second range, even if it changes across the boundary on the first range side of the double set boundary, the encoding The rate control signal remains in a state that causes the coding rate corresponding to the first range to be selected. Then, when the state quantity further changes and changes across the boundary on the second range side of the double-set boundary, the encoding rate control tall
The signal changes from a state causing selection of the coding rate corresponding to the first range to a state causing selection of the coding rate I· corresponding to the second range.

Conversely, when the state quantity changes from the second range to the first range, even if the state quantity changes across the second range side boundary of the double set boundary, the encoding The rate control signal remains in a state that causes selection of a coding rate corresponding to the second range. Then, when the state quantity further changes and changes across the border on the first range side of the above-mentioned doubly set border, the encoding rate control signal changes to the second range.
The state changes from a state in which the coding rate corresponding to the range of is selected to a state in which the coding rate I· corresponding to the first range is selected.

Thus, when the state changes across a double boundary between adjacent ranges, the encoding rate control 20 signal will change with a predetermined bisteresis, correspondingly The encoding rate of the output of the variable rate encoding device also changes with the above-mentioned histolysis.

Therefore, even if the above-mentioned state quantity changes near the boundary between adjacent ranges, the present invention can prevent the coding rate from frequently changing.

[Embodiment] In an embodiment of the present invention, in a variable rate encoding device having a block configuration similar to that shown in FIG. 4 described above, the encoding rate is changed with hysteresis as described above. Control.

This control is performed in the selection control circuit 12 shown in FIG. The configuration other than the selection control circuit 12 shown in FIG. 4 may be completely the same as the conventional configuration described above. Note that the average power level of the audio signal input described above is the state quantity.

FIG. 2 is a diagram showing threshold values for encoding rate switching control in the embodiment of the present invention. As shown in FIG. 2, a 4-pitch hADPcM encoded signal should be selected in a range where the average power level of the audio signal input is high.
In the range where the average power level of the audio signal input is low, the ADPCM encoded signal should be selected.
According to the invention, double thresholds A and B are set at the boundaries of the two ranges.

As a result, if the average power level of the audio signal input changes from a high range to a low range, the average power level of the audio signal input will be within the double boundary set above. Even when changing across the threshold value A, the encoding rate control signal (rate information) output by the selection control circuit 12 is still in a state that selects the 4-bit ADPCM encoded signal. Then, the average power level of the audio signal input changes further and -1-
When changing across threshold B, the encoding rate control signal described above causes a 2-bit ADPCM encoded signal to be selected from a state that causes a 4-bit ADPCM encoded signal to be selected. change in state.

Conversely, if the average power level of the audio signal input changes from a low range to a high average power level of the audio signal input, the average power level of the audio signal input will exceed the double boundary set above. Even if it changes across threshold B, the encoding rate control signal (rate information) output by the selection control circuit 12 is still in a state that selects the 2-bit ADPCM encoded signal. Then, when the average power level of the audio signal input changes further and crosses the above threshold A, the above coding rate control signal is 2-pill-A DP CM coded. The state changes from a state in which a signal is selected to a state in which a 4-bit ADPCM encoded signal is selected.

Thus, as the average power level of the audio signal input changes across a double threshold between the above range of high average power level of the audio signal input and low average power level of the audio signal input, In this case, the encoding rate control signal changes with a predetermined hysteresis, and correspondingly, the encoding rate of the output of the variable rate encoding device also changes with the above-mentioned hysteresis.

FIG. 3 is a diagram showing the timing of switching the audio signal level and encoding rate in the embodiment of the present invention. Third
As shown in the figure, the present invention allows the average power level of the audio signal input to change near the boundary between the range where the average power level of the audio signal input is high and the range where the average power level of the audio signal input is low. Even in such a case, according to the present invention, it is possible to prevent frequent switching of encoding rates, and to relatively shorten the time during which the S/N decreases (the time during which sound quality deteriorates). I can do it.

The selection control circuit 12 shown in FIG. 4 that performs the above control can be realized by a hardware logic circuit or by software that performs the above control.

〔Effect of the invention〕

According to the variable rate encoding device of the present invention, the power level of the input signal or the S/N of the encoded signal is
It is possible to shorten the time during which the S/N of the encoded signal decreases when it is at a level around the threshold for switching the encoding rate.

[Brief explanation of drawings]

FIG. 1 is a basic configuration diagram of the present invention. FIG. 2 is a diagram showing the threshold value of the encoding sea 1 switching control in the embodiment of the present invention. FIG. Figure 4 shows the hardware configuration of a typical example of a variable rate encoding device to which the present invention is applied. FIG. 5 is a diagram showing a configuration for receiving and decoding encoded data, and FIG. 5 is a diagram showing threshold values for encoding rate switching control in a conventional variable rate encoding device. is A.D.
FIG. 7 is a diagram showing an example of the timing of switching the coding rate in a PCM coding device, and FIG. 7 is a diagram showing the timing of switching the audio signal level and coding rate in a conventional variable rate coding device. . [Explanation of codes] 11112112, ... a plurality of encoding means, 2...
Control means, 3... Selection means, 4... Output 1 stage, 11
,...4-bit ADPCM encoder, 112...2 bits) ADPCM encoder, 12...Selection control circuit, I3
... Selector, 14... Multiplexing circuit, 15... Transmission line, 16... Receiving side demultiplexing circuit, 17... 4
/2-bit ADPCM decoder.

Claims (1)

[Claims] 1. An encoding device that adaptively varies the encoding rate according to a predetermined state quantity, comprising a plurality of encoding means (1_1, 1_2, . . . 1_n) and a control means ( 2), selection means (3), and output means (4).
), and the plurality of encoding means (1_1, 1_2, ... 1_n
) receives the same input signal in parallel and encodes and outputs each signal at a different encoding rate, and the selection means (3) selects the plurality of encoding means (1_1).
, 1_2, . The output means (4) selects and outputs one of the signals encoded at different encoding rates, and the output means (4) outputs the signal selected by the selection means (3) and the signal corresponding to the signal. The control means (2) outputs a coding rate control signal in association with the coding rate control signal, and the control means (2) outputs the coding rate control signal for each of a plurality of ranges of a predetermined state quantity indicating the state of a signal to be coded in the coding device. The coding rate of the signal to be selected in the selection means (3) is stored in correspondence with the range, and the state quantity is detected and the coding rate corresponding to the range in which the detected state quantity is included is stored. outputting the encoding rate control signal that controls the selection means (3) so that the selection means (3) selects a signal; and the plurality of ranges of the state quantity cover possible ranges of the state quantity. and the boundary between adjacent ranges is set doubly so that when the state quantity changes across the boundary, the encoding rate control signal changes with a predetermined hysteresis. A variable rate encoding device characterized by: 2. The variable rate encoding device according to claim 1, wherein the state quantity is an average power level of the input signal over a predetermined time. 3. The variable rate encoding device according to claim 1, wherein the state quantity is an encoding error of the output of the selection means (3). 4. The plurality of encoding means (1_1, 1_2, . . . 1
_n) is an ADPCM encoder (
2. The variable rate encoding device according to claim 1, comprising: an ADPCM encoder (11_2) with 2 bits of quantization bits.