JP2001188573A - Voice coding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve compression ration in the case of predicting coding of multi-channel voice signals, and to enables a reproduction side to reproduce them on two stereo channels, using a simple configuration. SOLUTION: A mix and matrix circuit 1' down mixes six-channel PCM data to a two-channel (L, R) stereo, and also classifies the original six channels (Lf, C, Rf, Ls, Rs, Lfe) into a two-channel stereo and four channels related to another group, and converts the four channels into correlated signals '3'-'6'. Coding parts 2'-1, 2'-2 perform predictive-coding of the PCM data of the two- channel (L, R) stereo and the four channels '3'-'6', respectively, and classify the data into bit streams of each group for formatting them.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a speech coding method for predictively coding a multi-channel speech signal.

[0002]

2. Description of the Related Art As a method of predictive encoding of a speech signal,
In the prior application (Japanese Patent Application No. 9-289159), the inventor of the present invention applied a plurality of linearizers of a current signal from a past signal in the time domain to a one-channel original digital audio signal using a plurality of predictors having different characteristics. A method is proposed in which a prediction value is calculated, a prediction residual for each predictor is calculated from the original digital audio signal and the plurality of linear prediction values, and a minimum value of the prediction residual is selected.

[0003]

However, in the above method, the original digital audio signal has a sampling frequency = 96.
Although a certain compression effect can be obtained when the kHz and the quantization bit number are about 20 bits, recent DVD audio discs use twice the sampling frequency (= 192 kHz). Since 24 bits also tend to be used, the compression ratio needs to be improved. Furthermore, when a multi-channel audio signal is predictively coded and transmitted, it is necessary to consider that the reproducing side reproduces the signal on two stereo channels without downmixing.

[0004] Therefore, the present invention can improve the compression ratio when predictive coding of a multi-channel audio signal is performed, and also enables the reproduction side to reproduce the sound on two stereo channels without downmixing the multi-channel. It is an object to provide an encoding method.

[0005]

The present invention comprises the following means to achieve the above object. That is,

Downmixing the original multi-channel audio signal into a two-channel stereo audio signal; a first group including the two stereo channels obtained in the step; Converting the audio signals of at least each channel of the second group into correlated audio signals by a predetermined matrix operation, wherein the stereo two channels are divided into a second group including a plurality of channels; And a second group of correlated audio signals in response to an audio signal input for each channel, obtaining a first sample value, and a plurality of predictions of a current signal predicted from past signals in the time domain. Selecting a linear prediction method that minimizes the prediction residual among the values, and the selected linear prediction method The steps and, the speech coding method consisting of formatting the bitstream grouping predictive coded data and second groups of the two stereo channels and a prediction residual with a predetermined first sample value.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a first embodiment of a speech encoding apparatus to which the present invention is applied and a speech decoding apparatus corresponding to the speech encoding apparatus. FIG. 2 is a block diagram showing the encoding unit of FIG. 1 in detail. 1, an explanatory diagram showing a bit stream encoded by the encoding unit in FIG. 2, FIG. 4 is a block diagram showing the decoding unit in FIG. 1 in detail, FIG. 5 is an explanatory diagram showing a format of a DVD pack, and FIG. Is an explanatory diagram showing the format of a DVD audio pack, and FIGS. 7 and 8 are flowcharts showing an audio transmission method.

Here, for example, the following four systems are known as multi-channel systems. (1) Four-channel system As in the Dolby surround system, a total of four channels including three channels of front L, C, and R + one channel of rear S (2) Five-channel system S in the Dolby AC-3 system
Like without W channel, 3 channels of front L, C and R + 2 channels of rear SL and SR, total 5 channels (3) 6 channel system DTS (Digital Theater)
6) (L, C, R, SW (Lfe), SL, SR) like the Dolby AC-3 system (4) 8-channel system SDDS (Sony Dynamic D
digital sound), forward L, LC, C, R
6 channels of C, R, SW + 2 channels of rear SL, SR, total 8 channels

The 6-channel (ch) mix and matrix circuit 1 'on the encoding side shown in FIG. 1 includes a front left (Lf), a center (C), a front right (Rf), a surround left ( Ls), surround light (Rs) and Lfe (Low Frequency Effe)
ct) of the 6-channel PCM data by coefficients mij (i = 1, 2, j)
= 1, 2 to 6), and downmixes to two stereo channels (L, R) by the following equation (1). L = m11 · Lf + m12 · Rf + m13 · C + m14 · Ls + m15 · Rs + m16 · Lfe R = m21 · Lf + m22 · Rf + m23 · C + m24 · Ls + m25 · Rs + m26 · Lfe (1)

The mixer & matrix circuit 1 'classifies the original 6 channels (Lf, C, Rf, Ls, Rs, Lfe) into 2 channels for the front group and 4 channels for the other groups, and divides the 4 channels into the following equation (2). , And 2ch (L, R) to the first encoder 2′-1, and 4ch “3” to “6” to the third signal “3” to “6”. And outputs the result to the 2 coding unit 2′-2. “1” = L “2” = R “3” = C− (Ls + Rs) / 2 “4” = Ls + Rs “5” = Ls−Rs “6” = Lfe−C (2)

As shown in detail in FIG. 2, the first and second encoders 2'-1 and 2'-2 which constitute the encoder 2 'respectively have 2ch "1", "2" and 4ch "3". "~" 6 "PC
The M data is predictively encoded for each channel, and the encoded prediction data is transmitted as a bit stream as shown in FIG. 3 to the decoding side via a recording medium 5 or a communication medium 6 such as a satellite line or a telephone line. On the decoding side, the first and second decoding units 3'-1 and 3'-2 constituting the decoding unit 3 'respectively perform 2ch "1" for the forward group, as shown in detail in FIG.
The prediction coded data of "2" and 4ch "3" to "6" relating to the other groups are decoded into PCM data for each channel. Next, the original 6 ch (Lf, C, Rf,
Ls, Rs, Lfe) and restore stereo 2
The ch data (L, R) is output as it is.

Referring to FIG. 2, encoding sections 2'-1, 2'-
2 will be described in detail. PC for each channel "1" to "6"
The M data is stored in one frame buffer 10 for each frame. Then, the sample data of each of the channels “1” to “6” of one frame are respectively supplied to the prediction circuits 13D1 and 13D
2, 15D1 to 15D4 and each channel
First sample data (stored in a restart header described later) of each frame of “1” to “6” is applied to the unpacking circuit 8 and the formatting circuit 19. The sampling frequency (fs) and the number of quantization bits (Qb) when the PCM data is A / D converted are applied to the packing circuit 18 and the formatting circuit 19.
The prediction circuits 13D1, 13D2, and 15D1 to 15D4 respectively calculate the PCM data of each channel “1” to “6”.
A plurality of predictors (not shown) having different characteristics calculate a plurality of linear prediction values of the current signal from a past signal in the time domain, and then perform prediction for each predictor from the original PCM data and the plurality of linear prediction values. Calculate the residual. The following buffer
The selectors 14D1, 14D2, 16D1 to 16D4 are prediction circuits 13D1, 13D2, 15D1 to 15D, respectively.
4 is temporarily stored, and the minimum value of the prediction residual is selected for each subframe specified by the selection signal / DTS (decoding time stamp) generator 17.

The selection signal generator 17 outputs a bit number flag of the prediction residual to a packing circuit 18 and a formatting circuit 19.
, And a predictor selection flag indicating the predictor with the smallest prediction residual and a correlation coefficient as described later are applied to the formatting circuit 19. Packing circuit 1
8 is a buffer / selector 14D1, 14D2, 16D1.
The prediction residual for 6 ch selected by 16D4 is packed with the specified number of bits based on the bit number flag specified by the selection signal generator 17.

The following formatting circuit 19 formats the data into user data as shown in FIG. This user data is a variable rate bit stream BS including 2ch (1) and (2) prediction coded data for the front group.
0 and the variable rate bit stream BS1 including the prediction coded data of 4ch (3) to (6) regarding other groups.
And a bit stream header provided before the streams BS0 and BS1. The streams BS0 and BS1 for one frame include: a frame header; first sample data of one frame of each channel (1) to (6); and each subframe of each channel (1) to (6). A predictor selection flag; a bit number flag for each subframe of each channel (1) to (6); a prediction residual data sequence (variable number of bits) for each channel (1) to (6); The correlation coefficient described later is multiplexed. According to such predictive coding,
When the original signal has, for example, a sampling frequency of 96 kHz, the number of quantization bits = 24 bits, and six channels, a compression ratio of 71% can be realized.

Next, referring to FIG. 4, the decoding units 3'-1,
3′-2 will be described. The variable-rate bit stream data BS0 and BS1 in the above format are separated by the deformatting circuit 21 based on the stream data and the frame header. And each channel "1" ~
The head sample data of one frame of “6” and the predictor selection flag are stored in the prediction circuits 24D1, 24D2, and 23D, respectively.
1 to 23D4, and the bit number flags of each channel “1” to “6” and the prediction residual data sequence are stored in the unpacking circuit 2
2 is applied. Here, the prediction circuits 24D1, 24D
2, a plurality of predictors (not shown) in 23D1 to 23D4 are prediction circuits 13D1, 13D2, and 1 on the encoding side, respectively.
The characteristics are the same as those of the plurality of predictors in 5D1 to 15D4, and those having the same characteristics are selected by the predictor selection flag.

The unpacking circuit 22 is provided for each channel "1" to
The prediction residual data string of “6” is separated based on each bit number flag, and is divided into prediction circuits 24D1, 24D2, and 23, respectively.
It outputs to D1-23D4. Prediction circuits 24D1, 24D
2, 23D1 to 23D4, the current prediction residual data of each of the channels “1” to “6” from the unpacking circuit 22 and each of the plurality of internal predictors selected by the predictor selection flag. The previous predicted value predicted by one frame is added to calculate the current predicted value, and then the PC of each sample is determined based on the first sample data of one frame.
M data is calculated.

Here, the coding units 2'-1 shown in FIG.
When the variable-rate bit stream data that has been predictively encoded by 2′-2 is recorded on a DVD audio disc as an example of a recording medium, it is packed in an audio (A) pack shown in FIG. This pack is 203
For 4 bytes of user data (A packet, V packet), 4 bytes of pack start information and 6 bytes of S
It is configured by adding a 14-byte pack header of CR (System Clock Reference: system time reference value) information, 3-byte Mux rate (rate) information, and 1-byte stuffing (1 pack = 2048 total).
Part-Time Job). In this case, the time of the A pack in the same title can be managed by setting the SCR information as the time stamp to be “1” in the first pack in the ACB unit so as to be continuous in the same title.

The A packet of the compressed PCM has a packet header of 9 to 22 bytes and a compressed P
The CM private header and 1 to 2015 bytes of audio data (compressed P
CM). The private header of the compressed PCM is: 1-byte substream ID, 2 bytes of UPC / EAN-ISRC (Universal Prism).
oduct Code / European Article Number-International S
tandard Recording Code) number and UPC / EAN-
ISRC data, 1-byte private header length, 2-byte first access unit pointer, 4 bytes of audio data information (ADI), and 0 to 7 bytes of stuffing bytes. ing.

The forward access unit search pointer for searching for the access unit one second later and the backward access unit search pointer for searching for the access unit one second earlier in the ADI are both 1
Set in bytes. Specifically, the forward access unit search pointer is set in the first byte of the ADI, and the backward access unit search pointer is set in the eighth byte. Thus, ADI can store up to 2015 bytes of audio data in order to reduce it to 4 bytes in compressed PCM.

The audio data area in the compressed PCM (PPCM) audio packet shown in FIG. 6 is composed of a plurality of PPCM access units as shown in FIG. 7, and the PPCM access unit is composed of PPCM sync information and sub-packets. I have. First PP
The subpacket in the CM access unit includes a directory, a substream “BS0”, a CRC (1 byte or 2 bytes), a substream “BS1”,
C and extra information, and the sub-streams “BS0” and “BS1” are composed of only PPCM blocks. Sub-packets in the second and subsequent PPCM access units also include a directory, a sub-stream “BS0”, a CRC, and a sub-stream “BS1”.
, CRC and extra information, and the sub-streams “BS0” and “BS1” have a restart header and P
It is composed of PCM blocks.

The encoding units 2'-1, 2 'shown in FIG.
When the variable rate bit stream data predicted and coded according to -2 is transmitted through a network, the coding side packetizes the data for transmission as shown in FIG. 8 (step S41), and then attaches a packet header (step S41). (Step S42) Then, the packet is sent out onto the network (Step S43). On the decoding side, the header is removed as shown in FIG. 9 (step S51), the data is restored (step S52), and the data is stored in a memory and decoding is waited (step S53).

In the above embodiment, the stereo 2ch data (L, R) is transmitted as it is, but “1” = L + R “2” = LR “3” to “5” are the same “6” = Lfe −a × C However, 0 ≦ a ≦ 1... (2) ′ may be converted into a correlated signal together with the six channels “1” to “6” for predictive coding (second embodiment). Form). In this case, the mix & matrix circuit 4 ′ on the decoding side can generate the channel L by adding the channels “1” and “2”, and generate the channel R by subtracting the channel L. In the above embodiment, the multi-channel (6ch) and the stereo (2ch) are restored, but it goes without saying that either one may be restored.

FIG. 10 is a diagram showing the third embodiment. In this case, without downmixing, 2ch “1” and “2” relating to the front group are changed to “1” = Lf + Rf “2” = The signal is transmitted as Lf-Rf, and it is necessary to downmix when reproducing stereo 2ch data (L, R) on the reproducing side.

Next, a fourth embodiment will be described with reference to FIG. 11, FIG. 12, and FIG. In the above embodiment,
Although one group of correlated signals “1” to “6” are configured to be predictively coded, in the fourth embodiment, a plurality of groups of correlated signals are generated and predicted and coded. It is configured to select the prediction coded data of the group having the highest compression ratio. Further, in this embodiment, the encoding in one group is not classified and converted into 2ch for the front group and 4ch for the other group as in each of the above-described embodiments. FIG. 1 shows a configuration in which the combined encoding process is performed.
1 is shown as a diagram corresponding to FIG. Also,
FIG. 12 shows a detailed block of the encoding unit.
In this embodiment, n correlation circuits 1-1 to 1-n are provided on the mix & matrix circuit 1 'side.
These n correlation circuits 1-1 to 1-n are, for example, 6 ch (L
f, C, Rf, Ls, Rs, and Lfe) PCM data are converted into n types of 6-channel signals “1” to “6” having different correlations.

For example, the first correlation circuit 1-1 converts as follows: "1" = Lf "2" = C- (Ls + Rs) / 2 "3" = Rf-Lf "4" = Ls-a × Lfe “5” = Rs−b × Rf “6” = Lfe Further, the n-th correlation circuit 1-n converts as follows: “1” = Lf + Rf “2” = C−Lf “3” = Rf−Lf “4” = Ls−Lf “5” = Rs−Lf “6” = Lfe−C Further, other correlation circuits perform conversion as in the first embodiment.

Further, a prediction circuit 15 and a buffer / selector 16 are provided for each of the correlation circuits 1-1 to 1-n, and the group having the highest compression ratio is determined based on the data amount of the minimum value of the prediction residual for each group. Are selected by the correlation selection signal generator 17b. At this time, the formatting circuit 19 adds and multiplexes the selection flag (correlation circuit selection flag, correlation coefficients a and b of the correlation circuit).

FIG. 13 shows a data area corresponding to FIG. 6 described above.
Instead of using “S1”, the sub-stream “BS0” alone is used.

Further, on the decoding side shown in FIG. 14, n correlation circuits 4 are provided for the correlation circuits 1-1 to 1-n on the encoding side.
−1 to 4-n (or one correlation circuit 4 whose coefficients a and b can be changed) are provided. Note that when the prediction circuits of the n groups shown in FIG. 12 have the same configuration,
As shown in FIG. 4, there is no need to provide prediction circuits for n groups, and prediction circuits for one group are sufficient. Then, one of the correlation circuits 4-1 to 4-n is selected based on the selection flag transmitted from the encoding device, or coefficients a and b are set and the original 6 ch (Lf, C, Rf, Ls, Rs, Lfe) are restored, and the multi-channel is downmixed according to equation (1) to generate stereo 2-ch data (L, R).
Further, the 6-channel system having the number of channels “1” to “6” is an example, and another system such as a 5-channel system may be used.

In the first embodiment, one kind of correlation signal "1" to "6" is configured to be predictively coded. However, the signals "1" to "6" are encoded. And the group of the original signals (Lf, C, Rf, Ls, Rs, Lfe) may be predictively coded and the group with the higher compression ratio may be selected.

According to the present invention, the following inventions are provided in addition to the inventions described in the claims. (1) Classifying the original multi-channel audio signal into a first group including at least the front two channels and a second group including other channels, and correlating at least the audio signals of the second group of channels. Correlating means for converting a plurality of predicted values of the correlated sound signals of the first group and the second group for each channel, and calculating each predicted residual of the plurality of predicted values. A plurality of predictive encoding means for calculating a difference and selecting a minimum value of the plurality of predictive residuals; and predictive coded data including the predictive residual selected by the predictive encode means in the first and second prediction encoded data. Means for formatting into bit streams classified for each group of. (2) In the speech coding apparatus according to claim 1, the correlation means converts the original multi-channel speech signal into a plurality of groups of second multi-channel speech signals having different correlations. Speech coding characterized by comprising a plurality of correlating means, wherein said plurality of predictive coding means are provided for each group, and select a minimum value of a prediction residual of a group having the highest compression rate. apparatus.

[0031]

As described above, according to the present invention, it is possible to provide a speech encoding method in which a multi-channel speech signal is subjected to linear prediction encoding to improve the compression ratio.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of a speech coding apparatus to which the present invention is applied and a speech decoding apparatus corresponding thereto.

FIG. 2 is a block diagram illustrating an encoding unit of FIG. 1 in detail.

FIG. 3 is an explanatory diagram showing a bit stream encoded by an encoding unit shown in FIGS. 1 and 2;

FIG. 4 is a block diagram illustrating a decoding unit of FIG. 1 in detail;

FIG. 5 is an explanatory diagram showing a format of a DVD pack.

FIG. 6 is an explanatory diagram showing a format of a DVD audio pack.

FIG. 7 is an explanatory diagram showing a format of an audio data area in FIG. 6 in detail;

FIG. 8 is a flowchart showing a voice transmission method.

FIG. 9 is a flowchart showing a voice transmission method.

FIG. 10 is a block diagram showing a third embodiment of a speech coding apparatus to which the present invention is applied and a speech decoding apparatus corresponding thereto.

FIG. 11 is a block diagram showing a fourth embodiment of a speech encoding device to which the present invention is applied and a speech decoding device corresponding thereto.

FIG. 12 is a block diagram illustrating a fourth embodiment of the speech encoding device to which the present invention has been applied.

FIG. 13 is an explanatory diagram of another embodiment corresponding to FIG. 7;

FIG. 14 is a block diagram illustrating a fourth embodiment of a speech decoding device to which the present invention has been applied.

[Explanation of symbols]

1 '6ch mix & matrix circuit (correlation means, downmix means) 13D1, 13D2, 15D1-15D4 Prediction circuit (buffer / selector 14D1, 14D2, 16D1-1)
Together with 6D4, it constitutes a predictive coding means. 14D1, 14D2, 16D1-16D4 buffer
Selector 19 Formatting circuit (Formatting means)

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Claims (1)

[Claims] An audio signal of an original multi-channel is downmixed and converted into an audio signal of two stereo channels, a first group including the two stereo channels obtained by the step, and the downmixing is not performed. Dividing the audio signals of at least each channel of the second group into a correlated audio signal by a predetermined matrix operation; A first sample value is obtained in response to an audio signal input for each channel of correlated audio signals of two channels and the second group, and a plurality of current signals predicted from past signals in the time domain are obtained. Selecting a linear prediction method that minimizes the prediction residual among the prediction values of And encoding the prediction coded data including the prediction residual and a predetermined leading sample value into a bit stream grouped into the stereo two-channel group and the second group.