JP2001195096A - Voice coder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the compression rate of multi-channel voice signals. SOLUTION: A mix and matrix circuit 1' adds, subtracts and mixes individual six ch PCM data and computes the correlation of each channel by a prescribed equation for every one of correlation circuits 1-1 to 1-n. On the basis of these correlation data, the predictive residual of every channel is computed by each predicting circuit 15. A predictor selection signal generator 17a selects the minimum data among these predictive residuals. The data are supplied to a formatting circuit 19 through a packing circuit 18 and a prescribed bit stream is formatted.

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.

Accordingly, an object of the present invention is to provide a speech encoding method capable of improving a compression ratio when predictive encoding of a multi-channel audio signal is performed.

[0005]

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

Down-mixing the original multi-channel audio signal into a stereo two-channel audio signal; and correlating each of the plurality of un-downmixed original audio signals by a predetermined matrix operation. Converting to a certain audio signal, obtaining a first sample value in response to the audio signal input for each channel of the stereo two channels and the correlated audio signal, and predicting from the past signal in the time domain. Selecting a linear prediction method whose prediction residual is a minimum value among a plurality of prediction values of the current signal, and a linear prediction method selected by the step, the prediction residual, a predetermined leading sample value, And formatting the prediction encoded data into a predetermined bit stream.

[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); A 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 6 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” for the front group are changed to “1” = Lf + Rf “2” = It is transmitted as Lf-Rf. Then, on the reproduction side, the stereo two-channel signal Lf, which is not downmixed and output from the subsequent mix & matrix circuit 4 ′, as desired.
It is also possible to use Rf, or to use the stereo two-channel signals L and R that are downmixed and extracted in the circuit 4 '.

Next, a fourth embodiment will be described with reference to FIG. 11, FIG. 12, and FIG. In the above embodiment, 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. Then, it is configured to perform predictive encoding and select predictive encoded data of a group having the highest compression ratio. Further, in this embodiment, the encoding in the one group is not performed by classifying and converting into 2ch for the front group and 4ch for the other group as in the above-described embodiments. FIG. 11 is a diagram corresponding to the above-described FIG. 1 in a configuration in which the encoding process is integrated into one. For this reason, in the encoding unit shown in FIG. 12, first to n-th correlation circuits 1-1 to 1-n are provided, and the n correlation circuits 1-1 to 1-n have, for example, 6 channels (Lf, Cf). , Rf, L
s, Rs, and Lfe) 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.

[0030]

As described above, according to the present invention, it is possible to provide a speech coding method capable of improving the compression ratio particularly when predictive coding of a multi-channel speech signal is performed. .

[Brief description of the drawings]

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

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

FIG. 14 is a block diagram showing a fourth embodiment of the speech decoding device to which the present invention is 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] 1. Downmixing an original multi-channel audio signal to convert it into a stereo 2-channel audio signal; and correlating each of the plurality of original audio signals which are not down-mixed by a predetermined matrix operation. Converting to a stereophonic audio signal; and obtaining a first sample value in response to the audio signal input for each channel of the stereo two channels and the correlated audio signal, and from a past signal in the time domain. Selecting a linear prediction method whose prediction residual is a minimum value among a plurality of prediction values of the current signal to be predicted; and a linear prediction method selected by the step, the prediction residual, and a predetermined first sample. And a step of formatting predicted encoded data including a value into a predetermined bit stream.