ENCODING METHOD, DECODING METHOD, ENCODER, DECODER, PROGRAM, AND RECORDING MEDIUM

• US 20140019145A1
• Filed: 03/26/2012
• Published: 01/16/2014
• Est. Priority Date: 04/05/2011
• Status: Active Grant

• Current Assignee: Nippon Telegraph and Telephone Corporation
• Original Assignee: Nippon Telegraph and Telephone Corporation
• Inventors: Moriya, Takehiro, Harada, Noboru, Kamamoto, Yutaka, Hiwasaki, Yusuke, Fukui, Masahiro
• Granted Patent: US 10,515,643 B2
• Time in Patent Office: Days
• US Class Current: 704/500
• CPC Class Codes: G10L 19/0017 Lossless audio signal coding; Perfect reconstruction of coded audio signal by transmission of coding error G10L19/24 takes precedence
• CPC Class Codes: G10L 19/005 Correction of errors induced by the transmission channel, if related to the coding algorithm
• CPC Class Codes: G10L 19/008 Multichannel audio signal coding or decoding using interchannel correlation to reduce redundancy, e.g. joint-stereo, intensity-coding or matrixing
• CPC Class Codes: G10L 19/0212 using orthogonal transformation
• CPC Class Codes: G10L 19/032 Quantisation or dequantisation of spectral components
• CPC Class Codes: G10L 19/035 Scalar quantisation
• CPC Class Codes: G10L 19/038 Vector quantisation, e.g. TwinVQ audio
• CPC Class Codes: G10L 19/167 Audio streaming, i.e. formatting and decoding of an encoded audio signal representation into a data stream for transmission or storage purposes
• CPC Class Codes: G10L 19/24 Variable rate codecs, e.g. for generating different qualities using a scalable representation such as hierarchical encoding or layered encoding
• CPC Class Codes: G10L 21/038 using band spreading techniques

Abstract

In encoding, a frequency-domain sample sequence derived from an acoustic signal is divided by a weighted envelope and is then divided by a gain, the result obtained is quantized, and each sample is variable-length encoded. The error between the sample before quantization and the sample after quantization is quantized with information saved in this variable-length encoding. This quantization is performed under a rule that specifies, according to the number of saved bits, samples whose errors are to be quantized. In decoding, variable-length codes in an input sequence of codes are decoded to obtain a frequency-domain sample sequence; an error signal is further decoded under a rule that depends on the number of bits of the variable-length codes; and from the obtained sample sequence, the original sample sequence is obtained according to supplementary information.

Claims

1. An encoding method for encoding, with a predetermined number of bits, a frequency-domain sample sequence derived from an acoustic signal in a predetermined time interval, the encoding method comprising:

an encoding step of encoding, by variable-length encoding, an integer corresponding to the value of each sample in the frequency-domain sample sequence to generate a variable-length code;

an error calculation step of calculating a sequence of error values each obtained by subtracting the integer corresponding to the value of each sample in the frequency-domain sample sequence from the value of the sample; and

an error encoding step of encoding the sequence of error values with the number of surplus bits obtained by subtracting the number of bits of the variable-length code from the predetermined number of bits to generate error codes.

2. The encoding method according to claim 1, wherein, among error samples constituting the sequence of error values, error samples whose corresponding integers are not 0 are encoded with priority with the number of surplus bits in the error encoding step.

3. The encoding method according to claim 1, wherein, among error samples constituting the sequence of error values, error samples whose corresponding power-spectrum-envelope values, whose corresponding approximate values of the power-spectrum-envelope values, or whose corresponding estimated values of the power-spectrum-envelope values are large are encoded with priority with the number of surplus bits in the error encoding step.

4. The encoding method according to one of claims 1 to 3, wherein, among error samples constituting the sequence of error values, information indicating whether the value of each error sample to be encoded is positive or negative is encoded with one bit in the error encoding step.

5. The encoding method according to claim 4, wherein a value determined on the basis of the integer is regarded as the absolute value of a reconstructed value, the absolute value of the reconstructed value is regarded as a reconstructed value corresponding to the error sample when the error sample is positive, and the value obtained by subtracting the absolute value of the reconstructed value from 0 is regarded as a reconstructed value corresponding to the error sample when the error sample is negative;

and

when the number of surplus bits is larger than the number of error samples constituting the sequence of error values, information indicating whether the value obtained by subtracting the reconstructed value corresponding to each error sample from the value of the error sample is positive or negative is further encoded with one bit in the error encoding step.

6. The encoding method according to claim 5, wherein the absolute value of a reconstructed value obtained when the integer is not 0 is larger than the absolute value of a reconstructed value obtained when the integer is 0.

19. A program for causing a computer to execute the steps of the method according to one of claim 1 or 7.

20. A computer-readable recording medium having stored thereon a program for causing a computer to execute the steps of the method according to one of claim 1 or 7.

7. A decoding method for decoding an input code formed of a predetermined number of bits, the decoding method comprising:

a decoding step of decoding a variable-length code included in the input code to generate a sequence of integers;

an error decoding step of decoding an error code included in the input code, the error code being formed of the number of surplus bits obtained by subtracting the number of bits of the variable-length code from the predetermined number of bits, to generate a sequence of error values; and

an adding step of adding each sample in the sequence of integers to a corresponding error sample in the sequence of error values.

8. The decoding method according to claim 7, wherein, among error samples constituting the sequence of error values, the error samples being represented with the number of surplus bits, error samples whose corresponding integers are not 0 are decoded in the error decoding step.

9. The decoding method according to claim 7, wherein, among error samples constituting the sequence of error values, the error samples being represented with the number of surplus bits, error samples whose corresponding power-spectrum-envelope values, whose corresponding approximate values of the power-spectrum-envelope values, or whose corresponding estimated values of the power-spectrum-envelope values are large are decoded in the error decoding step.

10. The decoding method according to one of claims 7 to 9, wherein values determined on the basis of the integers are regarded as the absolute values of reconstructed values;

and

the value of each error sample in the sequence of error values is a value obtained by reflecting the positive or negative sign determined by one-bit information corresponding to the error sample, the information being obtained by decoding the error code, in the absolute value of a reconstructed value based on an integer corresponding to the error sample in the error decoding step.

11. The decoding method according to claim 10, wherein, when there is another piece of one-bit information corresponding to the value of each error sample, the value of each error sample is a value obtained by adding the value obtained by reflecting the positive or negative sign, to a value obtained by reflecting the positive or negative sign determined by the other piece of one-bit information in half of the absolute value of the reconstructed value based on the integer corresponding to the error sample in the error decoding step.

12. The decoding method according to claim 10, wherein the absolute value of a reconstructed value obtained when the integer is not 0 is larger than the absolute value of a reconstructed value obtained when the integer is 0.

21. The decoding method according to one of claim 11, wherein the absolute value of a reconstructed value obtained when the integer is not 0 is larger than the absolute value of a reconstructed value obtained when the integer is 0.

13. An encoder for encoding, with a predetermined number of bits, a frequency-domain sample sequence derived from an acoustic signal in a predetermined time interval, the encoder comprising:

an encoding unit adapted to encode, by variable-length encoding, an integer corresponding to the value of each sample in the frequency-domain sample sequence to generate a variable-length code;

an error calculation unit adapted to calculate a sequence of error values each obtained by subtracting the integer corresponding to the value of each sample in the frequency-domain sample sequence from the value of the sample; and

an error encoding unit adapted to encode the sequence of error values with the number of surplus bits obtained by subtracting the number of bits of the variable-length code from the predetermined number of bits to generate error codes.

14. The encoder according to claim 13, wherein the error encoding unit encodes, among error samples constituting the sequence of error values, error samples whose corresponding integers are not 0 with the number of surplus bits with priority.

15. The encoder according to claim 13, wherein the error encoding unit encodes, among error samples constituting the sequence of error values, error samples whose corresponding power-spectrum-envelope values, whose corresponding approximate values of the power-spectrum-envelope values, or whose corresponding estimated values of the power-spectrum-envelope values are large with the number of surplus bits with priority.

16. A decoder for decoding an input code formed of a predetermined number of bits, the decoder comprising:

a decoding unit adapted to decode a variable-length code included in the input code to generate a sequence of integers;

an error decoding unit adapted to decode an error code included in the input code, the error code being formed of the number of surplus bits obtained by subtracting the number of bits of the variable-length code from the predetermined number of bits, to generate a sequence of error values; and

an adder adapted to add each sample in the sequence of integers to a corresponding error sample in the sequence of error values.

17. The decoder according to claim 16, wherein, among error samples constituting the sequence of error values, the error samples being represented with the number of surplus bits, the error decoding unit decodes error samples whose corresponding integers are not 0.

18. The decoder according to claim 16, wherein, among error samples constituting the sequence of error values, the error samples being represented with the number of surplus bits, the error decoding unit decodes error samples whose corresponding power-spectrum-envelope values, whose corresponding approximate values of the power-spectrum-envelope values, or whose corresponding estimated values of the power-spectrum-envelope values are large.