CODING WITH NOISE SHAPING IN A HIERARCHICAL CODER

• US 20110224995A1
• Filed: 11/17/2009
• Published: 09/15/2011
• Est. Priority Date: 11/18/2008
• Status: Active Grant

• Current Assignee: Orange S.A.
• Original Assignee: Orange S.A.
• Inventors: Le Guyader, Alain, Kovesi, Balazs, Ragot, Stéphane
• Granted Patent: US 8,965,773 B2
• Time in Patent Office: Days
• US Class Current: 704/500
• CPC Class Codes: G10L 19/04 using predictive techniques
• 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 19/265 Pre-filtering, e.g. high frequency emphasis prior to encoding

Abstract

A method is provided for hierarchical coding of a digital audio signal comprising, for a current frame of the input signal: a core coding, delivering a scalar quantization index for each sample of the current frame and at least one enhancement coding delivering indices of scalar quantization for each coded sample of an enhancement signal. The enhancement coding comprises a step of obtaining a filter for shaping the coding noise used to determine a target signal and in that the indices of scalar quantization of said enhancement signal are determined by minimizing the error between a set of possible values of scalar quantization and said target signal. The coding method can also comprise a shaping of the coding noise for the core bitrate coding. A coder implementing the coding method is also provided.

Claims

1. A method of hierarchical coding of a digital audio signal comprising, for a current frame of the input signal:

performing, on a processor, a core coding, delivering a scalar quantization index for each sample of the current frame and

performing, on the processor, at least one enhancement coding delivering indices of scalar quantization for each coded sample of an enhancement signal,

wherein the enhancement coding comprises a step of obtaining a filter for shaping coding noise used to determine a target signal and the indices of scalar quantization of said enhancement signal are determined by minimizing error between a set of possible values of scalar quantization and said target signal.

2. The method as claimed in claim 1, wherein the determination of the target signal for a current enhancement coding stage, comprises the following steps for a current sample:

obtaining an enhancement coding error signal by combining the input signal of the hierarchical coding with a signal reconstructed partially based on a coding of a previous coding stage and of the past samples of the reconstructed signals of the current enhancement coding stage;

filtering by the noise shaping filter obtained, of the enhancement coding error signal so as to obtain the target signal;

calculating the reconstructed signal for the current sample by addition of the reconstructed signal arising from the coding of a previous coding stage and of the signal arising from the quantization step; and

adapting of memories of the noise shaping filter based on the signal arising from the quantization step.

3. The method as claimed in claim 1, wherein the set of the possible scalar quantization values and the quantization value of the error signal for the current sample are values denoting quantization reconstruction levels, scaled by a level control parameter calculated with respect to the core bitrate quantization indices.

4. The method as claimed in claim 3, wherein the values denoting quantization reconstruction levels for an enhancement stage k are defined by the difference between the values denoting the reconstruction levels of the quantization of an embedded quantizer with B+k bits, B denoting the number of bits of the core coding and the values denoting the quantization reconstruction levels of an embedded quantizer with B+k−

1 bits, the reconstruction levels of the embedded quantizer with B+k bits being defined by splitting the reconstruction levels of the embedded quantizer with B+k−

1 bits into two.

5. The method as claimed in claim 4, wherein the values denoting quantization reconstruction levels for the enhancement stage k are stored in a memory space and indexed as a function of the core bitrate quantization and enhancement indices.

6. The method as claimed in claim 1, wherein the number of possible values of scalar quantization varies for each sample.

7. The method as claimed in claim 1, wherein the number of coded samples of said enhancement signal, giving the scalar quantization indices, is less than the number of samples of the input signal.

8. The method as claimed in claim 1, wherein the core coding is an ADPCM coding using a scalar quantization and a prediction filter.

9. The method as claimed in claim 1, wherein the core coding is a PCM coding.

10. The method as claimed in claim 8, wherein the core coding further comprises the following steps for a current sample:

obtaining a prediction signal for the coding noise based on past quantization noise samples and based on past samples of quantization noise filtered by a predetermined noise shaping filter; and

combining the input signal of the core coding and the coding noise prediction signal so as to obtain a modified input signal to be quantized.

11. The method as claimed in claim 10, wherein said noise shaping filter used by the enhancement coding is also used by the core coding.

12. The method as claimed in claim 1, wherein the noise shaping filter is calculated as a function of said input signal.

13. The method as claimed in claim 1, wherein the noise shaping filter is calculated based on a signal locally decoded by the core coding.

15. A non-transitory computer program product comprising code instructions for the implementation of the steps of the coding method as claimed in claim 1, when these instructions are executed by a processor.

16. The method as claimed in claim 9, wherein the core coding further comprises the following steps for a current sample:

obtaining a prediction signal for the coding noise based on past quantization noise samples and based on past samples of quantization noise filtered by a predetermined noise shaping filter; and

combining the input signal of the core coding and the coding noise prediction signal so as to obtain a modified input signal to be quantized.

17. The method as claimed in claim 10, wherein the noise shaping filter is calculated as a function of said input signal.

18. The method as claimed in claim 10, wherein the noise shaping filter is calculated based on a signal locally decoded by the core coding.

19. The method as claimed in claim 16, wherein said noise shaping filter used by the enhancement coding is also used by the core coding.

20. The method as claimed in claim 16, wherein the noise shaping filter is calculated as a function of said input signal.

21. The method as claimed in claim 16, wherein the noise shaping filter is calculated based on a signal locally decoded by the core coding.

14. A hierarchical coder of a digital audio signal for a current frame of the input signal comprising:

a core coding stage, delivering a scalar quantization index for each sample of the current frame; and

at least one enhancement coding stage delivering indices of scalar quantization for each coded sample of an enhancement signal,

wherein the enhancement coding stage comprises a module for obtaining a filter for shaping the coding noise used to determine a target signal and a quantization module delivering the indices of scalar quantization of said enhancement signal by minimizing the error between a set of possible values of scalar quantization and said target signal.