Coding with noise shaping in a hierarchical coder

Patent metadata

Field	Value
Publication number	US-8965773-B2
Application number	US-200913129483-A
Country	US
Kind code	B2
Filing date	Nov 17, 2009
Priority date	Nov 18, 2008
Publication date	Feb 24, 2015
Grant date	Feb 24, 2015

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.

First claim

The invention claimed is:

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 to at least one enhancement coding layer; 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 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 layer and of the past samples of the reconstructed signals of the current enhancement coding layer, and a step of obtaining a noise shaping filter and filtering the enhancement coding error signal with this noise shaping filter 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 for each sample of the current frame and said target signal,
wherein the noise shaping filter is further modified by adapting memories of the noise shaping filter based on the output of the scalar quantization step corresponding to the determined indices of scalar quantization for each coded sample of the enhancement signal.

2. The method as claimed in claim 1 , wherein it further comprises the following step for a current sample:
calculating the reconstructed signal for the current sample by addition of the reconstructed signal arising from the coding of a previous coding layer and of the signal arising from the enhancement 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 enhancement coding 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 layer 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 layer is an ADPCM coding layer using a scalar quantization and a prediction filter.

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

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 layer 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 layer is also used by the core coding layer.

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 layer.

14. 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.

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

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

17. The method as claimed in claim 14 , wherein said noise shaping filter used by the enhancement coding is also used by the core coding.

18. The method as claimed in claim 14 , wherein the noise shaping filter is calculated as a function of said input signal.

19. The method as claimed in claim 14 , wherein the noise shaping filter is calculated based on a signal locally decoded by the core coding.

20. A hierarchical coder of a digital audio signal for a current frame of the input signal comprising:
a core coding module; and
at least one enhancement coding module,
wherein the core coding module delivers a scalar quantization index for each sample of the current frame to the at least one enhancement coding module;
wherein the at least one enhancement coding module delivers indices of scalar quantization for each coded sample of an enhancement signal,
wherein the enhancement coding module comprises a module for obtaining an enhancement coding error signal by combining the input signal of the hierarchical coder with a signal reconstructed partially based on a coding of a previous coding layer and of the past samples of the reconstructed signals of the current enhancement coding module, a module for obtaining a noise shaping filter, a module for filtering the enhancement coding error signal with this noise shaping 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, and
wherein the noise shaping filter is further modified by adapting memories of the noise shaping filter based on the output of the scalar quantization step corresponding to the determined indices of scalar quantization for each coded sample of the enhancement signal.

21. 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.

Assignees

• Kovesi Balazs
• Ragot Stéphane
• Guyader Alain Le
• Orange

Inventors

• Kovesi Balazs
• Ragot Stéphane
• Le Guyader Alain

Classifications

• G10L19/24 Primary

  Variable rate codecs, e.g. for generating different qualities using a scalable representation such as hierarchical encoding or layered encoding · CPC title

• G10L19/04

  using predictive techniques · CPC title

• G10L19/265

  Pre-filtering, e.g. high frequency emphasis prior to encoding · CPC title

• G10L19/005 Primary

  Correction of errors induced by the transmission channel, if related to the coding algorithm · CPC title

• H03M7/30

  Compression (speech analysis-synthesis for redundancy reduction G10L19/00; for image communication H04N); Expansion; Suppression of unnecessary data, e.g. redundancy reduction · CPC title