Device and Method for Graduated Encoding of a Multichannel Audio Signal Based on a Principal Component Analysis

• US 20090083045A1
• Filed: 03/08/2007
• Published: 03/26/2009
• Est. Priority Date: 03/15/2006
• Status: Active Grant

• Current Assignee: Orange S.A.
• Original Assignee: Orange S.A.
• Inventors: Briand, Manuel, Virette, David
• Granted Patent: US 8,359,194 B2
• Time in Patent Office: Days
• US Class Current: 704/500
• 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 19/24 Variable rate codecs, e.g. for generating different qualities using a scalable representation such as hierarchical encoding or layered encoding

Abstract

A system and a method for the scalable coding of a multi-channel audio signal comprising a principal component analysis (PCA) transformation of at least two channels (L, R) of the audio signal into a principal component (CP) and at least one residual sub-component (r) by rotation defined by a transformation parameter (θ), comprising the following steps: formation of a frequency subband-based residual structure (Sf_r) on the basis of the at least one residual sub-component (r), and definition of a coded audio signal (SC) comprising the principal component (CP), at least one residual structure (Sf_r) of a frequency subband and the transformation parameter (θ).

Claims

1. A scalable coding method of a multi-channel audio signal (C₁, . . . , C_M), comprising a principal component analysis (PCA) transformation of at least two channels (L, R) of the said audio signal into a principal component (CP) and at least one residual sub-component (r) by rotation defined by a transformation parameter (θ

), wherein the method comprises the steps of;

forming a frequency subband-based residual structure (Sf_r) on the basis of the at least one residual sub-component (r); and

defining a coded audio signal (SC) comprising the principal component (CP), at least one residual structure (Sf_r) of a frequency subband and the sad transformation parameter (θ

).

2. The method according to claim 1, comprising a formation of at least one energy parameter (E) as a function of the at least one residual sub-component (r).

3. The method according to claim 2, wherein said at least one energy parameter (F) is formed by a frequency subband-based extraction of energy difference between a decomposition of the principal component (CP) and the at least one residual sub-component (r).

4. The method according to claim 2, wherein said at least one energy parameter (E) corresponds to a subband-based energy of the at least one residual sub-component (r).

5. The method according to claim 2, comprising a frequency analysis applied to the at least one residual sub-component (r) as a function of the at least one energy parameter (E) so as to form the residual structures (Sf_r) of the frequency subbands.

6. The method according to claim 1, comprising a determined order of transmission of the residual structures of the frequency subbands.

7. The method according to claim 6, wherein said determined order of transmission is carried out according to a perceptual order of the subbands or an energy criterion.

8. The method according to claim 1, wherein said at least one residual sub-component is a frequency residual sub-component (A(n,b)) carried out according to a principal component analysis in the frequency domain.

9. The method according to claim 8, wherein the principal component analysis (PCA) transformation in the frequency domain comprises the steps of:

decomposing the at least two channels (L, R) of the said audio signal into a plurality of frequency subbands (l(n,b₁), . . . , l(n,b_N), r(n,b₁), . . . , r(n,b_N));

calculating the at least one transformation parameter (θ

(n,b_i)) as a function of at least a part of the said plurality of frequency subbands;

transforming at least a part of the plurality of frequency subbands into the said at least one frequency residual sub-component (A(n,b₁), . . . , A(n,b_N)) and at least one frequency principal sub-component (CP(n,b₁), . . . , CP(n,b_N)) as a function of the at least one transformation parameter (θ

(n,b₁), . . . , θ

(n,b_N)); and

forming the principal component (CP(n)) on the basis of the at least one frequency principal sub-component (CP(n,b₁), . . . , CP(n,b_N)).

10. The method according to claim 9, wherein said plurality of frequency subbands (l(n,b₁), . . . , l(n,b_N), r(n,b₁), . . . , r(n,b_N)) is defined in accordance with a perceptual scale.

11. The method according to claim 1, comprising a frequency subband-based analysis of the at least one residual sub-component (r).

12. The method according to claim 11, wherein said frequency subband-based analysis comprises the steps of:

applying a short-term Fourier transform (STFT) to the at least one residual sub-component (r) to form at least one frequency residual sub-component (r(b)); and

filtering of the at least one frequency residual sub-component by a frequency filter bank to obtain the residual structures Sf_r(b) of the frequency subbands.

13. The method according to claim 1, comprising an analysis of correlation between the at least two channels (L, R) to determine a corresponding correlation value (c), and in that the coded audio signal furthermore comprises the correlation value (c).

14. The method of decoding a reception signal comprising a coded audio signal constructed according to claim 1, the decoding method comprising a transformation by inverse principal component analysis (PCA⁻

1) to form at least two decoded channels (L′

, R′

) corresponding to the at least two channels (L, R) arising from the original multi-channel audio signal, wherein the method comprises the decoding of at least one residual structure (Sf_r) of a frequency subband so as to synthesize at least one decoded residual sub-component (r′

;

A′

(n,b)).

15. The decoding method according to claim 14, comprising the steps of:

receiving the coded audio signal (SC);

extracting a decoded principal component (CP′

) and at least one decoded transformation parameter;

decomposing the decoded principal component (CP′

) into at least one decoded frequency principal sub-component;

transforming the at least one decoded principal sub-component and the at least one decoded residual sub-component (A′

(n,b)) into decoded frequency subbands; and

combining the decoded frequency subbands to form the at least two decoded channels (L′

, R′

).

16. The decoding method according to claim 14, comprising the steps of:

receiving the coded audio signal (SC);

extracting a decoded principal component (y′

) and at least one decoded transformation parameter; and

forming the at least two channels (L′

, R′

) decoded by the inverse principal component analysis as a function of the at least one decoded transformation parameter, of the decoded principal component (y′

) and of the at least one decoded residual sub-component (r′

).

18. A scalable decoder of a reception signal comprising a coded audio signal constructed according to claim 1, the decoder comprising transformation means (44) based on inverse principal component analysis (PCA⁻

1) for forming at least two decoded channels (L′

, R′

) corresponding to the at least two channels (L, R) arising from the original multi-channel audio signal, wherein the decoder comprises frequency synthesis means 45 for decoding at least one residual structure (Sf_r) of a frequency subband so as to synthesize at least one decoded residual sub-component (r′

;

A′

(n,b)).

19. System comprising:

a scalable encoder of a multi-channel audio signal (C₁, . . . , C_M), comprising transformation means (28) based on principal component analysis (PCA) transforming at least two channels (L, R) of the audio signal into a principal component (CP) and at least one residual sub-component (r) by rotation defined by a transformation parameter (θ

, θ

(b_i)), wherein the encoder comprises;

(i) structure formation means (30) for forming a frequency subband-based residual structure (Sf_r) on the basis of the at least one residual sub-component (r), and

(ii) defining means (29) for defining a coded audio signal (SC) comprising the principal component (CP), at least one residual structure (Sf_r) of a frequency subband and the transformation parameter (θ

); and

a scalable decoder of a reception signal comprising a coded audio signal constructed according to claim 1, the decoder comprising transformation means (44) based on inverse principal component analysis (PCA<sup>−

1</sup>) for forming at least two decoded channels (L′

, R′

) corresponding to the at least two channels (L, R) arising from the original multi-channel audio signal, wherein the decoder comprises frequency synthesis means 45 for decoding at least one residual structure (Sf_r) of a frequency subband so as to synthesize at least one decoded residual sub-component (r′

;

A′

(n,b)).

20. A computer program downloadable from a communication network and/or stored on a medium readable by computer and/or executable by a microprocessor, wherein the computer program comprises program code instructions for executing the steps of the coding method according to claim 1, when it is executed on a computer or a microprocessor.

21. A computer program downloadable from a communication network and/or stored on a medium readable by computer and/or executable by a microprocessor, wherein the computer program comprises program code instructions for executing the steps of the decoding method according to claim 14, when it is executed on a computer or a microprocessor.

17. A scalable encoder of a multi-channel audio signal (C₁, . . . , C_M), comprising transformation means (28) based on principal component analysis (PCA) transforming at least two channels (L, R) of the audio signal into a principal component (CP) and at least one residual sub-component (r) by rotation defined by a transformation parameter (θ

, θ

(b_i)), wherein the encoder comprises;

structure formation means (30) for forming a frequency subband-based residual structure (Sf_r) on the basis of the at least one residual sub-component (r); and

defining means (29) for defining a coded audio signal (SC) comprising the principal component (CP), at least one residual structure (Sf_r) of a frequency subband and the transformation parameter (θ

).