CRITICAL SAMPLING ENCODING WITH A PREDICTIVE ENCODER

• US 20110178809A1
• Filed: 10/05/2009
• Published: 07/21/2011
• Est. Priority Date: 10/08/2008
• Status: Active Grant

• Current Assignee: Orange S.A.
• Original Assignee: Orange S.A.
• Inventors: Philippe, Pierrick, Virette, David
• Granted Patent: US 8,880,411 B2
• Time in Patent Office: Days
• US Class Current: 704/500
• CPC Class Codes: G10L 19/0212 using orthogonal transformation
• CPC Class Codes: G10L 19/022 Blocking, i.e. grouping of samples in time; Choice of analysis windows; Overlap factoring
• CPC Class Codes: G10L 19/04 using predictive techniques
• CPC Class Codes: G10L 19/107 Sparse pulse excitation, e.g. by using algebraic codebook
• CPC Class Codes: G10L 19/20 using sound class specific coding, hybrid encoders or object based coding

Abstract

A method for encoding and decoding a digital audio signal is provided, said method comprising the steps of: encoding a first sequence of samples of the digital signal according to a transform encoding; encoding a second sequence of samples of the digital signal according to a predictive encoding; wherein the second sequence starts before the end of the first sequence, a subsequence common to the first and second sequences being thus encoded both by predictive encoding and by transform encoding.

Claims

1. A method for coding a digital signal, comprising the steps of:

coding a first sequence of samples of the digital signal according to a transform coding;

coding a second sequence of samples of the digital signal according to a predictive coding;

wherein the second sequence begins before the end of the first sequence, a sub-sequence common to the first and second sequences thus being coded at one and the same time by predictive coding and by transform coding.

2. The method as claimed in claim 1, wherein the transform coding of the first sequence comprises:

applying an analysis window making it possible to deduce from a perfect reconstruction relation for the digital signal a synthesis window comprising at least three parts;

a first nominal part,

a second substantially zero terminal part, and

a third continuous intermediate part between the first and second parts,

wherein at least parts of the analysis window making it possible to deduce respectively said second and third parts of the synthesis window are applied to the sub-sequence common to the two sequences.

3. The method as claimed in claim 1, wherein the transform coding is a critical sampling coding.

4. The method as claimed in claim 2, wherein the synthesis window further comprises a fourth part of a smooth transition between an initial value and a value of the nominal part, and the third part is an abrupt transition between a value of the nominal part and a value of the substantially zero part.

5. The method as claimed in claim 1, wherein the first and second sequences belong to one and the same frame of the digital signal.

10. A non-transitory computer program product comprising instructions for the implementation of the method as claimed in claim 1 when the program is executed by a processor.

6. A method for decoding a digital signal, comprising the steps of:

receiving a transform vector coding a first sequence of samples of the digital signal according to a transform coding;

receiving a prediction vector coding a second sequence of samples of the digital signal according to a predictive coding;

wherein the second sequence begins before the end of the first sequence, a sub-sequence common to the first and second sequences thus being received coded at one and the same time by predictive coding and by transform coding; and

wherein the method further comprises the steps of;

a) applying to the transform vector a transform inverse to the transform coding to decode a sub-sequence of the first sequence not coded by predictive coding;

b) decoding at least in the prediction vector the sub-sequence common to the first and second sequences at least by a predictive decoding, based on at least one sample arising from step a); and

c) decoding in the predictive vector by a predictive decoding a sub-sequence of the second sequence not coded by transform coding, based on at least one sample arising from one of steps a) and b).

7. The method as claimed in claim 6, wherein step b) comprises the sub-steps of:

b1) decoding in the predictive vector the sub-sequence common to the first and second sequences by a predictive decoding, based on at least one sample arising from step a);

b2) applying to the transform vector a transform inverse to the transform coding to decode the sub-sequence common to the first and second sequences; and

b3) decoding the sub-sequence common to the first and second sequences by combining at least one sample arising from step b1) with a corresponding sample arising from step b2).

8. The method as claimed in claim 6, wherein step b) comprises the sub-steps of:

b4) decoding in the predictive vector the sub-sequence common to the first and second sequences by a predictive decoding, based on at least one sample arising from step a);

b5) creating on a basis of at least one sample arising from step b4) a sample containing an aliasing equivalent to a transform coding followed by a transform decoding;

b6) applying to the transform vector a transform inverse to the transform coding to decode the sub-sequence common to the first and second sequences; and

b7) decoding the sub-sequence common to the first and second sequences by combining at least one sample arising from step b5) with a corresponding sample arising from step b6).

9. The method as claimed in claim 6, wherein step a) comprises:

applying a synthesis window comprising at least three parts;

a first nominal part,

a second substantially zero terminal part,

a third continuous intermediate part between the first and second zones,

and wherein at least the second and third parts of the synthesis window are applied to samples coding the sub-sequence common to the two sequences.

11. A non-transitory computer program product comprising instructions for the implementation of the method as claimed in claim 6 when the program is executed by a processor.

12. A coding entity for a digital signal, comprising:

a transform coder for coding a first sequence of samples of the digital signal according to a transform coding; and

a predictive coder for coding a second sequence of samples of the digital signal according to a predictive coding;

wherein the second sequence begins before the end of the first sequence, a sub-sequence common to the first and second sequences thus being coded at one and the same time by predictive coding and by transform coding.

13. A decoding entity for a digital signal, comprising a receiver for receiving:

a transform vector coding a first sequence of samples of the digital signal according to a transform coding; and

a prediction vector coding a second sequence of samples of the digital signal according to a predictive coding;

wherein the second sequence begins before the end of the first sequence, a sub-sequence common to the first and second sequences thus being coded at one and the same time by predictive coding and by transform coding; and

wherein the decoding entity further comprises;

a first decoder for applying to the transform vector a transform inverse to the transform coding to decode a sub-sequence of the first sequence not coded by predictive coding;

a second decoder for decoding at least in the predictive vector the sub-sequence common to the first and second sequences at least by a predictive decoding, based on at least one sample arising from the first transform decoder; and

a third predictive decoder for decoding in the predictive vector by a predictive decoding a sub-sequence of the second sequence not coded by transform coding, based on at least one sample arising from one of the first and second decoders.

14. The decoding entity as claimed in claim 13, wherein the second decoder comprises:

first elements for decoding in the predictive vector the sub-sequence common to the first and second sequences by a predictive decoding, based on at least one sample restored by the first transform decoder;

second elements for applying to the transform vector a transform inverse to the transform coding to decode the sub-sequence common to the first and second sequences; and

third elements for decoding the sub-sequence common to the first and second sequences by combining at least one sample arising from the first elements with a corresponding sample arising from the second elements.

15. The decoding entity as claimed in claim 13, wherein the second decoder comprises:

first elements for decoding in the predictive vector the sub-sequence common to the first and second sequences by a predictive decoding, based on at least one sample restored by the first transform decoder;

fourth elements for creating an aliasing on a basis of at least one sample arising from the first elements equivalent to a transform coding followed by a transform decoding;

fifth elements for applying to the transform vector a transform inverse to the transform coding to decode the sub-sequence common to the first and second sequences; and

sixth elements for decoding the sub-sequence common to the first and second sequences by combining at least one sample arising from the fourth elements with a corresponding sample arising from the fifth elements.