Advanced encoding of multi-channel digital audio signals

1. A method for coding a multi-channel audio signal representing a sound scene comprising a plurality of sound sources, comprising:

decomposing the multi-channel signal into frequency bands; and

obtaining data representative of a direction of the sound sources of the sound scene;

selecting a set of sound sources of the sound scene constituting principal sources;

adapting the data representative of the direction of the selected principal sources, as a function of restitution characteristics of the multi-channel signal, by modification of a position of the sources to obtain a separation between two sources;

determining a matrix for mixing the principal sources as a function of the adapted data;

matrixing the principal sources by the matrix determined to obtain a sum signal with a reduced number of channels; and

coding the data representative of the direction of the sound sources and formation of a binary stream comprising the coded data, the binary stream being transmittable in parallel with the sum signal.

2. The method as claimed in claim 1 , wherein the data representative of the direction are information regarding directivities representative of a distribution of the sound sources in the sound scene.

3. The method as claimed in claim 2 , wherein the coding of the information regarding directivities is performed by a parametric representation procedure.

4. The method as claimed in claim 2 , wherein the coding of the directivity information is performed by a principal component analysis procedure delivering base directivity vectors associated with gains allowing the reconstruction of the initial directivities.

5. The method as claimed in claim 2 , wherein the coding of the directivity information is performed by a combination of a principal component analysis procedure and of a parametric representation procedure.

6. The method as claimed in claim 1 , comprising coding secondary sources from among unselected sources of the sound scene and inserting coding information for the secondary sources into the binary stream.

7. A method for decoding a multi-channel audio signal representing a sound scene comprising a plurality of sound sources, with the help of a binary stream and of a sum signal, comprising:

extracting from the binary stream and decoding data representative of the direction of the sound sources in the sound scene;

adapting at least some of the direction data as a function of restitution characteristics of the multi-channel signal, by modifying a position of the sources obtained by the direction data, to obtain a separation between two sources;

determining a matrix for mixing the sum signal as a function of the adapted data and calculation of an inverse mixing matrix;

dematrixing the sum signal by the inverse mixing matrix to obtain a set of principal sources; and

reconstructing the multi-channel audio signal by spatialization at least of the principal sources with the decoded extracted data.

8. The decoding method as claimed in claim 7 , further comprising:

extracting, from the binary stream, coding information for coded secondary sources;

decoding the secondary sources with the help of the coding information extracted; and

grouping the secondary sources with the principal sources for the spatialization.

9. A coder of a multi-channel audio signal representing a sound scene comprising a plurality of sound sources, the decoder being configured for:

decomposing the multi-channel signal into frequency bands;

obtaining data representative of a direction of the sound sources of the sound scene;

selecting a set of sound sources of the sound scene constituting principal sources;

adapting the data representative of the direction of the selected principal sources, as a function of restitution characteristics of the multi-channel signal, by an element for modifying a position of the sources to obtain a separation between two sources;

determining a matrix for mixing the principal sources as a function of the data arising from the adaptation module;

matrixing the principal sources selected by the matrix determined to obtain a sum signal with a reduced number of channels;

coding the data representative of the direction of the sound sources; and

forming a binary stream comprising the coded data, the binary stream being transmittable in parallel with the sum signal.

10. A decoder of a multi-channel audio signal representing a sound scene comprising a plurality of sound sources, that receives as input a binary stream and a sum signal, the decoder being configured for:

extracting and decoding data representative of a direction of the sound sources in the sound scene;

adapting at least some of the direction data as a function of restitution characteristics of the multi-channel signal, by an element for modifying the position of the sources obtained by the direction data, to obtain a separation between two sources;

determining a matrix for mixing the sum signal as a function of the data arising from the module for adapting and for calculating an inverse mixing matrix;

dematrixing the sum signal by the inverse mixing matrix to obtain a set of principal sources; and

reconstructing the multi-channel audio signal by spatialization at least of the principal sources with the decoded extracted data.

11. A non-transitory computer program product comprising code instructions for the implementation of the steps at least one of the coding method as claimed in claim 1 and of the decoding method for decoding a multi-channel audio signal representing a sound scene comprising a plurality of sound sources, with the help of a binary stream and of a sum signal, comprising:

extracting from the binary stream and decoding data representative of the direction of the sound sources in the sound scene;

adapting at least some of the direction data as a function of restitution characteristics of the multi-channel signal, by modifying a position of the sources obtained by the direction data, to obtain a separation between two sources;

determining a matrix for mixing the sum signal as a function of the adapted data and calculating an inverse mixing matrix;

dematrixing the sum signal by the inverse mixing matrix to obtain a set of principal sources; and

reconstructing the multi-channel audio signal by spatialization at least of the principal sources with the decoded extracted data, when these instructions are executed by a processor.