COMPLEX-TRANSFORM CHANNEL CODING WITH EXTENDED-BAND FREQUENCY CODING

• US 20110035226A1
• Filed: 10/19/2010
• Published: 02/10/2011
• Est. Priority Date: 01/20/2006
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Chen, Wei-Ge, Mehrotra, Sanjeev
• Granted Patent: US 9,105,271 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 21/038 using band spreading techniques

Abstract

An audio encoder receives multi-channel audio data comprising a group of plural source channels and performs channel extension coding, which comprises encoding a combined channel for the group and determining plural parameters for representing individual source channels of the group as modified versions of the encoded combined channel. The encoder also performs frequency extension coding. The frequency extension coding can comprise, for example, partitioning frequency bands in the multi-channel audio data into a baseband group and an extended band group, and coding audio coefficients in the extended band group based on audio coefficients in the baseband group. The encoder also can perform other kinds of transforms. An audio decoder performs corresponding decoding and/or additional processing tasks, such as a forward complex transform.

Claims

1. In an audio encoder, a computer-implemented method comprising:

receiving multi-channel audio data, the multi-channel audio data comprising a group of plural source channels;

performing channel extension coding on the multi-channel audio data, the channel extension coding comprising;

encoding a combined channel for the group; and

determining plural parameters for representing individual source channels of the group as modified versions of the encoded combined channel, the plural parameters comprising a parameter representing an imaginary-to-real ratio of cross-correlation between the individual source channels; and

performing frequency extension coding on the multi-channel audio data.

2. The method of claim 1 wherein the frequency extension coding comprises:

partitioning frequency bands in the multi-channel audio data into a baseband group and an extended band group; and

coding audio coefficients in the extended band group based on audio coefficients in the baseband group.

3. The method of claim 1 further comprising:

sending the encoded combined channel and the plural parameters for representing individual source channels of the group as modified versions of the encoded combined channel to an audio decoder; and

sending frequency extension coding data comprising plural parameters for representing extended-band coefficients to the audio decoder;

wherein the encoded combined channel, the plural parameters for representing individual source channels of the group as modified versions of the encoded combined channel, and the frequency extension coding data facilitate reconstruction at the audio decoder of at least two of the plural source channels.

4. The method of claim 1 wherein the audio encoder comprises a base transform module, a frequency extension transform module, and a channel extension transform module.

5. The method of claim 1 further comprising performing base coding on the multi-channel audio data;

and

performing a multi-channel transform on base-coded multi-channel audio data.

6. The method of claim 1 wherein the plural parameters for representing extended-band coefficients comprise scale parameters and shape parameters.

7. The method of claim 1 wherein the plural parameters for representing extended-band coefficients are determined for extended-band coefficients in the combined channel, and wherein the plural parameters for representing extended-band coefficients are omitted for one or more frequency ranges in one or more of the plural source channels.

8. The method of claim 1 wherein the plural parameters for representing individual source channels of the group as modified versions of the encoded combined channel further comprise plural power ratios representing power of the individual source channels relative to the combined channel.

9. The method of claim 1 wherein the combined channel is a sum channel.

10. The method of claim 1 wherein the combined channel is a difference channel.

11. The method of claim 1 wherein the channel extension coding is performed for less than all of the multi-channel audio data.

12. A computer-readable storage medium storing computer-executable instructions for causing a computer programmed thereby to perform the method of claim 1.

13. In an audio decoder, a computer-implemented method of decoding encoded multi-channel audio data, the method comprising:

receiving channel extension coding data comprising;

a combined audio channel;

plural power ratios representing power of individual audio channels relative to the combined audio channel; and

a complex parameter representing an imaginary-to-real ratio of cross-correlation between the individual audio channels;

receiving frequency extension coding data comprising scale and shape parameters for representing extended-band coefficients as scaled versions of baseband coefficients; and

reconstructing the individual audio channels using the channel extension coding data and the frequency extension coding data.

14. The method of claim 13 wherein the reconstructing comprises frequency extension processing using the frequency extension coding data followed by channel extension processing using the channel extension coding data.

15. The method of claim 13 wherein the reconstructing comprises performing a real portion of a forward channel extension transform followed by frequency extension processing.

16. The method of claim 15 wherein the forward channel extension transform is a modulated complex lapped transform comprising the real portion and an imaginary portion.

17. The method of claim 13 wherein the reconstructing comprises:

using a complex transform as a channel extension transform; and

using a non-complex transform as a frequency extension transform.

19. In an audio decoder, a computer-implemented method comprising:

receiving encoded multi-channel audio data in a bitstream, the encoded multi-channel audio data comprising channel extension coding data and frequency extension coding data, wherein the channel extension coding data comprises a combined channel for the plural audio channels and plural parameters for representing individual channels of the plural audio channels as modified versions of the combined channel;

determining based on information in the bitstream whether the plural parameters comprise (a) normalized correlation matrix parameters, or (b) a complex parameter representing a ratio comprising an imaginary component and a real component of cross-correlation between two of the plural audio channels;

based on the determining, decoding the plural parameters; and

reconstructing plural audio channels using the channel extension coding data and the frequency extension coding data.

18. A computer-readable storage medium storing computer-executable instructions for causing a computer programmed thereby to perform the method of claim 20.

20. A computer-readable storage medium storing computer-executable instructions for causing a computer programmed thereby to perform the method of claim 19.