Complex transforms for multi-channel audio

• US 20070172071A1
• Filed: 01/20/2006
• Published: 07/26/2007
• 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 8,190,425 B2
• Time in Patent Office: Days
• US Class Current: 381/23
• CPC Class Codes: H04S 3/008 in which the audio signals are in digital form, i.e. employing more than two discrete digital channels data reduction aspects thereof based on psychoacoustics G10L19/02

Abstract

An audio encoder encodes a combined channel (e.g., a sum channel) for a group of plural physical audio channels. The encoder determines plural parameters for representing individual physical channels of the group as modified versions of the encoded combined channel. The plural parameters comprise ratios of power in each individual channel to power in the combined channel (e.g., a ratio of the power of a right channel to the power of the combined channel, and a ratio of the power of the left channel to the power of the combined channel). The plural parameters can include a complex parameter. The combined channel and the plural parameters facilitate reconstruction at the audio decoder of source channels. An audio decoder performs a forward complex transform on the multi-channel audio data and reconstructs plural channels from the multi-channel audio data. The decoder can maintain second-order statistics for the source channels.

Claims

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

encoding a combined channel for a group of plural physical audio channels; and

determining plural parameters for representing individual physical channels of the group as modified versions of the encoded combined channel, wherein the plural parameters comprise ratios of power in each individual channel to power in the combined channel.

2. The method of claim 1 wherein the encoding a combined channel and the determining plural parameters is performed selectively on a frequency-band basis.

3. The method of claim 1 wherein a decoder uses the encoded combined channel and the plural parameters in reconstruction of at least two of the plural physical channels.

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

5. The method of claim 1 wherein the plural parameters further comprise a complex parameter.

6. The method of claim 5 wherein the complex parameter is an imaginary-to-real ratio representing cross-channel correlation.

7. The method of claim 1 wherein the plural parameters are sufficient to for an audio decoder to derive a normalized power correlation matrix for representing individual physical channels of the group as modified versions of the encoded combined channel.

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

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

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

encoding a combined channel for the group;

determining plural parameters for representing individual source channels of the group as modified versions of the encoded combined channel, wherein the plural parameters comprise at least one complex parameter having an imaginary number component and a real number component; and

sending the encoded combined channel and the plural parameters to an audio decoder;

wherein the encoded combined channel and the plural parameters facilitate reconstruction at the audio decoder of at least two of the plural source channels.

10. The method of claim 9 wherein the at least one complex parameter is derived at the audio encoder using a forward complex transform.

11. The method of claim 9 wherein:

the plural parameters comprise a power ratio for each of the plural source channels, where the power ratio comprises for each of the plural source channels, a ratio of power in the source channel to power in the encoded combined channel; and

the power ratios are jointly quantized.

12. The method of claim 9 wherein the plural parameters are determined on a per-band basis.

13. The method of claim 9 wherein the plural parameters vary by time and are interpolated between different time instances.

14. The method of claim 13 wherein the interpolation is selectively applied.

15. The method of claim 9 wherein the at least one complex parameter comprises a ratio of imaginary component to real component.

16. A computer-readable medium storing computer-executable instructions for causing a computer programmed thereby to perform the method of claim 9.

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

receiving encoded multi-channel audio data, the encoded multi-channel data comprising an encoded combined channel; and

decoding the audio data, wherein the decoding comprises;

performing a forward complex transform on the multi-channel audio data; and

reconstructing plural channels from the multi-channel audio data.

18. The method of claim 17 wherein the performing the forward complex transform comprises deriving spectral coefficients for the encoded combined channel.

19. The method of claim 18 further comprising:

scaling the derived spectral coefficients using complex scale factors.

20. A computer-readable medium storing computer-executable instructions for causing a computer programmed thereby to perform the method of claim 17.