Complex-transform channel coding with extended-band frequency coding

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.

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.