Inter-channel bandwidth extension

A method of decoding a signal, the method comprising:

• receiving a bitstream from an encoder, the bitstream comprising at least a low-band mid channel bitstream, a high-band mid channel bandwidth extension (BWE) bitstream, and a stereo downmix/upmix parameter bitstream;
• decoding, at a decoder, the low-band mid channel bitstream to generate a low-band mid signal and a low-band mid excitation signal;
• generating a non-linear harmonic extension of the low-band mid excitation signal corresponding to a high-band BWE portion;
• decoding the high-band mid channel BWE bitstream to generate a synthesized high-band mid signal based on the non-linear harmonic extension of the low-band mid excitation signal and based on high-band mid channel BWE parameters;
• determining an inter-channel bandwidth extension (ICBWE) gain mapping parameter corresponding to the synthesized high-band mid signal, the ICBWE gain mapping parameter based on a selected frequency-domain gain parameter that is extracted from the stereo downmix/upmix parameter bitstream;
• performing a gain scaling operation on the synthesized high-band mid signal based on the ICBWE gain mapping parameter to generate a reference high-band channel and a target high-band channel;
• and
• outputting a first audio channel and a second audio channel, the first audio channel based on the reference high-band channel, and the second audio channel based on the target high-band channel.

A non-transitory computer-readable medium comprising instructions for decoding a signal, the instructions, when executed by a processor within a decoder, cause the processor to perform operations comprising:

• receiving a bitstream from an encoder, the bitstream comprising at least a low-band mid channel bitstream, a high-band mid channel bandwidth extension (BWE) bitstream, and a stereo downmix/upmix parameter bitstream;
• decoding the low-band mid channel bitstream to generate a low-band mid signal and a low-band mid excitation signal;
• generating a non-linear harmonic extension of the low-band mid excitation signal corresponding to a high-band BWE portion;
• decoding the high-band mid channel BWE bitstream to generate a synthesized high-band mid signal based on the non-linear harmonic extension of the low-band mid excitation signal and based on high-band mid channel BWE parameters;
• determining an inter-channel bandwidth extension (ICBWE) gain mapping parameter corresponding to the synthesized high-band mid signal, the ICBWE gain mapping parameter based on a selected frequency-domain gain parameter that is extracted from the stereo downmix/upmix parameter bitstream;
• performing a gain scaling operation on the synthesized high-band mid signal based on the ICBWE gain mapping parameter to generate a left high-band channel and a right high-band channel;
• and
• generating a first audio channel and a second audio channel, the first audio channel based on the left high-band channel, and the second audio channel based on the right high-band channel.

An apparatus comprising:

• means for receiving a bitstream from an encoder, the bitstream comprising at least a low-band mid channel bitstream, a high-band mid channel bandwidth extension (BWE) bitstream, and a stereo downmix/upmix parameter bitstream;
• means for decoding the low-band mid channel bitstream to generate a low-band mid signal and a low-band mid excitation signal;
• means for generating a non-linear harmonic extension of the low-band mid excitation signal corresponding to a high-band BWE portion;
• means for decoding the high-band mid channel BWE bitstream to generate a synthesized high-band mid signal based on the non-linear harmonic extension of the low-band mid excitation signal and based on high-band mid channel BWE parameters;
• means for determining an inter-channel bandwidth extension (ICBWE) gain mapping parameter corresponding to the synthesized high-band mid signal, the ICBWE gain mapping parameter based on a selected frequency-domain gain parameter that is extracted from the stereo downmix/upmix parameter bitstream;
• means for performing a gain scaling operation on the synthesized high-band mid signal based on the ICBWE gain mapping parameter to generate a left high-band channel and a right high-band channel;
• and
• means for outputting a first audio channel and a second audio channel, the first audio channel based on the left high-band channel, and the second audio channel based on the right high-band channel.