Audio decoder for audio channel reconstruction
A method and apparatus for reconstructing N audio channels from M audio channels is disclosed. The method includes receiving a bitstream containing an encoded audio signal representing the M audio channels and decoding the encoded audio signal to obtain a frequency domain representation of the M audio channels. The method further includes extracting a parameter from the bitstream and reconstructing at least one of the N audio channels using the parameter. The parameter represents an angle between two signals, at least one of which is included in the M audio channels.
1. A method performed in an audio decoder for reconstructing N original audio channels from M audio channels, the method comprising:
receiving a bitstream containing a parameter, φ, and an encoded audio signal representing the M audio channels;
decoding the encoded audio signal to obtain a frequency domain representation of the M audio channels;
extracting the parameter, φ, from the bitstream; and
reconstructing at least one of the N original audio channels from the M audio channels based on:
a′=m cos φ+ s sin φ,
where a′ is the at least one reconstructed audio channel, m is one of the M audio channels, s is derived from a weighted or unweighted combination of the N original channels, φ is an angle representing amounts of signal m and s present in a′, and M is equal to two.
2. The method of claim 1 wherein the parameter, φ, includes a parameter for each of a plurality of frequency bands, and the reconstructing is performed for each of the plurality of frequency bands using the corresponding parameter for that band.
3. The method of claim 1 wherein m and s are decorrelated.
4. The method of claim 1 wherein m and s are normalized using an energy of m and s, respectively.
5. The method of claim 1 wherein the parameter is quantized.
6. The method of claim 1 further comprising denormalizing the at least one reconstructed audio channel by multiplying the at least one reconstructed audio channel by a square root of an energy of m or s.
7. A non-transitory computer readable medium comprising instructions that when executed by a processor perform the method of claim 1 .
8. An apparatus for reconstructing N original audio channels from M audio channels, the audio decoder comprising:
an input interface for receiving a bitstream containing a parameter, φ, and an encoded audio signal representing the M audio channels;
a decoder for obtain a frequency domain representation of the M audio channels;
an extractor for obtaining the parameter, φ, from the bitstream; and
a recontructor for generating at least one of the N original audio channels from the M audio channels based on:
a′=m cos φ+ s sin φ,
where a′ is the at least one reconstructed audio channel, m is one of the M audio channels, s is derived from a weighted or unweighted combination of the N original channels, φ is an angle representing amounts of signal m and s present in a′, and M is equal to two.
9. The apparatus of claim 8 wherein the parameter, φ, includes a parameter for each of a plurality of frequency bands, and the reconstructing is performed for each of the plurality of frequency bands using the corresponding parameter for that band.
10. The apparatus of claim 8 wherein m and s are decorrelated.
11. The apparatus of claim 8 wherein m and s are normalized using an energy of m and s, respectively.
12. The apparatus of claim 8 wherein the parameter is quantized.
13. The apparatus of claim 8 further comprising a denormalizer for multiplying the at least one reconstructed audio channel using a square root of an energy of m or s.