Method, apparatus, and storage medium for decoding encoded audio channels
Multiple channels of audio are combined either to a monophonic composite signal or to multiple channels of audio along with related auxiliary information from which multiple channels of audio are reconstructed, including improved downmixing of multiple audio channels to a monophonic audio signal or to multiple audio channels and improved decorrelation of multiple audio channels derived from a monophonic audio channel or from multiple audio channels. Aspects of the disclosed invention are usable in audio encoders, decoders, encode/decode systems, downmixers, upmixers, and decorrelators.
1. A method for decoding M encoded audio channels representing N audio channels, where N is two or more, and a set of one or more spatial parameters, wherein one or more of said spatial parameters are differentially encoded, the method comprising:
a) receiving said M encoded audio channels and said set of spatial parameters,
b) applying a differential decoding process to the differentially encoded spatial parameters,
c) deriving N audio signals from said M encoded channels, wherein each audio signal is divided into a plurality of frequency bands, wherein each band comprises one or more spectral components,
d) generating a multichannel output signal from the N audio signals and the spatial parameters, and
e) synthesizing, by an audio reproduction device, the multichannel output signal, wherein:
M is two or more,
at least one of said N audio signals is a correlated signal derived from a weighted combination of at least two of said M encoded audio channels,
said set of spatial parameters includes a first parameter indicative of the amount of an uncorrelated signal to mix with a correlated signal and
step d) includes deriving at least one uncorrelated signal from said at least one correlated signal, and controlling the proportion of said at least one correlated signal to said at least one uncorrelated signal in at least one channel of said multichannel output signal in response to one or ones of said spatial parameters, wherein said controlling is at least partly in accordance with said first parameter.
2. The method of claim 1 wherein said differential decoding process is applied across time.
3. The method of claim 1 wherein said differential decoding process is applied across frequency.
4. The method of claim 1 wherein said differential decoding process is applied across both time and frequency.
5. An apparatus for decoding M encoded audio channels representing N audio channels, where N is two or more, and a set of one or more spatial parameters, wherein one or more of said spatial parameters are differentially encoded, the apparatus comprising a processor configured to:
a) receive said M encoded audio channels and said set of spatial parameters,
b) apply a differential decoding process to the differentially encoded spatial parameters,
c) derive N audio signals from said M encoded channels, wherein each audio signal is divided into a plurality of frequency bands, wherein each band comprises one or more spectral components, and
d) generate a multichannel output signal from the N audio signals and the spatial parameters, wherein:
M is two or more,
at least one of said N audio signals is a correlated signal derived from a weighted combination of at least two of said M encoded audio channels,
said set of spatial parameters includes a first parameter indicative of the amount of an uncorrelated signal to mix with a correlated signal,
generating a multichannel output signal from the N audio signals and the spatial parameters includes deriving at least one uncorrelated signal from said at least one correlated signal, and controlling the proportion of said at least one correlated signal to said at least one uncorrelated signal in at least one channel of said multichannel output signal in response to one or ones of said spatial parameters, wherein said controlling is at least partly in accordance with said first parameter, and
the apparatus synthesizes, by an audio reproduction device, the multichannel output signal.
6. The apparatus of claim 5 wherein said differential decoding process is applied across time.
7. The apparatus of claim 5 wherein said differential decoding process is applied across frequency.
8. The apparatus of claim 5 wherein said differential decoding process is applied across both time and frequency.
9. A non-transitory storage medium comprising a program of instructions, wherein the program of instructions, when executed by one or more devices, causes the one or more devices to perform a method for decoding M encoded audio channels representing N audio channels, where N is two or more, and a set of one or more spatial parameters, wherein one or more of said spatial parameters are differentially encoded, the method comprising:
a) receiving said M encoded audio channels and said set of spatial parameters,
b) applying a differential decoding process to the differentially encoded spatial parameters,
c) deriving N audio signals from said M encoded channels, wherein each audio signal is divided into a plurality of frequency bands, wherein each band comprises one or more spectral components, and
d) generating a multichannel output signal from the N audio signals and the spatial parameters, and
e) synthesizing, by an audio reproduction device, the multichannel output signal, wherein:
M is two or more,
at least one of said N audio signals is a correlated signal derived from a weighted combination of at least two of said M encoded audio channels,
said set of spatial parameters includes a first parameter indicative of the amount of an uncorrelated signal to mix with a correlated signal, and
generating a multichannel output signal from the N audio signals and the spatial parameters includes deriving at least one uncorrelated signal from said at least one correlated signal, and controlling the proportion of said at least one correlated signal to said at least one uncorrelated signal in at least one channel of said multichannel output signal in response to one or ones of said spatial parameters, wherein said controlling is at least partly in accordance with said first parameter.
10. The medium of claim 9 wherein said differential decoding process is applied across time.
11. The medium of claim 9 wherein said differential decoding process is applied across frequency.
12. The medium of claim 9 wherein said differential decoding process is applied across both time and frequency.