Reconstructing audio signals with multiple decorrelation techniques
A method performed in an audio decoder for decoding M encoded audio channels representing N audio channels is disclosed. The method includes receiving a bitstream containing the M encoded audio channels and a set of spatial parameters, decoding the M encoded audio channels, and extracting the set of spatial parameters from the bitstream. The method also includes analyzing the M audio channels to detect a location of a transient, decorrelating the M audio channels, and deriving N audio channels from the M audio channels and the set of spatial parameters. A first decorrelation technique is applied to a first subset of each audio channel and a second decorrelation technique is applied to a second subset of each audio channel. The first decorrelation technique represents a first mode of operation of a decorrelator, and the second decorrelation technique represents a second mode of operation of the decorrelator.
1. A method performed in an audio decoder for reconstructing N audio channels from an audio signal having M audio channels, the method comprising:
receiving a bitstream containing the M audio channels and a set of spatial parameters, wherein the set of spatial parameters includes an amplitude parameter and a correlation parameter;
decoding the M encoded audio channels, wherein each audio channel is divided into a plurality of frequency bands, and each frequency band includes one or more spectral components;
extracting the set of spatial parameters from the bitstream;
analyzing the M audio channels to detect a location of a transient;
decorrelating the M audio channels to obtain a decorrelated version of the M audio channels, wherein a first decorrelation technique is applied to a first subset of the plurality of frequency bands of each audio channel and a second decorrelation technique is applied to a second subset of the plurality of frequency bands of each audio channel;
deriving N audio channels from the M audio channels, the decorrelated version of the M audio channels, and the set of spatial parameters, wherein N is two or more, M is one or more, and M is less than N; and
synthesizing, by an audio reproduction device, the N audio channels as an output audio signal,
wherein both the analyzing and the decorrelating are performed in a frequency domain, the first decorrelation technique represents a first mode of operation of a decorrelator, the second decorrelation technique represents a second mode of operation of the decorrelator, and the audio decoder is implemented at least in part in hardware.
2. The method of claim 1 wherein the first mode of operation uses an all-pass filter and the second mode of operation uses a fixed delay.
3. The method of claim 1 wherein the analyzing occurs after the extracting and the deriving occurs after the decorrelating.
4. The method of claim 1 wherein the first subset of the plurality of frequency bands is at a higher frequency than the second subset of the plurality of frequency bands.
5. The method of claim 1 wherein the M audio channels are a sum of the N audio channels.
6. The method of claim 1 wherein the location of the transient is used in the decorrelating to process bands with a transient differently than bands without a transient.
7. The method of claim 6 wherein the N audio channels represent a stereo audio signal where N is two and M is one.
8. The method of claim 1 wherein the N audio channels represent a stereo audio signal where N is two and M is one.
9. The method of claim 1 wherein the first subset of the plurality of frequency bands is non-overlapping but contiguous with the second subset of the plurality of frequency bands.
10. A computer readable medium containing instructions that when executed by a processor perform the method of claim 1 .
11. An audio decoder for decoding M encoded audio channels representing N audio channels, the audio decoder comprising:
an input interface for receiving a bitstream containing the M encoded audio channels and a set of spatial parameters, wherein the set of spatial parameters includes an amplitude parameter and a correlation parameter;
an audio decoder for decoding the M encoded audio channels, wherein each audio channel is divided into a plurality of frequency bands, and each frequency band includes one or more spectral components;
a demultiplexer for extracting the set of spatial parameters from the bitstream;
a processor for analyzing the M audio channels to detect a location of a transient;
a decorrelator for decorrelating the M audio channels, wherein a first decorrelation technique is applied to a first subset of the plurality of frequency bands of each audio channel and a second decorrelation technique is applied to a second subset of the plurality of frequency bands of each audio channel;
a reconstructor for deriving N audio channels from the M audio channels and the set of spatial parameters, wherein N is two or more, M is one or more, and M is less than N; and
an audio reproduction device that synthesizes the N audio channels as an output audio signal,
wherein both the analyzing and the decorrelating are performed in a frequency domain, the first decorrelation technique represents a first mode of operation of a decorrelator, and the second decorrelation technique represents a second mode of operation of the decorrelator.