[Vorbis-dev] 5.1 surround channel coupling
sgeseman at uni-paderborn.de
Fri Feb 2 16:01:22 PST 2007
Richard Lee wrote:
> But there is a caveat. Does Vorbis coupling preserve "phase" relations? Any references explaining this in simple detail?
"coupling" is a rather loose term in the sense that it doesn't exactly
specify HOW it's done. It can be understood as the opposite of coding
channels independently. Obviously there are many ways to do coupling.
Both a "lossless" variant and a "lossy" is possible within the Vorbis
specification. The former is supposed to exploit redundancies between
channels only while the latter is also a kind of irrelevancy reduction
(like ignoring phase relations for intensity stereo).
If you really want to know the gritty details you should take a look at
the Vorbis specification and the Vorbis Stereo modes HTML page.
In a nutshell:
"residue vector": A residue vector contains roughly speaking normalized
spectral coefficients for one channel, one packet. Its components
represent the "fine MDCT structure" and can be understood as function of
frequency for a certain time slot.
- arbitrary pairs of residue vectors can be transformed in-place
(square polar mapping). Cascading these transforms is possible.
- residue vectors can be interleaved to form larger vectors
- vectors are coded via multi-stage vector quantization
More information about the Vorbis-dev