[CELT-dev] Stereo <-> Mono

Gregory Maxwell gmaxwell at gmail.com
Wed Jan 12 11:00:44 PST 2011

On the plus side- CELT has no real per frame overhead.  All you really
lose by coding N mono signals as N mono signals is the ability to take
advantage of redundancy between the channels, which won't exist if
ther are unrelated.

On 1/12/11, Timothy B. Terriberry <tterribe at xiph.org> wrote:
>> Does Celt (in particular version 0.7.1) exploits correlation between the
>> two channels in stereo mode?
>> In practice, is it possible to use the two channels as two mono signals
>> without affecting quality?
> CELT does indeed use a variant of mid-side stereo to exploit correlation
>   between channels. Version 0.7.1 in particular did not switch to
> intensity mode in the higher bands, so it should not be _terrible_ if
> fed two mono signals, but a) you won't get much, if any, savings in
> bitrate compared to using two independent streams if things really are
> uncorrelated, and b) in all cases CELT decides whether or not to use
> short blocks on a frame-by-frame basis, so there will definitely be some
> quality loss if the transients do not appear in the same place.
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