[CELT-dev] Stereo <-> Mono

Timothy B. Terriberry tterribe at xiph.org
Wed Jan 12 10:12:21 PST 2011

> 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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