[Vorbis] Mono encoding w/ a stereo source.

[Monty]

On Wed, Nov 16, 2005 at 06:03:31PM +0000, John Edwards wrote:
> 
> 
> Michael Smith wrote:
> >On 11/16/05, Ian A. Underwood <agentgrn at dcne.net> wrote:
> >>I'm not sure since this is what I got from Lou at SpacialAudio:
> >>
> >>"We do not merge the channels for the encoding - this is all done by
> >>Ogg.  A simple method is usually to just add the left channel to the
> >>right to get the mono channel.  Although this is the correct way
> >>theoretically, in pratice it sounds too loud.  Thus I guess this is what
> >>they are doing in the Ogg encoder."
> >
> >What I said was a simple fact. Libvorbis has, internally, no
> >capabilities to produce a mono encoding from anything other than a
> >mono input. Libvorbis does not do downmixing ever, under any
> >circumstances - there's simply no code there to do it.
> >
> >So, either this person was confused, and gave you an incorrect answer,
> >or perhaps they're using some third-party wrapper library around
> >libvorbis that does the downmixing - in that latter case, they might
> >not be aware that the wrapper library is doing the downmixing (from
> >your report, apparently incorrectly), and not libvorbis.
> >
> >Since we don't know anything about how they're using libvorbis, we
> >can't really do more than what I've said above - which is just
> >guessing.
> >
> >Feel free to point the SpatialAudio people in my direction if they're
> >still confused about this.
> >
> 
> Unless, of course, someone is using the reference encoder which does 
> offer downmixing by adding the left and right channels and halving the 
> result.

...which does not result in the downmix being louder.

Perhaps they've set up a mono encode and are passing in a stereo
buffer without thinking?  You can pass a stereo buffer to a mono
encode; the right channel will simply be completely ignored.

Monty