[mythtv-users] Digital Audio with myth

Steve Adeff adeffs at gmail.com
Mon Nov 28 16:50:03 EST 2005

On Monday 28 November 2005 16:18, Robert Denier wrote:
> On Monday 28 November 2005 02:08 pm, Nick wrote:
> > On 25/11/05, Phill Edwards <philledwards at gmail.com> wrote:
> [snip]
> > That's because the S/PDIF is outputting a digital stream which the
> > receiver decodes and is responsible for amplifying. I don't think it's
> > possible to dynamically adjust a digital audio stream before it hits
> > the amp.
> It is always possible to scale numbers and a digital stream is just a
> stream of numbers.  Now, as to what the sound card actually supports and
> what the drivers support, I have no idea.  Certainly not being able to
> control the volume from the digital jack is not a new thing.  I suppose the
> mixer controls probably control analog mixers on a sound cards...?  If that
> is the case, then it explains why control of the digital output level is
> generally not found.
> From a practical perspective, your better off to pass the unscaled numbers
> to your home theatre receiver.  The reason for this is if say you cut the
> volume to 1/4  (1/(2^2)) of its maximum in amplitude and you are sticking
> with 16 bits of precision then you have lost 2 bits of precision.
> Of course even hearing the difference between 14 and 16 bits is not that
> easy, and hearing the difference once you move to 24bits may in fact be
> impossible.
> -Robert

digital signals don't contain absolute volume levels, only relative within a 
dynamic range. You can't do normal volume control for an SPDIF signal. You 
can do range alterations, but then you loose quality.


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