On Sun, Dec 14, 2008 at 10:53:57PM +0000, Dieter wrote:
> > > > Something of an idle question: According to audioctl, my azalia
> > > > device only supports 16-bit audio, but according to the data sheet
> > > > the codec also offers 20- and 24-bit audio.  Are there any plans
> > > > to add support for this?
> > > > 
> > > > No, I have no idea what you would actually use this for.  In particular,
> > > > I doubt that the analog inputs and outputs offer anywhere near that
> > > > dynamic range.  Still, you'd think the codec designers included these
> > > > capabilities for a reason.
> > > 
> > > we could support 24-bit but there are bigger fish to fry, imo.
> > 
> > hmm, this is even trickier than I thought.
> > 
> > the problem is 20 and 24-bit formats are actually 20 and 24 bits
> > of data in a 32 bit sample.  internally audio(4) uses "precision"
> > as the exact sample size.  so, we have to distinguish between
> > "padded" and non-padded formats in audio(4) first.
> > 
> > btw, 32-bit formats should already be supported, afaics.  they
> > aren't "padded".
> 
> Could one pretend that 20 and 24 bits are 32 bits with the lower bits
> zero?

you're missing the point, I guess I'm not clear.  internally, audio
would use 32 bits.  that is the sample size.  so when you query
it with audioctl, it'll say it's using 32-bit, but really you are
using 24-bit.  we just need a clever way to distinguish this without
causing a "flag day" API/ABI change in all the drivers/apps, etc.

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