On Mon, 2005-03-28 at 22:36 -0500, Lee Revell wrote:
> On Mon, 2005-03-28 at 09:42 +1000, Benjamin Herrenschmidt wrote:
> > It seems that Apple's driver has an in-kernel framework for doing volume
> > control, mixing, and other horrors right in the kernel, in temporary
> > buffers, just before they get DMA'ed (gack !)
> >
> > I want to avoid something like that. How "friendly" would Alsa be to
> > drivers that don't have any HW volume control capability ? Does typical
> > userland libraries provide software processing volume control ? Do you
> > suggest I just don't do any control ? Or should I implement a double
> > buffer scheme with software gain as well in the kernel driver ?
>
> alsa-lib handles both mixing (dmix plugin) and volume control (softvol
> plugin) in software for codecs like this that don't do it in hardware.
> Since Windows does mixing and volume control in the kernel (ugh) it's
> increasingly common to find devices that cannot do these. You don't
> need to handle it in the driver at all.
Yah, OS X does it in the kernel too lately ... at least Apple drivers
are doing it, it's not a "common" lib. They also split treble/bass that
way when you have an iSub plugged on USB and using the machine internal
speakers for treble.
> dmix has been around for a while but softvol plugin is very new, you
> will need ALSA CVS or the upcoming 1.0.9 release.
Ok.
Ben.
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