On Fri, 28 Mar 2003, Takashi Iwai wrote:
> At Thu, 27 Mar 2003 23:14:22 -0400,
> Manuel Jander wrote:
> >
> > Hi,
> >
> > Paul Davis wrote:
> >
> > >>When an application opens a mono substream, the sound has to
> > >>be sent to one channel only or must the low level driver
> > >>transparently convert it to stereo ?
> > >>
> > >>
> > >
> > >one channel only.
> > >
> > >in ALSA, low level drivers do not do any kind of format
> > >conversion. that is accomplished (if necessary) by code running in
> > >user-space, typically part of alsa-lib. the low level driver simply
> > >advertises the capabilities of the hardware, provides ways to use
> > >those capabilities, and lets the midlevel code and alsa-lib do the rest.
> > >
> > >
> >
> > ...but, if you are doing mono playback, your sound driver has to setup
> > your soundcard to playback on both channels the same mono channel. The
> > Vortex
> > driver (still not in the main branch) for example splits the mono signal
> > on its internal
> > mixer into 2 identical signals which are feed one into each CODEC channels.
>
> no, please don't do that.
> in the ALSA, instead of the lowlevel driver, alsa-lib (and
> oss-emulation module) will do this job.
>
> the driver is supposed to inform exactly what it supports.
> in this case, both channels_min and channels_max will be 2.
> the difference of configuration will be absorbed by the plug-in of
> alsa-lib and oss-emulation module.
In other words: Keep the lowlevel driver code as simple as possible....
Jaroslav
-----
Jaroslav Kysela <[EMAIL PROTECTED]>
Linux Kernel Sound Maintainer
ALSA Project, SuSE Labs
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