Subject: Re: [linux-audio-dev] OSS difference between SOUND_MIXER_PCM & SOUND_MIXER_ALTPCM
From: Fred Gleason (fredg_AT_wava.com)
Date: Tue May 07 2002 - 14:01:55 EEST
On Tuesday 07 May 2002 03:38, Lucia Cappellato wrote:
> I see that with SOUND_MIXER_PCM & SOUND_MIXER_ALTPCM
> the value of volume change but which is the most important?
It depends upon the architecture of the specific sound card in question. Many
of the "consumer" type cards (e.g. Soundblasters & such) have an internal
buss to which many separate sources (PCM, CD, AUX, LINE_IN, whatever) can mix
to, with a "Master" output that typically feeds the "Line Out" jack.
Unfortunately, this can be quite card-specific, with even some of the
consumer type cards (SBLive, Ensoniq AudioPCI) offering features beyond the
basic set described here. And for "Pro" type cards (e.g. the Midiman series)
all bets are off -- these types of cards tend to use radically different
architectures. This is why you will commonly see mixers written for a
specific model of card. For my own work, I've found what works best is to
standardize on a specific type of card, learn all it's idiosyncrasies, and
then use that for all projects.
> Why SOUND_MIXER_VOLUME & SOUND_MIXER_SPEAKER don't
> influence the volume of a playback soundtrack?
Probably because you are not monitoring the card's output through a port
controlled by one of these settings. Again, very card specific. You'll need
to experiment.
Cheers!
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