I have some very basic questions about how sound works under Linux that
aren't answered by either of the relevant Howto's. Perhaps someone here
can help.
First of all, I haven't been able to find a good explanation of the
fundamental model of how sound works, and Section 2 of the Sound Howto
only partially addresses the problem. One basic question is how
/dev/audio differs from /dev/dsp. I know from the Howto that /dev/audio
is a
Sun-compatible audio device and that /dev/dsp is a digital sampling
device - but what I don't know is how the behavior of /dev/dsp differs
from that of /dev/audio or how to decide which one to use for a
particular purpose such as recording.
Another question is how /dev/audio and/or /dev/dsp relates to (a) the
inputs available to the sound card, (b) the visible output of the mixer,
and (c) the signal sent by the sound card to the speakers. I've seen
references to the "recording source" (CD, microphone, line in), but it
wasn't clear whether these are sent to /dev/audio regardless of the
mixer settings. Also, if the mixer settings do determine what is sent
to /dev/audio, then what is the function of the recording source--since
the mixer can look at all sources at once? And if /dev/audio receives
the output of a single recording source, how can I access the output of
the mixer? Does the main mixer volume control affect the volume of the
recorded signal or only the volume of the attached speakers?
A further problem is that the two mixer programs I've looked at,
ossmixer and xmix, have very uninformative man pages. Looking at the
xmix 2.1 display, I see that each bar has a mouse icon underneath, but
the function of the mouse icon isn't explained. Also, "Bass", "Treble",
and "Reclvl" are grayed out but it isn't clear why, or precisely what
their functions are. Ossmixer has a different set of controls and
doesn't include the "recording source" selector that xmix does. That
difference in basic functionality is very puzzling. The icons of
ossmixer are even more mysterious since they aren't labeled. And
incidentally, what happens when two mixers are active at once?
By the way, I've managed to get sound to play through the speaker (I
have a Creative Labs PCI128 card) and also have done a little recording,
but haven't been able to record from CD so far. So my problems are not
with the basic setup or kernel configuration but rather with the
intelligent usage of the relevant software.
Any help would be appreciated.
Paul Abrahams
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