Sound card driver data formats

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Date: 30 Jul 2004 18:03:23 +0100

I want to play synthetic sounds through my sound card. I've
recompiled the kernel and made the devices. The sound card
is working.

cat /kernel > /dev/dsp clicks and hisses as expected.

I've written a program to generate a ramp, but is sounds
wrong, and my oscilloscope shows that the waveform is bent.
I assumed that /dev/dsp was 8-bit unsigned linear. Maybe it
is mu-law or A-law? What about dspW? Is it 16 bit linear?
What about stereo? Do I send alternate 16 words to alternate
channels? dsp seems to be mono.

dmesg say sbc0 <ESS 688> at port 0x220-0x22f irq 5 drq 1
flags 0x15 on isa

Do the drivers abstract away differences between cards, or
do I need to know what my particular card does?

Are the technical details written down somewhere? The
FreeBSD handbook and the driver manual pages are written
from the perspective of setting up the sound card to use
with a program that some-one else has written for you. It
misses out the format information that you need to write
such a program yourself. There is stuff on IOCTLs in a
soundcard.h. There is plenty of information, 1300 lines of
it, but it assumes a lot of background information I don't
have, such as actual data formats. It will take me days
to work it out with by trial and error.

Does anyone have a webpage with the format details?

Alan Crowe
Edinburgh
Scotland

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