dev file for speakers and microphones

ashlesha · 03-30-2007, 01:32 PM

what is the name of the device file that represents the microphone and the loudspeaker in Ubuntu? i can see a char device called audio in /dev.

If this is the microphone file, then is reading from it as simple as using fopen and fread?

Thanks,
Ashlesha.

indienick · 03-31-2007, 04:15 PM

I'm pretty sure your sound card is treated as a single device, despite however many inputs and outputs it may have.

Give it a shot - try using fopen() and fread(), what's the worst that could happen?

ashlesha · 03-31-2007, 06:53 PM

ok, i will try that --- i have another question though --
say I have a wav file that i want to play at 8kHz -- is there a way to calculate how many processor cycles are taken up by each instruction in my program so that I can output the file at exactly that frequency?

Thanks,
ashlesha.

indienick · 04-01-2007, 11:59 AM

I wish I could answer you on this one, but that's very much past any of my knowledge.

You'd probably want to direct your question to a C buddha, or a Linux-80x86 ASM programmer.

clb · 04-09-2007, 02:51 PM

I believe the soundcard is /dev/dsp. Not sure about the microphone though, but sound out definitely works through /dev/dsp. You can do cat "afile" > /dev/dsp and the speakers will make an annoying buzzing noise.

Hope this helps,
Chris

burninGpi · 04-09-2007, 05:08 PM

There are some other files in /dev/sound, but that's probably system-dependent.

/dev/dsp is used with the OSS API. The documentation for OSS might be of use (I'd post a link, but I haven't done any sound programming).

EDIT: Oh, and don't cat anything to the dev file; it'll make some odd noise if you're lucky, and make some loud, odd noise if you aren't.

clb · 04-11-2007, 12:02 PM

I shall remember that burninGpi, can't remember where it was I read about cating things to /dev/dsp - someone advised me to in order to test sound. Didn't realise it was OSS specific though, thanks

hacker supreme · 04-11-2007, 12:18 PM

you can cat RAW audio files to /dev/dsp. It works very well. Just be very careful that you don't cat your sound input to /dev/hda. Never been there. Never want to!

BTW: Also works with .wav files.

omnio · 04-11-2007, 12:33 PM

Quote:

Originally Posted by clb

I shall remember that burninGpi, can't remember where it was I read about cating things to /dev/dsp - someone advised me to in order to test sound. Didn't realise it was OSS specific though, thanks

I remember something like:

Code:

cat /dev/urandom > /dev/dsp

(you can try that, don't worry - just be prepared and lower the volume before doing it (master and pcm).

ntubski · 04-11-2007, 08:41 PM

Here's an articles that has some examples of this with recording too: http://www.linuxjournal.com/article/2793

Code:

# record 4 seconds of audio from microphone
% dd bs=8k count=4 </dev/audio >sample.au
# play back sound
% cat sample.au >/dev/audio

From C I guess you can use OSS or ALSA. ALSA is supposed to have an emulation layer for OSS so that should still work even if you're using ALSA (it is possible to disable the emulation via kernel compilation options).