real time sound

Rich Lafferty rich+rhl at lafferty.ca
Sun Mar 21 02:55:34 UTC 2004


On Sat, Mar 20, 2004 at 09:04:10PM -0500, S. Gongola <gongolas at verizon.net> wrote:
> It seems like I can only get real time sound without a delay when I'm logged 
> in only as root. How can I get real time sound when I'm logged in as a user. 
> What device permissions do I need to change, or adding the user to a certain 
> group can solve the problem.

Low-latency audio is hard -- you're not using a real-time operating
system, after all, so it's mostly a matter of doing everything you can
to get other things out of the way of the audio devices.

The short version is that regular users don't have the flexibility to
play with scheduling enough to get near real-time operation. Root does,
which is why you see what you do.

I recently installed the audio metadistribution from Stanford's CCRMA,
which includes a low-latency kernel with capability support (to grant
the ability to play with scheduling to non-root users without granting
the whole shebang). See:

   http://www-ccrma.stanford.edu/planetccrma/software/

Planet CCRMA uses ALSA, and relies heavily on the Jack audio connection
kit.

Also useful is the Linux Audio Developers' mailing list and website:

   http://www.linuxdj.com/audio/lad/

and the Linux Audio Quality HOWTO:

   http://www.linuxdj.com/audio/quality/

Cheers,

  -Rich

-- 
Rich Lafferty --------------+-----------------------------------------------
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