[linux-audio-dev] ALSA performance issues?

James Courtier-Dutton James at superbug.co.uk
Sat Dec 23 15:03:13 UTC 2006

Mario Lang wrote:
> Hi.
> I just tried to get sound working on a LinkSys NSLU2 (ARM) running
> Debian Etch using a USB sound card.
> What I discovered I find pretty strange, and would like to know some
> more details.  Apparently, all ALSA native clients don't
> manage to play sound click-free, they actually have underruns all the
> time.  However, if I use OSS (via the snd-pcm-oss module) and set
> libao to use the oss driver, I get perfect playback with about
> 20% CPU use at maxiumum by the user-space app playing/decoding files.
> This is a bit strange, isn't it.  OSS-emulation actually uses the same
> kernel code to access the actual hardware.  I am just very vaguely
> familiar with the whole ALSA architecture, but it feels as if
> the problem here actually lies inside the user-space alsa libraries?
> Did anyone ever see such an effect, and investigate more closely
> what is the reason for the difference?

Which applications have this problem?
What quite often happens is an application's ALSA interface code is 
written wrongly. For example, if the application uses OSS is uses a nice 
big sound buffer, so no clicks, but if the application uses ALSA, it 
requests minute buffer sizes that results in lots of clicks.
So, please explain which applications have the problem.


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