[alsa-devel] a11y: howto reduce latency with alsa's dmix plugin?

[Takashi Iwai]

At Sun, 23 Aug 2009 09:55:18 +0000 (UTC),
Halim Sahin wrote:
> 
> Hello,
> Is there a way to reduce latency on audiocard if the dmix plugin is in
> use?
> I am asking because there is a strange problem with asistive
> technologies which are outputing through alsa.
> E. G. speech-dispatcher takes almost a half sec to stop the
> speech-synthesizer.
> If the user navigates quickly through menus, there are simultane outputs
> at a time.
> (tested with an usb logitech headset, snd-intel8x0 based card,
> snd-hda-intel).
> The same problem can be reproduced by running mplayer with alsa output
> driver and pressing
> quickly left/right arrow.
> You should hear several samples at a time.
> 
> Using an sblive card which doesn't use dmix doesn't have such problems.
> 
> Using the dmix plugin should audio much faster to avoid this problem.

It's a bit hard to guess.  This could be the difference of PCM drain
implementation between hw and dmix, but a half second is still too
long.

Could you prepare a small test case to reproduce the buggy behavior?


thanks,

Takashi