[alsa-devel] trouble using dmix with tts systems (accessibility )

Halim Sahin halim.sahin at freenet.de
Mon Mar 23 13:26:42 CET 2009

Hello Takashi
On Mo, Mär 23, 2009 at 11:07:15 +0100, Takashi Iwai wrote:
> At Fri, 20 Mar 2009 09:28:02 +0000 (UTC),
> Halim Sahin wrote:
> > 
> > hello,
> > 
> > I have asked this question to alsa user list but got no useful answer.
> > 
> > I am a blind linux user and need asistive Technology to use my pc.
> > The problem I have experienced with alsa is that it is sometimes too slow to stop
> > previous output before starting a new one.
> > The result of this ends in several speech outputs at a time.
> > The problem only occurs if the dmix plugin is used.
> Could you elaborate how the previous output is stopped, and how the
> next sample is started?  Are they different processes, open/close
> sequences, or snd_pcm_drop() / prepare / re-start, or what?

It seems that the speech-server is using the following functions to handle sound output through alsa:
snd_pcm_drop, snd_pcm_status..., snd_pcm_prepare, snd_pcm_resume ....

The server can be found here:
The alsa code can be found in file
> It'd be best if you could show a small test-case program to reproduce
> the problem...
Please have a look to speech-dispatcher , which shows the problem.

I can reproduce the mentioned problem with other apps as well like mplayer.
mplayer -ao alsa *.mp3
During playback simply press right/left for forward/backward.
This step uses dmix if it is enabled!
Then try the same with:
mplayer -ao alsa:device=hw=0.0 *.mp3

Please ask if you have more questions.
I.ll be happy if we can find a working solution for the speech stuff.
Thanks a lot
for your response.

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