PulseAudio and Alsa
cerha at brailcom.org
Sun Jan 4 18:37:25 GMT 2009
Mitchell Smith wrote:
> Just to update the list on my progress, I have completely removed PulseAudio
> and reconfigured Ubuntu to use Alsa by default.
Yes, this is the safe setup. I believe it is theoretically possible to
run PulseAudio with other ALSA aplications as you suggested, but didn't
have a chance to experiment with this. I only vaguely know, that
PulseAudio normally deactivates DMIX (the ALSA software mixing plugin)
since it provides its own software mixing. If it was possible to make
PulsaAudio run on top of ALSA with DMIX, it should then be possible to
have pulse enabled and still use ALSA output directly from Speech
Dispatcher. If anyone finds out more on this topic, I'd be interested
> I first tried configuring speech-dispatcher as a user service after adding
> my user to the audio group, the test was successful and I can get spd-say to
> work correctly however when speech-dispatcher is running orca is no longer
> able to speak.
This is strange. Does your Speech Dispatcher really use ALSA output?
Are you able to run other ALSA applications simmultaneously?
> I am able to run python -c "import speechd" with no problem however Orca
> does not see speech-dispatcher as an option I can use as my speech system,
> only gnome-speech.
> Of course I have to kill off speech-dispatcher in order to get Orca to read
> anything so maybe it can't see it because it's not running at the time.
Yes, that is the problem. So if you sort out the first problem and are
able to run orca with Speech Dispatcher running, you should see it as an
option. The other way might be to configure orca to use speech
dispatcher through Orca's text setup (orca -t), but I wouldn't recommend
switching to SD before you solve the problem with audio device sharing.
If you want to experiment, you should keep a backup copy of a working
Orca configuration (the .orca directory in your home).
> I seem to recall that in the past if you used Alsa you are able to have
> multiple apps sharing the same sound device, it is only with OSS that you
> could only have one sound source at a time, is that not the case?
Yes, exactly. If you have a single channel sound card, you need to
aviod running any application accessing the sound card through OSS
directly. A single OSS application will block the device for all the
Hope it helps,
More information about the Ubuntu-accessibility