[alsa-devel] Plugin default and sw_params

Emmanuel Milou emmanuel.milou at savoirfairelinux.com
Wed Mar 26 14:38:49 CET 2008

Hi all,

I have some questions about the /default/ plugin. I am developping a 
softphone based on ALSA on Ubuntu 7.10.
I use read/write IO. When I open a device with the /plughw /plugin, 
quite everything works fine, the quality sound is good. But with the 
/default/ plugin or the /dmix/ plugin ( the user can choose one of them 
), I can't set my own hw parameters or sw parameters. Actually  I set my 
own value of period size, buffer size, start threshold, stop threshold, 
but when I check in /proc/asound/cardx/pcm0p/sub0/sw_params or 
/proc/asound/cardx/pcm0p/sub0/hw_params, the values are totally 
different. For instance, the start threshold is set to 1 even if I set 
it to period_size. As a result, I get crackling sound. I suspect this is 
due to buffer underrun. Maybe if I could change the start threshold or 
the period size, the sound would be better. So my question: is it 
possible to modify this values for /default/ plugin without changing the 
alsa config file ( asoundrc ) ?

Thank you very much


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