[alsa-devel] snd_pcm_writei() -last value sustained

[Alan Horstmann]

Working on an app I am seeing several strange effects, and this is one of 
them.

It can be demonstrated with the pcm.c example program, and I have attempted to 
attach a small shot of Audacity capturing the effect.

After writing to the pcm with snd_pcm_writei() a certain amount of data (I 
have pcm.c doing 2 periods) the value captured from the soundcard remains at 
the last value thereafter; clearly this card doesn't have DC elimination or 
this would not be seen.

The sound card is ice1712 (DMX6fire); I had always noticed the PCM meters in 
envy24control often stayed high if something like XMMS was stopped or paused 
during play, but thought it a metering fault.  Now it appears to be actual 
pcm value that 'gets stuck'.

Close examination with Audacity shows it is in fact the last-but-one value 
that is sustained.

Is this expected behaviour, configuration fault, driver bug or other problem?  
I had expected that after the block of data had been written out as audio the 
signal would return to zero straightaway.  Can anyone give me any clues?

Alan


-------------- next part --------------
A non-text attachment was scrubbed...
Name: Output-stays-high-cut-pcmex-ice1712.png
Type: image/png
Size: 7651 bytes
Desc: not available
Url : http://mailman.alsa-project.org/pipermail/alsa-devel/attachments/20080704/885d621f/attachment.png