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

Alan Horstmann gineera at aspect135.co.uk
Fri Jul 4 10:38:53 CEST 2008

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

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?


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