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Re: [Discuss-gnuradio] Distorted playback of real-time audio on Linux

From: Elvis Dowson
Subject: Re: [Discuss-gnuradio] Distorted playback of real-time audio on Linux
Date: Fri, 13 Aug 2010 03:47:12 +0400

Hi Eric,
               I came across an old thread, 

"There is a general issue related to the fact that when using
usrp_wfm_rcv and similar applications that there are in fact two clock
domains, and that they are guaranteed not to match.  There's an osc on
the USRP and an osc associated with the sound card.  We made an API
change in the audio interfaces that can specify that it's NOT OK to
block when accessing the audio interface.  When used in a flow graph 
that contained both an audio sink or source and a USRP sink or source, this
would result in the USRP being the master clock, and would dodge the
"two clocks" problem.  Although the parameter was added to all (most)
audio interfaces, I believe that it currently only works on the
portaudio interface.  Please feel free to fix this for gr-audio-alsa,
gr-audio-oss and gr-audio-osx."

This could potentially explain the issue I have, with distorted and crackling 
audio. It might also explain the nearly un-reproduceable random behaviour when 
it sometimes works giving clear audio output (so far has happened only 4 times 
in 6 weeks, approx 16 hours a day). 

How would one go about fixing this for gr-audio-alsa? Perhaps if you can give 
me some high level tips and pointers, I could try to make the changes.

Best regards,

Elvis Dowson

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