[alsa-devel] While recording from mono codec twice as much data is received

Louis Lee lwhlee at hotmail.com
Fri Jul 10 22:53:52 CEST 2009

> Date: Fri, 10 Jul 2009 10:29:24 +0100
> <snip...>
> On Thu, Jul 09, 2009 at 03:27:17PM -0600, Louis Lee wrote:
> >   However, when recording using the exact same setup for the data
> >   interface I am not getting favorable results.  For instance, if I
> >   record for 5 seconds I get output in a file for 10 seconds of audio
> >   (arecord or sox).  This results in my recording being stretched.  I
> >   change the DAI to stereo capture and record two channels and the
> >   recorded output comes back correctly (5 seconds recorded is 5
> >   seconds).
> This suggests that either the CODEC is configured to run at twice the
> expected sample rate or that there are enough bit clocks being generated
> for stereo data and the CPU DAI is trying to record data for each bit
> clock cycle.  Is the CPU or the CODEC the clock master in your system?
Mark, thanks again for your insights.  I believe the sample rate is correct.I can see it on the scope and FRAME frequency is equivalent to thesample rate.  I ran into a bit of a problem though.  If you are right aboutthat each bit in the clock cycle is being recorded I think I have just enoughbits in my clock for stereo data.  If I reduce it though I run into theproblem where I don't have enough bits to clock through all my data. :(
This probably seems like a complete noob question.  How exactly do I modify the CPU DAI to not account for each bit in the clock cycle?
The CODEC is the clock master in my system.
Thanks Mark!  You have been tremendous help.
> >   I'm stuck now.  From my understanding the clocks are setup the same
> >   way for both playback and capture.  Has anyone ran into this problem
> >   before?  The WM8974 is a mono codec so I should not have to set the
> >   DAI to stereo in order to capture data properly.
> It should be possible to do what you want, yes.
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