[alsa-devel] While recording from mono codec twice as much data is received
lwhlee at hotmail.com
Fri Jul 10 22:53:52 CEST 2009
> Date: Fri, 10 Jul 2009 10:29:24 +0100
> 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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