On 5/4/2017 12:12 PM, chris hermansen wrote:
Jay and list,

On Thu, May 4, 2017 at 9:23 AM, Jay Foster <j...@systech.com <mailto:j...@systech.com>> wrote:


    On Thu, May 4, 2017 at 8:24 AM, Jay Foster <j...@systech.com
    <mailto:j...@systech.com>> wrote:

        I have encountered a strange problem.  About 6 months ago, I
        added a USB
        sound adapter and alsa to an ARM based linux system.  I used
        aplay to
        play wav files successfully.
        Now, the playback has a crackling noise in it.  I can not
        find anything
        that has changed.  A few units still play with no noise, but
        I cannot
        determine any difference between them and the ones with the
        noise.

        One odd thing is if I run an application to make the CPU busy
        while
        playing the audio wav file, the noise seems to go away.  Any
        ideas on
        where to look for the root cause?

        Jay


    I have had a similar experience using an AudioQuest DragonFly and
    a CuBox i4. In my case, errors were reported in syslog.  Do you
    show any errors there?

    Do you have any other USB sound cards to try out?
    I have tried 3 different USB audio dongles (all C-Media chip
    based).  No difference.
    No messages in /var/log/messages.
    I had to put the following in my /etc/asound.conf file to get
    clean playback when I originally got this working (the CPU is too
    under powered to do the default rate conversion).

        defaults.pcm.rate_converter "linear"

    The noise is also present using 'speakertest -c 2 -t wav'.  What
    bugs me is that this used to work fine, and still does if I make
    the CPU busy, which seems counter intuitive.


Hmm. any reason you are doing rate conversions? Have you tried to play your files with the hw:CARD=???,DEV=??? argument?



--
Chris Hermansen · clhermansen "at" gmail "dot" com

C'est ma façon de parler.
Yes. Without it, the audio would keep pausing every 0.5 seconds with underruns. The default rate scaling is too CPU intensive for my platform. Using the linear rate conversion is what was recommended to me by someone on this list, and seemed to work fine. Some of the audio is 22050 Hz (mono) which needs to be scaled to 44100 Hz (the card only supports 44100 and 48000 rates.

I am not familiar with the hw:CARD=???,DEV=??? argument. The aplay man page and --help do not document it. I did try adding the '-D front' option to aplay and the noise went away (yeah). I got the PCM name, front, from the output of aplay -L.

Jay
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