Re: Crackling Noise In Playback

Jay Foster <jay@xxxxxxxxxxx> · Thu, 4 May 2017 14:22:49 -0700



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

    
      Jay and list,

        
          On Thu, May 4, 2017 at 9:23 AM, Jay
            Foster <jay@xxxxxxxxxxx>
            wrote:

            
                          On Thu, May 4, 2017
                            at 8:24 AM, Jay Foster <jay@xxxxxxxxxxx>
                            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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