Re: Crackling Noise In Playback

Jay Foster <jay@xxxxxxxxxxx> · Thu, 4 May 2017 14:39:16 -0700



    On 5/4/2017 2:22 PM, Jay Foster wrote:

    
      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

    
    With a bit more testing, I found that the '-D front' only works for
    two channel audio files, not my mono files.  I have found that
    '-Dplughw:0' works for both.  Thanks for pointing me there.  I still
    need the scaling too.

    Jay

  
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