title: USB audio input have many noises in my arm device?
body: <p>I have a linux-based embedded device which has a capture usb device. It connect Mac with usb line. I run arecord in my device, and then press play button in itunes. Thus I will get a wav file in my device.</p>
  
  <p>My question is:
  Usually the wave file I was listened is fine. But if I run a shell bash in the background before I run arecord，then the wave file has many noises.
  The shell bash:</p>
  
  <pre><code>#!/bin/sh
  while true
  do
      if [ -d "/etc" ];then          
          x=1
      fi
      usleep 100000
  done
  </code></pre>
  
  <p>I cut the wav's header and silence from the noise file and normal file. The compared result :
  <a href="https://i.stack.imgur.com/IHL4m.png" rel="nofollow noreferrer">The compared wav files</a></p>
  
  <p>Thanks a lot.</p>