title: Converting a stereo channel audio file to left channel only, through command line
body: <p>Say I have a bunch of mp3 files. How would I go about using an audio software command-line tool to decrease the volume completely on one side of the audio file (right), leaving on the left side of the audio file complete? I would then like to save this file to a new mp3 file. This needs to be done entirely over the command line.</p>
  
  <p>As an another approach. Is it possible to use a command line audio file tool to convert a stereo mp3 file to mono, then to merge this mono file with a "silent" track of the same length, creating a left-headphone track with sound and a right-headphone track with silence?</p>
  
  <p>In this SO question, there seems to be a number of approaches to a rather eccentric end goal. In the first possible solution, I just want to decrease the volume of the right side. In the second possible solution, I want to combine a few more common steps to achieve the same end result. </p>
  
  <p>The problems here are that:</p>
  
  <ul>
  <li>I can't find a good command-line tool for modifying audio files, even to do the second approach which should be a more common request.</li>
  <li>I'm expecting that I'll first need to convert the mp3 file to wav, using a similar or second tool</li>
  <li>This query is eccentric so there aren't many links about it on the web.</li>
  </ul>
  
  <p>Thanks for any help. Audacity would be my go-to normally, but it appears to be GUI only.</p>