title: Reduce volume of audio file by percentage value using SOX
body: <p>I would like to reduce the volume of an audio file by 10% (so that the new volume will be 90% of the original).  How can this be done using SOX?  According to the SOX manual it supports a volume option:</p>
  
  <blockquote>
    <p>-v, --volume FACTOR</p>
    
    <p>Adjust volume by a factor of FACTOR. This is a linear (amplitude) adjustment, so a number less than 1 decreases the
    volume; greater than 1 increases it. If a negative number is given,
    then in addition to the volume adjustment, the audio signal will be
    inverted.</p>
  </blockquote>
  
  <p>Does that mean that the command <code>sox -v 0.9 audio.wav audio.wav</code> will give me an audio file at 90% the volume of the original?</p>