manual/include/strip-silence-from-audio-regions.html

<p>
  From the region context menu, choose <kbd class="menu">Edit &gt; Strip
  Silence</kbd> to detect silence (based on a user-chosen threshold in 
  <abbr title="Decibels relative to Full Scale">dBFS</abbr>), split a 
  region based on the boundaries of the silent segments, and remove the 
  silence. You can also specify a minimum length for silence&mdash;useful
  when editing very percussive material and just needing to 
  automatically trim the ends of a region. The dialog looks like this:
</p>
<img src="/images/a3_strip_silence.png" alt="strip silence dialog" />
<p>
  The edit applies to all selected regions, allowing batch processing. 
  You can also see in the screenshot how the main editor window is used 
  to show silent segments and report the number and durations of the 
  shortest segments.
</p>