manual/include/inserts.html

<p>
  <dfn>Inserts</dfn> are signal tap points that can be placed anywhere
  inside a channel strip. Unlike Auxes, they will interrupt the signal flow,
  feeding the signal from before the insert point to its <dfn>Insert
  send(s)</dfn>, and connecting the remainder of the channel strip to the
  <dfn>Insert return(s)</dfn>, both of which are JACK ports which are
  visible to other JACK applications.<br>
  Inserts are the JACK equivalents of normalized switching jacks on an 
  analog console.
</p>
<p>
  An insert allows you to either use a special external DSP JACK 
  application that is not available as a plugin, or to splice an external
  analog piece of gear into your channel strip, such as a vintage
  compressor, tube equalizer, etc. In the latter case, you would first
  connect your inserts to a pair of hardware ports, which are in turn
  connected to the outboard gear.
</p>
<p>
  To disable (bypass) an insert, click on its LED in the processor box.
</p>
<p class="note">
  When you create an insert, the signal will be interrupted until you make
  the relevant connections to the insert ports!
</p>
<p class="note">
  Inserts will incur an additional JACK period of latency, which can be
  measured and compensated for during mixing, but not during tracking! 
</p>