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 either audio device or JACK ports.
</p>

<p class="note">
  When an insert is created, the signal will be interrupted until the relevant
  connections to the insert ports are made!
</p>

<p>
  While jack ports are visible to other JACK applications, ALSA ports are only
  useful for patching in audio equipment external to the computer. If inserting
  a software processor is required, a plugin would be the first choice. If a plugin
  is not available then the jackd audio backend would have to be used. This is
  not very common any more but there are some older jack clients that require
  using jack.
</p>
<p>
  Inserts work the same as the inserts on analog consoles except they are not
  normalled like most jacks on an analog console.
</p>
<p>
  An insert allows 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 a channel strip, such as a vintage
  compressor, tube equalizer, etc. In the latter case, the inserts would first
  be connected to a pair of hardware ports, which are in turn connected to the
  outboard gear. This is done on the <kbd class="tab">Send/Output</kbd> and
  <kbd class="tab">Return/Input</kbd> tabs of the <kbd class="window">Insert</kbd>
  dialog respectively.
</p>

<figure>
  <img class="hdimage" src="/images/port-insert-send.png" alt="Insert / Send">
  <figcaption>
    Insert Dialog, the Send/Output tab
  </figcaption>
</figure>

<p>
  Apart from providing access to the connections matrix, the dialog allows adjusting
  the output gain and toggling phase inversion for Send/Output, as well as measuring
  and adjusting latency for the insert.
</p>

<p class="note">
  Inserts will incur an additional period of latency, which can be
  measured and compensated for during mixing, but not during tracking!
</p>

<p>
  Disabling (bypassing) an insert is done by clicking on its LED in the processor box.
</p>