manual/include/automation-mode.html

<p>
  Ardour offers two modes for connecting automation control points: <kbd
  class=menu>Discrete</kbd> and <kbd class=menu>Linear</kbd>. To change the mode
  right click on the automation lane header and choose your mode from the mode
  menu.
</p>

<p>
  <kbd class=menu>Discrete</kbd> mode has stair steps between each point on the
  automation track. This is useful for on-off automation like mute or sustain
  pedal (on a piano MIDI track).
</p>

<p>
  If you record automation via MIDI (for example a pitch bend from a keyboard),
  Ardour always uses discreet mode.
</p>

<p>
  <kbd class=menu>Linear</kbd> mode has straight lines betwen each point on the
  automation track. This is useful when you want gradual shifts in your
  automation lanes, such as gradual increase in volume on the fader.

  Linear is the default mode for most automation lanes created via mouse input
  (versus recording via MIDI).
</p>