manual/include/generic-midi-and-encoders.html

<p>
  Encoders are showing up more frequently on controllers. However, they use
  the same MIDI events as Continuous Controllers and they have no standard
  way of sending that information as MIDI events. Ardour 4.2 has implemented
  4 of the more common ways of sending encoder information.
</p>
<p>
  Encoders that send the same continuous values as a pot would are not
  discussed here as they are already supported by <code>ctl</code>.
</p>
<P>
  Encoders as this page talks about them send direction and offset that the
  DAW will add to or subtract from the current value.
</p>
<p>
  The 4 kinds of encoder supported are:
</p>
<ul>
<li>
  enc-r:  On the bcr/bcf2000 this is called "Relative Signed Bit". The most
  significant bit sets positive and the lower 6 significant bits are the
  offset.
</li>
<li>
  enc-l: The bcr2000 calls this "Relative Signed Bit 2". The most
  significant bit sets negative and the lower 6 significant bits are the
  offset. If you are using one of these two and the values are right but
  reversed, use the other. This one is the one the Mackie Control Protocol
  uses.
</li>
<li>
  enc-2: The bcr2000 calls this one "Relative 2s Complement". Positive
  offsets are sent as normal from 1 to 64 and negative offsets are sent as
  2s complement negative numbers.
</li>
<li>
  enc-b: The bcr2000 calls this one "Relative Binary Offset". Positive
  offsets are sent as offset plus 64 and negative offsets are sent as 64
  minus offset.
</li>
</ul>
<p>
  If the wrong one is chosen, either the positive or negative side will act
  incorrectly. It is not really possible to auto detect which one the
  controller is using. Trial and error is the only way if the specification
  of the controller is not known.
</p>
<p>
  Many controllers have more than one choice as well, check the manual for
  the surface.
</p>