How to use MIDI Learn
From CockosWiki
first, you need to make sure your controller is enabled as a control device. just for reference, this is what the prefs should look like
on your vsti, look in the upper right hand corner, and you will see the "learn" button.
it will give a drop down menu:
select the parameter you want to automate, in this case ill try the rotator speed... then you will see this box.
move the knob of any controller that is enabled as a control in the preferences, and you will get this
here it shows exactly what is being sent to reaper. we need to go to the envelopes button on the track
now it will bring up a list of all the available envelopes to automate.
you have to select the same parameter you just selected for midi learn. make it visible and arm it.
would be nice to have this step bypassed... a bit tedious, but anyway...
next you want to make sure the right automation mode is selected
in this case, latch automation (not sure why)
after moving the knob around during playback or in this case, recording of the track --
VIOLA!