Want to help Pro Tools and your MIDI controller interact really smoothly when using a MIDI Learn-enabled virtual instrument? For example, want to use a knob on your M-Audio Axiom to adjust a frequency filter on an XPand! synth patch? Use the MIDI Learn function.
In all A.I.R. products from Digidesign (Xpand!, Hybrid, Strike, Velvet, and Structure) and a few third-party virtual instruments like Stylus RMX, you can use the MIDI Learn function to map the knobs and sliders on your MIDI controller to the parameter knobs and sliders in a virtual instrument.
Check it out. First, open up a virtual instrument, e.g., Digidesign’s free XPand! plug-in. Then, right-click or Control-click on a parameter that you’d like to have control over and choose “Learn” from the menu, as in the screen shot. Turn the knob, slider, etc. on your MIDI controller and the parameter in the virtual instrument will follow your movements. The continuous controller number that you assign to the parameter (e.g., CC25) is displayed in the menu. You can change the assignment using the “Assign” menu item or delete the assignment by choosing the “Forget” menu item.

Pro Tools will remember and enable you to use that knob, slider, etc, on the controller to adjust the parameter until you change the instrument’s patch, take that virtual instrument off of the track, or close the session without saving. If you save the session, Pro Tools will remember the controller/parameter map for the next time you open the session. However, if you change the instrument’s patch, you’ll lose the map. So, I recommend saving the patch once you’ve got the controller/parameter map assignment, using the “Save Settings” or “Save Settings As” commands from the plug-in menu, as in the screen shot below.

As of now, I don’t think there’s a way to copy a controller/parameter map from one patch in an instrument to another (which would be totally awesome), but if I’m wrong, maybe one of you can tell me how… I’d be much obliged.