Please note that the Audio Unit (AU) plug-in format does not support MIDI Learn on effect plug-ins so you will have to work with Smart Controls assignments:
- Load your UVI plug-in as an AU effect in a Logic track (for e.g. Rotary).
- Select Show Smart Controls from menu View.
- Click on the Information icon at upper-left corner.
- Click on the wished parameter in the Smart Controls window (for e.g. Rotary Speed Mode).
- Go to External Assignment, click Learn then move any controller on your MIDI device.
Your parameter is now assigned to your MIDI controller.