Please note that the Audio Unit (AU) plug-in format does not support MIDI Learn on effect plug-ins, so you will have to use the MIDI Map mode in Ableton Live:
- Load your UVI plug-in as an AU effect on a track (for e.g. Rotary).
- Unfold the Device Parameters in the plug-in box at the bottom of the screen to display the plug-in parameters.
- Turn on the MIDI Map Mode by clicking on MIDI at right-upper corner.
- Click on the plug-in's parameter you want to control via MIDI.
- Send a MIDI message by moving a knob or a fader on your MIDI controller. The parameter is now assigned, you will see that a new MIDI mapping is listed in the Mapping Browser.