Mapping an Expression pedal to control plug-in parameters in Logic

1. Check that the required MIDI input device is enabled in Logic Preferences

Use Track Start Controls to Map an expression pedal to Wah Thing

2. Click on the Smart Controls button, click the 'i' button 

3. Map the Wah Thing Manual Parameter to a control

4. Click 'Learn' for External Assignment, then move the expression pedal to capture the MIDI CC message