Map MIDI controls to FX parameters in REAPER

Used this to quickly map the controls for a USB MIDI mixer to volume/EQ gains in REAPER.

  1. Click the Track Envelopes button to select FX parameters
    REAPER track with Envelopes toggle button hovered

  2. Tick 'Active' checkbox (the one of the left). If deactivating, you might also need to uncheck 'Visible' to hide the row
    Envelope selection UI, with volume and EQ effects selected

  3. There are little "learn" buttons in the Select Envelopes popup, otherwise click the MIDI Learn button on the track
    Learn MIDI button hovered

  4. Move MIDI controller, then click OK
    Learn MIDI dialog open

For non-FX things like volume and panning, can use the View Actions menu, select the action (for example "Set volume for track 1"), and click Add to add a control.