Using Reason’s MIDI Learn function (which is also called Remote
Override Mapping), you first need to make sure your MIDI controller is properly configured and that the correct drivers are installed. This is done in Reason’s Preferences within the “Control Surfaces and Keyboards” page.
PC: Edit > Preferences or Mac: Reason > Preferences.
If your keyboard doesn’t show up when clicking “Auto-detect Surfaces,” click the “Add Button” to manually add it. Once Reason recognizes the controller, all the knobs, sliders, and buttons on it will work within the program. Note that some controllers already have “Presets” mapped out for different devices (such as the REX player) in Reason. If your controller has a “Reason Mixer” preset, you must create a sequencer track and set its output to the Mixer in order for it to function.