External MIDI Instrument Introduction The External MIDI Instrument is a device designed for controlling external MIDI instruments, i.e. instruments that live outside of Reason. These could be other software synths or external hardware instruments that are hooked up to a MIDI interface on your computer. The External MIDI Instrument is treated like any other instrument device in the Reason sequencer, including Note Lanes and automatable controls. One exception, though, is that the External MIDI Instrument device does not produce any sound of its own; it has to be routed via MIDI Out to an external MIDI instrument.