A MIDI guitar lets a guitarist play a synthesizer using a guitar. In order to play MIDI guitar, you need a hexaphonic pickup and a guitar synthesizer. Some guitars, such as the Godin LGX-SA and Brian Moore i8.13, have a built-in hexaphonic pickup. These are sometimes referred to as "Roland ready" or "synth access" guitars.
Older Roland guitar synthesizers used the GK-1 pickup with a 24-pin cable.
Newer Roland guitar synthesizers such as the GR-20, GR-30 and GR-33 use the GK-2, GK-2A, or GK-3 pickup with a 13-pin cable. The Yamaha G1D pickup also has a 13-pin output and is compatible with newer Roland guitar synthesizers.
Bass synthesizer pickups are also available. The GK-2B and GK-3B from Roland, or the B1D from Yamaha can be mounted on a bass guitar.