The Yamaha QX21 is a digital sequence recorder that was released in 1985. It has an internal memory capacity of 8,100 notes (6,000 notes with velocity) and is equipped with MIDI IN, MIDI OUT, MIDI THRU, and foot switch cassette interfaces¹. The QX21 is a 16-track sequencer that allows users to record and edit MIDI data. It has been used by many professional musicians and producers, including Depeche Mode, The Prodigy, and The Chemical Brothers.