Originally called Musicraft, Sonix is a Music Composition and Instrument Synthesis tool. It was written by Mark Riley of Everyware, Inc. and produced by Gary Koffler.
Apparently Commodore owned the rights to "Musicraft" for which they were to pay $0.25 for every copied bundled with an Amiga sold. This did not end up happening, and in August of 1986, the people at Aegis tracked down Mark Riley and had him re-write some parts of the program and the result is Sonix.
It's important to note that most (if not all) of this program is written in assembly language which made it very fast and responsive and Sonix was used to create many Amiga scores before the popularity of trackers grew.