The workflow for this couldn't be easier.
My partner in crime Janet Mader whipped up a score in MuseScore 2, which was then outputted as a MIDI. We ran this through an online MIDI to RTTL converter. The resulting ringtone text file was then run through a Processing sketch to convert the RTTL to gCode with a reasonable degree of accuracy. Run this on the machine and tada, music.
So to sum up: Score - MIDI - RTTL - gCode - linuxCNC.
Simple.
