The gopen program models the open strings of a guitar. The strings of the guitar run parallel to the y-axis on the radio drum surface as shown in the diagram below:
Baton 1 can strum the strings to produce sound. Baton 2 will dampen the notes. As baton 1 strums higher off the surface of the drum, the attack velocity of the notes gets softer.
This program can be expanded with chord control of some sort.