http://esolangs.org/wiki/velato :
Velato is an esoteric programming language by User:Rottytooth, which uses MIDI files as source code. Programs in Velato are defined by the pitch and order of notes. Velato is intended to allow for flexibility in composition, so functional programs will not necessarily sound like random notes. There is a tendency for Velato programs to have jazz-like harmonies.

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This is a sheet music representation of one possible "Hello, World" program: