Note: this post is from 2007, outbound links may be broken.

Kepler’s Orrery – Generative music based on a gravity simulator

Simran Gleason has released Kepler’s Orrery as open source software.

Kepler’s Orrery is a generative music system that uses gravity equations to “compose” and play music.

Kepler's Orrery - Threesomes
Kepler’s Orrery – Threesomes

How does it work?

Start with planets (or stars or particles) that each have mass, position, and velocity, then run a n-body gravity simulator to make them move. They attract each other, accelerate, swirl around, and slingshot off each other. Sometimes they collide, and that’s what plays the music.

Each body can have a melody attached to it, and plays its next note when it collides.

Composing for this system is tricky, but fun. You set up the initial world by specifying where the planets and the rocks (represented by squares; they have mass and position, but don’t move) are, give them initial velocities, and see how they move. Then you have to make melodies that work when played randomly against the other melodies, with no control of when the notes get played or for how long — just the order.

Check this page for some cool videos of what Kepler’s Orrery is capable of, or try out Kepler’s Orrery online in this java applet.

Visit this page for more generative music projects.

Link via CDM

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