The Open Spark project isn't your average cover band. Well, unless your average cover band plays all of its songs using Tesla coils, because that's exactly what's going on here. This isn't a visualizer. The coils are the instrument.
So, how does it work? Open Spark's Ian Charnas dropped some info in an interview with Boing Boing:
It turns out, you can make music out of anything that makes noise, just by turning it on and off very rapidly.
If you record a noise of you tapping your fingers on your laptop keyboard, and then speed it up so you hear 440 taps per second, you'll hear A4, the A above middle C on the standard keyboard. Likewise with the tesla coils, we make a giant spark and then turn it on and off at the right audio frequency for the note we want to play.
This is accomplished by a series of circuits and microchips we designed, which convert a standard MIDI signal (coming from a MIDI keyboard or from the MIDI output on our laptop) to the fiber-optic signal that the tesla coil requires. Why fiber optic? Because we don't want a copper wire connecting our keyboardist to the thing that makes a million volts.
You can even submit music of your own to see played on the Tesla coils.
Check out a demo of the system in the video below as the coils bust out "This is the Remix" by mashup artist Girl Talk. Want some more? You can see plenty more on the team's YouTube channel.