This is the output of a visualization system I thought of a couple of days ago.
In a piano, notes repeat every 12 semitones (or keys, both black and white), and each whole interval doubles the frequency of these notes. Together, these notes form what we call a pitch class.
It occurred me that the shape of a spiral has all the correct properties to represent this relation between notes. So I wondered, how would piano music look like if it was represented as a spiral of keys?
I quickly hacked together a PHP script that reads MIDI files and creates the frames of this video you see now. It's a rough draft, but it works pretty well!
In this representation, the notes with higher frequencies are in the center of the spiral, starting with C8 (as in the piano, from right to left). Each radial block of keys represents a single pitch class, so octaves (when two adjacent notes of the same pitch class are played togeter) look like a pair of keys being pressed radially.