I stumbled upon this project by Jonas Friedemann Heuer. Clavilux 2000 is “an interactive instrument for generative music visualization” as Heuer calls it.
The visual concept of Clavilux 2000 is quite simple. For every note played on the keyboard a new visual element appears in form of a stripe, which follows in its dimensions, position and colour the way the particular key was stroke: The length and vertical position show the velocity, the stripe’s width reflects the length of each note.
By mapping the color wheel on the circle of fifths, the colours finally give the viewer and listener an impression of the harmonic relations. Notes belonging to one specific tonality always get colors from one specific area of the color wheel. Therefore each key gets it’s own color scheme and “wrong” notes stand out in contrasting colors. The more different tonalities a piece has, the more colorful the visualization will be.