Synaesthesia is a program that represents music graphically in real time
as coruscating field of fog and glowing lines.  It is intended as a visual
accompaniment to music.  Synaesthesia seeks to provide not just a visual
representation of sound, but a representation of how sound is perceived.

Its display combines information about frequency, location, and diffuseness
of sound.  The display is sufficiently detailed to allow to distinguish
several individual instruments, singers, or special effects on screen by
their location, shape and color, and sufficiently fast to distinguish
individual drum beats and notes.

WWW: http://www.logarithmic.net/pfh/synaesthesia