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 accompanyment to music.  Synaesthesia seeks to provide
not just a visual representation of sound, but a representation of
how sound is percieved.  Its display combines information about
the frequency, location and diffuseness of sound.  The display is
sufficiently detailed to make it possible 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