Do you want to learn processing ?

Very nice set of 5 tutorials with which you can follow an introduction to processing.
In the last one, a final little demo is generated using input audio and displaying the different band levels in an interesting fading effect.

Created by switchboard (Andy Best).

Processing Tutorial #1 from Switchboard on Vimeo.

Processing Tutorial #2 from Switchboard on Vimeo.

Processing Tutorial #3 from Switchboard on Vimeo.

Processing Tutorial #4 from Switchboard on Vimeo.

Processing Tutorial #5 from Switchboard on Vimeo.