Browsers - what started out as programs to view enhanced text a.k.a. HTML can now do just about anything you want (or don't want).
(You will need to have Google Chrome for best or Firefox 3+ for good results, Safari & Opera support is choppy the author says. Also this will not work in Internet Explorer!)
Here's the direct link:
If that doesn't work, try going to the author's article first:
and click the "Clicky" link there.
PS: For all you Radiohead fans, try this: http://www2.nihilogic.dk/labs/canvas_music_visualization/ also by the same guy.
Jacob Seidelin's page
thx unconed for the link