Might be loud!
And if you don't see the sound spectrum, try updating your flash plugin. Some versions seem to have problems rendering those (no idea why).
Discovered the access to sound spectrum in flash not long ago (actually it is already used in my last game). So I tried some beat detection, but getting the correct frequency is not as easy as I thought. Anyway, here is my current result. You can change the sliders on top and try to find a better frequency spectrum than I did. If you find a good combination, post it in the comments.
Music: Strobe - Lights Up (Omnipony Remix)
Want to use your own music? See here: [link]