ActionScript 3.0 has a new SoundMixer.computeSpectrum() method

From Adobe Edge (May/June 2007)

“Another killer function is audio spectrum analysis — the tool you would need to build a music visualizer, for instance (such as the ones you see demonstrated in the Ascension application for Apollo). The new SoundMixer class includes a method called computeSpectrum() that turns your music into numbers. Then you draw based on those numbers to create cool audio animations and visualizations. For an amazingly effective tutorial on this topic, read Peter deHaan's blog post about it.”

http://blogs.adobe.com/pdehaan/2006/06/soundmixercomputespectrum.html