[neltnerb]

So this is fairly up to the user, actually. There are several implementations of a FFT like algorithm that run on the Arduino, so any of those should be usable to get frequency data. It's also of course possible to do something like wavelet analysis to pick out more complex patterns. For my example I just did a simple envelope follower with beat detection and a rotating hue, but that's just because I'm (personally) not a great programmer. I think that the right person could make this way, way better than I could on my own =) I see this as one of the great strengths of doing this open source, we can build it together instead of each keeping our secrets like the "big fish".