This reminds me of a project I built in a class during my EE degree--I wanted a thing that would pick out the beat in a song and flash an LED accordingly. I tho

This reminds me of a project I built in a class during my EE degree--I wanted a thing that would pick out the beat in a song and flash an LED accordingly. I thought it would be pretty easy to just look for spikes, but you can't have a constant threshold or else you will just run the LED for the entire duration of some high-energy portion of the song (or else you will hardly ever run it at all). It needed to be adaptive, but the adaptive threshold needed to be able to respond quickly to changes in the "average energy" of a song. It took quite a lot of calibrating to make it work properly, and I learned a lot in the process.