Well, that's the thing -- I don't know if I need to only look at volume spikes. Listening for a beat seems more like a task that requires continuous monitoring of the audio stream, rather than just kicking off a call to Lanterne any time the audio volume reaches a particular level... But yeah, let me take a look at VUmeter; I've never really used it before. (Have I mentioned that I've never played with audio streams at all before? )

Also, my personal goal for this app is to teach myself about the low-level details of the N900's hardware (as well as to sharpen my coding skills), so I would like to know how it's actually done.

Ah, absolutely! I used to use a little red light when I was into astronomy; makes it possible to read star charts without completely destroying your night vision.

I have no clue how anybody codes for these LEDs (there's practically no documentation anywhere), but I have found a V4L2 identifier for the indicator LED, so I'll try and get that into the next update.