I've finished the lightbar controller!
This device analyses the music it picks up via the electret microphone, then flashes the LEDs in time to the music. It's encased in the box SparkFun sent me the microphones in, since the box was just begging to be used as a case for something! I'm sure that was intentionally designed.
Getting a bit more technical:
The microphone picks up the noise and sends this to the LM386 amp, which amplifies it about 200x before it's read by the ATtiny13's ADC at 8-bit resolution. The ATtiny13 then keeps a running average of the noise level, and flashes the LEDs if the current volume exceeds the average by a scalar amount.
As a result, the LEDs flash on when the music hits a peak, and are off
otherwise - no matter what volume.
The brightness of the LEDs is also somewhat correlated to the loudness of the peak, since a louder peak will generally keep the LEDs on for longer.
Check out the video of it in action:
Download the schematic, PCB layout, code:
https://randomskk.net/projects/lightstrip/ (all files released under Creative Commons BY-SA-NC 3.0).