[Adam Grieg] recently posted this video of his LED lightbar controller at work making a strip of LEDs flash to the beat of his music. The controller does it by picking up the music via an electret microphone, then amplifying it with an LM386 Amp. The ATtiny13 microcontroller keeps track of the noise level and makes the LED array flash whenever it senses a peak.
In addition to the parts listed, [Grieg] used a small SparkFun box as the enclosure for the controller. If you’re considering trying your hand at this project, check out [Grieg]’s schematics and code. It’s relatively cheap to make, so it wouldn’t be that hard to rig up several of these set to flash at different frequencies.