This is a nice example of how to sync LED’s to music. It uses an ATtiny13 and a microphone to sample the audio and control the show. You can download the schematics, PCB files and code on the web site.
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.