PaulS:
If you have some different idea about what "in sync with some music" means, you need to spell them out.
Yeah sorry, I was trying to figure out how to word it but I don't know in what ways I could measure the audio coming in to the arduino, or exactly how sound transfer works. For example, does the voltage level vary in a consistent manner, so that I could use the voltage (relative to min and max) to set the power of the LEDs? Different LEDs don't need to light up at different points, I just want the power of the LEDs to match up with some aspect of the song; drum beats, noise level, whatever works.
Hopefully that conveys what I want haha.