Audio sampling from music playing over iTunes?

I am working on a project which involves a pretty simple concept; getting LED's to fade and blink synchronously with music. Overall, I have two options: 1. Hook up a mic to an analog input and simply map the voltage at the source to 0-255. 2. Keep the Arduino hooked up via USB to my desktop and directly read data while the music is playing.

I can't do option 1 as I don't have any background in circuits or any of the parts. Is option 2 in any way possible? How would I make it work? I like to play my music using iTunes, but is there any the data could somehow be sent and received over the USB leading to the Arduino?

The USB connection provides a duplex serial connection, so the Arduino can send messages to an application on the PC and vice versa. I think the simplest way to achieve what you’re looking for is to write a PC application which reads the audi stream being played on the PC, uses whatever algorithm you like to convert that to a stream of 0 … 255 brightness values, and writes those values to the Arduino’s serial port. On the Arduino side you would have a trivial sketch which reads bytes from the serial port as they arrive, and sends the corresponding PWM output to drive an LED at the specified brightness.

Chooise a suitably high speed for the serial port, and make sure your PC application sends brightness change messages slower than the maximum speed of the serial connection - this will ensure that the transmit buffers don’t back up, which would introduce a lot of latency on the communication.