This code was originally written by openmusiclabs.com , all credit to them, they deserve it.
The program has parts coded in assembly, which makes it a bit difficult to understand.

The main idea is to read the A0 analog value and represent the level of the audio signal using bars. The code makes the FFT of the input signal and then averages the value.

• If the signal is too weak or too strong, you can adjust the level using the gain potentiometer.
• You can change the intensity of the light changing the line

  lc.setIntensity(i, 10); // 15 = brightest

• I have included all the libraries in the same folder so you don't need to install them. Just unzip and compile!

Hope you like it: