Here’s a tutorial describing how to design a stereo 7 band equalizer display using an Arduino and two MSGEQ7 ICs. The MSGEQ7 does most of the work by reading the input signal and outputting 7 voltage levels depending on the strength of their respective bands in the signal. The output is time multiplexed, meaning you read them one after the other, and control the timing through the strobe and reset pins.
The diffused reflection on the mat made the leds look like hands and the eq bands look like fingers. Kind of makes want to do a 5 band eq shaped like hands… not sure why or what purpose it would have, though, other than looking like hands.