A simple project inspired by Make your own LED Sign VU Meter by GreatScott!. The catch-phrase should be familiar if you subscribe to his channel;-)

It's a VU meter, but rather than doing the "bar graph" thing à la LM3915, it pulses the intensity of all LEDs to the volume of the incoming audio.

As always, all notes, schematics and code are in the Little Electronics & Arduino Projects repo on GitHub.