Rainbow Wave Vumeter
Plug your microphone. Put music on and enjoy ! The rainbow draws the wave of sound. You can adjust sensitivity to control the input of microphone. Mine is not really sensible. That's why sensitivity is put to 16. You may need a smaller value.
This is a pre-project for a full demo as in the 1980s with computers like Amstrad CPC.
For example : https://www.youtube.com/watch?v=juRdjF_9o5Q