https://www.wothke.ch/sc68meter/
This add-on to the WebAudio based AtariST music emulator (see earlier “Jack-in-the-box” post) provides real-time visualization of the volume of the three emulated Yamaha sound-chip voices.
https://www.wothke.ch/psychedelic/
But where is the fun without at least some WEBGL? There had to be a “psychedelic” version to fix that shortcoming.