I found a demo. Visually, it's very much a product of its time, being made in 1987. Musically though... it holds up really goddamn well, despite not making use of the SID chip's filters, hard sync, nor ring modulation (at least from what I can hear). No combined waveforms either, it's all just pulse waves and noise. It's moving, it's moody, it's powerful... how could it have been done this early on? I expected this to be a tune from the 2000s or later, but no, it was made while the C64 was still being sold. I've chosen to link an oscilloscope visualization instead of the original demo; the visuals aren't very interesting. It's just scrolling text over a picture.
Think Twice III (C64) by The Judges (composed by Jeroen Kimmel) (
CSDb)
This one's pretty good, and it's made by another Jeroen, arguably a more famous one. No visuals; this is purely a music track. It does, however, turn out that oscilloscope visualizations are often the highest-quality versions of a song (with the caveat that it's almost always emulated, not real hardware) if available, so I've decided to link that here.
Alternative Fuel (C64) by Jeroen Tel (
CSDb)
Another one by lft. I've sorta slept on this one, thinking it's too simple, but something clicked in me and made me realize that it's actually quite good. That's a single microcontroller doing all the work, BTW. No helper chips; all video and audio is done on the chip itself.
Craft (ATmega88) by lft (
Pouet.net)