Turn on your subwoofer!
This is a 512 byte intro I made for inercia 2022, a demoparty that took place in Lisbon over the weekend. It's the first time that I put the no longer secret 0x808 audio channel to use, with around 200 bytes of the (compressed) code spent on generating the music.
I was pleased to find that techniques used for golfing down visual effects' code size transfer quite well to audio. There are a lot of expressions in there that change meaning over time in a way that produces some kind of structured progression -- some planned, some not so planned. The whole thing is really a single effect, with a lot of janky math to roll out different audio and gfx layers at different times. I can't completely explain how it works in places, but feel free to ask about anything if you like!
This version has commented code in tab 0, but it is probably not a good example to get started with audio synthesis. For anyone game to try using 0x808, here is a simpler example that generates a sine wave at middle C (256Hz)