FM
Six sine waves, and a diagram saying which of them bends which. No filter anywhere: bells, electric pianos and that bass are all made by oscillators modulating each other, which is a different trade from anything else on this site.
Everything you hear is synthesized or chopped in the browser: no audio framework, just Web Audio and two AudioWorklets. The engine is a plain TypeScript package (@mixpigeon/engine) that drops into any site, game or art piece. The instance on this page lives at window.mixpigeon.
Koalition