Bitcrust.

Bitcrust’s DSP is written from scratch in C++, against public datasheets and general DSP literature. The 6581 / 8580 architecture is the starting point, not the destination: oscillators, envelope, filter, and the glue between them are designed to capture the SID’s character — the bit-crushing, the leaky integrators, the resonant bite — without trying to be a bit-accurate or cycle-accurate emulation. Where the silicon is interesting, we lean in. Where it gets in the way of a usable instrument, we don’t.

Each of the twelve voices runs three independent chip instances — thirty-six in total — so per-oscillator volume is a real control, not a software overlay on top of a fixed chip architecture. The SID chip came in two revisions — the gritty, distorted 6581 and the cleaner, tighter 8580 — and their filters sound nothing alike. Bitcrust models both curves in the same engine and lets you blend between them continuously, so you can dial in tones that never existed in real hardware.