I thought all these were all simulations and not replicas of silicon. I'm talking about something that keeps all the interference flaws and weirdness of the analog synth intact, and every chip being just a little bit unique, like the original.
reSID is one of the best simulators, and actually does capture a lot of the quirks of the 6581. Take a look at the source, some of the models are actually based on electrical characteristics (filter.cc and filter.h for example).
