C64 sid audio chip uses pulse width modulation (PWM). You can use any PWM capable synth (also a Renoise instrument by using a simple saw wave + a reversed saw wave and detune/offset them = modulating pulse wave) + a reducer like renoise’s internal (or leave the reducer for hq). Also add some filter devices to the result, bandpass or highpass. If you use Renoise internal or a decent vst synth for PWM, the result will also sound like chip tune only better than sid. Or buy a vst like quadrasid to get the original sound. But the programming of original emulations like quadrasid isn’t so cool.