It actually is weird and exotic. The analog SVF filter is made with digital components and is highly nonlinear. No one fabricates these any more though it would be technically possible.
Emulating the distortion is done with varying levels of accuracy.
Additionally the fabrication varied from part to part and from rev to rev. So the sound of any SID is a combo of its batch of substrates limiting bandwidth and the intermodulation distortion (IMD) of its FETs' imperfect emulation linear adding and multiplication functions increasing the bandwidth. Note that these non-linearities are in a feedback loop.
Furthermore the external caps ("matched") used for the filter varied considerably, but this is more easily reproduceable.
The envelopes are unconventional too, but more easily emulated than the filter. They are a mix of linear and exponential and use the non-linear FET multiplier.
Also the oscillators are not simple analog oscillators. They're high frequency lookup tables with digital aliasing related to the key the music is written in. The noise waveform is not analog, either, but a variable frequency LFSR, although this is easy to reproduce in FPGA and somewhat in software, although the max frequency can be challenging.
Finally the entire signal chain is replete with IMD so any melody/rhythm played on one voice is affected and influenced by what is played on the other voices.
In summary the SID was designed by electronic musician Bob Yannes who modeled it after typical analog synths but was technically limited by the fabrication of the age to make it less clean than even the grungiest cold war soviet synth. Still it was better than everything else at the time and it got a lot of loving attention from devs and musicians who squeezed every ounce of juice from it.
Emulating the distortion is done with varying levels of accuracy.
Additionally the fabrication varied from part to part and from rev to rev. So the sound of any SID is a combo of its batch of substrates limiting bandwidth and the intermodulation distortion (IMD) of its FETs' imperfect emulation linear adding and multiplication functions increasing the bandwidth. Note that these non-linearities are in a feedback loop.
Furthermore the external caps ("matched") used for the filter varied considerably, but this is more easily reproduceable.
The envelopes are unconventional too, but more easily emulated than the filter. They are a mix of linear and exponential and use the non-linear FET multiplier.
Also the oscillators are not simple analog oscillators. They're high frequency lookup tables with digital aliasing related to the key the music is written in. The noise waveform is not analog, either, but a variable frequency LFSR, although this is easy to reproduce in FPGA and somewhat in software, although the max frequency can be challenging.
Finally the entire signal chain is replete with IMD so any melody/rhythm played on one voice is affected and influenced by what is played on the other voices.
In summary the SID was designed by electronic musician Bob Yannes who modeled it after typical analog synths but was technically limited by the fabrication of the age to make it less clean than even the grungiest cold war soviet synth. Still it was better than everything else at the time and it got a lot of loving attention from devs and musicians who squeezed every ounce of juice from it.