And then there is music that used those chips quirks to the advantage, like how imperfect (IIRC) volume control in SID was used as crude DAC in some cases, but later better version of chip "broke" that "feature". Later people figured out other weird trick to get a DAC out of it even out of "fixed" chips by tactically resetting the waveform generators

And that one did contain actual analog multi-mode filter.