YES! Someone finally used the audio-in pins! The SID has audio-in that can be summed with internally-synthesized sounds and routed through the on-chip filters

YES! Someone finally used the audio-in pins! The SID has audio-in that can be summed with internally-synthesized sounds and routed through the on-chip filters before going back out. I found this pinout in the programmer's reference guide and tinkered with it a bit as a kid, but I didn't really know what I was doing, so it never went beyond a novelty. Who knew, forty years later, that it'd get proper treatment as an effects generator!