STSID is a new hardware project for the Commodore C64 by Tony P. If Tony’s name strikes a cord you may recall that Tony was working on a SID emulator in 2018 called SID XMC.
The new STSID has the following features:
Stereo or Dual sid possible.
Dual pin pwm, 5bit+5bit for 10bit with less r/c filtering.
X/Y paddle adc.
Midi in/out, uses $d41d and $d41e
wildcard at $d41f, like small program download/firmware upload.
and for permanent settings.
Pad 5 and C(with analog) can be used for diy stuff,
like a wire for dual sid or a wire to Restore key that if you hold it down for 2sec it will pull C64 Reset low etc.
You can learn more about STSID and get your own on the Lemon64 forums.