a backwards-compatible successor to the AY-3-8910, with increased volume resolution, duty cycle control, three envelopes and highly configurable noise generator.
sadly, this soundchip has only ever observed minimal success, and has remained rather obscure since.
it is known for being used in the Covox Sound Master, which didn't sell well either.
while emulation of this chip is mostly complete, hardware comparison hasn't been performed yet due to its scarcity. it also was emulated in a now-abandoned tracker with similar goal as Furnace, which sparked interest on the chip.