ym-opll

Emulator for the Yamaha OPLL sound chip, also known as YM2413. Used in the Sega Master System FM sound unit expansion as well as the NES VRC7 mapper's expansion audio chip.

VRC7 has the same FM core as YM2413 but VRC7 has 6 channels instead of 9, VRC7 doesn't have rhythm mode, and VRC7 has a different set of fixed instrument patches in instrument ROM.