OPL (FM synthesis)

OPL stands for FM Operator Type-L, a family of chips from Yamaha. The chip that played it, the YM3812 (OPL2), arrived in 1985 and became famous through the AdLib card and then Sound Blaster, which built in the same part. FM synthesis assembles tones from sine waves that modulate one another — cheap in silicon and distinctly metallic in timbre, far from a real instrument but infinitely better than the PC speaker's beep.

OPL3, the YMF262, came in 1990 and doubled the channel count, adding four-operator voices and stereo. The FM era ended when sample-based cards like the Gravis UltraSound and Sound Blaster's own sample channels made it possible to play back real instruments instead of imitating them. Even so, the OPL sound is so ingrained that whole chiptune genres recreate it on purpose.