Yamaha YM3526
The YM3526, a.k.a. OPL, is a sound chip developed by Yamaha as a low-cost nine channel, two operator FM synthesis chip. It was notably used in a Commodore 64 expansion, the Sound Expander, as well as several arcade games, such as Terra Cresta and Bubble Bobble.
A very closely related chip is the Y8950, or MSX-AUDIO, which was used as an MSX expansion. It is essentially a YM3526 with ADPCM recording and playback capability.
