Yamaha OPL
The OPL (FM Operator Type-L) series is a family of sound chips developed by Yamaha. It consists of low-cost sound chips providing FM synthesis for use in computing, music and video game applications.
The OPL series of chips enabled the creation of affordable sound cards for IBM PC compatibles in the late 1980s such as the AdLib and Sound Blaster, effectively becoming a de-facto standard until they were supplanted by "wavetable synthesis" cards in the early-to-mid 1990s.