Yamaha YM3812

The Yamaha YM3812 also known as the OPL2 (OPL is an acronym for FM Operator Type-L) is a sound chip (i.e. integrated circuit) created by Yamaha Corporation in 1985 and famous for its wide use in IBM PC-based sound cards such as the AdLib and Sound Blaster, as well as several arcade games mostly by Nichibutsu.

It is backwards compatible with the OPL aka YM3526, to which it is very similar – in fact, it only adds 3 new waveforms. An upgraded version of the OPL2, the OPL3 aka YMF262, was also popular in later sound cards such as the Sound Blaster 16. Another related chip is the YM2413 (OPLL), which is a cut down version.

Creative Labs and other companies often hid the original Yamaha labels

Yamaha YM3812-F SMD (surface mount OPL2 chip)

YM3812, showing the die surface

The circuit has 244 different write-only registers. It can produce 9 channels of sound, each made of two oscillators or 6 channels with 5 percussion instruments available. Each oscillator can produce sine waves which may also be modified into 3 other waveforms – the negative part of the sine can be muted or inverted, and pseudo sawtooth waves (¼ sine waves upward only with silent sections in between) can also be produced. This odd way of producing waveforms give the YM3812 a characteristic sound. Each wave generator has its own ADSR envelope generator. Its main method of synthesis is Frequency modulation synthesis, done by phase modulation of the phase of one of the channel's oscillators by the output of the other.

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