Yamaha YMF278

The Yamaha YMF278B, also known as the OPL4 (OPL is an acronym for FM Operator Type-L), is a sound chip that incorporates both FM synthesis and sample-based synthesis (often incorrectly called "wavetable synthesis").

The sample synthesis part is based on pulse-code modulation (PCM). It features:

The PCM synthesizer part accepts:

The FM part is essentially a YMF262 (OPL3) block; thus, it is also backwards-compatible with the YM3526 (OPL) and the YM3812 (OPL2). Like the OPL3, it can operate in one of four ways:

Four-operator FM allows more complex sounds but reduces polyphony.

Eight waveforms are available for the FM synthesis:

Unlike the OPL3, which has four channels for sound output, the OPL4 features six channels.

The YMF278B was used in the Moonsound MSX sound card and in Yamaha's SoundEdge sound card for IBM PC and compatibles.

A stripped-down version of the YMF278 (removing the FM synthesis section) was built for Sega as the MultiPCM. Yamaha internally identifies the chip as the YMFA1005 whereas Sega uses the part number 315-5560. This version of the chip was used in conjunction with the YM3438 which provided sound timer controls.

For ROM wave data access, the Yamaha YRW801 2MB ROM chip can be connected to the OPL4. It holds approximately 330 samples, mostly 22.05-kHz 12-bit samples with some drums at 44.1 kHz. It is compatible with the General MIDI standard (128 melody sounds, 47 percussion sounds).

For sound effects, the OPL4 can be connected to the Yamaha YSS225 effects processor (EP), which adds various sound effects.

Like all its predecessors, the OPL4 outputs audio in digital-I/O form, thus requiring an external DAC chip. For this purpose, the Yamaha YAC513 DAC was designed.

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