The FM part is essentially a YMF262 (OPL3) block; thus, it is also backward-compatible with the YM3526 (OPL) and the YM3812 (OPL2). Like the OPL3, it can operate in one of four ways:
18 two-operator FM channels
6 four-operator FM channels + 6 two-operator FM channels
15 two-operator FM channels + 5 FM drums
6 four-operator FM channels + 3 two-operator FM channels + 5 FM drums
Four-operator FM allows more complex sounds but reduces polyphony.
Eight waveforms are available for the FM synthesis:
simple sine
half sine
absolute sine
quarter sine (pseudo-sawtooth)
alternating sine
"camel" sine
square
logarithmic sawtooth
Unlike the OPL3, which has four channels for sound output, the OPL4 features six channels.
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 chip was used here.
Applications
[edit]YMF278B on a Yamaha Sound Edge SW20 PC card (near top left)
The YMF278 was used in the MoonsoundMSXsound card and in Yamaha's SoundEdge sound card for IBMPC and compatibles.
