Yamaha YMF278
The Yamaha YMF278 or YMF278B, also known as the OPL4, is a sound chip that incorporates both FM synthesis and sample-based synthesis by Yamaha.
Frequency modulation synthesis component
The FM part is essentially a YMF262 block; thus, it is also backward-compatible with the YM3526 and the YM3812. 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
Eight waveforms are available for the FM synthesis:
- simple sine
- half sine
- absolute sine
- quarter sine
- alternating sine
- "camel" sine
- square
- logarithmic sawtooth
Sample-based synthesis component
The sample synthesis part is based on pulse-code modulation. It features:- Up to 24 simultaneous sounds
- Output sampling frequency of 44.1 kHz
- Waveform data lengths of 8, 12, or 16 bits
- Stereo output
- Up to 4 MB of external memory for wave data
- Up to 512 samples
- External ROM or Static [random access memory|SRAM] memory. If SRAM is connected, then wave data can be downloaded from the OPL4.
- Chip select signals for 128 KB, 512 KB, 1 MB, or 2 MB memory can be output.
Connectivity
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.For sound effects, the OPL4 can be connected to the Yamaha YSS225 effects processor, which adds various sound effects.
Like its predecessors, the OPL4 outputs audio in digital-I/O form, thus requiring an external DAC chip. For this reason, the OPL4 is used with the Yamaha YAC513 DAC chip, which was developed for the earlier OPL3 chip.