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 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.
A low-frequency oscillator and an envelope generator drive an FM operator to produce floating-point output for the DAC.
A quarter of the log-transformed sine waveform is stored as a sampled approximation in a 256-word read-only memory (ROM) table, computed by
[2] Another 256-word ROM stores the exponential function as a lookup table, used to convert the logarithmic scale signal back to linear scale when required, as the final stage where the oscillator-outputs are summed together (just prior to the DAC-output bus), with the modulator waveform always delayed by one sample before the carrier waveform.
The YM3526, introduced in 1984, was the first in the OPL family, providing a nine channel, two operator synthesizer.
The YM3526's output, a sequence of floating point numbers clocked at a sampling frequency of approximately 49716 Hz, is sent to a separate digital-to-analog converter (DAC) chip, the YM3014B.
[5]: 27.14–17.16 Among its newly-added features is the ability to pick between four waveforms for each individual oscillator by setting a register.
[6] The YM3812 is used with an external YM3014B monophonic DAC chip to output its audio in analog form, like with the YM3526.
It improves on the feature-set of the YM3812, which notably includes the ability to use four-operator FM synthesis.
This makes the YMF262 produce more harmonically richer sound than its predecessors, similar to that of contemporary consumer synthesizer keyboards such as Yamaha DX100.
Like its predecessors, the OPL3 outputs audio in digital form, requiring an external DAC chip such as the YAC512.
In 1995, Yamaha produced a fully compatible, low-power variant of the YMF262 called the YMF289 (OPL3-L), targeting PCMCIA sound cards and laptop computers.
The drivers for Windows 9x incorporate their own custom instrument patches which make use of this extended mode.
[9] ESFM's output in this mode is moderately faithful to the YMF262 overall, but some tones are rendered quite differently, resulting in unique distortions in the sound and music of some games.
ESS's Maestro series of PCI-based sound chips rely on a software implementation of FM synthesis that lacks ESFM's special features.
The YM3526 was notably used in a Commodore 64 expansion, the Sound Expander, as well as several arcade games, such as Terra Cresta and Bubble Bobble.
A modified version of the YM3526 with ADPCM audio known as the Y8950 (MSX-AUDIO) was used in the MSX computer as an optional expansion.
The YM2413 was used in the FM Sound Unit expansion for the Sega Mark III and the Japanese model Sega Master System, as well as the MSX-MUSIC standard, which was released both as separate enhancement cards (such as the Panasonic FM-PAC) and built-in into several MSX2+ and the MSX TurboR computers.
