Yamaha YMF262

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Yamaha YMF262 (year 1994)
decapsulated YMF262 with die surface visible
Decapsulated YMF262, showing the die surface

The Yamaha YMF262, also known as the OPL3 (OPL is an acronym for FM Operator Type-L), is an FM synthesis sound chip. It is an improved version of the Yamaha YM3812 (OPL2), adding the following features:

  • twice as many channels (18 instead of 9)
  • simple stereo (hard left, center or hard right)
  • 4 channel sound output
  • 4 new waveforms (alternating-sine, "camel"-sine, square and logarithmic sawtooth)
  • 4 oscillator mode, pairing 2 channels together to create up to six 4 oscillator FM voices
  • reduced latency for host-register access (the OPL2 had much longer I/O access delays)
  • subtle differences in the sine-wave lookup table and envelope generator from YM3812 (eg. the modulator waveform on YM3812 is delayed by one sample, whereas both carrier and modulator waveforms on OPL3 are properly synchronized)

YMF262 also removed support for the little-used CSM mode, featured on YM3812 and YM3526.

The YMF262's FM synthesis mode was configurable in different ways.

  • Its basic mode provided 18 two-operator FM channels.
  • One setting, common to the OPL line, converts 3 of the FM channels into a 5-channel percussion set.
  • Another setting, introduced with this chip, causes 12 of the channels to be paired up into 6 four-operator channels. This trades in polyphony for more complex sound formation.
  • The two settings can be used separately or in conjunction, resulting in four total modes:
    • 18 2-operator channels
    • 15 2-operator channels + 5 drum channels (drum setting on)
    • 6 2-operator channels + 6 4-operator channels (4-op setting on)
    • 3 2-operator channels + 6 4-operator channels + 5 drum channels (both settings on)

The YMF262 was used in many sound cards, including the popular Sound Blaster Pro 2.0, Sound Blaster 16 ASP and AWE family.

Like its predecessor, the OPL3 outputs audio in digital-I/O form, requiring an external DAC chip like the YAC512. Competing sound chip vendors (such as ESS, OPTi, Crystal and others) designed their own OPL3-compatible audiochips, with varying degrees of faithfulness to the original OPL3. Yamaha also produced a low-power variant of the OPL3 called the YMF289. Yamaha's later PC audio controllers, including the YMF278 (OPL4), the single-chip Yamaha YMF718/719S, and the PCI YMF724/74x family, included the YMF262's FM synthesis block for backward compatibility with legacy software. See YMF7xx for more information.

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