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# Yamaha OPL
a series of FM sound chips which were very popular in DOS land. it was so popular that even Yamaha made a logo for it!
essentially a downgraded version of Yamaha's other FM chips, with only 2 operators per channel.
however, it also had a drums mode, and later chips in the series added more waveforms (than just the typical sine) and even a 4-operator mode.
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the original OPL (Yamaha YM3526) was present as an expansion for the Commodore 64 and MSX computers (erm, a variant of it). it only had 9 two-operator channels and drums mode.
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its successor, the OPL2 (Yamaha YM3812), added 3 more waveforms and was one of the more popular chips because it was present on the AdLib card for PC.
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later Creative would borrow the chip to make the Sound Blaster, and totally destroyed AdLib's dominance.
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the OPL3 (Yamaha YMF262) added 9 more channels, 4 more waveforms, rudimentary 4-operator mode (pairing up to 12 channels to make up to six 4-operator channels), quadraphonic output (sadly Furnace only supports stereo) and some other things.
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afterwards everyone moved to Windows and software mixed PCM streaming...
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# effects
- 10xx: set AM depth. the following values are accepted:
- 0: 1dB (shallow)
- 1: 4.8dB (deep)
- this effect applies to all channels.
- `11xx` : set feedback of channel.
- `12xx` : set operator 1 level.
- `13xx` : set operator 2 level.
- `14xx` : set operator 3 level.
- only in 4-op mode (OPL3).
- `15xx` : set operator 4 level.
- only in 4-op mode (OPL3).
- `16xy` : set multiplier of operator.
- `x` is the operator (1-4; last 2 operators only in 4-op mode).
- `y` is the mutliplier.
- 17xx: set vibrato depth. the following values are accepted:
- 0: normal
- 1: double
- this effect applies to all channels.
- `18xx` : toggle drums mode.
- 0 disables it and 1 enables it.
- only in drums system.
- `19xx` : set attack of all operators.
- `1Axx` : set attack of operator 1.
- `1Bxx` : set attack of operator 2.
- `1Cxx` : set attack of operator 3.
- only in 4-op mode (OPL3).
- `1Dxx` : set attack of operator 4.
- only in 4-op mode (OPL3).
