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Updated OPL docs (for OPL4).

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This is actually freq-mod's work, I'm just putting it in the same PR.
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Electric Keet 2024-10-03 11:21:53 -07:00 committed by tildearrow
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14
doc/7-systems/opl.md
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@ -7,11 +7,15 @@ however, it also had a [drums mode](opll.md), and later chips in the series adde
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.
Y8950 is essentially the same chip, but with one channel of ADPCM sampling, exactly the same as the one found in YM2608.
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.
later Creative would borrow the chip to make the Sound Blaster, and totally destroyed AdLib's dominance.
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 and some other things.
the OPL4 (Yamaha YMF278) retains the FM block from OPL3, but adds *twenty four* sample channels on top! samples are 44100 Hz, can be between 8, 12 or 16-bit, stereo (with 16 different levels) and can read PCM data from ROM or SRAM (up to 4 MB).
afterwards everyone moved to Windows and software mixed PCM streaming...
## effects
@ -24,9 +28,9 @@ afterwards everyone moved to Windows and software mixed PCM streaming...
- `12xx`: **set operator 1 level.**
- `13xx`: **set operator 2 level.**
- `14xx`: **set operator 3 level.**
- only in 4-op mode (OPL3).
- only in 4-op mode (OPL3 and OPL4).
- `15xx`: **set operator 4 level.**
- only in 4-op mode (OPL3).
- only in 4-op mode (OPL3 and OPL4).
- `16xy`: **set multiplier of operator.**
- `x` is the operator (1-4; last 2 operators only in 4-op mode).
- `y` is the new MULT value..
@ -81,7 +85,7 @@ afterwards everyone moved to Windows and software mixed PCM streaming...
## info
this chip uses the [FM (OPL)](../4-instrument/fm-opl.md) instrument editor.
these chips use the [FM (OPL)](../4-instrument/fm-opl.md) instrument editor. Y8950 ADPCM uses [Generic Sample](../4-instrument/sample.md) and [ADPCM-B](../4-instrument/adpcm-b.md) instrument editors.
when two channels are joined for 4-op mode, the channel bar will show `4OP` on a bracket tying them together.
@ -95,3 +99,7 @@ additionally, in OPL3:
- **Chip type**: sets the chip model. OPL3-L uses resampling.
- **Compatible panning**: for compatibility with old Furnace.
additionally, in OPL4:
- **RAM Size**: sets the RAM size for sample storage