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# Yamaha YM2151
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the sound chip powering several arcade boards, the Sharp X1/X68000 and the Commander X16. eight 4-op FM channels, with overpowered LFO and almost unused noise generator.
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it also was present on several pinball machines and synthesizers of the era, and later surpassed by the YM2414 (OPZ) present in the world-famous TX81Z.
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in most arcade boards the chip was used in combination with a PCM chip, like [SegaPCM ](segapcm.md ) or [OKI's line of ADPCM chips ](oki.md ).
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# effects
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- `10xx` : **set noise frequency of channel 8 operator 4.** `00` disables noise while `01` to `20` enables it.
- `11xx` : **set feedback of channel.**
- `12xx` : **set operator 1 level.**
- `13xx` : **set operator 2 level.**
- `14xx` : **set operator 3 level.**
- `15xx` : **set operator 4 level.**
- `16xy` : **set multiplier of operator.**
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- `x` is the operator (1-4).
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- `y` is the multiplier.
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- `17xx` : **set LFO speed.**
- `18xx` : **set LFO waveform.**
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- `00` : saw
- `01` : square
- `02` : triangle
- `03` : noise
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- `19xx` : **set attack of all operators.**
- `1Axx` : **set attack of operator 1.**
- `1Bxx` : **set attack of operator 2.**
- `1Cxx` : **set attack of operator 3.**
- `1Dxx` : **set attack of operator 4.**
- `1Exx` : **set LFO AM depth.**
- `1Fxx` : **set LFO PM depth.**
- `30xx` : **enable envelope hard reset.**
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- this works by inserting a quick release and tiny delay before a new note.
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- `50xy` : **set AM of operator.**
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- `x` is the operator (1-4). a value of 0 means "all operators".
- `y` determines whether AM is on.
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- `51xy` : **set SL of operator.**
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- `x` is the operator (1-4). a value of 0 means "all operators".
- `y` is the value.
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- `52xy` : **set RR of operator.**
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- `x` is the operator (1-4). a value of 0 means "all operators".
- `y` is the value.
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- `53xy` : **set DT of operator.**
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- `x` is the operator (1-4). a value of 0 means "all operators".
- `y` is the value:
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- `0` : +0
- `1` : +1
- `2` : +2
- `3` : +3
- `4` : -0
- `5` : -3
- `6` : -2
- `7` : -1
- `54xy` : **set RS of operator.**
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- `x` is the operator (1-4). a value of 0 means "all operators".
- `y` is the value.
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- `55xy` : **set DT2 of operator.**
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- `x` is the operator (1-4). a value of 0 means "all operators".
- `y` is the value.
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- `56xx` : **set DR of all operators.**
- `57xx` : **set DR of operator 1.**
- `58xx` : **set DR of operator 2.**
- `59xx` : **set DR of operator 3.**
- `5Axx` : **set DR of operator 4.**
- `5Bxx` : **set D2R/SR of all operators.**
- `5Cxx` : **set D2R/SR of operator 1.**
- `5Dxx` : **set D2R/SR of operator 2.**
- `5Exx` : **set D2R/SR of operator 3.**
- `5Fxx` : **set D2R/SR of operator 4.**
