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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
- `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.
- `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. `xx` may be one of the following:
- `00` : saw
- `01` : square
- `02` : triangle
- `03` : noise
- `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.
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- `1Exx` : set LFO AM depth.
- `1Fxx` : set LFO PM depth.
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- `30xx` : enable envelope hard reset.
- this works by inserting a quick release and tiny delay before a new note.
- `50xy` : set AM of operator.
- `x` is the operator (1-4). a value of 0 means "all operators".
- `y` determines whether AM is on.
- `51xy` set SL of operator.
- `x` is the operator (1-4). a value of 0 means "all operators".
- `y` is the value.
- `52xy` set RR of operator.
- `x` is the operator (1-4). a value of 0 means "all operators".
- `y` is the value.
- `53xy` set DT of operator.
- `x` is the operator (1-4). a value of 0 means "all operators".
- `y` is the value:
- 0: +0
- 1: +1
- 2: +2
- 3: +3
- 4: -0
- 5: -3
- 6: -2
- 7: -1
- `54xy` set RS of operator.
- `x` is the operator (1-4). a value of 0 means "all operators".
- `y` is the value.
- `55xy` set DT2 of operator.
- `x` is the operator (1-4). a value of 0 means "all operators".
- `y` is the value.
- `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.
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- `5Fxx` : set D2R/SR of operator 4.
