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# Neo Geo/Yamaha YM2610
originally an arcade board, but SNK shortly adapted it to a rather expensive video game console with the world's biggest cartridges because some people liked the system so much they wanted a home version of it.
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its soundchip is a 4-in-1: 4ch 4-op FM, YM2149 (AY-3-8910 clone) and 2 different format ADPCM in a single package!
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# effects
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- `10xy` : **set LFO parameters.**
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- `x` toggles the LFO.
- `y` sets its speed.
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- `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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- `18xx` : **toggle extended channel 2 mode.**
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- 0 disables it and 1 enables it.
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- only in extended channel 2 chip.
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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.**
- `20xx` : **set SSG channel mode.**
- `0` : square
- `1` : noise
- `2` : square and noise
- `3` : nothing (apparently)
- `4` : envelope and square
- `5` : envelope and noise
- `6` : envelope and square and noise
- `7` : nothing
- `21xx` : **set noise frequency.** range is `00` to `1F` .
- `22xy` : **set envelope mode.**
- `x` sets the envelope shape:
- `0` : `\___` decay
- `4` : `/___` attack once
- `8` : `\\\\` saw
- `9` : `\___` decay
- `A` : `\/\/` inverse obelisco
- `B` : `\¯¯¯` decay once
- `C` : `////` inverse saw
- `D` : `/¯¯¯` attack
- `E` : `/\/\` obelisco
- `F` : `/___` attack once
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- if `y` is 1 then the envelope will affect this channel.
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- `23xx` : **set envelope period low byte.**
- `24xx` : **set envelope period high byte.**
- `25xx` : **slide envelope period up.**
- `26xx` : **slide envelope period down.**
- `29xy` : **enable SSG auto-envelope mode.**
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- in this mode the envelope period is set to the channel's notes, multiplied by a fraction.
- `x` is the numerator.
- `y` is the denominator.
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- if `x` or `y` are 0 this will disable auto-envelope mode.
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- `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:
- 0: +0
- 1: +1
- 2: +2
- 3: +3
- 4: -0
- 5: -3
- 6: -2
- 7: -1
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- `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 SSG-EG of operator.**
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- `x` is the operator (1-4). a value of 0 means "all operators".
- `y` is the value (0-8).
- values between 0 and 7 set SSG-EG.
- value 8 disables it.
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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.**
