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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
- `10xy` : set LFO parameters.
- `x` toggles the LFO.
- `y` sets its speed.
- `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).
- `y` is the mutliplier.
- `18xx` : toggle extended channel 2 mode.
- 0 disables it and 1 enables it.
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- only in extended channel 2 system.
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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. `xx` may be one of the following:
- `00` : square
- `01` : noise
- `02` : square and noise
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- `03` : nothing (apparently)
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- `04` : envelope and square
- `05` : envelope and noise
- `06` : envelope and square and noise
- `07` : nothing
- `21xx` : set noise frequency. `xx` is a value between 00 and 1F.
- `22xy` : set envelope mode.
- `x` sets the envelope shape, which may be one of the following:
- `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
- if `y` is 1 then the envelope will affect this channel.
- `23xx` : set envelope period low byte.
- `24xx` : set envelope period high byte.
- `25xx` : slide envelope period up.
- `26xx` : slide envelope period down.
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- `29xy` : enable SSG auto-envelope mode.
- 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.
