furnace/papers/doc/7-systems/ym2610.md

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.

its soundchip is a 3-in-1: FM, YM2149 (AY-3-8910 clone) and ADPCM in a single package!

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.
  • only in extended channel 2 system.
• 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
  • 03: nothing (apparently)
  • 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.
• 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.
  • if x or y are 0 this will disable auto-envelope mode.