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furnace/doc/7-systems/opll.md
tildearrow c6a9277d51 document chip options
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Yamaha YM2413/OPLL

the YM2413, otherwise known as OPLL, is a cost-reduced FM synthesis sound chip, based on the Yamaha YM3812 (OPL2).

OPLL also spawned a few derivative chips, the best known of these is:

  • the famous Konami VRC7. used in the Japan-only video game Lagrange Point, it was another cost reduction on top of the OPLL! this time just 6 channels...
  • Yamaha YM2423, same chip as YM2413, just a different patch set...
  • Yamaha YMF281, ditto.....

technical specifications

the YM2413 is equipped with the following features:

  • 9 channels of 2 operator FM synthesis
  • a drum/percussion mode, replacing the last 3 voices with 5 rhythm channels, with drum mode tones hard-defined in the chip itself, like FM instruments. only pitch might be altered.
    • drum mode works like following: FM channel 7 is for Kick Drum, which is a normal FM channel but routed through mixer twice for 2× volume, like all drum sounds. FM channel 8 splits to Snare, Drum, and Hi-Hat. Snare Drum is the carrier and it works with a special 1 bit noise generator combined with a square wave, all possible by overriding phase-generator with some different synthesis method. Hi-Hat is the modulator and it works with the noise generator and also the special synthesis. channel 9 splits to Top-Cymbal and Tom-Tom, Top-Cymbal is the carrier and only has the special synthesis, while Tom-Tom is basically a 1op wave.
    • special synthesis mentioned already is: 5 square waves are gathered from 4×, 64× and 128× the pitch of channel 8 and 16× and 64× the pitch of channel 9 and they go through a process where 2 HH bits OR'd together, then 1 HH and 1 TC bit OR'd, then the two TC bits OR'd together, and those 3 results get XOR'd.
  • 1 user-definable patch (this patch can be changed throughout the course of the song)
  • 15 pre-defined patches which can all be used at the same time
  • support for ADSR on both the modulator and the carrier
  • sine and half-sine based FM synthesis
  • 9 octave note control
  • 4096 different frequencies for channels
  • 16 unique volume levels (NOTE: volume 0 is NOT silent.)
  • modulator and carrier key scaling
  • built-in hardware vibrato support

effects

  • 10xx: change patch.
  • 11xx: set feedback of channel.
  • 12xx: set operator 1 level.
  • 13xx: set operator 2 level.
  • 16xy: set multiplier of operator.
    • x is the operator, either 1 or 2.
    • y is the new MULT value..
  • 18xx: toggle drums mode.
    • 0 disables it and 1 enables it.
    • only in drums mode.
  • 19xx: set attack of all operators.
  • 1Axx: set attack of operator 1.
  • 1Bxx: set attack of operator 2.
  • 50xy: set AM of operator.
    • x is the operator, either 1 or 2. a value of 0 means "all operators".
    • y determines whether AM is on.
  • 51xy: set SL of operator.
    • x is the operator, either 1 or 2. a value of 0 means "all operators".
    • y is the value.
  • 52xy: set RR of operator.
    • x is the operator, either 1 or 2. a value of 0 means "all operators".
    • y is the value.
  • 53xy: set VIB of operator.
    • x is the operator, either 1 or 2. a value of 0 means "all operators".
    • y determines whether VIB is on.
  • 54xy: set KSL of operator.
    • x is the operator, either 1 or 2. a value of 0 means "all operators".
    • y is the value.
  • 55xy: set EGT of operator.
    • x is the operator, either 1 or 2. a value of 0 means "all operators".
    • y determines whether EGT is on.
  • 56xx: set DR of all operators.
  • 57xx: set DR of operator 1.
  • 58xx: set DR of operator 2.
  • 5Bxy: set KSR of operator.
    • x is the operator, either 1 or 2. a value of 0 means "all operators".
    • y determines whether KSR is on.

info

this chip uses the FM (OPLL) instrument editor.

chip config

the following options are available in the Chip Manager window:

  • Clock rate: sets the rate at which the chip will run.
  • Patch set: changes the chip model, providing different built-in sounds.

the following options are visible in drums mode:

  • Ignore top/hi-hat frequency changes: in drums mode, makes the top/hi-hat channels not write frequency since they share it with snare and tom.
  • Apply fixed frequency to all drums at once: sets the frequency of all drums to that of a fixed frequency OPLL drums instrument when one note with it is reached.