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
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 options
- 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.