OPL3 Percussion Mode Map

I've looked for a clear explanation of all the parameters in the OPL3's percussion mode, but I've never found one. So I sat down with my MIDIbox FM V2.0 Prototype and drew a diagram of what parameters influence what sound, with a vaguely accurate idea of how they do so. To be clear, these are the parameters for the two channels and four operators that are made into HH/SD/TT/CY within the OPL3, not any parameters specific to MIDIbox FM V2.0.

There has been much misinformation circulating on the 'net about these instruments, specifically which instruments' tuning can be controlled. Vladimir Arnost's helpful breakdown of the OPL3 datasheet, the "Programmer's Guide to Yamaha YMF 262/OPL3 FM Music Synthesizer", states that "only Bass Drum, Snare Drum and Tom-Tom frequencies can be set. Cymbal and Hi-Hat frequencies are fixed." TK states in the MIDIbox FM V1 user manual that "Due to OPL3 limitations it isn't possible to use independent frequencies on HiHat/Tom/Cymbal (Bass Drum has it's own frequency and the base frequency of the Snare Drum is static and can only be multiplied)." On the other hand, the Adlib Tracker help page says "This mode is slightly hard to use (particularly the "SD/TT/TC/HH" tracks) so it is not recommended unless you know how it works or gain familiarity with it after several experiments :-)" I have found that all the percussion instruments' frequencies are modulatable, but the "metal noise" waveform which the HH and CY are based on is generated from some sort of modulation (sounds like ring mod) combining the two channels' frequencies (i.e. the frequencies that also apply to SD and TT respectively), so they are not independently modulatable. This is why there's a picture! This fact is not the least of the oddities of this mode. However, one thing to note: the HH sound is in one way technically the most complex sound the OPL3 can generate, since nowhere else in the synth but in HH and CY is a sound modulatable by two frequencies independently (as opposed to the integer FMults), and HH has the addition of feedback.