I have updated the SEGA Mega Drive / MIDI Interface by adding a mapping for the channel 3 "special mode" for the YM2612 sound chip. The YM2612 is an FM chip with six channels whereby each channel has four operators. Normally, each operator is tuned in relation to a fundamental channel frequency. For example, to create an additive synthesis sort of organ sound, one might have the first operator set to 1 x, the second operator set to 2 x, the third operator set to 4 x and the fourth operator set to 8 x. Each of these multipliers refers to a multiplication of a fundamental frequency, so if the fundamental frequency changes, so does the frequency of all of the operators with respect to their multiplier values; they are thus all tied together.
However, channel three of the YM2612 can be put in a "special mode" whereby each operator is tuned completely independently from the fundamental frequency. This allows for different sounds, and for the possibilities of chords using only a single channel. I have added this functionality (i.e. control over the special mode) to the SEGA Mega Drive / Genesis MIDI Interface. I have started with a pretty basic mapping, but I hope to expand upon it quite soon.