YM2612 is a 6 channel FM synthesis (Frequency Modulation) sound synthesizer IC produced by Yamaha. It belongs to a family of Yamaha FM synthesizer chips, and can be considered an ancestor to the OPL2 (YM3812) and OPL3 (YMF262) FM ICs that were used in the popular AdLib and Creative LabsSoundBlaster PC soundcards.
The YM2612 was notably used in the Sega Mega Drive (aka Sega Genesis) game console and has the following features:
Six concurrent FM channels (or voices)
The sixth channel can be used as an FM or DAC channel (but not both)
Each channel may be assigned to either left, right or both (centre) of the stereo output.
The special sixth channel can act as a DAC (Digital to Analogue Converter) by means of the 'DAC Enable' register, this allows the chip to play 8-bit PCM sound samples. Enabling the DAC disables the FM for that channel. Data is written to the DAC via an 8-bit register. The YM2612 does not provide any timing or buffering of the PCM samples, so all frequency control and buffering must be done in software by the host processor.
The synth patches used by the YM2612 in Mega Drive games are compatible with certain members of the Yamaha DX/TX synthesizers, such as the DX100.
In my brief experience of working with the YM2612, I've come to the conclusion that the problems with sound in emulators are often due to extremely small timing inaccuracies with the writes to the chip.
Since Gens queues YM2612 writes for each scanline and then writes them in a block at the end, it is messing with the timing quite a lot.
It's the instruments themselves, like the guitar in TF4, which I'm interested in, I believe it is the minute interactions of the operators which changes the type of sound, and the exact time which they are programmed does not make a difference.
The YM2612 does not provide any timing or buffering of the PCM samples, so all frequency control and buffering must be done in software by the host processor.
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