I'm a big NES chiptune fanatic and like the NES, the PC Engine is a "pure" chip tune synth run by the custom CPU. It's not a separate MIDI synth with it's own clock like the SNES or N64. I'm a bit chiptune fan and would love to run this stuff on hardware.
PCe being 8-bit is kind of in between an NES and a Genesis sound wise.
Just a couple of nitpicks: MIDI doesn't have sound. No sound at all. It's just a delivery format for how music is stored as instruments (it's a format and it's a driver/protocol). There's actually a PCE game that uses a MIDI playback engine. As for snes, there *might* be a handful of drivers that were MIDI compatible, but the vast majority either used their own engine or Nintendo supplied one.
Also, bitness can't be applied to sound chip directly. The YM in the Genesis is basically an 8bit sound chip (8bit single DAC, 8bit interface, etc) - doing so doesn't really describe the class or capability of the chip. Unless you're implying 8bit as in generation (and not literal), which is still wrong.
I didn't mean MIDI literally, but the SNES and N64 have discrete soundchips that sound very much like primitive MIDI synthesizers. There's a ton of instrument definitions that get recycled over again in a variety of games. That's why many SNES and N64 games had orchestral sounding compositions, some of which were extremely good.
I assume these instrument profiles were probably defined by audio libraries included with the dev kits and likely stored somewhere in the game code. I don't pretend to know how they operate, but many of the instruments sound very similar to MIDI sound, ie select an instrument profile and play a note.
Soundtracks of 4th and 5th generation Nintendo games were incredible, but they don't have the rawness of chip synths like the NES, PCe, and Genesis / Megadrive. Genesis games excelled at rock and techno sounding tracks, SNES excelled at orchestral sounding tracks. Not trying to beat around, but each console had it's own distinctive soundchips. SNES was just more MIDI sounding, less chiptuney, for lack of a better word.
When I think of chiptunes, I think of stuff like square, rectangle, triangle, sawtooth, sine, noise generators, etc. Take shapes from basic math functions and build them into sound waves. As synths began to get more sophisticated, it became possible to adjust the individual wave forms and decay rates making them more organic so that they emulate real instruments. That is what MIDI does at it's core.
Of course with wave sound or redbook from CD audio, you can play back anything from live recordings to digitally synthesised audio, instruments, vocals, anything.
