#msxmusic

2PLAYER answered my question. You can visit his tumblr here. 

Channels 7, 8, and 9 have 6 slots and are used to generate the 5 rhythmic sounds. Bass drum uses 2 slots with FM while the other 4 sounds are created using the OPL white noise oscillator combined with frequency data. So yes, you could make your own OPL drums with the 9 channels but this allows you to squeeze 5 drums out of 3 channels.

Hello everyone!

A couple weeks ago I responded to a question about the sound behind the MSX and the Metal Gear 2: Solid Snake soundtrack. But there's actually something regarding the description of the soundchips in MSX-AUDIO and MSX-MUSIC that I've never understood when reading about them. I'd be interest if someone can provide an answer.

According to wikipedia and other sources, both MSX-AUDIO and MSX-MUSIC are described as having:

9 channels of FM sound (without drums), or 6 channels of FM sound + 5 FM drums.

Does anyone know why that is, or what that means? You can create percussive sounds with FM synthesis. And with the Sega Genesis YM2612, for example, that doesn't require a special feature or different mode. You can use one of the 6 FM channels to make a drum sound as you would make any other sound. 

Is there a reason you can't use the first 9 channels however you want (ignoring MSX-MUSIC having presets)? Or is it that you can do that with MSX-AUDIO, but they found a way to create drums with less resources, making it better to have an option that allows for 5 channels of drums with only sacrificing 3 "normal" channels? Does that come from restricting the number of operators?