Being dissatisfied with the VRC7 emu I'm currently using, I've been looking into writing my own. FM Synth is a new territory for me... and the docs aren't quite as straight-forward as NESSOUND.txt was... so I'm still having a few problems understanding the whole picture.
The big references I've been using have been:
http://www.shipbrook.com/jeff/sb.html - OPL2 programming document. (to my understanding... VRC7's sound is a dumbed down OPL2). This doc is more for musicians looking to use the chip rather than for people looking to emulate it... so the descriptions are poor/non-existant... so I've also been using:
http://www.smspower.org/maxim/forumstuff/ym2413am/ - This OPLL document. It provides much greater detail but is clearly for a different (but similar) chip. I'm wondering if the info and constants in this doc can be applied to the OPL2.
These are really the best docs I could find. After several searches, I was unable to find a more descriptive doc relating strictly to the OPL2. If anyone knows of some other docs, I'd love to get my hands on anything I can.
Anyway, after much reading, I've got a general understanding of how everything works. A few of the specifics are still missing, but nothing that can't be ironed out later. There's still some questions relating to the fundamentals which are still nagging at me:
1) KSL / KSR affects both modulator and carrier output I'd assume... correct? Or is it just the carrier?
2) Does the modulator have any effect at all when feedback is on? The way I understand it... the carrier sends its output back on itself (basically taking the modulator's place in the normal formula). Is that right? Or is the modulator still involved somehow? The docs didn't cover feedback that much.
3) I'm confused about purcussive tones. (Bytes 20-35 in the OPL2 doc linked above... when bit 5 is cleared). When this is in effect, do you simply skip the sustain phase and go straight to release? This is the impression I'm under... but a graphic image in the OPLL doc (direct link) clearly shows the release phase being different from the sustain phase (like they both fade out, but the release phase does it faster). Can anyone clarify this?
That's about it for now. I'd really appreciate any help anyone can give me.
The big references I've been using have been:
http://www.shipbrook.com/jeff/sb.html - OPL2 programming document. (to my understanding... VRC7's sound is a dumbed down OPL2). This doc is more for musicians looking to use the chip rather than for people looking to emulate it... so the descriptions are poor/non-existant... so I've also been using:
http://www.smspower.org/maxim/forumstuff/ym2413am/ - This OPLL document. It provides much greater detail but is clearly for a different (but similar) chip. I'm wondering if the info and constants in this doc can be applied to the OPL2.
These are really the best docs I could find. After several searches, I was unable to find a more descriptive doc relating strictly to the OPL2. If anyone knows of some other docs, I'd love to get my hands on anything I can.
Anyway, after much reading, I've got a general understanding of how everything works. A few of the specifics are still missing, but nothing that can't be ironed out later. There's still some questions relating to the fundamentals which are still nagging at me:
1) KSL / KSR affects both modulator and carrier output I'd assume... correct? Or is it just the carrier?
2) Does the modulator have any effect at all when feedback is on? The way I understand it... the carrier sends its output back on itself (basically taking the modulator's place in the normal formula). Is that right? Or is the modulator still involved somehow? The docs didn't cover feedback that much.
3) I'm confused about purcussive tones. (Bytes 20-35 in the OPL2 doc linked above... when bit 5 is cleared). When this is in effect, do you simply skip the sustain phase and go straight to release? This is the impression I'm under... but a graphic image in the OPLL doc (direct link) clearly shows the release phase being different from the sustain phase (like they both fade out, but the release phase does it faster). Can anyone clarify this?
That's about it for now. I'd really appreciate any help anyone can give me.