Correction to Akao documentation. I've been testing it in the PSX version to avoid any errors brought on by PC port. I was also notified by someone that field code allows for multiple effects to be played at the same time (like the Summon effects in battle). This isn't working in PC version. I did some digging, and here are the amendments:
OPERATION 0x20:The parameter is assigned to a channel. Since operation 0x20 can only take one parameter, it is in fact no different to operation 0x28.
OPERATION 0x21:Allows 2 effects to be played using channel 1 and channel 2. This is simply a short-hand way of using operation 0x28 and 0x29.
param1=Panning,
param2=Effect ID for channel 1
param3= Effect ID for channel 2
OPERATION 0x22:Allows 3 effects to be played using channel 1, channel 2, and channel 3. This is a short-hand way of using operation 0x28, 0x29 and 0x2A.
param1=Panning,
param2=Effect ID for channel 1
param3= Effect ID for channel 2
param4= Effect ID for channel 3
OPERATION 0x23:Allows 4 effects to be played using channel 1, channel 2, channel 3, and channel 4. This is a short-hand way of using operation 0x28, 0x29, 0x2A, and 0x2B.
param1=Panning,
param2=Effect ID for channel 1
param3= Effect ID for channel 2
param4= Effect ID for channel 3
param5= Effect ID for channel 4
You see how ridiculous this is? It's just to save every last byte in some really crappy way. Again. Just confusing and useless. If not using my DLL, you can fix these broken OPERATIONs by just using the working counterparts. I.e., for operation 0x23, you'd use 0x28, 0x29, 0x2A, and 0x2B to set the 4 effects.
It's not even like 0x21,22,23 were even needed. They could have just checked to see if an argument was zero and then skipped if so - but stupidly they use 0 for the "stop effect".
OPERATION 0x30 Play a sound effect on channel #4, and ignore operation 0xF1 [param1=Panning, param2=Effect ID]
http://wiki.qhimm.com/view/FF7/Field/Script/Opcodes/F2_AKAOUpdated. I think that's everything now.