[Audio] GBA midi editing, issues with soundfont/voicegroups

Hi All! I am trying to edit music using midi files in the Pokeemerald decomp (thank you everyone who have/continues to work on this). My midi editor (LMMS) appears even more confused than I am which is unsettling.

I am trying to edit the .mid files with LMMS, using a gba soundfont (.sf2 found on google pretty easily, not sure if I should link it). The midi files open up, but many of the songs are playing the wrong instruments. For example, the percussion is always set to instrument 0 (piano). I have figured out that most of the instruments can be fixed by manually changing instrument but am worried why this is occurring in the first place. In short, I'm pretty sure that LMMS doesn't know what voicegroup is used, and maybe the midi file doesn't contain this information.

Has anyone tried this? I don't mind digging deeper into this but I am stuck and wondering if there is a simpler way to approach this. Do the .mid and .sf2 files contain any information about the voicegroups, and is there an easy way to check midi or sf2 for errors/missing info? Do the majority of people do music hacking with .s files, and is there any linux software that can edit .s files (not using windows/sappy lol rip me)?

Also I can't find any guides on music hacking using the decomp, and I wouldn't mind making one if I figure this out since this is a headache. I don't mind moving this thread to the decomp if it fits there better. Thank you everyone.

Have you figured out a fix for this? I am stuck in a similar situation...

The voicegroup that each song uses in pokeemerald is marked in the .s file for the particular song near the top of the file. Each voicegroup has organized the instruments a bit differently from each other, although there are some patterns. Like you noticed, the first instrument in a voicegroup (which is at the 0 index) is often percussion. Most midi editors tend to put acoustic grand piano as the first instrument, so this is a common issue. The only way to see what instruments are used in any given midi is to first look at the .s file, see which voicegroup is being used, then look at each track, noticing the number given for any "VOICE" command, and finding the instrument at that value index within the proper voicegroup. I tend to edit the midi as much as I can in a midi editor (I like to use MidiEditor, since it's really simple), and then any specific changes I make, including instrument changes and voicegroup selections, I do in the .s file. Notepad++ works quite nicely for editing .s files. Hopefully that answered your question(s). If not, just ask me for some clarification, and I'll be happy to give it!

In relation to a guide to decomp music editing, I'm actually currently in the works of writing one up. Once I finish a few projects that I'm currently working on, I'll be able to devote more time to it and post it.