How could I undub Summon Night 2?

[Shadicluigi]

The first game had no voices, which I was fine with but this has crusty english voices and i'd much rather have none/the japanese voices. Any tools I can use to go through sound files and things?

 

[FAST6191]

The GBA does have a format that is common to many games, generally known as Sappy (though some favour some other things).
https://www.romhacking.net/documents/462/
https://www.romhacking.net/utilities/948/
http://www.romhacking.net/?page=uti...l=&perpage=20&title=&desc=sappy&utilsearch=Go

http://www.feshrine.net/ultimatetutorial/ has some things as well. Golden Sun hacking also has a fair bit but I don't know where that is located these days.

If the game uses that format (I have hacked it extensively but not in the audio aspects) then you have any number of things you could either use to extract and overwrite, or just silence.

Alternatively if silence is a thing you can do with then you can disable the calls to the audio -- if getting hit causes a yell then whatever subtracts from health will somewhere along the line call the audio (which fiddles with specific parts of the GBA hardware nothing else will, you don't have to understand it just stop it from executing).

Beyond that time to get into GBA audio hacking in earnest.
http://belogic.com/gba/
http://problemkaputt.de/gbatek.htm#gbasoundcontroller has a bunch of stuff as well
https://www.cs.rit.edu/~tjh8300/CowBite/CowBiteSpec.htm#Sound Controls is older but some things too, most of it on the above.
http://www.coranac.com/tonc/text/sndsqr.htm http://www.coranac.com/tonc/text/asm.htm