The fuck? How did I not know about this? New tool for GB/GBC music editing just released.
https://github.com/dannye/crystal-trackerCan open, edit, save and playback .asm music for pokecrystal and pokegold as well as many others.
Until now you had to either manually type each note and parameters in by hand, or use a shitty broken decade-old tool.
https://youtu.be/veBEnq6Xnf0