GBAMusRiper is a tool I use to extract soundbanks and MIDI data from GBA games. The success rate of it depends on what sound engine the cartridge uses. For the most part, there is no need to transcribe anymore... I personally use it to understand the songs from the Fire Emblem series, like Binding Blade, Blazing Blade, and Sacred Stones.
It uses the command line, and there is a readme file included in the package. If there are any questions you have about this tool or how I specifically use it, feel free to PM or respond back.