It differs from game to game. If you are lucky your game uses non-sequenced music in a compressed format like 8-bit ADPCM (common on GC because the DSP natively reads that format). With some knowledge about the format you can easily "see" 8-bit ADPCM data in an hex editor (8 byte blocks, 1st byte should be about the same in blocks near each other). If you are less lucky the game uses sequenced music (aka. MIDI-like files) where the music data is basically a succession of reference to samples stored in a "sample database" file. In that case it's harder to recognize the data (in my experience).
AFC files should be related to audio if I remember correctly. If your game is not using big data archives on disc, enabling logging in Dolphin and checking the file monitor logs will tell you what files the game accesses, which should help in finding the right files.
AFC files should be related to audio if I remember correctly. If your game is not using big data archives on disc, enabling logging in Dolphin and checking the file monitor logs will tell you what files the game accesses, which should help in finding the right files.