This is for both the EU and USA versions of the game. Even when the game is running at 60 fps, the audio crackles very badly. Sometimes the frames may drop to 55 then go back up to 60. But it's usually at 60 with 4 players. I also play Mario Kart 8 (50-56 fps), Super Mario 3D World (58-60 fps), and Mario Tennis (60 fps) and the audio plays perfectly. For Breath of the Wild (30 frames max), no stuttering or crackling at 12-30 fps. This seems to be an issue with Smash Bros only. I checked out...
Super Smash Bros. for Cemu 1.15.9c Audio Crackling
Super Smash Bros. for Cemu 1.15.9c Audio Crackling