I'm not a lawyer but when I Wikipedia "Fair use", I see: "Fair use is a doctrine that permits limited use of copyrighted material without acquiring permission from the rights holders. Examples of fair use include... research...."
I'd like to research some music on Spotify and wondering how technically to get it into WAV format?
even if you are researching it, you probably wouldn't want to get it from spotify. likely they are using a compressed format which wouldn't be suitable for research anyway.