I don’t know about psychology, but for music I do have some ideas.
Try to find a famous composer, Beethoven or Mozart, and try to find the frequencies they used in their compositions. It’s a relatively advanced topic for a math SL student to work upon. Don’t be discouraged though. Link it to personal engagement if you are really into music.
Note: I am not discouraging you, but generally students who write on music tend to get lower scores only because they don’t explain their music terms which the moderator doesn’t understand.