Duplicate files · Where it looks and what it skips
Is my Music folder checked for duplicate files?
Short answer: No. On this Mac the duplicate finder covers Downloads, Documents, Desktop, Movies and Pictures, not the Music folder. For songs in the Music app, use File → Library → Show Duplicate Items in Music and remove them there.
No — the This Mac source covers Downloads, Documents, Desktop, Movies and Pictures, and your Music folder isn't one of them. Song files stored in those five folders are compared like any other file.
If you use the Music app, it has its own way to spot repeated songs: in the Music app, choose File → Library → Show Duplicate Items. Remove duplicates from inside Music so its library stays consistent.
Remember that the duplicate finder only matches exact copies, so the same song in two formats or at two quality levels wouldn't be grouped anyway.