Find, compare, delete duplicate music files with Terminal
Use iTunes as per Apple's note 


  Choose View > Show Duplicate Items to show duplicate items (matches are based on the song name and artist). 
  
  Duplicate items will be sorted next to one another. Review each item to determine which one you'd like to remove from your library. You can compare the track length, date added, genre, play count, size, bit rate, and more to help you determine which item you'd like to keep and which item you'd like to remove.


Then choose the item to delete and hit the delete key

There are apps that automate more of this e.g. Dupin