How can stop or reduce music duplication in Itunes? I keep all of my music in a folder on my back up drive. I use Media player to edit and genre categorize the music. Then copy / transfer the folder to Itunes which converts the music to ACC format.

My problem is when I add a new song or album(s) to my master folder, Itunes wants to copy the whole folder again causing massive duplications and it wants to change my genre categorization on some songs. 

It also sometimes takes songs in an album and separates them listing each separately. So instead of on e album listing 15 songs. I get 15  listings of the album with one song listed.
Open iTunes preferences and click advanced.

Uncheck the Copy line item...



You still have to clean up the old dupes, but any new imports will be left on the filesystem where you stored them and not copied or moved to where iTunes would like them to be stored.