Q: The contents in one of my playlists have been duplicated somehow, not my doing. Do I manually delete each duplicate song or is there a better way?
A: If these are just a few songs in a given playlist, the simplest way is just to clean them up manually. Although iTunes won’t automatically remove duplicates for you, it can help you filter out the duplicates by listing only those entries that have duplicate tracks.
To do this, select View, Show Duplicates from your iTunes menu:
Your current track listing will then be filtered to show only those tracks that have duplicates. For this purpose, iTunes considers a track to be a duplicate if it has the same song and artist name, so if you have the same track on two or more albums by the same artist, these will also show up as duplicates, even if they are different mixes or variations.
Once in this view, however, you should easily be able to select those tracks that are duplicates and remove them from the current playlist.
Note that the “Show Duplicates” option is stored with the current view in iTunes, so if you turn it on for a given playlist, it will remain on when you return to that playlist. This can be confusing if you forget to turn it off, however an indicator does appear somewhat prominently at the bottom of the iTunes track listing to remind you that you are currently only viewing duplicate tracks:
To return to showing all items, select the “Show All” button at the bottom of the screen, or choose View, Show All from the iTunes menu.
Note as well that newer versions of iTunes will warn you when you attempt to add a track to a playlist that is already contained in that playlist: