For most people who have relied on digital downloads as their main source of music, the iTunes library can be a massive collection of digital music files. It is inevitable the duplicates will occur. It may be because the same file was imported multiple times. Or there were duplicate purchases made. Or it could simply boil down to a messy music organization method. Not everyone likes to rename files or fill up other fields. Duplicates can be annoying because it contributes to more chaos in your already chaotic music library. Depending on your import settings, it might also use additional space.
So once in a while, it might be prudent to do some housecleaning.
Take the time to search for your duplicates and get rid of them. Just leave one copy of the file. iTunes in OS X Lion is great because it gives users a much easier way to search for these duplicates. No need to scrutinize each and every file to see if there is a duplicate somewhere.
Launch iTunes from the dock or applications folders. If you have an iPod connect, it will most likely launch by default.
Select File and click Display Duplicates. This will identify duplicates based on the name and artist. Sometime, if you like a song, you buy different versions or covers of it. If that is the case, click Option, select File and Display Exact Duplicates. This is now based on name, artist, and album.
The best way to see the duplicates is to sort by date added. You can either delete the newer entries or the older entries. Simply highlight the files that you want and press Edit the click Delete. Command+Delete also works.