I'll let others chime in on utilities that might be helpful. The ones I've tried I''ve not been impressed with or I'm doing something wrong.
Dealing with duplicates can be interesting. One of the ways that duplicates can appear in the list is if you have two tracks with the same title though it comes from two different artists/same artists on different albums. It can also occur if you have multiple unidentified tracks that have several named track 1, several named track 2, etc. Because off these things the duplicate finder in iTunes is often not very good.
Here's what I have done in the past. I can be time-consuming but has helped me a few times.
1. Open iTunes and go to Preferences>Advanced. If either of the first two boxes are checked make sure both are unchecked. After we're done you can out things back the way they were. Close the preference sheet.
2. Make sure you are in the music section then select everything (Command A). Now hit delete. This is deleting the current pointers in the library it
does not delete the files. You will be asked whether you want t9o delete the files. Choose No.
3. All the current pointers to the songs have now been deleted. To correct that go to the iTunes
File menu >
Add to Library. Find your music folder and open it. This forces iTunes to rebuild the links. It may take some time depending upon the size of your library.
4. If you have songs that do not have correct titles etc. select the track and choose
File>Get Info (Command I). This allows you to edit the track tags.
Once everything is done you can go back to iTunes Preferences>Advanced and set the music folder preferences back to what they were.
You might find either or both of these articles helpful
http://www.macworld.com/article/2047675/itunes-tagging-basics-and-tips.html
http://www.macworld.com/article/2148967/the-ultimate-itunes-tagging-guide-cleaning-up-your-tags.html
