[OS X] &*$!**!& iTunes
Am in the midst of converting a 500 CD collection from .wav to .aif format (let's not get into why I'm doing this, let's just agree that it's being done for a good reason).
The .wav files for the 500 albums are in a library located on a Macbook Pro.
Here's my methodology:
1) Select 5-10 albums at a time and convert them to .aif fomat.
2) This results in each album's folder having both a .wav and a .aif file for each track.
3) I then go into the Finder and copy each album's .aif files to a 1TB Lacie external drive.
4) Once the .aif files are copied to the Lacie drive I delete the .aif files from the Library folder in the Macbook Pro using the Finder, thus leaving only the .wav files on the Macbook Pro.
At this point I eject and disconnect the external drive, close iTunes, and then relaunch iTunes....... and low and behold I have two entries for each track for each album - one for a .wav (on the internal drive) and one for the .aif on the external drive which is not even connected to the Mac!!!!!
How do I get rid of ALL the now phantom .aif track entries in the iTunes Library? There's got to be a way to do this via a script/tool/command. Using iTunes 11.0.2 (26)
My theory for why this is happening is that each element in the itunes library is actually an alias to the folder on disk. Somehow, when you copy the file over to the external drive, it's modifying the itunes alias to point to the external drive while leaving the original copy of the file untouched. You can work around this by deleting the entry from the library before moving the files over, just make sure to select the "keep files" option when removing them from the library.
To your question at hand, I've converted my entire library from MP3 to AAC and had a similar issue. The easiest way to do it (assuming you are using iTunes 11) is to go to Music in the top left dropdown, then click the 'songs' tab on the top bar.
In the view that results, RIGHT click on the column header (where it says name/time/artist etc) and click on "Kind". This will add a column that tells you the media type of each file. Now LEFT click on the Kind header and it will sort everything by kind. This should group all of the aiff files together, and you should be able to select and delete them.
(Note that making a smart playlist with aiff files will also show you all of them, but won't work for you, because you can't delete library entries from a playlist, just the playlist entry)
I use Linux, OS X, iOS and Windows. Let the OS wars die.