I've got a problem recently. The problem is I have too many music in WMA and MP3 files. Some of them hasn't any tags filled. During listening to my playlist I often noticed duplicates but searching for them manually was a real pain.
You know, I found several programs that looking for duplicates but all of them can identify only full duplicates - with the same bitrate and same format. I think they are using file checksums or tags for the comparison.
The only program that can identify duplicates by their sound is Audio Comparer. In some magical way it found the same songs in MP3 and WMA formats with different bitrate!
Just want to share my experience. If you have a similar problem, save your time, try Audio Comparer first.