windows 7 - Find all files that are NOT of a specific type/extension in folder?

Windows 7 Ultimate 64bit:

I'm looking for a way to find all the files in a directory that are NOT of a specific file type or extension.

Example: I'd like to find every file that isn't an .mp3 in my music folder (and all sub folders).

Answer

type this in the search box of the directory you want to search

NOT *.mp3