Join Bobby Owsinski for an in-depth discussion in this video Using the Mastered for iTunes Audio To WAVE Droplet, part of Mastering for iTunes.
Just as the Master for iTunes droplet tool made encoding to AAC easier, the Audio to WAVE droplet makes converting an AAC file back to WAVE easy as well. You can find it in your Applications/Utilities folder after the iTunes Mastering tools have been installed. But once again, I've put it on the Desktop for easy access. Not only it does work with the AAC file format, but it also works with any audio files that are natively supported on Mac OS X, such as MPEG or CAP files. To use the Audio to WAVE Droplet, drag and drop audio source files or folders containing those files onto the droplet.
The droplet will then convert those files to WAVE format files. The newly created WAVE files will be named using the names of their corresponding source files and will be placed in the same folder.