Join Bobby Owsinski for an in-depth discussion in this video Using the iTunes Plus tools: iTunes Droplet, part of Mastering for iTunes.
The Master for iTunes droplet is a stand-alone drag and drop tool that's a quick and easy way to encode your masters to the AAC format that iTunes uses. You can find it in your Applications/Utilities folder after the iTunes Mastering tools have been installed, but I've put it on the Desktop for easy access. All you have to do is drag and drop the source audio file or a folder containing source files onto the droplet. Most of the time, these will be either AIFF or WAV files. Utility will create a temporary Core Audio file in the same folder as your source file.
When the file is finally converted to AAC, the Core Audio temp file is automatically deleted. You won't see a progress bar while a conversion is taking place, and it may take a few moments. The droplet then gives you a prompt when the process is completed. The new file will have a M4A file extension, which means it's an AAC file. Keep in mind that regardless of the sample rate, the droplet will automatically convert the file to 44.1 kHz. Once again, the only reason that you'll be converting your sound files to the AAC file format is to hear what the file will actually sound like after it's posted on the iTunes store, not to use this file to submit to iTunes.
iTunes does not accept the AAC files, as the conversion is done by Apple from an AIFF or WAV file. After your files are converted, give them a good listen on some good monitors, high-quality headphones, and ear buds. Know what you'll be giving your listeners before the day the record hits the iTunes store. And better still, have the chance to make any adjustments to your Master if need be. (music playing)