Convert iTunes AAC Music files to MP3 for free
If you want to play those unprotected AAC music files you purchased in iTunes on other media player that doesn't support AAC or if you need an MP3 version of an AAC song for other uses, this article that will tell you an easy and free method to convert AAC songs to MP3 formats easily in iTunes and the sound quality will be perfect.
The tool which we'll use in this tutorial is "iTunes". Very few person know that iTunes can be used to convert audio files, In fact its the best tool for this task(not only converting AAC to MP3 files, iTunes also can convert MP3 WAV and other music files to AAC or M4A and preserve audio quality while converting files). Following is a step-by-step method to convert iTunes AAC songs to MP3 files for free:
1. First download iTunes if you don't have it:
Download iTunes
http://www.apple.com/itunes/download/
2. Now install it and run the program. in iTunes, click on the Edit menu and select Preferences. then go to "Advanced" tab and click on "Importing" Settings, Change the "Import using" setting to "MP3 Encoder"

3.Select the desired quality level on the "Setting" list. the higher Quality will take more time but encodes the best quality MP3. you also can select "Custom" to change Stereo Bit Rate, Sample Rate, Channels, Stereo Mode according to your requirements

4.Click "OK" twice to Save those settings and exit the Preferences box.
5.Select the AAC track you want to convert in the iTunes window (you can click and convert more than one at a time if you wish) right-click on it;
6.Choose "Create MP3 version" from the popup menu to convert them to MP3.
Note: if you purchased the songs from iTunes, some protected AAC music files(M4P) or all of them could be copy-protected and you won't be able to convert those to MP3.
And apple recently launched iTunes Plus which allows you to remove the DRM from your iTunes track and upgrade it to a higher quality format. but you need pay for 30 cents a song for this upgrade. It's basically like having to buy the song over again just to remove the DRM.
For iTunes Protected Music files, you can refer to this tutorial - 2 Ways Convert iTunes Protected Music files to MP3
