When converting from a compressed to uncompressed file format (for example, from MP3 to AIFF) you shouldn't notice any reduction in sound quality. However, when converting between compressed formats (for example MP3 and AAC), you may notice a reduction in the sound quality. For the best results, if you want your music encoded in a different file format, you should import the music again from the original source using the new encoding format.
To convert a song's file format
- Open iTunes Preferences.
Windows: Choose Edit Preferences.
Mac: Choose iTunes > Preferences.
- Click the General button, then click the Importing Settings… button in the lower section of the window.
- From the Import Using pop-up menu, choose the encoding format that you want to convert the song to, then click OK to save the settings.
- Select one or more songs in your library, then from the File > Create New Version menu, choose one of the following (the menu item changes to show what's selected in your Importing preferences):
- Create MP3 version
- Create AAC version
- Create AIFF version
- Create WAV version
- Create Apple Lossless version
If you haven't imported some songs into iTunes yet, you can import and convert them at the same time. This will create a converted copy of the file in your iTunes Library based on your iTunes preferences. To convert all the songs in a folder or on a disk, hold down the Option key (Mac) or Shift key (Windows) and choose File > Create New Version > Convert [import preference setting]. The Import preference setting will match what you chose in step 3. iTunes will prompt you for the location of the folder or disk you want to import and convert. All the songs in the folder or on the disk will be converted. Note: Older purchased songs are encoded using a Protected AAC format that prevents them from being converted. If you need to convert these to another format, follow the instructions in this article to upgrade them.
The song in its original format and the newly converted song appear in your library.
When you convert a song, some data may be lost due to the way certain formats compress data. For this reason these formats are sometimes called "lossy" formats. The advantage of using a "lossy" format is that the file sizes are much smaller, which means you can store more songs in the same amount of disk space. The disadvantage is that the sound quality may not be as good as the original, uncompressed format. Depending on the song, the speakers or headphones, and the player you use to play the song, you may not be able to tell the difference between a compressed "lossy" song and a song that is not compressed.
Once a song is compressed (meaning some of its data is lost) you cannot retrieve the data by uncompressing it. If you convert a song from a "lossy" format to a uncompressed format, the quality of the song will not improve and the file will only take up more disk space. For example, if you convert a song in MP3 format (a compressed format) to AIFF (an uncompressed format) the song will take up much more space on the hard disk, but it will still sound the same as the compressed file. In order to take advantage of uncompressed formats you should only import songs using these formats.
A note about copyright
iTunes software may be used to reproduce materials. It is licensed to you only for reproduction of non-copyrighted materials, materials in which you own the copyright, or materials you are authorized or legally permitted to reproduce. If you are uncertain about your right to copy any material, you should contact your legal advisor. See the iTunes Store Terms of Service for additional information.