Audio files come in a number of different formats. Some are lossy, such as AAC and MP3; they save space compared to the original files, but some of the original data is lost during compression. Some formats are lossless, such as Apple Lossless, FLAC, and SHN; these files can be converted back to their original form without the loss of a single bit. Finally, some are uncompressed, such as WAV and AIFF; they represent the exact data from a CD or a master.
f you’ve bought music from the iTunes Store, you’ll have AAC files at 256 kbps (that’s kilobits per second, an indication of the quality of the compression; higher numbers are better). If you’ve purchased from Amazon, you’ll have MP3 files, most likely in VBR (variable bit rate compression), so the bit rate you see will be an average. Files from other sites may be in FLAC or even WAV format; the former is the most common for lossless files, notably from sites that sell live or classical music.
There may come a time when you’ll want to convert some of your audio files to a different format. Depending on your originals, and the reason for the conversion, there are different ways you can do so.
Use iTunes to convert your audio files
One reason to convert files to another format, or even another bit rate, is to save space. You can have iTunes convert music files to 128-kbps AAC when syncing to an iOS device if you wish, for example. This often makes sense if your device has limited storage and/or you listen to your music outdoors or on the go, where a difference in quality (say from 256 kbps to 128 kbps) won’t be very noticeable. Just check the Convert Higher Bit Rate Songs To 128 Kbps AAC option on iTunes’ Summary screen for your device when it’s connected to iTunes, and the process will happen automatically when you sync. (Note that such a conversion can take a long time if you have a lot of files to convert.)
Even though this window says Import Settings, it's where you choose the settings to convert files.
But you can use iTunes to convert in other ways as well. iTunes supports AAC, Apple Lossless, MP3, AIFF, and WAV files. You can convert to or from any of these formats as needed. Say you have some AAC files you bought from the iTunes Store (DRM-free, as all recent iTunes music comes) and want to play them on a device that only supports MP3 files; iTunes can do this for you. Here’s how:
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