An Overview of Audio File Formats Supported By iTunes

Every once in a while, I see some very odd comments about audio file formats. I just read a comment to an article about high-resolution files suggesting that that FLAC compresses the dynamic range of files.

I thought it would be useful to discuss the audio formats that iTunes supports (and talk about FLAC as well).

iTunes supports five different audio file formats. You can see them by choosing iTunes > Preferences, clicking the General tab, then clicking Import Settings.

• AAC Encoder: This default choice compresses files in AAC (Advanced Audio Coding) format. AAC is not, as many people think, a proprietary format created by Apple. It is part of the MP4 standard and can be used by any hardware or software. In the early days of the use of AAC, not all devices supported this format, but now, pretty much every device – both for portable use and for use with a home stereo – can handle AAC.
• AIFF Encoder: Both AIFF and WAV files encapsulate raw sound data (in PCM, or pulse code modulation, format) from a music CD in file headers so the data can be used on computers. This format is uncompressed, and it takes up a lot of space, around 600–700 MB per disc, or about 10 MB per minute of audio.
• Apple Lossless Encoder: Apple Lossless is a lossless format that Apple created. It retains all the original musical data while taking up much less space than AIFF. Audio from a CD ripped in Apple Lossless format takes up about 250–400 MB, or around 7 MB per minute, depending on the type of music. (See this article for some real-world examples of the actual amount of compression achieved with Apple Lossless.)
• MP3 Encoder: Most people are familiar with MP3 files, which were the catalyst for the digital music revolution. MP3 files can play on just about any device or program that handles digital music.
• WAV Encoder: Like AIFF, WAV is uncompressed, and takes up the same amount of space.

There are a few important things to be aware of with audio formats. First, you can transcode one lossless format to another with no loss of data. This means that you can rip a CD to WAV, convert it to AIFF, then to Apple Lossless, then back to WAV, and you’ll have the exact same data – and the same music, at the same quality – as the original. However, if you rip a CD to AAC or MP3, then convert those files to a lossless format, such as Apple Lossless or WAV, you wan’t have the exact same quality; you’ll simply have a larger file at the quality of the AAC or MP3 file.

I said above that I would discuss FLAC. This is an open-source format, and stands for the Free Lossless Audio Codec. It is equivalent to Apple Lossless, and converting between the two causes no loss in quality. And, to address the comment I mentioned earlier, neither FLAC nor Apple Lossless have any effect on the dynamic range (the difference between the softest and loudest volume) of music. (You may want to know why iTunes doesn’t support FLAC.)

It’s worth noting that in late 2011, Apple released the Apple Lossless format specifications as open source. While this format was not widely used in the past, notably on Web sites selling digital music, this has changed a lot since then, as not only will more sites sell files in this format, but more software and hardware offer support as well.

Some people claim that WAV files “sound better” than lossless compressed files (Apple Lossless or FLAC). This may have been the case years ago, when the actual processing of decompressing the lossless files may have caused problems, but they are bit perfect replicas of each other, so it’s simply impossible for them to sound different.

For this reason, if you want to maximal quality, Apple Lossless is exactly the same as WAV or AIFF, and the characteristics of Apple Lossless offer more flexibility in tagging files (editing their metadata) and adding album art. WAV and AIFF files notable have limitations regarding tags. (In this article, I speculate on when Apple may start selling files in Apple Lossless format on the iTunes Store.)

It’s also useful to know that if you are interested in high-resolution audio, Apple Lossless can handle such formats, as can FLAC. So if you buy high-resolution music in FLAC format, you can convert it to Apple Lossless to better manage the files in iTunes (if you want to use iTunes). I recommend using the free XLD for converting audio files.

Note: iTunes can also play a number of other audio formats that QuickTime supports. This Wikipedia article gives more details. Not all of these formats are supported very well for tagging. iTunes can also play Audible files, in several different bit rates.

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