Everything you need to know about audio formats.
Whether you use iTunes or buy and download digital music, you will find a number of terms and abbreviations that describe digital audio files. This alphabet soup can be quite confusing. What are audio file formats or codecs? What is the bit rate and what is the sample rate? What does it mean when the music is “high definition”?
This article explains what you need to know about digital audio files. I’ll tell you the difference between lossy and lossless files, explain why bitrate matters (or not), and help you understand the various file formats you can encounter.
Compression: lossy and lossless
When you buy a CD, the audio on the disc is not compressed. You can rip (or import) CDs with iTunes or other software, converting CD audio into digital audio files for use on a computer or portable device. In iTunes, you can copy in two uncompressed formats: WAV and AIFF (other software supports other formats). Both formats simply encapsulate the PCM (Pulse Code Modulation) data stored on CD so that it can be read as audio files on a computer, and their bit rate (you’ll find the one below) is 1411 kbps.
WAV and AIFF files can be quite large. Therefore, digital audio files are compressed to save space. There are two types of compression: lossless and lossy. Lossless includes formats (or codecs for short codec algorithms) such as Apple Lossless and FLAC (Free Lossless Audio Codec). Lossy includes the ubiquitous MP3 and AAC formats. (AAC, which stands for Advanced Audio Coding, is actually MP4, the successor to the old MP3. Although Apple adopted it in the early days of iTunes, Apple was not involved in its creation and does not own the format.)
You can also view other audio formats, although they are less common. These include Ogg Vorbis, Monkey’s Audio, Shorten, and others. Some of these codecs are lossy and some are not. However, if you use iTunes and Apple hardware, you will only find WAV, AIFF, MP3, AAC, and Apple Lossless, at least for music.
iTunes can copy or import audio files in these formats. Select the one you want to use in iTunes> Preferences> General> Import Settings.
When you copy or convert an uncompressed audio file to a lossless format and then play that file back, it is a perfect copy of the original (provided the data was read correctly from the CD). Thus, you can convert from one lossless format to another without quality loss.
However, when you copy to a lossy format, if you later convert the file to another format, it loses some of its quality. This is similar to how a photocopy of a photocopy does not look as good as the original.
Some people prefer lossless formats because they play audio like CDs. Lossy compression is a tradeoff to save space, allowing you to store more music on your portable device or hard drive and speed up downloads. However, most people cannot tell the difference between a CD and a lossy file at high data rates, so if you’re ripping your music to sync to iPhone, lossless files are superfluous.
Lossless ripping is a good way to back up your files as you can convert them to other formats without losing quality. And you can have iTunes automatically convert them to AAC files when syncing. Check out this article for more information on this automatic conversion, as well as other lossless file questions.
Bit rates
The best way to measure the quality of an audio file, relative to its original quality rather than its musical or engineering quality, is to look at its bitrate. The bit rate of audio files is measured in thousands of bits per second or kbps. I mentioned earlier that the CD contains 1411kbps audio, and when you convert that audio into a lossy file, its bitrate is much lower.
The higher the bit rate the better, so a 256 kbps MP3 or AAC file is better than a 128 kbps file. However, this is not the case for lossless files. Lossless file transfer speed depends on the density and volume of your music. Two lossless tracks on the same album can have bit rates of, say, 400 kbps and 900 kbps, but when played back, they reproduce the original CD audio at the same level of quality. Lossless compression uses as many bits as necessary and no more.
