iPod & iTunes: The Missing Manual, Fourth Edition

Compressed Audio Formats

Up until a few years ago, the MP3 format was the only game in town for playing quality song files on your computer, whether downloaded from the Internet or taken from CDs. MP3 still dominates the Internet, but other formats—like Ogg Vorbis (an audio format favored by Linux fans and the open source software crowd; details at http://www.vorbis.com)—have dedicated fans, too.

Ogg Vorbis isn’t on the list of iPod-compatible formats, but many others are, including MP3, AAC, AIFF, Apple Lossless, and WAV. Here’s a brief explanation of each Podworthy format.

MP3

Suppose you copy a song from a Lena Horne CD directly onto your computer, where it takes up 35.3 MB of hard disk space. Sure, now you could play that song without the CD in your CD drive, but you’d also be out 35.3 megs of precious hard drive real estate.

Now, say you put that Lena Horne CD in your computer and use your favorite encoding program like iTunes to convert that song to an MP3 file. The resulting MP3 file still sounds really good, but it only takes up about 3.2 MB of space on your hard drive—about 10 percent of the original. Better yet, you can burn a lot of MP3 files onto a blank CD of your own—up to 11 hours of music on one disc, which is enough to get you from Philadelphia to Columbus, Ohio on I-70 with tunes to spare.

How it works

MP3 files are so small because the format’s compression algorithms use perceptual noise shaping, a method that mimics the ability of the human ear to hear certain sounds. ...