A Digital Music Glossary: File Formats and Bit Rates
by Kirk McElhearn

While many of MusicWeb's readers have embraced digital music, many others are still watching from the sidelines, trying to understand this new landscape. Having adapted to CDs over the years, a change to new ways of buying and listening to music can be daunting to some.

I'm planning to write a series of articles about digital music to help those who feel left behind by the digital music revolution. While this world may seem complex, you'll see that by taking things slowly, you can open up new ways of buying, listening to and storing your music.

In this first article, I want to start by providing the first of a series that will provide a digital music glossary. One of the most complex factors in learning about new technologies is getting beyond the words used to describe them. You read about "formats" and "bit rates," but you may not know what they mean. Read on to learn the key terms used in digital music.

Talking about files
Since you use a computer, you know what files are. Digital music is sold in files, which are similar to the word-processing or image files on your computer. However, some of the terms you'll meet may confuse you:

Format: all types of files have formats. For word processing, you have Word files, RTF files, text files and more; each of these file types is a "format." For images, you have JPG files, TIFF files and others. You have dozens of formats for files on your computer, and, in some cases, you can tell what format a file is by its extension: Word files are .doc or .docx; PDF files are, well, .pdf; and so on.

In digital music, there are several main file formats:

MP3: the most common digital file format, this uses lossy compression (more about that later) to reduce the size of files and allow them to be played on portable devices. All lossy compressed files can have different bit rates, which determine their size and quality.

AAC: Advanced Audio Coding is another name for the MP4 audio format. This is the format that Apple uses for the music it sells on the iTunes Store. Note that the "A" doesn't stand for Apple. Many people think this is a proprietary format created by Apple, but this is not the case.

FLAC: Free Lossless Audio Codec is a lossless format. (See below for more on lossless and lossy formats.)

Apple Lossless: Sometimes abbreviated as ALAC (Apple Lossless Audio Codec), this is Apple's version of a lossless format.)

WAV and AIFF: These are two uncompressed music formats. The music on CDs is in WAV or AIFF format. (The two formats are almost the same; they are simply containers for the raw musical data on CDs.)

On sites selling digital music, you'll see MP3s (Amazon, eMusic, etc.), AAC (Apple's iTunes Store), and FLAC (some classical dealers; live music websites; band sites.) So with these different formats, how do you choose?

Lossy versus lossless compression
As I mentioned above, there are two types of compression: lossy and lossless. The former removes non-essential data to compress files to the smallest possible size. The latter retains all the data, but takes advantages of repetitions to shrink files.

The best way to understand the difference is to compare them with compression used for other types of computer files. You're probably familiar with Zip files, used to compress all types of files on computers. If you take, say, a word processor file and want to compress it to save space, you can use the Zip format. This is - and has to be - lossless compression, because when you expand the file, you don't want to be missing any words or letters. This is what lossless compression does with music. It uses a number of techniques to shrink files while removing none of the original music data. The actual amount of space saved for a file depends on that file.

Lossy compression, on the other hand, targets a certain file quality, measured by a bit rate, and removes non-essential data to reach that size. Without getting into complications, suffice it to say that lossy compressed files sound fine to most people, if the bit rate is high enough. Plenty of people have run blind tests (and I have done so with a group of MusicWeb reviewers) showing that people cannot reliably tell the difference between compressed files at appropriate bit rates and uncompressed files.

But if you want to use lossy compression - MP3 or AAC - the bit rates should be high enough. For example, Apple sells music on its iTunes Store at 256 kbps (that's thousands of bits per seconds). Uncompressed music is 1411 kbps, so you can see that this saves a lot of space. Nevertheless, hardly anyone can reliably tell files at this bit rate from uncompressed files. For MP3s, Amazon sells music at 256 kbps as well. Anything at this bit rate is fine. But you can go ever lower.

Personally, many years ago, I did some blind tests at different bit rates. I found that, for me, I can't tell the difference between AAC files compressed at 160 kbps and uncompressed files. And this allows me to store much more music on my computer and on my iPods.

So the bottom line is this: you shouldn't consider that music in MP3 or AAC formats is sub-par. Quite the contrary; these types of compression allow you to put much more music on the device you use to store your music. If you have a chance, get together with some friends and set up a blind listening test. Create files at different bit rates, and play them at random, noting your impressions. Or simply hook up some good headphones to your computer and try this test, then try this one. You may be surprised.

I'll be continuing this series with more about digital music. You can e-mail me if you have any specific questions you want me to cover.

About the author
Kirk McElhearn is a freelance writer and Senior Contributor to Macworld. He writes about Macs and digital music on his blog Kirkville You can follow him on Twitter. Kirk's latest book is Take Control of iTunes 10: The FAQ.