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
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
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
You can follow him on Twitter.
Kirk's latest book is Take
Control of iTunes 10: The FAQ.