MP3 Guide
How MP3 Files Work
The MP3 format is a compression system for music. The
MP3 format helps reduce the number of bytes in a song
without hurting the quality of the song's sound. The
goal of the MP3 format is to compress a CD-quality song
by a factor of 10 to 14 without losing the CD quality
of the sound. With MP3, a 32 megabyte song on a CD compresses
down to 3 megabytes or so. This lets you download a
song in minutes rather than hours, and it lets you store
hundreds of songs on your computer's hard disk without
taking up that much space.
Is it possible to compress a song without hurting its
quality? We use compression algorithms for images all
the time. For example, a GIF file is a compressed image.
So is a JPG file. We create ZIP files to compress text.
So we are familiar with compression algorithms for images
and words and we know they work. To make a good compression
algorithm for sound a technique called perceptual noise
shaping is used. The "perceptual" part in the name means
that the MP3 format uses characteristics of the human
ear to design the compression algorithm. For example:
Using facts like these about the human ear, certain
parts of a song can be eliminated without significantly
hurting the quality of the song for the listener. Compressing
the rest of the song with well-known compression techniques
shrinks the song considerably -- a factor of 10 at least.
[If you would like to learn more about the specific
compression algorithms, see the links at the bottom
of this article.] When you are done creating an MP3
file, what you have is "near CD" quality. The MP3 version
of the song will not sound exactly the same as the original
CD because some of the song has been removed, but it
will be close.
From this description you can see that MP3 is nothing
magical. It is simply a file format that compresses
a song into a smaller size so it is easier to move around
on the Internet and store.
