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Thursday, 11/20/2008 How MP3 Works
If you have ever wondered
how MP3 music works, or if you have heard about MP3 song files and wanted to know how to use them,
then read on. We will discuss the MP3 format and how you can download and listen to MP3 music.
The
MP3 Format
CDs store
a song as digital information. The data on a CD uses an uncompressed,
high-resolution format. Here's what happens when a CD is created:
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Source
music is sampled at a rate of over 44,000 times per second. Each
sample is 2 bytes (16 bits) long.
-
Separate
samples are taken for the left and right sides to create stereo.
Therefore, a CD stores a huge number of bits for each song - a little
over 1.4 million bits for each second (stereo). For example, take a
song that's 3 minutes long. That works out to around 32 million bytes
of space on a CD, a lot of information for one song. Imagine trying to
download that on a dialup line.
The MP3
format is used as a compression system. It helps reduce the number of
bytes in a song without damaging the quality of the music. The goal of
MP3 is to compress a song by a factor of 10 to 14 without noticeably
affecting the quality. So a 32 megabyte song would now take up about 3
million bytes of space.
So what
about quality of replay? Does this much compression destroy the
fidelity of the music? Well, compression is used for images all the
time. For example, GIF and JPG are commonplace on web pages, both for
saving storage space and to speed up page downloading. To make a good
compression system for sound, a technique called perceptual noise
shaping is used. Here's the basic idea:
-
There are
certain sounds the human ear cannot hear
-
There are
certain sounds the human ear hears much better than others
-
If there
are two sounds playing simultaneously, we hear the louder one but
cannot hear the softer one
Using
these concepts, certain parts of a song can be eliminated without
significantly lowering the quality. Once these parts are removed, the
remaining information can be compressed and the combination of these
two techniques reduces size considerably. This produces what is known
as "near CD quality" music. The MP3 version does not sound exactly the
same as the original because some of it has been removed, but it's
very close. And it is much smaller.
Taking the Files With You
There are a huge variety of small, portable MP3 players that can be used to
carry your songs with you. They plug into either the FireWire or USB
port of your computer to download MP3 music using software that is
supplied with the player. You can create your own custom play lists
and arrange the order of playback. Some even have a randomizing
routine so you don't know which one will be played next. Sort of like
a surprise every time you listen. These players are very small and can
be carried virtually anywhere. And the sound is awesome as long as
good quality headphones are used. So go ahead and download MP3 music and get started. |