MP3 - What's it all about?
10-31-2002
By: Robert O'Connor
In the early 1980s, the Moving Pictures Experts Group (MPEG) was set up by the International Organisation for Standardisation (ISO) to develop a standard for the encoded representation of pictures. After a meeting held in Hanover in 1988, MPEG decided to increase its responsibility and added sound formats to its area of standardisation. The result of this was MPEG-1 Layer 3, which has become known throughout the world by its more user-friendly file extension name, MP3.
MP3 is based around the idea of file compression. File compression techniques are used by computer systems to reduce the amount of space required to store information without any notable loss of data. A good example of this is the following simple text compression algorithm. Consider the sentence:
"Ask not what your country can do for you, but ask what you can do for your country"
This sentence contains 82 characters (mainly letters) making 18 English words and various punctuation marks. If we assign a unique identifier to each word in the sentence such as:
1 ask
2 not
3 what
4 your
5 country
6 can
7 do
8 for
9 you
and rewrite the sentence using these identifiers, instead of the words we get:
"1 2 3 4 5 6 7 8 9, 10 1 3 9 6 7 8 4 5"
we can decrease the amount of disk space required to store it on a computer system. The table defining what each identifier stands for (lookup table) must also be stored, so in the case of this example any saving would be negligible. However, by using this simple algorithm with a large text file, we could noticeably reduce the amount of storage disk space required.
Research into the compressed storage of audio signals was carried out by a group of scientists in Fraunhofer Institute for Integrated Circuits in Bavaria under the supervision of Karlheinz Brandenburg. Brandenburg applied this idea of file compression to audio waveforms and greatly reduced the amount of memory required to store these signals without any significant loss in quality. He utilized work performed in the field of psychoacoustics, which is the study of how the human ear and brain perceive sound, to develop a compression algorithm called perceptual filtering. This algorithm is based on the following characteristics of the human ear:
* There are sounds the ear cannot hear.
* There are sounds the ear hears better than others.
* When two sounds are being played at the same time, the ear hears the louder one and ignores the softer one.
By using these facts, certain parts of a sound wave can be eliminated without any noticeable loss in quality to the listener. This is the basis of MP3 file compression.
MP3 compression is most impressive when compared with the way compact discs store audio information. CDs use a high-resolution, uncompressed sampling technique to store sound. Music is sampled at 44,100 times per second, with each sample being 2 bytes (i.e. 16 ones or zeroes) in length. In a stereo system, samples are taken for both left and right speaker channels, so this increases the storage space by a factor of 2.
So an average three-minute song takes up 32 million bytes or 32 Megabytes of memory and an album of 12 three minutes songs would take up 384 Megabytes. Imagine how much space would be required to store any reasonably sized album collection?
On a computer's hard disk, this is considered impractical use of space. Using the MP3 file format however, CD audio can be compressed by a factor of 10 to 14 without any noticeable reduction in quality. So our three-minute song now takes up roughly 3 Megabytes, which is a significant improvement. It is still too big to fit on a floppy disk, but you can fit many such files on bigger Iomega Zip Disks, or a hard disk.
The main force behind the popularity of MP3 technology is the overwhelmingly large number of quality products that are freely available for download to the general public. If you type the words "MP3" into a search engine (e.g. www.google.com) you can see this for yourself. One of the most popular MP3 products is Winamp (www.winamp.com), which allows users to play MP3 files, create playlists and customize the look and feel of the program. Other products, such as Musicmatch Jukebox (www.musicmatch.com) have an added recording feature, which gives users the opportunity to create MP3s from their existing CD collections and if they have a CD-Writer, create CDs from their MP3 collection. Most of these programs allow users to download their files to handheld MP3 devices like the MP3 Walkman, now becoming less expensive and more popular.
Of course, major record companies are taking a negative stance with MP3 as they claim the free distribution of MP3 tracks hurts revenues, takes away from artists' incomes and thus decreases their ability to create new music. These arguments were cited in the recent Napster case, which gained much publicity. Those on the pro-MP3 side state that MP3 is more consumer friendly, and affords people greater flexibility with their musical choice. This is a debate that will continue for some time yet and the outcome will greatly affect the way the music industry operates.
Notwithstanding the opposition, MP3 technology has been so widely adopted experts agree that it is here to stay, whatever form it may take in the future.
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