Digital Music Formats : MP3
What is MP3?
MP3 is a digital audio format developed by Fraunhofer-Gesellschaft
and Thompson Multimedia in
the late 1980s and brought to the mainstream through the Internet
beginning in 1997.
MP3 refers to a type of digital audio file and a form of information compression. In short
it stands for MPEG-1 Audio Layer
III, which was developed by the Moving Picture Experts’ Group (MPEG) and has been further developed by the Fraunhofer Institute.
MP3 music files are compressed recordings that
occupy approximately one tenth to one twelfth less file space than the
equivalent CD format WAV/AIFF file, which is achieved by filtering out all
noise that is not detectable to the human ear. (Our ears cannot hear all the audio frequencies of a recording. The human
hearing range is between 20Hz to 20KHz and it is most sensitive between 2
to 4KHz.)
MP3 is a compressed audio format that allows
for smaller file sizes with similar sound quality to PCM WAV format, the
format found on music CDs. Thompson and
Fraunhofer helped develop the coding algorithm, or system of rules and
processes, that encoded audio to this format.
An MP3 file nearly maintains
the sound quality of the original, but is greatly reduced in size.
Before there were MP3s, digital audio files were very large and
rarely downloaded. On a 56K modem, however, MP3s download in just a
few minutes. MP3s are widely recognized as the most popular format
for storing and listening to music on the Internet.
Because of its reduced file size, you can take more files
with you. It also means
you can fit a lot more music on a recordable CD or in the memory of
your MP3 player. Now, you really can take your music with you.
Using MP3s
Most people
start using the MP3 format on their PC or Mac computers. You can
download and share MP3 files in many places on the Internet. You can
also convert your existing music CDs to MP3 files. Windows Media Player is one example of a PC application which can be used to convert a CD to a digital audio file on your computer. Many people convert their CD collection to MP3 files and then offload their entire library of songs to an Apple iPod player for music "on the go".
To play MP3s, you
have to have an MP3 Player or device that decodes the MP3 format.
MP3 files can be burned onto recordable CDs (CD-R or CD+RW), copied
from your computer directly to an MP3 Player, or copied to removable
solid-state memory media (like Secure Digital memory, SDMI, Sony Memory Stick).
Why MP3 is Popular
The popularity of MP3 comes from its practical uses. Music tracks in WAV
format are extremely large in file size, averaging around 50MB in size.
Since it is so large, it is not practical to send WAV files through email
or offer them for download on the Internet.
MP3 compresses WAV
audio on average of 10 to 12 times smaller than the original size. The
result is audio tracks around 3 to 4 MB in size, good for downloading
and sending through the Internet. Thus, custom MP3 format CDs can be
created with 10 to 12 times the amount of tracks of a normal 12-15 track
audio CD, producing CDs with over 100 tracks easily.
The format is also
popular for turning your PC into a jukebox of hundreds or thousands of
songs or loading them into a portable mp3 player and taking your music
collection wherever you want.
Is MP3 legal?
MP3 is simply a file
format. There is nothing illegal about MP3 files themselves. Just like a normal CD, MP3s can be pirated or used
illegally. Using an MP3 file is legal if the song's copyright holder
(artist, record label, etc.) has granted permission to download and
play the song. However, it is illegal to encode CDs into MP3 format
and trade them without permission from the copyright holder.
How does the MP3 format
accomplish its radical feats of compression and decompression, while
still managing to maintain an acceptable level of fidelity to the
original source material? The entire MP3 phenomenon is made possible by the confluence
of several distinct but interrelated elements: A few simple insights
into the nature of human psychoacoustics, a whole lot of number
crunching, and conformance to a tightly specified format for
encoding and decoding audio into compact bitstreams.
Well-encoded MP3 files can sound pretty good, considering how
small they are. Your typical MP3 file is around
one-tenth the size of the corresponding uncompressed audio source.
How is this accomplished? That's a somewhat complex topic.
MPEG Audio Compression
Uncompressed audio, such as that found on CDs, stores more data than
your brain can actually process. For example, if two notes are very
similar and very close together, your brain may perceive only one of
them. If two sounds are very different but one is much louder than
the other, your brain may never perceive the quieter signal. And of
course your ears are more sensitive to some frequencies than others.
The study of these auditory phenomena is called psychoacoustics,
and quite a lot is known about the process; so much so that it can
be quite accurately described in tables and charts, and in
mathematical models representing human hearing patterns.
MP3 encoding tools
analyze incoming source signal, break it down into mathematical
patterns, and compare these patterns to psycho-acoustic models stored
in the encoder itself. The encoder can then discard most of the data
that doesn't match the stored models, keeping that which does. The
person doing the encoding can specify how many bits should be
allotted to storing each second of music, which in effect sets a
"
tolerance" level-the lower the data storage allotment, the more
data will be discarded, and the worse the resulting music will
sound. The process is actually quite a bit more complex than that.
This kind of compression is called
lossy, because data is lost in the process. However, a second
compression run is also made, which shrinks the remaining data even
more via more traditional means (similar to the familiar
"zip" compression process).
MP3 files are composed
of a series of very short
frames, one after another, much like a filmstrip. Each frame of
data is preceded by a
header that contains extra information about the data to come.
In some encodings, these frames may interact with one another. For
example, if one frame has leftover storage space and the next frame
doesn't have enough, they may team up for optimal results.
At the beginning or end
of an MP3 file, extra information about the file itself, such as the
name of the artist, the track title, the name of the album from
which the track came, the recording year, genre, and personal
comments may be stored. This is called "
ID3" data, and will become increasingly useful as your
collection grows. We'll look at the structure of MP3 files and their
ID3 tags, and the process of creating and using ID3 tags.
Sound and codecs
The universe is made of waves, and all
waves oscillate at different lengths (a wavelength is defined as the
distance between the peak of one wave and the peak of the next).
Waves vibrating at different frequencies manifest themselves
differently, all the way from the astronomically slow pulsations of
the universe itself to the inconceivably fast vibration of matter
(and beyond). Somewhere in between these extremes are
wavelengths that are perceptible to human beings as light and sound.
Just beyond the realms of light and sound are sub- and ultrasonic
vibration, the infrared and ultraviolet light spectra, and billions
of other frequencies imperceptible to humans (such as radio and
microwave). Our sense organs are tuned only to very narrow
bandwidths of vibration in the overall picture. In fact, even our
own musical instruments create many vibrational frequencies that are
imperceptible to our ears.
Frequencies are typically described in units called
Hertz (Hz), which translates simply as "cycles per
second." In general, humans cannot hear frequencies below 20Hz
(20 cycles per second), nor above 20kHz (20,000 cycles per second).
While
hearing capacities vary from one individual to the next, it's
generally true that humans perceive midrange frequencies more
strongly than high and low frequencies, and that sensitivity to
higher frequencies diminishes with age and prolonged exposure to
loud volumes. In fact, by the time we're adults, most of us can't
hear much of anything above 16kHz.
The most sensitive range of hearing for most people hovers between
2kHz to 4kHz, a level probably evolutionarily related to the normal
range of the
human voice, which runs roughly from 500Hz to 2kHz.
These are simple and
well-established empirical observations on the human hearing
mechanism. However, there's a second piece to this puzzle, which
involves the mind itself. Some have postulated
that the sane mind functions as a sort of "reducing
valve," systematically bringing important information to the
fore and sublimating or ignoring superfluous or irrelevant data. In
fact, it's been estimated that we really only process a billionth
of the data available to our five senses at any given time. Clearly,
one of the most important functions of the mind is to function as a
sieve, sifting the most important information out of the incoming
signal, leaving the conscious self to focus on the stuff that
matters.
The basic principle of any
perceptual codec is that there's little point in storing information
that can't be perceived by humans anyway. As obvious as this may
sound, you may be surprised to learn that a good recording stores a
tremendous amount of audio data that you never even hear, because
recording equipment (microphones, guitar pickups, and so on) is
sensitive to a broader range of sounds and audio resolutions than is
the human ear.
Codec- compression/decompression
What is MPEG -The Moving Picture Experts Group ?
The Moving Picture Experts
Group is a working group of ISO/IEC in
charge of the development of international standards for compression,
decompression, processing, and coded representation of moving pictures,
audio and their combination.
The Moving Picture Coding Experts
Group (MPEG) was established in January 1988 with the aim to
develop standards for coded representation of moving pictures, audio and
their combination. It operates in the framework of the
bd>Joint ISO/IEC Technical Committee (JTC 1) on
Information Technology and is formally WG11 of SC29.
Starting from its first meeting in May 1988 when 25
experts participated, MPEG has grown to an unusually large committee.
Usually some 350 experts from some 200 companies and organizations from
about 20 countries take part in MPEG meetings. As a rule, MPEG meets three
times a year (in March, July and November) but meets more frequently when
the workload so demands.
To date MPEG has
produced: MPEG-1, the standard for
storage and retrieval of moving pictures and audio on storage media
(approved Nov. 1992). MPEG-2, the standard
for digital television (approved Nov. 1994).
bd>MPEG-4, the standard for multimedia applications -
version 1 was approved Oct. 1998 - version 2 was approved Dec. 1999.
MPEG is now
developing: MPEG-4 versions 3, 4
and 5 MPEG-7, the content representation
standard for multimedia information search, filtering, management and
processing.
MPEG-21, the multimedia framework.
MP3 Players
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Audio Glossary
AAC - Nicknamed MP4 because it is the next
generation of audio compression called Advanced Audio Compression.
AIFF - Audio format
of consumer HiFi CDs.
ATRAC3 - Compressed music format
developed by Sony as an equivalent to MP3. MiniDiscs use a similar
format called ATRAC
(Adaptive TRansform Acoustic Coding).
Bit-rate
- The name given to the amount of data an application handles per
second. An MP3 with a high bit-rate gives excellent sound
reproduction.
Burn - The term given to the process of
recording a CD.
Byte - Eight bit string of
information.
Compact Flash - Popular removable FLASH
memory card developed for digital cameras and now used in portable
MP3 players for music storage - developed by
SanDisk.
Decoder - Use of software or a device that
changes/decodes one file format back to another, i.e. MP3 to
AIFF.
Download - The action of copying a file (i.e. MP3)
from the internet to your personal computer or from your personal
computer to a portable
MP3 player.
Gigabyte (Gb) - The size of
a chunk of computer memory that is equal to 1,024 Mb (see
megabyte).
Encoding - Changing an original file format to
another format such as compressing WAV/AIFF to MP3.
Kilobyte
(k) - Computer memory that is equal to 1,024 bytes of
information.
Liquid Audio - Alternative compressed audio
format with built-in copyright security to rival MP3 and
ATRAC3.
Megabyte (Mb) - Computer memory that is equal to
1,024 kilobytes of data.
MIDI - Known as Musical
Instrument Digital Interface which is the format by which music is
generated by the interface of synthesizers and computers
together.
Mini Disc - Developed by Sony, this disc can store audio recordings like a CD only in a smaller form factor. Portable MD players can fit in a shirt pocket and with the LP2 mode can record the equivalent of two CDs on one disc. MD can record audio from sources like radio, CD player, voice without the need for a computer.
MMC (Multimedia Card) - FLASH memory card in
miniature used in some MP3 players for music storage and extensively
used in mobile phones.
MP3 - Abbreviated name for MPEG-1
audio layer 3 developed by the Moving Picture Experts Group (MPEG)
for digital compression of audio. The resultant file being between
one twelfth and one tenth of its original size.
MPEG-4 -
The next generation of audio/video compression. MP4 - Nickname given to both
AAC and MPEG-4 -the next generation of audio compression.
Parallel
Port
- Computer's interface to peripheral devices - mainly used for
printer connections and some portable MP3 players connect in
this way.
Real Audio - Alternative compression format of music
files obtainable over the internet which is of lower quality
than that of MP3.
Real G2 - Media player which allows streaming of audio
and video to be played live on your computer without the need
to download the entire clip. Audio/video is buffered in memory
to allow continuous playback.
Real Video - The compression format for showing videos
over the internet.
RIAA - Stands for the Recording Industry Association of
America who have been one of the main critics against the use
of MP3.
Ripper - Software for converting an audio track on a audio CD into an MP3 format music file, or a ripper may
only copy the file from the CD to your computer without
conversion.
SD (Secure Digital) - Fast transfer media card for
data.
SDMI - (Secure Digital Music Initiative) - Set up by
the music industry to help prevent the illegal distribution
and violation of copyright of digital music by the adding of a
security code to the music file.
Serial Port - Computer interface for peripheral
connections common to Macs and PCs.
Skins - The name given to a type of plug-in which is
used to change the look of the interface of a software MP3
player.
SmartMedia - Toshiba's equivalent to the MMC. Used in
cameras and MP3 players for picture and music storage
respectively.
Streaming - The method of listening to audio over an
internet connection without downloading the whole file to
disc.
Upload - The name given to the transfer of files onto
the internet, i.e. web pages or the transfer of music files
from computer to MP3 player. Otherwise known as
"posting".
USB (Universal Serial Bus) - Connection method now
being adopted by Mac/PC/Hardware manufacturers for peripheral
device connection/disconnection of up to 127 devices while the
computer is switched on.
VBR (Variable Bit Rate) - MP3s can be encoded in this
way where the bit rate of the varies accordingly to the
audible differences of the softest and loudest parts of the
music. Generally, the softer the music, the smaller the bit
rate required for quality reproduction. The bit rate is
increased for more quality from the louder sections.
WAV (Waveform) - The default audio format of PCs. (not compressed)
WMA (Windows Media Audio) - Music format similar to MP3
developed by Microsoft for use on PCs and some portable MP3
players.
Winamp - a popular software program for playing MP3 files on a PC. winamp.com
Windows Media Player - Software application from Microsoft to play and manage music files on your personal computer.
iPod - The Apple iPod is the most popular portable music player. You can also view photos.
iTunes - Software application and online store from Apple Inc. to play and manage music and other audio files on your computer, internet and portable media player.
Podcast - What is a podcast? Podcast comes from two words, iPod and broadcast. A podcast is a digital media file, or a collection of such files (usually audio), that is distributed over the Internet using syndication feeds for playback on portable media players and personal computers.
The author of a podcast is called a podcaster. People can "subscribe" to the feed by submitting the feed address to an aggregator (like iTunes - software that runs on the consumer's computer). When new "episodes" become available in the podcast they will be automatically downloaded to that user's computer. Unlike radio or streaming content on the web, podcasts are not real-time. The material is pre-recorded and users can check out the material at their leisure, offline.
Podcasts are popular in education, allowing students and teachers to share information. An absent student can download a recorded lesson and catch up. Books can be recorded and downloaded. Video podcasts are also available.
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