MP3 is a popular digital audio encoding and
lossy compression format invented and standardized in 1991 by a
team of engineers working in the framework of the ISO/IEC MPEG
audio committee under the chairmanship of Professor Hans Musmann
(University of Hannover - Germany). It was designed to greatly
reduce the amount of data required to represent audio, yet still
sound like a faithful reproduction of the original uncompressed
audio to most listeners. In popular usage, MP3 also refers to files
of sound or music recordings stored in the MP3 format on
computers.
MP3 is a lossy compression format. It provides a representation of
pulse-code modulation-encoded (PCM) audio data in a much smaller
size by discarding portions that are considered less important to
human hearing (similar to JPEG, a lossy compression for
images).
A number of techniques are employed in MP3 to determine which
portions of the audio can be discarded, including psychoacoustics.
MP3 audio can be compressed with different bit rates, providing a
range of tradeoffs between data size and sound quality.
The MP3 format uses, at its heart, a hybrid transformation to
transform a time domain signal into a frequency domain
signal:
* 32-band polyphase quadrature filter
* 36 or 12 tap MDCT; size can be selected independent for sub-band
0...1 and 2...31
* Aliasing reduction postprocessing
MP3 Surround, a version of the format supporting 5.1 channels for
surround sound, was introduced in December 2004. MP3 Surround is
backward compatible with standard stereo MP3, and file sizes are
similar.
In terms of the MPEG specifications, AAC (Advanced audio coding)
from MPEG-4 is to be the successor of the MP3 format, although
there has been a significant movement to create and popularize
other audio formats. Nevertheless, any succession is not likely to
happen for a significant amount of time due to MP3's overwhelming
popularity (MP3 enjoys extremely wide popularity and support, not
just by end-users and software but by hardware such as DVD and CD
players).
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