Originally defined as the third audio format of the MPEG-1 standard, it was retained and further extended—defining additional bit-rates and support for more audio channels—as the third audio format of the subsequent MPEG-2 standard.A third version, known as MPEG 2.5—extended to better support lower bit rates—is commonly implemented, but is not a recognized standard.The MUSICAM format, based on sub-band coding, became the basis for the MPEG Audio compression format, incorporating, for example, its frame structure, header format, sample rates, etc.While much of MUSICAM technology and ideas were incorporated into the definition of MPEG Audio Layer I and Layer II, the filter bank alone and the data structure based on 1152 samples framing (file format and byte oriented stream) of MUSICAM remained in the Layer III (MP3) format, as part of the computationally inefficient hybrid filter bank.And the fourth group was SB-ADPCM, by NTT and BTRL.These two codecs, along with block-switching contributions from Thomson-Brandt, were merged into a codec called ASPEC, which was submitted to MPEG, and which won the quality competition, but that was mistakenly rejected as too complex to implement.In 1990, Brandenburg became an assistant professor at Erlangen-Nuremberg.While there, he continued to work on music compression with scientists at the Fraunhofer Society's Heinrich Herz Institute (in 1993 he joined the staff of Fraunhofer HHI).
The MP3 lossy audio data compression algorithm takes advantage of a perceptual limitation of human hearing called auditory masking. Mayer reported that a tone could be rendered inaudible by another tone of lower frequency. did not immediately influence the mainstream of psychoacoustic codec development. In 1985, Atal and Schroeder presented code-excited linear prediction (CELP), an LPC-based perceptual speech coding algorithm with auditory masking that achieved a significant compression ratio for its time.
As a doctoral student at Germany's University of Erlangen-Nuremberg, Karlheinz Brandenburg began working on digital music compression in the early 1980s, focusing on how people perceive music. MP3 is directly descended from OCF and PXFM, representing the outcome of the collaboration of Brandenburg—working as a postdoc at AT&T-Bell Labs with James D.
Johnston ("JJ") of AT&T-Bell Labs—with the Fraunhofer Institute for Integrated Circuits, Erlangen (where he worked with Bernhard Grill and four other researchers – "The Original Six"), with relatively minor contributions from the MP2 branch of psychoacoustic sub-band coders.
It was primarily designed for Digital Audio Broadcasting (digital radio) and digital TV, and its basic principles disclosed to the scientific community by CCETT (France) and IRT (Germany) in Atlanta during an IEEE-ICASSP conference in 1991, together with Radio Canada and CRC Canada during the NAB show (Las Vegas) in 1991.
The implementation of the audio part of this broadcasting system was based on a two chips encoder (one for the subband transform, one for the psychoacoustic model designed by the team of G. The simplicity of the corresponding decoder together with the high audio quality of this codec using for the first time a 48 k Hz sampling frequency, a 20 bits/sample input format (the highest available sampling standard in 1991, compatible with the AES/EBU professional digital input studio standard) were the main reasons to later adopt the characteristics of MUSICAM as the basic features for an advanced digital music compression codec.
The second group was ASPEC, by AT&T, France Telecom, Fraunhofer Gesellschaft, Deutsche and Thomson-Brandt.