Chapin Cutler, Bernard M. Oliver and Henry C. Harrison. Peter Elias in 1955 published two papers on predictive coding of signals. Linear predictors were applied to speech analysis independently by Fumitada Itakura of Nagoya University and Shuzo Saito of Nippon Telegraph and Telephone in 1966 and in 1967 by Bishnu S. Atal, Manfred R. Schroeder and John Burg. Itakura and Saito described a statistical approach based on maximum likelihood estimation; Atal and Schroeder described an adaptive linear predictor approach; Burg outlined an approach based on principle of maximum entropy. In 1969, Itakura and Saito introduced method based on partial correlation (PARCOR), Glen Culler proposed real-time speech encoding, and Bishnu S. Atal presented an LPC speech coder at the Annual Meeting of the Acoustical Society of America. In 1971, realtime LPC using 16-bit LPC hardware was demonstrated by Philco-Ford; four units were sold. LPC technology was advanced by Bishnu Atal and Manfred Schroeder during the 1970s1980s. In 1978, Atal and Vishwanath et al. of BBN developed the first variable-rate LPC algorithm. The same year, Atal and Manfred R. Schroeder at Bell Labs proposed an LPC speech codec called adaptive predictive coding, which used a psychoacoustic coding algorithm exploiting the masking properties of the human ear. This later became the basis for the perceptual coding technique used by the MP3 audio compression format, introduced in 1993. Code-excited linear prediction (CELP) was developed by Schroeder and Atal in 1985. LPC is the basis for voice-over-IP (VoIP) technology. In 1972, Bob Kahn of ARPA, with Jim Forgie (Lincoln Laboratory, LL) and Dave Walden (BBN Technologies), started the first developments in packetized speech, which would eventually lead to voice-over-IP technology. In 1973, according to Lincoln Laboratory informal history, the first real-time 2400 bit/s LPC was implemented by Ed Hofstetter. In 1974, the first real-time two-way LPC packet speech communication was accomplished over the ARPANET at 3500 bit/s between Culler-Harrison and Lincoln Laboratory. In 1976, the first LPC conference took place over the ARPANET using the Network Voice Protocol, between Culler-Harrison, ISI, SRI, and LL at 3500 bit/s. LPC coefficient representations LPC is frequently used for transmitting spectral envelope information, and as such it has to be tolerant of transmission errors. Transmission of the filter coefficients directly (see linear prediction for a definition of coefficients) is undesirable, since they are very sensitive to errors. In other words, a very small error can distort the whole spectrum,