Research on low bit rate speech coding at the Electrical Communication Laboratory, NTT
Fumitada Itakura · The Journal of the Acoustical Society of America · 1978
Since the introduction of speech analysis—synthesis based on the maximum likelihood spectrum estimation—in 1966, we have been conducting research activities on low bit rate speech coding techniques, and their aplication to audio response and low bit rate digital speech transmission. Parcor analysis-synthesis, demonstrated in 1969, was one of the most fundamental methods, and it has formed the basis of the present development of linear predictive coding. Recently, various kinds of techniques have been proposed to improve speech quality, such as interpolation and nonlinear quantization of parameters, spectral smoothing, etc. They have been applied in the hardware realization of a 4 CH multiplexed 2400 bps Vocoder. At present, the Parcor method is being applied to a wide range of speech coding from 1200 bps variable frame-rate coding to high quality 16 kbps adaptive, predictive coding.