Fifty years of progress in speech analysis (LPC)

Abstract

Although the history of statistical linear prediction is very long, it was first applied to speech analysis in 1966 at NTT to estimate the all-pole speech spectrum envelope in order to implement ASR and vocoder. All-pole spectral parameters are investigated in detail to find a better representation with respect to quantization and interpolation characteristics, partly at NTT and Bell Labs, leading to PARCOR and LSP. These parameters were applied to narrow band speech coders or LPC vocoders and speech synthesizer chips in the late 1970s and early 1980s, but the speech quality was insufficient for digital mobile telephone application. The problem was later solved by using hybrid CELP and MLP coding mainly at BTL. LPC analysis was also applied to acoustic front-end for ASR. Again it was found that LPC suffers with additive noise and linear/nonlinear distortions. Whereas computational efficiency of LPC was used to be the most prominent advantage, today we have gained thousands of times the processing power at a ten thousandth of the cost in 40 years. It is hoped a novel series of speech analysis methods, whose competence is comparable to human auditory system, should be developed at any expense of computational complexity.