Analysis-synthesis using pole-zero approximations to speech spectra

The speech quality of present day analysis-synthesis telephony systems is not sufficiently acceptable for many purposes. One cause of this is inaccuracies in the approximations to the spectral envelope of the speech signal. This paper describes an investigation into a method of approximating the spectral envelope with a filter transfer function represented by the ratio of two polynomials. Each polynomial is described by a set of log area ratios and an iterative procedure is used to determine the values of these parameters which minimize a suitable error measure. A 2400 bit/s speech transmission system which uses pole-zero approximations to the spectrum has been simulated.