All-pole modeling of speech based on the minimum variance distortionless response spectrum

We present all-pole models based upon the minimum variance distortionless response (MVDR) spectrum for spectral modeling of speech. The MVDR method, which is popular in array processing, provides all-pole spectra that are robust for modeling both voiced and unvoiced speech. Although linear prediction (LP) is a popular method for obtaining all-pole model parameters, LP spectral envelopes overestimate and overemphasize the medium and high pitch voiced speech spectral powers, thereby featuring unwanted sharp contours, and do not improve in spectral envelope modeling performance as the filter order is increased. In contrast, the MVDR all-pole spectrum which can be easily obtained from the LP coefficients, features improved spectral envelope modeling as the filter order is increased. In particular, the high order MVDR spectrum models voiced speech spectra very well, particularly at the perceptually important harmonics, and features a smooth contoured envelope. Furthermore, the MVDR spectrum can be based upon either conventional time domain correlation estimates or upon spectral samples, a task that is common in frequency domain speech coding. In particular, the MVDR spectrum of sufficient order provides an all-pole envelope that models a set of spectral samples exactly. In addition, the MVDR all-pole spectrum is also suitable for modeling unvoiced speech spectra.