MVDR based all-pole models for spectral coding of speech

We present several analytical properties of Minimum Variance Distortionless Response (MVDR) based all-pole models that demonstrate the advantages and usefulness of these models for speech spectral coding. In particular, we show that a sufficient order MVDR all-pole model provides a spectral envelope that fits a set of spectral samples exactly with a parameterization convenient for quantization purposes. In addition, we show that MVDR allpole filters provide a monotonically decreasing spectral distortion with increasing filter order. Furthermore, we show that the MVDR all-pole filter possesses the flexibility to be obtained from correlations based upon either spectral samples or conventional timedomain correlations. Finally, exploiting the insight gained from MVDR modeling, we introduce a novel class of constrained allpole models for efficient spectral coding. In this approach, a subset of the Line Spectral Frequency (LSF) parameters associated with the all-pole model are judiciously fixed, leading to a simpler model parameterization.