This paper presents improvements on the classical model which produces speech that is significantly better than currently available systems. The first major improvement results from treating speech as a two source phenomenon that can be separated for parallel but independent analysis/ synthesis. This two component decomposition is accomplished by making use of the quasi-periodic nature of 'voiced' speech. The second major improvement in bit compression and robustness of operation results from an efficient encoding of the prediction residuals of the two components. The key step is to encode the residual of the periodic component by picking out and transmitting the essential information for only one cycle (pitch period) of the residual.

Linear predictive coding of speech has traditionally used a least mean square (LMS) criterion for determining the optimal filter parameters. Auto-regressive (AR) models using LMS are in wide-spread use for low bit rate speech compression. These models are particularly susceptible to moderate amounts of added noise and distortion. This paper proposes a new model which does not use the least-mean-square criterion but rather uses the "peakiness" of the deconvolved waveform to determine the filter parameters. Since voiced output speech is reproduced with a maximally "peaked" waveform, viz, an impulse, this criterion is naturally suited for the characteristics of the synthesis process. Preliminary analysis also shows the feasability of implementing the proposed algorithm in microprocessor based hardware.

This paper reexamines Jelinek's proof that tree codes can be used to approach the rate-distortion bound. It is shown that the branching process used in Jelinek's proof is not a (strict-sense) branching process (SSBP) when the source is asymmetric. Branching processes with random environments (BPWRE) are introduced and used to extend the proof to general discrete-time memoryless sources. The theory developed indicates why a particular metric used in experiments performed better than another suggested by the original proof.