Higher pole correction in vocal tract models and terminal analogs

Abstract The Higher Pole Correction (HPC) function in analog and digital all-pole modelling of speech production is analyzed by comparing all-pole models with a Transmission Line (TL) model. The validity of the TL model, which was chosen as a computational reference system in the study, is tested by comparing its transfer functions to acoustical measurements made on a physical vocal tract model. The variation of effective length of the vocal tract turned out to be an important parameter in modelling the HPC. Even if the frequency responses of the HPC in analog and digital cases differ, the relative changes in the correction, influenced by the variations in the effective length of the vocal tract, are exactly the same in both cases. Therefore digital realizations should have a variable HPC also. A polynomial analysis of the vocal tract transfer function was done to obtain new practical models for the HPC. The work results in all-zero models, which can be used in analog as well as digital all-pole realizations to form a new type of pole-zero model for speech production. This new pole-zero model is related to the PARCAS terminal analog model [Laine, 1982].