Extracting formants from short segments of speech using group delay functions

Speech is a non-stationary signal, with the shape of the vocal tract changing over several pitch periods, and also within the open and closed glottis phases. The effect of these changes is reflected in the locations of the formants which correspond to the resonant frequencies of the vocal tract. To observe these changes, the analysis window should be small enough (relative to a pitch period), and appropriately anchored. A non-model based method is proposed in this paper to accurately determine formants from short segments (less than a pitch period) of speech signals. It makes use of high resolution properties of group delay function to estimate formants from segments of duration less than a pitch period. The main advantage of this method is its lack of dependence on the parameters of a model. Analysis segments are synchronised with instants of glottal closure, to increase the robustness of formant extraction. Since continuity or additional acoustic-phonetic knowledge are not used, this method is fairly reliable and robust.