Extraction of formant bandwidths using properties of group delay functions

• A new method for extraction of bandwidths of formant frequencies based on the properties of group delay function (GDF).
• Utilizes the prominence of resonant peaks and minimal influence of each resonance on the others in the GDF.
• An all-pole model of vocal tract system was assumed to illustrate the basis for the method.
• The method is illustrated by extracting bandwidths from short segments of synthetic and natural speech signals.
• The performance depends on the accuracy of extraction of glottal closure instants and formant frequencies.

Formant frequencies represent resonances of vocal tract system during the production of speech signals. Bandwidths associated with the formant frequencies are important parameters in analysis and synthesis of speech signals. In this paper, a method is proposed to extract the bandwidths associated with formant frequencies, by analysing short segments (2–3 ms) of speech signal. The method is based on two important properties of group delay function (GDF): (a) The GDF exhibits prominent peaks at resonant frequencies and (b) the influence of one resonant frequency on other resonances is negligible in GDF. The accuracy of the method is demonstrated for synthetic signals generated using all-pole filters. The method is evaluated by extracting bandwidths of synthetic signals in closed phase and open phase regions within a pitch period. The accuracy of the proposed method is also compared with that of two other methods, one based on linear prediction analysis of speech signals, and another based on filterbank arrays for obtaining amplitude envelopes and instantaneous frequency signals. Results indicate that the method based on the properties of GDF is suitable for accurate extraction of formant bandwidths, even from short segments of speech signal within a pitch period.