Excitation synchronous formant analysis

Abstract

Speech signals can be efficiently parametrised by the resonant frequencies of the vocal tract known as formants. The automatic analysis of the signal into a suitable set of formant parameters has however proved to be a difficult problem, particularly for female speech. The technique of excitation synchronous formant analysis has been proposed as an improved method of formant analysis [5]. The paper considers the performance of this technique, particularly where the analysis interval is over the closed phase of the larynx. The improved performance of closed-phase formant analysis is demonstrated by comparison with pitch-synchronous and fixed-frame formant analysis. The closed-phase region is determined first using a laryngograph signal and secondly using a modified form of the Gold-Rabiner fundamental-frequency estimator, using only the acoustic waveform. The improved performance of closed-phase formant analysis is also demonstrated by a better ability to follow the transient features of the signal, with fewer missed or extra formants, and better formant continuity. The ability to follow formant transitions during glides (e.g. w, r, l) and in voiced segments following plosives is particularly apparent. These improvements are illustrated in various phonetic contexts. The technique has been tested for sensitivity to analysis position, which is important when the glottal closures are determined from the acoustic waveform. This method of formant analysis is currently being applied to the development of speech synthesis by rule, and to provide a set of features for phonetic recognition.