Frequency modulations in the speech signal
A. S. Leonov, Igor Makarov, Victor N. Sorokin · Acoustical Physics · 2009
The paper examines physical mechanisms of frequency modulations in acoustics of the vocal tract and methods of estimation of these modulations in the speech signal. It has been found that vibrations of the tract walls make a negligibly small effect on modulations of its resonance frequencies. The model of the process of speech formation with account for the subglottal cavity shows that a change in boundary conditions at the open glottis produces noticeable variations in resonance frequencies. Along with this type of modulations, modulations determined by the shape of the source of excitation also arise in the speech signal. They substantially depend on the ratio of the frequency of the fundamental tone to the resonance frequency and of the parameters of methods estimating modulations and methods of analysis of the speech signal. Overall, this may sometimes cause unstable and unpredictable modulations of estimated formant frequencies in the speech signal.