The presence of amplitude and frequency modulations in individual formants of the speech signal was demonstrated using the discrete-time energy separation algorithm (DESA). Formant modulation estimates are valuable to the understanding of speech production, and have found several applications. While the DESA has been successfully applied in tracking the amplitude envelope of formants, the DESA frequency estimator has been relatively unexploited for tracking formant frequency modulation (FM) due to its lack of robustness to conditions commonly occurring in practice. We consider an alternate method of frequency estimation based on the Wigner distribution (WD) and investigate its application to the estimation of formant FM in speech signals. It is shown using simulated and speech signals that the WD estimator can track formant FM with high time resolution under a wider range of conditions and is more robust to additive noise present in the signal than the DESA estimator. Finally the computational complexities of the two methods are compared.
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