On the effect of fundamental frequency on amplitude and frequency modulation patterns in speech resonances

Amplitude modulation (AM) and frequency modulation (FM) in speech signals are believed to reflect various non-linear phenomena during the speech production process. In this paper, the amplitude and frequency modulation patterns are analyzed for the first three speech resonances in relation to the fundamental frequency (F0). The formant tracks are estimated, and the resonant signals are extracted and demodulated. The Amplitude Modulation Index (AMI) and Frequency Modulation Index (FMI) are computed, and examined in relation to the F0 value, as well as the relation between F0 and the first formant value (F1). Both AMI and FMI are significantly affected by pitch, with modulations being more frequently present in low F0 conditions. Evidence of non-linear interaction between the glottal source and the vocal tract is found in the dependence of the modulation patterns on the ratio of F1 over F0. AMI is amplified when pitch harmonics coincide with F1, while FMI shows complementary behavior.