Some problems in voice source analysis

This is an overview of some recent studies of voice source acoustics and glottal flow analysis and modelling performed at the KTH. Time and frequency domain aspects of the production process are discussed with a view of relating glottal flow parameters from inverse filtering and vocal tract transfer functions to formant amplitudes and bandwidths. Alternative methods of determining the time constant Ta = 1(2πFa) in the return phase of glottal flow derivative after the instant of excitation, and thus of spectral tilt, are discussed. Selective inverse filtering, removing all but one formant, is potentially useful for this purpose. The influence of uncertainties in quantifying the vocal tract transfer function is exemplified by a calculation of the effects of introducing a finite baffle effect of the human head adding a high-frequency emphasis above the standard + 6 dB/octave. Particular attention has been paid to temporal variations within an utterance as derived from continuous inverse filtering. Aspects of breathy voicing and female-male differences in voice production are discussed. It is demonstrated that the temporal profile of the excitation amplitude, Ee(t), within an utterance derived from a male speaker can be approximated by the envelope of the negative part of the speech wave.