Effects of nonstationary characteristics on vowel perception
René Carré · The Journal of the Acoustical Society of America · 1988
Amplitude transition effects were studied by means of a formant synthesizer. The signal amplitude control is located either between the vocal source and the formant filters or between the formant filters and the output. In the first configuration, corresponding to the human vocal tract situation, at the beginning of the amplitude transition, an impulse response of the formant filters is obtained. In the second configuration, the formant filters are always in a stationary state and, hence, the spectrum structure of the formant filter outputs is harmonic. The distortions introduced by the amplitude transitions do not induce more information on the transfer function of the formant filters. Clear spectral differences were obtained when comparing the two synthetic signals, at their onsets. Information on formant frequency can be obtained in the case of the first configuration even if F0 is high. It has been shown that signal differences obtained by the two configurations are specifically processed by the human auditory system and induce displacements of [i]-[e] boundaries. Moreover, the vowel spectra corresponding to the boundaries do not have a harmonic component in the center of the first formant.