Acoustic impact of the gradual glottal abduction degree on the production of fricatives: A numerical study

Abstract

The paper presents a numerical study about the acoustic impact of the gradual glottal opening on the production of fricatives. Sustained fricatives are simulated by using classic lumped circuit element methods to compute the propagation of the acoustic wave along the vocal tract. A recent glottis model is connected to the wave solver to simulate a partial abduction of the vocal folds during their self-oscillating cycles. Area functions of fricatives at the three places of articulation of French have been extracted from static MRI acquisitions. Simulations highlight the existence of three distinct regimes, named A, B, and C, depending on the degree of abduction of the glottis. They are characterized by the frication noise level: A exhibits a low frication noise level, B, which is a transitional unstable regime, is a mixed noise/voice signal, and C contains only frication noise. They have significant impacts on the first spectral moments. Simulations show that their boundaries depend on articulatory and glottal configurations. The transition regime B is shown to be unstable: it requires very specific configurations in comparison with other regimes, and acoustic features are very sensitive to small perturbations of the glottal configuration abduction in this regime.

A simplified vocal tract model for articulation of [s]: The effect of tongue tip elevation on [s]

“…The acoustic characteristics in the spectrograms were consistent with those observed in the spectrogram of /s/ in context /usui/ (Fig 1) and also the other word context [7]. This result indicates that the proposed simplified model is capable of producing the fricative /s/ in word contexts.…”

“…The articulatory mechanisms involved in producing a [s] sound have been investigated by measuring the tongue movement using electro-magnetic sensors [3–4], medical images [5–6], and measuring the glottal opening using an optical sensor [7]. Measurement based on electro-palatography [3] indicates that tongue contact on the hard palate occurs after the appearance of fricative noise, whereas the duration of the sound is longer than the duration of the tongue contact.…”

Automatic generation of the complete vocal tract shape from the sequence of phonemes to be articulated

“…However, it is possible to choose reasonably good values easily. Second, information about the glottal opening plays an essential role in the production of fricatives [3] and stops. The latter requires excellent coordination between the closure at the place of articulation and the opening at the glottis during the closure and the rapid opening, which gives rise to the burst.…”

Centerline articulatory models of the velum and epiglottis for articulatory synthesis of speech

“…The numerical acoustic simulations of the vocal tract have seen recent progress in the possibility of taking into account the complexity of the vocal tract geometry [1], [2], the specificities of vocal fold vibrations [3], [4] and production of consonants [5] or other complex speech sounds as trills [6]. These advances rely on numerical models that are more faithful to the acoustics of speech, but also on articulatory data that are more precise and accurate thanks to the emergence of Magnetic Resonance Imaging (MRI).…”