A glottal chink model for the synthesis of voiced fricatives

International audienceThis paper presents a simulation framework that enables a glottal chink model to be integrated into a time-domain continuous speech synthesizer along with self-oscillating vocal folds. The glottis is then made up of two main separated components: a self-oscillating part and a constantly open chink. This feature allows the simulation of voiced fricatives, thanks to a self-oscillating model of the vocal folds to generate the voiced source, and the glottal opening that is necessary to generate the frication noise. Numerical simulations show the accuracy of the model to simulate voiced fricative, and also phonetic assimilation, such as sonorization and devoicing. The simulation framework is also used to show that the phonatory/articulatory space for generating voiced fricatives is different according to the desired sound: for instance, the minimal glottal opening for generating frica-tion noise is shorter for /z/ than for /Z/

Glottal Opening and Strategies of Production of Fricatives

International audienceThis work investigates the influence of the gradual opening of the glottis along its length during the production of fricatives in intervocalic contexts. Acoustic simulations reveal the existence of a transient zone in the articulatory space where the frica-tion noise level is very sensitive to small perturbations of the glottal opening. This corresponds to the configurations where both frication noise and voiced contributions are present in the speech signal. To avoid this unstability, speakers may adopt different strategies to ensure the voiced/voiceless contrast of frica-tives. This is evidenced by experimental data of simultaneous glottal opening measurements, performed with ePGG, and audio recordings of vowel-fricative-vowel pseudowords. Voice-less fricatives are usually longer, in order to maximize the number of voiceless time frames over voiced frames due to the crossing of the transient regime. For voiced fricatives, the speaker may avoid the unstable regime by keeping low frication noise level, and thus by favoring the voicing characteristic, or by doing very short crossings into the unstable regime. It is also shown that when speakers are asked to sustain voiced fricatives longer than in natural speech, they adopt the strategy of keeping low frication noise level to avoid the unstable regime

Copy synthesis of running speech based on vocal tract imaging and audio recording

International audienceThis study presents a simulation framework to synthesize running speech from information obtained from simultaneous vocat tract imaging and audio recording. The aim is to numerically simulate the acoustic and mechanical phenomena that occur during speech production given the actual articulatory gestures of the speaker, so that the simulated speech reproduces the original acoustic features (formant trajectories, prosody, segmentic phonation, etc). The result is intended to be a copy of the original speech signal, hence the name copy synthesis. The shape of the vocal tract is extracted from 2D midsagittal views of the vocal tract acquired at a sufficient framerate to get a few images per produced phone. The area functions of the vocal tract are then anatomically realistic, and also account for side cavities. The acoustic simulation framework uses an extended version of the single-matrix formulation that enables a self-oscillating model of the vocal folds with a glottal chink to be connected to the time-varying waveguide network that models the vocal tract. Copy synthesis of a few French sentences shows the accuracy of the simulation framework to reproduce acoustic cues of natural phrase-level utterances containing most of French natural classes while considering the real geometric shape of the speaker. This is intended to be used as a tool to relate the acoustic features of speech to their articulatory or phonatory origins

Extension of the single-matrix formulation of the vocal tract: consideration of bilateral channels and connection of self-oscillating models of the vocal folds with a glottal chink

International audienceThe paper presents extensions of the single-matrix formulation (Mokhtari et al., 2008, Speech Comm. 50(3) 179 – 190) that enable self-oscillation models of vocal folds, including glottal chink, to be connected to the vocal tract. They also integrate the case of a local division of the main air path into two lateral channels, as it may occur during the production of lateral consonants. Provided extensions are detailed by a reformulation of the acoustic conditions at the glottis, and at the upstream and downstream connections of bilateral channels. The simulation framework is validated through numerical simulations. The introduction of an antiresonance in the transfer function due to the presence of asymmetric bilateral channels is confirmed by the simulations. The frequency of the antiresonance agrees with the theoretical predictions. Simulations of static vowels reveal that the behavior of the vocal folds is qualitatively similar whether they are connected to the single-matrix formulation or to the classic reflection-type line analog model. Finally, the acoustic effect of the glottal chink on the production of vowels is highlighted by the simulations: the shortening of the vibrating part of the vocal folds lowers the amplitude of the glottal flow, and therefore lowers the global acoustic level radiated at the lips. It also introduces an offset in the glottal flow waveform

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

International audienceThe paper presents a numerical study about the acoustic impact of the glottal chink 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 (palato-alveolar, alveolar, and labiodental) have been extracted from static MRI acquisitions. Simulations highlight the existence of three distinct regimes, named A, B, and C, depending on the chink opening. They are characterized by the frication noise level: A exhibits a low frication noise level, B is a mixed noise/voice signal, and C contains only frication noise. They have significant impacts on the first spectral moments. Boundaries of these regimes are defined in terms of minimal abduction of the vocal folds, and simulations show that they depend on articulatory and glottal configurations. Regime B is shown to be unstable: it requires very specific configurations in comparison with other regimes, and acoustic features are very sensitive in this regime