Glottal Opening and Strategies of Production of Fricatives

This 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 frication 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 fricatives. This is evidenced by experimental data of simultaneous glottal opening measurements, performed with ePGG, and audio recordings of vowel-fricative-vowel pseudowords. Voiceless 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.