Volume 120, Issue 2, August 2006
Index of content:
- SPEECH PRODUCTION 
The occurrence of the Coanda effect in pulsatile flow through static models of the human vocal folds120(2006); http://dx.doi.org/10.1121/1.2213522View Description Hide Description
Pulsatile flow through a one-sided diffuser and static divergent vocal-fold models is investigated to ascertain the relevance of viscous-driven flow asymmetries in the larynx. The models were 7.5 times real size, and the flow was scaled to match Reynolds and Strouhal numbers, as well as the translaryngeal pressure drop. The Reynolds number varied from 0–2000, for flow oscillation frequencies corresponding to 100 and life-size. Of particular interest was the development of glottalflow skewing by attachment to the bounding walls, or Coanda effect, in a pulsatile flow field, and its impact on speech. The vocal folds form a divergent passage during phases of the phonation cycle when viscous effects such as flow separation are important. It was found that for divergence angles of less than , the attachment of the flow to the vocal-fold walls occurred when the acceleration of the forcing function was zero, and the flow had reached maximum velocity. For a divergence angle of , the fully separated central jet never attached to the vocal-fold walls. Inferences are made regarding the impact of the Coanda effect on the sound source contribution in speech.
120(2006); http://dx.doi.org/10.1121/1.2211550View Description Hide Description
Classification of vocal fold vibrations is an essential task of the objective assessment of voice disorders. For historical reasons, the conventional clinical examination of vocal fold vibrations is done during stationary, sustained phonation. However, the conclusions drawn from a stationary phonation are restricted to the observed steady-state vocal fold vibrations and cannot be generalized to voice mechanisms during running speech. This study addresses the approach of classifying real-time recordings of vocal fold oscillations during a nonstationary phonation paradigm in the form of a pitch raise. The classification is based on asymmetry measures derived from a time-dependent biomechanical two-mass model of the vocal folds which is adapted to observed vocal fold motion curves with an optimization procedure. After verification of the algorithm performance the method was applied to clinical problems. Recordings of ten subjects with normal voice and ten dysphonic subjects have been evaluated during stationary as well as nonstationary phonation. In the case of nonstationary phonation the model-based classification into “normal” and “dysphonic” succeeds in all cases, while it fails in the case of sustained phonation. The nonstationary vocal fold vibrations contain additional information about vocal fold irregularities, which are needed for an objective interpretation and classification of voice disorders.
120(2006); http://dx.doi.org/10.1121/1.2208430View Description Hide Description
If more than one articulator is involved in the execution of a phonetic task, then the individual articulators have to be temporally coordinated with each other in a lawful manner. The present study aims at analyzing tongue-jaw cohesion in the temporal domain for the German coronal consonants /s, ʃ, t, d, n, l/, i.e., consonants produced with the same set of articulators—the tongue blade and the jaw—but differing in manner of articulation. The stability of obtained interaction patterns is evaluated by varying the degree of vocal effort: comfortable and loud. Tongue and jaw movements of five speakers of German were recorded by means of electromagnetic midsagittal articulography (EMMA) during /aCa/ sequences. The results indicate that (1) tongue-jaw coordination varies with manner of articulation, i.e., a later onset and offset of the jaw target for the stops compared to the fricatives, the nasal and the lateral; (2) the obtained patterns are stable across vocal effort conditions; (3) the sibilants are produced with smaller standard deviations for latencies and target positions; and (4) adjustments to the lower jaw positions during the surrounding vowels in loud speech occur during the closing and opening movement intervals and not the consonantal target phases.
120(2006); http://dx.doi.org/10.1121/1.2211548View Description Hide Description
Acoustic duration and degree of vowel reduction are known to correlate with a word’s frequency of occurrence. The present study broadens the research on the role of frequency in speech production to voice assimilation. The test case was regressive voice assimilation in Dutch. Clusters from a corpus of read speech were more often perceived as unassimilated in lower-frequency words and as either completely voiced (regressive assimilation) or, unexpectedly, as completely voiceless (progressive assimilation) in higher-frequency words. Frequency did not predict the voice classifications over and above important acoustic cues to voicing, suggesting that the frequency effects on the classifications were carried exclusively by the acoustic signal. The duration of the cluster and the period of glottal vibration during the cluster decreased while the duration of the release noises increased with frequency. This indicates that speakers reduce articulatory effort for higher-frequency words, with some acoustic cues signaling more voicing and others less voicing. A higher frequency leads not only to acoustic reduction but also to more assimilation.
An amplitude quotient based method to analyze changes in the shape of the glottal pulse in the regulation of vocal intensity120(2006); http://dx.doi.org/10.1121/1.2211589View Description Hide Description
This study presents an approach to visualizing intensity regulation in speech. The method expresses a voice sample in a two-dimensional space using amplitude-domain values extracted from the glottal flow estimated by inverse filtering. The two-dimensional presentation is obtained by expressing a time-domain measure of the glottal pulse, the amplitude quotient (AQ), as a function of the negative peak amplitude of the flow derivative . The regulation of vocal intensity was analyzed with the proposed method from voices varying from extremely soft to very loud with a SPL range of approximately . When vocal intensity was increased, the speech samples first showed a rapidly decreasing trend as expressed on the proposed graph. When intensity was further raised, the location of the samples converged toward a horizontal line, the asymptote of a hypothetical hyperbola. This behavior of the graph indicates that the intensity regulation strategy changes from laryngeal to respiratory mechanisms and the method chosen makes it possible to quantify how control mechanisms underlying the regulation of vocal intensity change gradually between the two means. The proposed presentation constitutes an easy-to-implement method to visualize the function of voice production in intensity regulation because the only information needed is the glottal flow wave form estimated by inverse filtering the acoustic speechpressure signal.