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Aug 2008

Volume 124, Issue 2, pp. 689-EL61

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Experimental investigation of the influence of a posterior gap on glottal flow and sound

Jong Beom Park and Luc Mongeau

J. Acoust. Soc. Am. Volume 124, Issue 2, pp. 1171-1179 (2008); (9 pages) | Cited 1 time

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The influence of a posterior gap on the airflow through the human glottis was investigated using a driven synthetic model. Instantaneous orifice discharge coefficient of a glottal shaped orifice was obtained from the time-varying orifice area and the velocity distribution of the pulsated jet measured on the axial plane using a single hot-wire probe. Instantaneous orifice discharge coefficient values were found to undergo a cyclic hysteresis loop when plotted versus Reynolds number and time, indicating a pressure head increase and a net energy transfer from the air flow to the orifice wall. The net energy transferred was estimated to be around 10% of the value presumably required to achieve self-sustained oscillation. The radiated sound pressure was measured to characterize the influence of the minimum flow through the posterior gap on the broadband component of the radiated sound. The presence of a posterior gap was found to significantly increase the broadband sound level produced over the frequency range in which human hearing is most sensitive.
Show PACS
43.70.Bk Models and theories of speech production
43.70.Aj Anatomy and physiology of the vocal tract, speech aerodynamics, auditory kinetics
43.28.Ra Generation of sound by fluid flow, aerodynamic sound and turbulence

Patterns of acquisition of native voice onset time in English-learning children

Joanna H. Lowenstein and Susan Nittrouer

J. Acoust. Soc. Am. Volume 124, Issue 2, pp. 1180-1191 (2008); (12 pages)

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Learning to speak involves both mastering the requisite articulatory gestures of one’s native language and learning to coordinate those gestures according to the rules of the language. Voice onset time (VOT) acquisition illustrates this point: The child must learn to produce the necessary upper vocal tract and laryngeal gestures and to coordinate them with very precise timing. This longitudinal study examined the acquisition of English VOT by audiotaping seven children at 2 month intervals from first words (around 15 months) to the appearance of three-word sentences (around 30 months) in spontaneous speech. Words with initial stops were excerpted, and (1) the numbers of words produced with intended voiced and voiceless initial stops were counted; (2) VOT was measured; and (3) within-child standard deviations of VOT were measured. Results showed that children (1) initially avoided saying words with voiceless initial stops, (2) initially did not delay the onset of the laryngeal adduction relative to the release of closure as long as adults do for voiceless stops, and (3) were more variable in VOT for voiceless than for voiced stops. Overall these results support a model of acquisition that focuses on the mastery of gestural coordination as opposed to the acquisition of segmental contrasts.
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43.71.Gv Measures of speech perception (intelligibility and quality)
43.70.Fq Acoustical correlates of phonetic segments and suprasegmental properties: stress, timing, and intonation

Compensation strategies for a lip-tube perturbation of French [u]: An acoustic and perceptual study of 4-year-old children

Lucie Ménard, Pascal Perrier, Jerôme Aubin, Christophe Savariaux, and Mélanie Thibeault

J. Acoust. Soc. Am. Volume 124, Issue 2, pp. 1192-1206 (2008); (15 pages) | Cited 1 time

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The relations between production and perception in 4-year-old children were examined in a study of compensation strategies for a lip-tube perturbation. Acoustic and perceptual analyses of the rounded vowel [u] produced by twelve 4-year-old French speakers were conducted under two conditions: normal and with a 15-mm-diam tube inserted between the lips. Recordings of isolated vowels were made in the normal condition before any perturbation (N1), immediately upon insertion of the tube and for the next 19 trials in this perturbed condition, with (P2) or without articulatory instructions (P1), and in the normal condition after the perturbed trials (N2). The results of the acoustic analyses reveal speaker-dependent alterations of F1, F2, and/or F0 in the perturbed conditions and after the removal of the tube. For some subjects, the presence of the tube resulted in very little change; for others, an increase in F2 was observed in P1, which was generally reduced in some of the 20 repetitions, but not systematically and not continuously. The use of articulatory instructions provided in the P2 condition was detrimental to the achievement of a good acoustic target. Perceptual data are used to determine optimal combinations of F0, F1, and F2 (in bark) related to these patterns. The data are compared to a previous study conducted with adults [ Savariaux et al., J. Acoust. Soc. Am. 106, 381–393 (1999) ].
Show PACS
43.71.Gv Measures of speech perception (intelligibility and quality)
43.70.Mn Relations between speech production and perception
43.70.Fq Acoustical correlates of phonetic segments and suprasegmental properties: stress, timing, and intonation
43.70.Bk Models and theories of speech production

A simple-shear rheometer for linear viscoelastic characterization of vocal fold tissues at phonatory frequencies

Roger W. Chan and Maritza L. Rodriguez

J. Acoust. Soc. Am. Volume 124, Issue 2, pp. 1207-1219 (2008); (13 pages) | Cited 1 time

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Previous studies reporting the linear viscoelastic shear properties of the human vocal fold cover or mucosa have been based on torsional rheometry, with measurements limited to low audio frequencies, up to around 80 Hz. This paper describes the design and validation of a custom-built, controlled-strain, linear, simple-shear rheometer system capable of direct empirical measurements of viscoelastic shear properties at phonatory frequencies. A tissue specimen was subjected to simple shear between two parallel, rigid acrylic plates, with a linear motor creating a translational sinusoidal displacement of the specimen via the upper plate, and the lower plate transmitting the harmonic shear force resulting from the viscoelastic response of the specimen. The displacement of the specimen was measured by a linear variable differential transformer whereas the shear force was detected by a piezoelectric transducer. The frequency response characteristics of these system components were assessed by vibration experiments with accelerometers. Measurements of the viscoelastic shear moduli (G′ and G″) of a standard ANSI S2.21 polyurethane material and those of human vocal fold cover specimens were made, along with estimation of the system signal and noise levels. Preliminary results showed that the rheometer can provide valid and reliable rheometric data of vocal fold lamina propria specimens at frequencies of up to around 250 Hz, well into the phonatory range.
Show PACS
43.70.Aj Anatomy and physiology of the vocal tract, speech aerodynamics, auditory kinetics
43.70.Bk Models and theories of speech production
43.35.Mr Acoustics of viscoelastic materials
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