Vocal tract modes based on multiple area function sets from one speaker

An age-dependent vocal tract model for males and females based on anatomic measurements

The purpose of this study was to take a first step toward constructing a developmental and sex-specific version of a parametric vocal tract area function model representative of male and female vocal tracts ranging in age from infancy to 12 yrs, as well as adults. Anatomic measurements collected from a large imaging database of male and female children and adults provided the dataset from which length warping and cross-dimension scaling functions were derived, and applied to the adult-based vocal tract model to project it backward along an age continuum. The resulting model was assessed qualitatively by projecting hypothetical vocal tract shapes onto midsagittal images from the cohort of children, and quantitatively by comparison of formant frequencies produced by the model to those reported in the literature. An additional validation of modeled vocal tract shapes was made possible by comparison to cross-sectional area measurements obtained for children and adults using acoustic pharyngometry. This initial attempt to generate a sex-specific developmental vocal tract model paves a path to study the relation of vocal tract dimensions to documented prepubertal acoustic differences.

Structure, Movement, Sound, and Perception

Models that take the form of artificial talkers and speech synthesis systems have long been used as a means of understanding both speech production and speech perception. The article begins with a brief history of two artificial speaking devices that exemplify the representation of speech production as a system of modulations. The development of a recent airway modulation model is then described that simulates the time-varying changes of the vocal tract and acoustic wave propagation. The result is a type of artificial talker that can be used to study various aspects of how sound is generated by humans and how that sound is perceived by a listener.

Phrase-level speech simulation with an airway modulation model of speech production

Artificial talkers and speech synthesis systems have long been used as a means of understanding both speech production and speech perception. The development of an airway modulation model is described that simulates the time-varying changes of the glottis and vocal tract, as well as acoustic wave propagation, during speech production. The result is a type of artificial talker that can be used to study various aspects of how sound is generated by humans and how that sound is perceived by a listener. The primary components of the model are introduced and simulation of words and phrases are demonstrated.

Developmental sexual dimorphism of the oral and pharyngeal portions of the vocal tract: an imaging study

PURPOSE

The anatomic origin for prepubertal vowel acoustic differences between male and female subjects remains unknown. The purpose of this study is to examine developmental sex differences in vocal tract (VT) length and its oral and pharyngeal portions.

METHOD

Nine VT variables were measured from 605 imaging studies (magnetic resonance imaging and computed tomography) of subjects between birth and age 19 years. Given sex differences in growth rate (Vorperian et al., 2009), assessment of sex differences was done through use of a localized comparison window of 60 months. Analysis entailed applying this comparison window first to 4 discrete age cohorts, followed by a progressive assessment in which this comparison window was moved in 1-month increments from birth across all ages.

RESULTS

Findings document significant postpubertal sex differences in both the oral and pharyngeal portions of the VT. They also document periods of significant prepubertal sex differences in the oral region first, followed by segments in the pharyngeal region.

CONCLUSIONS

Assessment of developmental sex differences using localized age ranges is effective in unveiling sex differences that growth rate differences may conceal. Findings on the presence of prepubertal sex differences in the oral region of the VT may clarify, in part, the anatomic basis of documented prepubertal acoustic differences.

Relation of vocal tract shape, formant transitions, and stop consonant identification

PURPOSE

The present study was designed to investigate the relation of formant transitions to place-of-articulation for stop consonants. A speech production model was used to generate simulated utterances containing voiced stop consonants, and a perceptual experiment was performed to test their identification by listeners.

METHOD

Based on a model of the vocal tract shape, a theoretical basis for reducing highly variable formant transitions to more invariant formant deflection patterns as a function of constriction location was proposed. A speech production model was used to simulate vowel-consonant-vowel (VCV) utterances for 3 underlying vowel-vowel contexts and for which the constriction location was incrementally moved from the lips toward the velar part of the vocal tract. These simulated VCVs were presented to listeners who were asked to identify the consonant.

RESULTS

Listener responses indicated that phonetic boundaries were well aligned with points along the vocal tract length where there was a shift in the deflection polarity of either the 2nd or 3rd formant.

CONCLUSIONS

This study demonstrated that regions of the vocal tract exist that, when constricted, shift the formant frequencies in a predictable direction. Based on a perceptual experiment, the boundaries of these acoustically defined regions were shown to coincide with phonetic categories for stop consonants.

Identification of synthetic vowels based on a time-varying model of the vocal tract area function

The purpose of this study was to conduct an identification experiment with synthetic vowels based on the same sets of speaker-dependent area functions as in Bunton and Story [(2009) J. Acoust. Soc. Am. 125, 19-22], but with additional time-varying characteristics that are more representative of natural speech. The results indicated that vowels synthesized using an area function model that allows for time variation of the vocal tract shape and includes natural vowel durations were more accurately identified for 7 of 11 English vowels than those based on static area functions.