This effect is supported theoretically, and has been repeatedly confirmed empirically. It has been well-established that longer vocal tracts are associated with lower formant frequencies. The role of vocal tract length in vowel production variability has been extensively studied and modeled, particularly with regard to the position and spacing of formant frequencies. These differences are particularly significant when one considers the relatively limited ability of most individuals to modulate vocal tract length, mainly through lip protrusion and laryngeal height. Even between adults, vocal tracts vary from approximately 13 cm to 20 cm in length.

The vocal tract lengthens throughout development, from an average length of approximately 8 cm at birth, up to 16 cm in adulthood. This structural characteristic of the speech production apparatus determines many aspects of the acoustic speech signal and, at the same time, is highly variable across speakers. The length of the vocal tract, measured along its midline from the glottis to the lips, is an essential parameter to consider for explaining behavioral variability in speech production. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Ĭompeting interests: The authors have declared that no competing interests exist. įunding: This work was supported by National Institutes of Health, grant DC007124 (SSN received funding). This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are creditedĭata Availability: The data used in this work are part of the USC-TIMIT database, which is publicly and freely available online at. Received: NovemAccepted: JPublished: July 15, 2015Ĭopyright: © 2015 Lammert, Narayanan. Moreover, theoretical insights are explained regarding the reason for differences in formant sensitivity.Ĭitation: Lammert AC, Narayanan SS (2015) On Short-Time Estimation of Vocal Tract Length from Formant Frequencies. Theoretical predictions of formant sensitivity reinforce this empirical finding. Empirical results show that the effectiveness of the proposed method is based on emphasizing higher formant frequencies, which seem less affected by speech articulation. Evaluations show improvements in accuracy over previously proposed methods, with 0.631 and 1.277 cm root mean square error on simulated and human speech data, respectively.

The proposed method is evaluated using acoustic characteristics of simulated vocal tracts ranging from 14 to 19 cm in length, as well as real-time magnetic resonance imaging data with synchronous audio from five speakers whose vocal tracts range from 14.5 to 18.0 cm in length. A framework for considering estimation methods is developed from the basic principles of vocal tract acoustics, and an estimation method is proposed that follows naturally from this framework. A method for accurate estimation of vocal tract length from formant frequencies would afford normalization of interspeaker variability and facilitate acoustic comparisons across speakers. Vocal tract length is highly variable across speakers and determines many aspects of the acoustic speech signal, making it an essential parameter to consider for explaining behavioral variability.

Speech timer estimator