A Dutch Jaw + An American Tongue + A Kiwi Neck = British English

A Dynamic Model of the Human Vocal TractBy Xiao Bo, Lu Supervised by: William Thorpe and Peter Bier

IntroductionThe human voice box has long been a puzzle. How do we relate what we hear to how we speak? Why does every person’s voice sound different? We know that the quality of voice is largely determined by the shape of the vocal tract (VT). By moving various vocal organs, you are able to manipulate your voice through the changing physical properties of the vocal tract. This project aims to synthesize speech based on a physiological model of the human vocal tract.

The “Talking Head”

First, the surrounding vocal organs were modelled to reproduce the voice box. Most of these models were based on human anatomical measurements, however they come from different origins.

The Kinematics Data

To simulate movements of these vocal organs, we used data collected from a number of electrical coils attached to a British man during the recording of a short English sentence.

The Moving Lips and Tongue

Based on the kinematic data, the movements of the lips, tongue and jaw were simulated by deforming the model in a way so as to match the resting positions of coils (Green) to their corresponding target positions (Red) at each time step.

By doing so, we reproduced the physical movements of the speech organs in the ‘Talking Head’.

Fit VT Models

The surfaces of the vocal organs were digitised to give a discrete representation of the enclosed vocal space (Left). The initial mesh served as the starting point (Middle). The mesh parameters were optimised for minimising the distances between the data points and mesh surface (Right).

We can further approximate the speech signal at the lips l(nT) by a glottal input g(nT) filtered by a high order digital filter

ResultsThe time-varying VT area function for the short English sentence ‘where were you while we were away’ were produced. The synthetic voice is partially recognisable. Compared with the traditional method, this articulatory model shows the ability to generate more realistic speech sounds.

A subject in an EMA experiment (adapted from Mulooly 2004)

SummaryWe present here a 3D finite element model of the vocal tract that is derived from a physiologically based model of speech. The model is constructed in such a way as to allow its shape to vary as the surrounding organs move. For the short English sentences tested in this model, the resulting time-varying area functions are compared with area functions computed from the speech audio by LPC analysis in order to validate the model. These results show that the model is able to provide a realistic representation of the time-varying vocal tract.

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