Development of a vocal tract design tool based on a growth curve of the vocal tract length

One of the advantages of speech synthesis based on the vocal tract shapes is flexibility in speech sounds depending on the articulatory parameters. In order to take advantage of the flexibility, preparing various vocal tract shapes is important. To achieve this, this paper describes the development of a vocal tract design tool based on a growth curve of the vocal tract length reported by literature. In this tool, the growth curve is used to calculate the size of the vocal tract. A user can obtain a vocal tract shape depending on the age and sex using a slide button on the interface window. The parameters that describe vocal tract shape and vocal folds are used to produce vowel sounds and their formant frequencies are obtained. According to literature, there is a relationship between the fundamental frequency and formant frequencies through the age. We compared the formant frequencies calculated from the tool with those estimated from the literature. The comparison showed that the calculated formant frequencies were in relatively good agreement with the estimated ones. In addition, the distribution of the first and second formant frequencies showed a typical pentagonal distribution.