Morphological normalization of vocal tract shape

The articulatory databases are not utilized so widely as acoustic databases. One of the reasons is the difficulty of reducing morphological variations among subjects. To reduce morphological differences in speech organs among speakers and remain their speech dynamics, this study proposed a framework of normalizing vocal tract by using a Thin-plate spline method. Electromagnetic Midsagittal Articulographic data for three subjects have been used in this research. The template for normalization was obtained by averaging all three subjects´ palates and tongue shapes. The landmarks of the template and subjects have been defined according to a gridline system of the vocal tract. The results show that the variances among subjects were reduced 0.8 mm in horizontal and 2.4 mm in vertical direction. The similar vowel structure of pre/post-normalization data indicates that speaker specific characteristics can be maintained by this framework. The effects of the normalization in acoustic space are also investigated by using a physiological articulatory model. Results show that the variations have also been reduced in acoustic space.