An MRI Study On Mandarin Vowel/i,(s)i,(sh)i/

It is very important to analyze vowels/i,(s)i,(sh)i/usingMagnetic ResonanceImaging (MRI). It will do a lot of good to speech production, speaker recognition,speech recognition and synthesis. MRI studies of vowels have involved severallanguages, such as English, Japanese and French etc. However, little work has beendone on Mandarin vowels using MRI. In this paper, we are going to investigate therelationship between the morphological difference and the acoustic difference amongthese three vowels.In this paper, the3D volumetric MRI data of eight subjects are used to studythese vowels. Image preprocessing, teeth superimposition, vocal tract segmentationand volume reconstruction are carried out on the MRI volumetric images to extract3D vocal tract shapes and area functions. Then transfer functions of each vowel arecalculated by transmission line model or FDTD method.Several experiments are carried on the real speech, area functions and transferfunctions of three vowels:(a) A comparison between calculated formant frequenciesfrom area functions and the measured formant frequencies from real speech in orderto evaluate the accuracy of MRI technique for acquiringvocal tract data;(b) Areafunctions and vocal tract shapes are analyzed to find the morphological differencesamong these three vowels;(c) Based on the area functions, we used sensitivityfunctions and simple model method to explain why the morphological differencescause the acoustic differences;(d) A FDTD method was used to analyze the detailedacoustic characteristics of the laryngeal cavity and side branches of these vowels.Results suggested that the major difference of these three vowels, which is thepalate constriction difference, causes the F1and F2difference among these vowels.Due to the sub-lingual cavity of vowel/(sh)i/, it has a relatively lower F3than theother two vowels. The inter-dental space of vowels/i/causes two spectral dips, whichare a little lower than the spectral dips caused by the inter-dental space of the othertwo vowels.