In this paper, we present a comparative study of natural and synthetic speech samples which vary in larynx height. The acoustics of isolated vowels was analyzed with respect to formant frequency changes and changes in voice quality. The synthetic stimuli show the same characteristics as the natural stimuli when special attention is paid to the synthetic excitation quality. One issue addressed behind this study is how the naturalness of speech synthesis can be improved by manipulating voice quality. Another issue is to find out how well the articulatory speech synthesizer used matches the real speech production process.