Influence of duration on static and dynamic properties of German vowels in spontaneous speech

Changes in speech rate severely affect the performance of continuous speech recognition systems. In order to better understand the underlying effects of speech rate changes an analysis was carried out on the influence of duration on the spectral properties of vowels in a large German corpus of spontaneous speech. The results show a strong centralisation effect of the vowel formant frequencies due to shorter duration while the formant movements are only slightly affected. The data suggest that the movement velocity is not changed in vowels with a limited duration. As the means of the onand offset frequencies also remain stable only the middle part of the vowels are affected by the centralisation effect. These results are discussed in the light of the modelling of varying speech rate in automatic speech recognition systems.