Mel-Cepstral Distortion of German Vowels in Different Information Density Contexts

This study investigated whether German vowels differ significantly from each other in mel-cepstral distortion (MCD) when they stand in different information density (ID) contexts. We hypothesized that vowels in the same ID contexts are more similar to each other than vowels that stand in different ID conditions. Read speech material from PhonDat2 of 16 German natives (m = 10, f = 6) was analyzed. Bi-phone and word language models were calculated based on DeWaC. To account for additional variability in the data, prosodic factors, as well as corpus-specific frequency values were also entered into the statistical models. Results showed that vowels in different ID conditions were significantly different in their MCD values. Unigram word probability and corpus-specific word frequency showed the expected effect on vowel similarity with a hierarchy between non-contrasting and contrasting conditions. However, these did not form a homogeneous group since there were group-internal significant differences. The largest distance can be found between vowels produced at fast speech rate, and between unstressed vowels.