Classification patterns in conversational English fricatives: Between- and within- speaker analyses

This study examines between- and within- speaker patterns in random forest classification models for fricatives in conversational English. Prior investigations on the categorization of fricatives have mostly focused on group-level analyses and careful speech. We use a corpus of sociolinguistic interview speech from Western Canadian English, which represents a more casual speech style, and we compare group-level results to the findings of classification models on individual speakers’ productions. The models use 23 different spectral, temporal, and amplitudinal measures to predict phonetic labels of the fricatives. Our results reveal that certain top-ranked predictors at the group level (e.g., spectral peak frequency, segment duration) are also important for fricative classification in the individual models. Other measures (e.g., midpoint kurtosis, RMS) show substantial variability in their relative prominence and play greater roles in individual- versus group-level modeling. We discuss the implications of these findings for our understanding of individual variation in connected speech and what the findings may imply about models of production and perception.