Automatic prosodic tone choice classification with Brazil’s intonation model

This paper examines the performance of automatically classifying five tone choices (i.e., falling, rising, rising-falling, falling-rising, and neutral) of Brazil’s intonation model. We tested two machine learning classifiers (neural network and boosting ensemble) in two configurations (multi-class and pairwise coupling) and a rule-based classifier. Three sets of acoustic features built from the TILT and Bézier pitch contour models and a new four-point pitch contour model we introduced here were investigated. Tone choices are one of the key elements of Brazil’s prosodic intonation model. We found the rule-based classifier, which was built on our four-point model, achieved better results than the others with an accuracy of 75.1 % and a Cohen’s kappa coefficient of 0.73. This research proves that it is possible to classify tone choices with an accuracy reaching close to the percentage of agreement between two human analysts. The findings further concluded that our four-point model was better for classifying Brazil’s tone choices than both of the TILT or Bézier models.