Using a sigmoid transformation for improved modeling of phoneme duration

The "sums-of-products" approach has emerged as one of the most promising avenues to model contextual influences on phoneme duration. The associated regression is generally applied after log-transforming the durations. This paper presents empirical and theoretical evidence which suggests that this transformation is not optimal. A promising alternative solution is proposed, based on a sigmoid function. Preliminary experimental results obtained on over 50,000 phonemes in varied prosodic contexts show that this transformation reduces the unexplained deviations in the data by more than 30%. Alternatively, for a given level of performance, it halves the number of parameters required by the model.