Comparing Articulatory and Acoustic Strategies for Reducing Non-Native Accents

This article presents an experimental comparison of two types of techniques, articulatory and acoustic, for transforming nonnative speech to sound more native-like. Articulatory techniques use articulators from a native speaker to drive an articulatory synthesizer of the non-native speaker. These methods have a good theoretical justification, but articulatory measurements (e.g., via electromagnetic articulography) are difficult to obtain. In contrast, acoustic methods use techniques from the voice conversion literature to build a mapping between the two acoustic spaces, making them more attractive for practical applications (e.g., language learning). We compare two representative implementations of these approaches, both based on statistical parametric speech synthesis. Through a series of perceptual listening tests, we evaluate the two approaches in terms of accent reduction, speech intelligibility and speaker quality. Our results show that the acoustic method is more effective than the articulatory method in reducing perceptual ratings of non-native accents, and also produces synthesis of higher intelligibility while preserving voice quality.