Cross-lingual Style Transfer with Conditional Prior VAE and Style Loss

In this work we improve the style representation for cross-lingual style transfer. Specifically, we improve the Spanish representation across four styles, Newscaster, DJ, Excited, and Disappointed, whilst maintaining a single speaker identity for which we only have English samples. This is achieved using Learned Conditional Prior VAE (LCPVAE), a hierarchical Variational Auto Encoder (VAE) approach. A secondary VAE is introduced, conditioned on one-hot encoded style information, resulting in a structured embedding space of the primary VAE. This places utterances of the same style in similar locations of the latent space irrespective of language. We also experiment with extending this model by incorporating a style loss. We perform subjective evaluations for style similarity using native Spanish speakers, and show an average relative improvement over the baseline of 3.5% with statistical significance (p-value<0.01) across all four styles. Interestingly the more expressive styles achieve a higher relative improvement of 4.4% compared to 2.6% for styles that are closer to neutral speech. We also demonstrate that this is whilst maintaining speaker similarity and in-lingual performance in all styles. Accent performance is maintained in three out of four styles with the exception of Excited, while naturalness performance is maintained in News and Disappointed styles.