Spectral and latent representation distortion for TTS evaluation

Abstract

One of the main problems in the development of text-to-speech (TTS) systems is its reliance on subjective measures, typically the Mean Opinion Score (MOS). MOS requires a large number of people to reliably rate each utterance, making the development process slow and expensive. Recent research on speech quality assessment tends to focus on training models to estimate MOS, which requires a large number of training data, something that might not be available in low-resource languages. We propose an objective assessment metric based on the DTW distance using the spectrogram and the high-level features from an Automatic Speech Recognition (ASR) model to cover both acoustic and linguistic information. Experiments on Thai TTS and the Blizzard Challenge datasets show that our method outperformed other baselines in both utterance- and system-level by a large margin in terms of correlation coefficients. Our metric also outperformed the best baseline by 9.58% when used in head-to-head utterance-level comparisons. Ablation studies suggest that the middle layers of the ASR model are most suitable for TTS evaluation when used in conjunction with spectral features.