Study Questions Reliability of Reference-Free Speech Quality Metrics for TTS

A new arXiv paper examines whether reference-free speech quality predictors such as UTMOS, DNSMOS and SCOREQ are dependable both as automatic evaluators for text-to-speech systems and as reward signals in preference optimization. The authors argue that these dual roles rest on assumptions about prediction accuracy that may not hold for modern TTS outputs. The work suggests current evaluation practices could mislead comparisons and reward-based training.