Objective metrics complement human preference
The authors state that objective metrics complement human preference rankings. ASR-based WER is a proxy for intelligibility and speaker similarity estimates voice identity preservation; neither directly measures naturalness, expressiveness, or listener preference.
Supporting evidence
Open TTS Leaderboard: Scalable Evaluation for Multilingual Text-to-Speech and Voice Cloning
Original excerpt
Importantly, the Open TTS Leaderboard does not replace human preference ranking. ASR-based WER provides a proxy for intelligibility, while speaker similarity estimates voice identity preservation. Neither directly measures naturalness, expressiveness, or listener preference. Nevertheless, they can even inform voting-based leaderboards which models to include in their evaluations.