The perceived naturalness of a voice is a prominent property emerging from vocal sounds, which affects our interaction with both human and artificial agents. Despite its importance, a systematic understanding of voice naturalness is elusive. This is due to (i) conceptual underspecification, (ii) heterogeneous operationalization, (iii) lack of exchange between research on human and synthetic voices, and (iv) insufficient anchoring in voice perception theory. This review reflects on current insights into voice naturalness by pooling evidence from a wider interdisciplinary literature. Against that backdrop, it offers a concise definition of naturalness and proposes a conceptual framework rooted in both empirical findings and theoretical models. Finally, it identifies gaps in current understanding of voice naturalness and sketches perspectives for empirical progress.
