PESQ (Perceptual Evaluation of Speech Quality, ITU-T P.862) is a full-reference algorithm that predicts how listeners would rate the quality of degraded speech by comparing the processed signal against the original clean reference. It models aspects of human hearing to output a score on a MOS-like scale, automating what would otherwise require a panel of listeners. For years PESQ was the industry standard for objectively testing narrowband and wideband VoIP, codecs, and network impairments. Its limitation is scope — it was designed for telephony-grade speech and doesn't cover modern super-wideband or general audio well — which is why the newer POLQA (P.863) superseded it for current systems. PESQ still appears widely in legacy test suites and literature.
