ViSQOL (Virtual Speech Quality Objective Listener) is an open, full-reference quality metric developed at Google that estimates perceived audio quality by measuring the spectro-temporal similarity between a reference and a degraded signal, mapping it to a MOS-like score. Unlike the telephony-focused PESQ and POLQA, ViSQOL has modes for both speech and general audio, making it useful for evaluating music codecs and neural codecs as well as voice. Being free and open, it became a popular way for researchers and engineers to benchmark codecs and enhancement systems quickly, without licensing costs or human listening panels. Like all objective metrics it is a proxy for subjective MOS, best used for relative comparison and trend-spotting rather than absolute verdicts.
