MOS (Mean Opinion Score)

Mean Opinion Score (MOS) is a subjective measure of audio quality, calculated by averaging the ratings human listeners give a sample, usually on a 1-to-5 scale. Unlike objective metrics such as SDR or PESQ, MOS captures how good audio actually sounds to people, which is why it is widely used to evaluate speech enhancement, separation, and synthesis. Its tradeoff is cost and time, since it requires human listeners.