Mean Opinion Score (MOS) is a metric used to evaluate the quality of audio on a phone call, using the averages of ranked scores. In telecommunications, MOS is most commonly used to measure VoIP call quality using scores from 1 to 5 generated algorithmically per call ("1" being "bad" and "5" being "excellent"). Automatically generated MOS scores have a maximum value based on both the codec and the algorithm, which often cannot exceed a MOS of 4.2.

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