R-value is a number, or score, that is used to quantitatively express the subjective quality of speech in communications systems, especially digital networks that carry voice over IP (VoIP) traffic, or for which VoIP service is under consideration. The R-value score, which is used in conjunction with voice testing processes, can range from 1 (worst) to 100 (best), and is based on the percentage of users who are satisfied with the quality of a test voice signal after it has passed through a network from a source (transmitter) to a destination (receiver).
The R-value score for voice quality is related to the mean opinion score (MOS) used in Perceptual Evaluation of Speech Quality (PESQ), also known as P.862. In theory, the lowest possible MOS, representing total lack of user satisfaction, is 1.0, and the highest possible MOS, representing perfect speech reproduction, is 5.0. (In practice, MOS scores rarely exceed 4.5.) One MOS point is equivalent to approximately 20 R-value points, although the relation is not perfectly linear. An older method of voice testing, known as Perceptual Speech Quality Measurement (PSQM) or P.861, uses a different scoring system that ranges from 0 (best) to infinity (worst).
The R-value scoring method is preferred over other scoring methods by the Telecommunications Industry Association, because it is considered to accurately portray, and thus can be used to predict, the effects of packet loss and delays in digital networks carrying voice signals.