The ITU-T standard defining the Perceptual Speech Quality Measurement (PSQM) method of objectively evaluating voice transmission quality. PSQM is an automated method developed to measure the perceived quality of real-time voice as impacted by compression codecs. An enhanced version known as PSQM+ was later developed to measure the effects of packet loss and other network impairments. PSQM compares a distorted voice sample to an original, clear voice sample and uses a complex analytical process to evaluate the difference in terms of factors that influence the perceptions of human listeners.The ultimate distortion score corresponds closely with the mean opinion score (MOS) yielded by the panel of human listeners employed using the P.800 method. P.861 was withdrawn and replaced by P.862, defining the Perceptual Evaluation of Speech Quality (PESQ). See also codec, compression, MOS, P.800, P.862, and PSQM.