Subjective evaluation of speech compression codecs and other non-linear voice-path devices for telephony applications

Subjective assessment plays a key role in characterizing the voice quality of new telecommunications devices, both individually and in conjunction with other network equipment. This article discusses subjective test methods for speech quality evaluation with a particular focus on methods used to evaluate speech compression codecs and other non-linear DSP techniques used in modern communications networks. Understanding test designs and trade-offs will help codec designers and network planners appreciate what subjective tests are capable of, what the results of the tests mean, and how the results of different tests may be compared.The general categories of listening tests and conversation tests are compared, ACR and DCR methods are considered, and the details of listening test design, testing procedure, data analysis, and interpretation of results are discussed in detail.