Speech quality of PCM system in digital telephone network
Nobuhiko Kitawaki, Kenzo Itoh, Kazuhiko Kakei · Electronics and Communications in Japan (Part I Communications) · 1982
Abstract PCM is the basic coding method in speech transmission in digital telephony for the future information network system (INS). This paper evaluates the speech quality of the PCM system in a digital telephone network. A category judgement test is employed for evaluation of speech quality. This evaluation method distinguishes five grades of overall speech quality by users. First the effects of such basic PCM parameters as the number of quantizing bits, amplitude companding and input speech level on speech quality are examined. Then other factors affecting speech quality such as overall reference equivalent, circuit noise and link connection associated with introduction of PCM into the telephone network are clarified. Finally, for evaluation of the coded speech quality with consideration of network design, white noise is employed in speech envelope correlation and 8‐bit PCM system is adopted as a reference for degradation.