A review of distortion and its measurement in p.c.m. telephony systems

Pulse code modulation systems as used in telephony networks are briefly described with particular regard to the inherent quantizing distortion (q.d.). Test methods for the evaluation of signal to q.d. ratio, from analogue input to analogue output, are reviewed. Three test stimuli are considered and their advantages and disadvantages discussed. The three stimuli are a sinusoid, a band-limited noise signal and a band-limited pseudo-random noise signal.