A physical method for measuring the quality of speech communication channels

Abstract

A physical method has been developed for measuring the quality of speech transmission systems. The method quantifies the deterioration of the intensity fluctuations of running speech. The decrease of these fluctuations as a function of the fluctuation rate (Modulation Transfer Function, MTF) is expressed by a single index, the Speech Transmission Index (STI). A hardware device using an artificial test signal determines the STI on the basis of the MTF's measured for each of the octavebands from 125 Hz up to 8 kHz. The method has been applied successfully to distortions as bandpass limiting, interfering noise, peak clipping, digital modulation methods, automatic gain control and reverberation. For a set of 200 of such communication channels a high correlation was found between the physical index STI and the PB-word score as determined with talkers and listeners.