SPEECH QUALITY MEASUREMENTS.

Modern speech transmission and processing techniques have reached a state of high perfection so that the description of speech quality in terms of intelligibility alone has become insufficient. An extended utilitarian definition of speech quality shall include besides intelligibility also preference, loudness and speaker recognizability. The paper studies the parameter preference which for many practical applications is assumed to give an advantageous and sufficient description of speech quality. The performance of several relative and absolute preference measurement methods is studied by evaluating with these methods various kinds of naturally and artificially distorted speech signals. Transitivity and signal discrimination capabilities of the different methods are discussed, as well as a comparison of results gained with these methods by projecting them on to a unified rating scale. The results of extensive testing and test repetitions indicate that the accuracy of preference evaluation seems not to be limited by the methods themselves, but by the variety and variability of listeners caused by training and accommodation effects. Author