Study of the Nature of Speech-Transmission-Circuit Quality by Means of the Direct Production of Equivalent Impairments
Peter D. Bricker · The Journal of the Acoustical Society of America · 1963
Fifty-one listeners were asked to match the over-all quality of a variety of voice circuits with fixed parameters by adjusting either the speech level or the noise level on a reference circuit. Thus, they were required to produce “equivalent impairments” directly, whereas such equivalents are usually arrived at by inference from subjective judgments of a variety of circuits. It was found that (1) individual listeners generally found the task difficult and exhibited 10 times more variance on heterogeneous matches (where a speech-level difference was balanced by a noise-level difference) than on homogeneous matches (where speech levels and noise levels could be matched exactly); (2) listeners nevertheless agreed with themselves better than with each other, so that interindividual differences cannot be dismissed as error; (3) a reference circuit-speech level that is too loud for a substantial portion of the listeners can lead to results that are uninterpretable in terms of a single dimension of “quality.” The results suggest that a statement about the relative over-all qualities of two heterogeneously paired circuits is meaningful only if it is a statement of a large difference.