QUANTIFYING THE RELATION BETWEEN SPEECH QUALITY AND SPEECH-INTELLIGIBILITY

The purpose of the present research was to examine the relation between speech quality and speech intelligibility. Speech quality measurements were made using continuous discourse and a category rating procedure for the following dimensions: intelligibility, pleasantness, loudness, effort, and total impression. Measurements were made using a group of listeners with normal hearing for a set of stimulus conditions in which intelligibility varied, and for a set of stimulus conditions in which intelligibility was held constant near 100%. When ratings were made for a set of stimulus conditions in which intelligibility was allowed to vary (a) intersubject reliability was high (i.e., different listeners interpreted the dimensions in a similar manner); and (b) the speech quality dimensions of intelligibility, effort, and loudness were indistinguishable. When ratings were made for a set of stimulus conditions in which intelligibility was held constant (a) intersubject reliability was reduced, indicating that different listeners interpreted the dimensions in different ways; (b) most listeners rated each dimension differently, indicating that the dimensions were unique; and (c) across listeners, no single dimension was highly correlated with total impression. These results can be used in order to examine the relation between speech quality and speech intelligibility.