THE EVALUATION OF CONTEXTUAL SPEECH MATERIALS.

Abstract

The energy level of contextual discourse (recorded lists of the CID Sentence Intelligibility materials) was measured by feeding the material into a speech-time analyzer. The energy levels of all 10 sentences contained in each list were integrated over 0.1 sec intervals by the analyzer, and counters displayed the amount of time that a given wave form fell below or exceeded certain arbitrary energy levels. Thus absolute energy level as well as absolute duration could be measured for each list. Intensity measurements were compared to intelligibility functions of the lists obtained by presenting each list at five signal-to-noise (S/N) ratios. Twenty normal subjects heard all 10 lists at 40 dB sensation level. Results showed no relation between absolute duration and intelligibility. Intelligibility curves for each list were evaluated in terms of the S/N ratio which yielded the 50% intelligibility point. Each list was compared in terms of its relative standing for absolute energy level and for S/N ratio at 50% intelligibility. With the exception of two lists, there was good correspondence between the rankings for absolute energy level and intelligibility. It is suggested that this measurement of speech energy levels will give a good indication of the relative intelligibility of contextual test materials.