Measuring the effects of echoes on speech intelligibility

Abstract

Speech intelligibility was measured as a function of the time interval between the onset of an original signal and the onset of its equal amplitude echo. Scores were obtained on three different speech tests for delay intervals ranging from 50 to 700 ms. Tests included the monosyllabic Modified Rhyme Test (MRT), the multi‐word CID sentences and the NSMRL Tri‐word Test of Intelligibility (TTI). Delay conditions were produced by a specially constructed digital delay line. Intelligibility was most degraded when echoes occurred 200 to 250 msec after the onset of the original signal. The multi‐word tests (CID and TTI) proved more sensitive than the single‐word (MRT) test under all conditions. TTI test words were analyzed according to their position within an utterance. Results suggest that the TTI provides information about echo delay conditions as they affect both single and multiple‐word tests. The correlation between the means for final word TTI items and the means obtained for the MRT across delay conditions was r = 0.80, while the correlation between means for middle word TTI items and the means obtained for the CID sentences was r = 0.95. These results are discussed in terms of temporal masking effects.