Effects of speech materials on the loudness discomfort level

Clinicians have used speech stimuli when measuring the loudness discomfort level (LDL) to determine the upper intensity limit for test stimulus presentation, and to select the saturation sound pressure level for an individual's hearing aid. Because little research has investigated the effects of speech stimuli on the LDL, this study was undertaken to compare LDLs using six commercially available speech materials on 120 normally hearing listeners. Our comparisons showed no significant differences between the mean scores for any of the speech stimuli. These findings suggest that any differences in the mean LDLs among studies probably are not attributable to the speech stimuli. The intrasession reliability of LDL measurement was also assessed using a modified method of limits procedure with 2-dB increments and instructions stressing initial discomfort. It was concluded that examiners probably could attain a high degree of reliability by simply averaging the results of two ascending trials, because 95% of these test/retest differences did not exceed 6 dB. Our findings were integrated with previous studies in terms of: (1) test stimuli; (2) listener experience; (3) instructional set; and (4) psychophysical method. This discussion points to many unanswered questions and concludes that the LDL should be interpreted very cautiously. Moreover, it is suggested that the stimuli selected for LDL measurement should reflect the examiner's purpose.