Effect of warble-tone frequency deviation on threshold measurement in cases with sloping audiometric configurations.

A 2.1-kc/s pure-tone (p-t) mask at 80 db SPL created for 7 normal-hearing young adults a hearing threshold configuration which sloped sharply in the 2-kc/s frequency region. Conventional masked audiometry at 1, 1.5, and 2 kc/s was performed with pure tones and with tones sinusoidally modulated at 20 c/s by +/- 5, 10, and 20%. In frequency regions where the masked audiogram was relatively flat, p-t and warble-tone (w-t) HTLs were equivalent. However, at 2 kc/s, w-t HTLs were substantially better (as much as 32 db) than p-t HTLs. The w-t vs p-t discrepancy increased with frequency deviation from 5-20%, attributable to the spread of modulated signal energy into frequency regions where hearing sensitivity was better than at the nominal test frequency. Clinicians should be alert to the possibility that testing with warbled tones may underestimate the amount of hearing loss for pure tones in those with sloping audiometric configurations.