Level discrimination as a function of level for tones from 0.25 to 16 kHz.

Difference limens for level (delta L in dB = 20 log [(p + delta p)/p], where p is pressure) were measured as a function of level for tones at 0.25, 0.5, 1, 2, 4, 8, 10, 12, 14, and 16 kHz. At each frequency, test levels encompassed the range from near threshold to 95 dB SPL in steps of 10 dB or smaller. The stimulus duration was 500 ms and the interstimulus interval was 250 ms. An adaptive two-alternative forced-choice procedure with feedback was used. Results for six normal listeners show individual differences among listeners, but the general trends seen in the average data clearly are present in the individual data and show the following. First, the delta Ls at all but the highest frequencies are generally smaller at high levels than at low levels. Second, the delta Ls at equal SPLs are largely independent of frequency up to about 4 kHz, but increase with frequency above 4 kHz. Third, at 8 and 10 kHz, the delta Ls are clearly nonmonotonic functions of level, showing consistent deterioration in the mid-level delta Ls relative to the low- and high-level delta Ls. The present data are discussed qualitatively in terms of current models of level discrimination.