ASA 129th Meeting - Washington, DC - 1995 May 30 .. Jun 06

5pPP11. Fine structure of 2f[sub 1]-f[sub 2] acoustic distortion product: Effect of L1/L2 ratio.

Ning-ji He

Richard A. Schmiedt

Dept. of Otolaryngol. and Commun. Sci., Medical Univ. of South Carolina, 171 Ashley Ave., Charleston, SC 29425-2242

The fine structure of the 2f[sub 1]-f[sub 2] acoustic distortion product (ADP) was measured in a group of normal-hearing subjects with different combinations of primary levels (L1 and L2). The frequency ratio (f[sub 2]/f[sub 1],f[sub 2]>f[sub 1]) was 1.2, and the f[sub 2] frequency was swept from 1781 to 2300 Hz in 1/32 octave steps. In condition 1, L1 was fixed at 50 dB SPL while L2 varied from 30 to 75 dB SPL in 5-dB steps. In condition 2, L2 was fixed at 50 dB SPL and L1 was varied as in condition 1. For a fixed L1, an upward frequency shift was evident in the ADP fine structure as the L2 level increased, whereas for fixed L2, a downward frequency shift in the ADP pattern was observable with an increasing L1. These results support a vector sum computer model for the ADP fine structure [Sun et al., 2166--2174, 2175--2183 (1994)], suggesting that ADP fine structure is largely generated in the overlap area of the traveling waves for the primary tones, and the effects of reemissions from the 2f1-f2 area are minimal. A large variance was observed in the best L1/L2 ratio, ranging from -7.5 to 20 dB both across and within subjects. [Work supported by NIDCD.]