Growth of L(f2--f1) and L(2f1--f2) with input level: influence of f2/f1.

The present investigation examined the effect of f2/f1 (where f1 and f2 are the frequencies of a two-tone input, f2 greater than f1) exerted on the slopes of the functions relating simple difference tone level (L(f2-f1)) and cubic difference tone level (L(2f1-f2)) to input level (L1 = L2, where L1 and L2 represent the levels of the tones at f1 and f2, respectively). Two normal-hearing young adults served as subjects. An adaptive 2AFC nonsimultaneous gap-masking paradigm was utilized to obtain estimates of distortion product magnitude. Parameters of the two-tone input were: f1 = 1550 Hz; f2/f1 = 1.08 and 1.41; and L1 = L2 = 35 to 85 dB SL. Results revealed that slopes for the functions relating L(f2-f1) and L(2f1-f2) to L1 = L2 were approximately 1.0 dB/dB for f2/f1 = 1.08. For f2/f1 = 1.41, however, a slope of 2.0 dB/dB was observed for L(f2-f1) while a slope of 3.0 dB/dB was obtained for L(2f1-f2). It is suggested that some combination of nonlinearities is needed to account for these data.