Influence of primary-level and primary-frequency ratios on human distortion product otoacoustic emissions

The combined influence of primary-level differences (L-1-L-2) and primary-frequency ratio (f(2)/f(1)) on distortion product otoacoustic emission (DPOAE) level was investigated in 20 normal-hearing subjects. DPOAEs were recorded with continuously varying stimulus levels [Neely et al. J. Acoust. Soc. Am. 117, 1248-1259 (2005)] for the following stimulus conditions: f(2) = 1, 2, 4, and 8 kHz and f(2)/f(1)=1.05 to 1.4; various L-1-L-2, including one individually optimized to produce the largest DPOAE. For broadly spaced primary frequencies at low L-2 levels, the largest DPOAEs were recorded when L-1 was much higher than L-2, with L-1 remaining relatively constant as L-2 increased. As f(2)/f(1) decreased, the largest DPOAEs were observed when L-1 was closer to L-2 and increased as L-2 increased. Optimal values for L-1-L-2 and f(2)/f(1) were derived from these data. In general, average DPOAE levels for the new L-1-L-2 and f(2)/f(1) were equivalent to or larger than those observed for other stimulus combinations, including the L-1-L-2 described by Kummer et al. [J. Acoust. Soc. Am. 103, 3431-3444 (1998)] and those defined by Neely et al. in which L-1-L-2 was evaluated, but f(2)/f(1) was fixed at 1.2. (c) 2006 Acoustical Society of America.