Cancellation level and phase of the (f2-f1) distortion product

The cancellation level and phase were measured for the (f2-f1) distortion product in six normal-hearing ears as a function of input level (L1,L2) and the frequency separation of the two input signals (f1,f2, where f2 greater than f1). The effects of input level were examined for L1 and L2, varied together (L1 = L2) and separately. Typically, f1 was 1500 Hz while f2/f1 was either 1.16, 1.32, 1.44, or 1.68. For L1 = L2, the median data indicate that the (f2-f1) level grows at a rate of approximately 1.1 dB/dB when averaged across all stimulus conditions. This slope tended to be higher (approximately 1.6 dB/dB) for L1 = L2 greater than 80 dB. Slopes for some subjects also increase as f2/f1 increases. The cancellation phase increases slightly (50 degrees - 100 degrees) with an increase in L1 = L2. With L1 at 75 to 80 dB, L2 ranging from 65 to 95 dB, and f2/f1 = 1.16, (f2-f1) increases monotonically with L2 up to L1 = L2. As L2 increases further (L2 greater than L1), the slopes for the growth of (f2-f1) decrease. For f2/f1 = 1.44, on the other hand, (f2-f1) appears to grow monotonically at a rate of approximately 0.5 dB/dB throughout the range of L2 values. The cancellation phase increases with L2 (approximately 100 degrees) only for the wider frequency separation of the two input signals (f2/f1 = 1.44). There are, however, sizable individual differences in the behavior of the (f2 - f1) distortion product.