Table III.

Effective level of the quadratic distortion product (QDT), defined as the input levels of a 244-Hz sinusoid needed to match the averaged spectral magnitude (in the addition waveform) of the FFR for the downward- and the upward-shifted complex tones at the QDT frequency of 300 Hz. The downward- and upward-shifted complex tones each consisted of three primaries (with frequencies of 544, 844, and 1144 Hz for the downward shift and 656, 956, and 1256 Hz for the upward shift) with a level of 70.2 dB per component. The effective level of the QDT was estimated by linear interpolation from each subject’s FFR growth function for the pure tone at 244 Hz (see Fig. 5). The bottom line gives the mean and the standard error across subjects.

	Effective QDT level (dB SPL)	Averaged spectral magnitude of FFR at QDT frequency for downward- and upward-shifted complex tones (dB re 0.01 μV)
Subject 1	68.0	18.6
Subject 2	>75.0	27.5
Subject 3	74.0	23.6
Subject 4	>75.0	22.4
Subject 5	>75.0	23.8
Subject 6	>75.0	25.4
Mean	>75.0	23.5 (1.21)