Rarefaction, not masker level, drives the audibility threshold maximum

Evidence

For the twice-integrated Gaussian impulses (Fig. 4.34a), almost no masking occurs during the first half of the period although a masker level as high as 140 dB is used, but a very distinct maximum appean; in the second (rarefaction) half. Indeed, the maximum coincides with the minimum of the masker’s time function, i.e. with the peak value of the rarefaction. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 583