Low-frequency maskers mask most during their rarefaction phase

Evidence

Below 75 dB of the 100-Hz masker, no masking occurs. For 85 dB, masking is larger for that part of the period of the masker during which rarefaction occurs. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 570