Masking measurements require noise slopes steeper than the ear’s own selectivity

Evidence

If masking effects on the slopes of such noises are sought, then care has to be taken to produce slopes of the attenuation of the noise as a function of frequency, that are at least as steep as the frequency selectivity of our hearing system. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 402