Equal-level narrow-band maskers mask less at higher centre frequencies

Evidence

A second effect is also noticeable: the maximum of the masked threshold shows the tendency to be lower for higher centre frequencies of the masker, although the level of the narrow-band masker is 60 dB at all centre frequencies. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 415

Categorization

• QUESTION: Why does a fixed 60-dB masker mask less effectively at higher frequencies? This seems to invoke something about excitation patterns and the auditory filter changing with frequency — worth chasing in later chapters.