Masked threshold rise toward high frequencies is about 100 dB per octave.

Evidence

Ascending from low frequencies, masked thresholds show a very steep increase, and after reaching the maximum, a somewhat flatter decrease. The increase amounts to about 100 dB per octave. This steep rise indicates the need for very steep filters, otherwise the frequency response of the filter and not that of our hearing system is measured. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 420

Categorization

• corroborated: 2 independent passages support this claim — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 420