Masking pattern shapes differ by center frequency even at equal masker level

Evidence

In this context, narrow-band noise means a noise with a bandwidth equal to or smaller than the critical bandwidth (about 100 Hz below and 0.2 f above 500 Hz, as outlined in Chap. 6). It is more meaningful when narrow-band noise is used to give data in terms of the total level of the noise instead of its density level. … The frequency dependence of the threshold masked by the I-kHz narrow-band noise is very similar on the axes of Fig. 4.3 to that produced by the 4-kHz narrow-band noise. The frequency dependence of the threshold masked by the 250-Hz narrow-band noise, however, seems to be broader. 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