Masked threshold rises once noise bandwidth exceeds the critical bandwidth

Evidence

Using uniform masking noise, it is possible to produce meaningful data at all frequencies so that the critical bandwidth can be measured as a function of frequency. Further, instead of using a number of tones of equal amplitude, noises can be used in the same way. In this case, uniform masking noise is used as masker and the threshold of an additional noise is measured as a function of the bandwidth of this additional noise. The results show the same effect: the threshold of this noise masked by uniform masking noise is independent of bandwidth for noise narrower than the critical bandwidth but increases ~ just like the data outlined in Fig. 6.2b ~ for bandwidths larger than the critical band. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 889