A frequency-modulated masker’s excursion along the critical-band scale sets the test-tone threshold.

Evidence

A frequency-modulated pure-tone masker produces constant SPL. However, its excitation level pattern moves up and down along the critical-band scale, with an extension corresponding to its frequency deviation and a temporal speed corresponding to its modulation frequency. If a long lasting tone is used as a test sound, the minimal excitation level of the masker produced within the modulation period at the critical-band rate of the test tone determines threshold. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 614