FM fluctuation strength scales with the number of critical bands crossed

Evidence

This decrease can be understood in terms of the number of critical bands encompassed at different centre frequencies by FI\I tones with a constant frequency deviation of 200 Hz. As an example, the FM tone at 0.5 kHz sweeps between 300 and 700 Hz, i.e. between critical-band rates of 3 and 6.5 Bark, respectively. At the 8-kHz centre frequency, the modulation occurs between frequencies of 7.8 and 8.2 kH7:, corresponding to 21.1 and 21.3 Bark, respectively. This means that at a centre frequency of 0.5 kH7:, the FM tone varies over a critical-band interval of 3.5 Bark, whereas at 8 kHz it varies only over 0.2 Bark. Hence. the critical-hand interval at 8 kHz is a factor of 17.5 slllaller than the critical-band interval at 0.5 kHz. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1401