Hearing detects AM better than FM only when sidebands fall within a critical bandwidth

Evidence

Sensitivity for the just-detectable amount of modulation can be measured either as the degree of AM or as the modulation index of FM. If differences occur, the difference must be related to the sensitivity of our hearing system for phase changes (in this case reversing of phase of one component of the complex). The results of such measurements, indicated in Fig. 6.5, show that the just-detectable degree of modulation (AM) is smaller than the justdetectable modulation index (FM) at low frequencies of modulation. In other words, in order to be heard as a modulation, the amplitude of the sidebands must be greater in FM than in AM. As the rate of modulation increases, however, and the sidebands are spread further apart, a point is reached beyond which the just-detectable modulation is the same for both FM and AM. At and beyond this point, the phase of the side bands no longer makes any difference to our hearing capabilities. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 900

Categorization

• FICTION: Could seed a character detail around a sound engineer or perception researcher fixating on whether the ear can tell AM from FM.