Figure 7.16: Why a low-frequency tone masks a high-frequency tone better than the reverse (a) When a low-frequency tone (such as that from a bassoon) and a high-frequency tone (such as that from a piccolo) are played simultaneously, the bassoon can mask the piccolo because the bassoon’s action on the basilar membrane encompasses the entire portion on which the piccolo acts. (b) But the piccolo cannot mask the bassoon because, even when played at high amplitude, the piccolo does not affect the distal part of the membrane to which the bassoon’s waves extend.
(Adapted from Scharf, 1964.)