stridency (n.)

In PHONETICS, a scale used to characterize sounds (specifically, FRICATIVES) in auditory terms on the basis of their perceived PITCH and LOUDNESS; also called sibilance. Sounds such as [s] are higher on a stridency scale, being relatively high-pitched and intense (they display more energy at higher FREQUENCIES); sounds such as [f] are much lower (displaying more energy at lower frequencies).