Pitch is a perceptual property that allows the ordering of sounds on a frequency-related scale. Pitches are compared as “higher” and “lower” in the sense associated with musical melodies, which require sound whose frequency is clear and stable enough to distinguish from noise. Pitch is a major auditory attribute of musical tones, along with duration, loudness, and timbre. Pitch may be quantified as a frequency, but pitch is not a purely objective physical property; it is a subjective psychoacoustical attribute of sound. Historically, the study of pitch and pitch perception has been a central problem in psychoacoustics, and has been instrumental in forming and testing theories of sound representation, processing, and perception in the auditory system.