Physical properties vs perceptual attributes

Pitch is a sensation generally related to the frequency of a periodic sound wave. Such wave may consist of a single tone or a composition of tones that are harmonically related in frequency. The pitch of a harmonic mixture described by a Fourier series is equivalent to the pitch of its fundamental (even if it is very quiet or missing). Although pitch-related musical scales are based on intervals (frequency ratios) which are often constant, perceptually uniform mel scale is more nonlinear. Pitch discrimination ability fails at both ends of the audible frequency range. The sensation of pitch also slightly increases with intensity.

Aperiodic, especially chaotic or random waveforms are generally perceived as unpitched. As the scale of randomness is continuous, it corresponds to a range of perceived tonality. For example, white noise has no pitch, while a very narrowband noise may be perceived as similar to a tone.