Loudness depends on the rate of supply of energy to the ear and the apparent loudness of the sound. The human ear generally has a logarithmic response to power levels at a given frequency, and a complicated response to power levels across the audible spectrum. The amplitude of the sound declines with increasing time and this is known as decay .
Pitch is the frequency of the principal note and has been defined in the previous section.
Quality or timbre is the name given to the instrument's harmonic spectrum and their relative intensities. The combination of quality and decay allow the human ear to differentiate between different instruments. Generally the lowest pitch is known as the fundamental and the higher pitches are known as overtones or partials . A bell however is a notable exception as the harmonic named the fundamental is not the lowest frequency and the term partials is used to denote all harmonics instead of all except the fundamental.