In audio the fundamental is the frequency of the root, or core pitch making up a pitched sound. Except for a few special cases the fundamental is always the lowest frequency making up any pitched sound and is generally the strongest pitch we hear (in a strict Physics sense the fundamental is, by definition, the lowest pitch of a sound). Most sounds are comprised of a combination of a fundamental pitch and various multiples of it known as overtones. When overtones are added to the fundamental, which occurs in almost all naturally occurring sounds, the character of the sound is changed. The relationship between the fundamental and the overtones are what gives each sound its basic timbre.