The vibration of some physical object, resulting in a pressure front moving through air molecules at 1130 feet per second, a zone of high pressure followed by a zone of low pressure. All sounds can be analyzed as having a number of specific characteristics: pitch (frequency), timbre (tone), amplitude (volume) and envelope (the shape of the sound as it changes over time.) What distinguishes one sound from another is the combination of harmonics and other partials that are present in the sound and how the amplitudes of the various partials change over time.