Physical Attributes of Acoustic Sound   

Sounds are the result of some kind of mechanical vibration disturbing the surrounding air. This creates momentary and sometimes periodic variations in the pressure of this air which radiates away from the sound source to the ear of a listener who experiences the sensation of sound. 
Three physical systems are involved in hearing acoustic sound: 
A sound source which emits energy. This can take any number of forms such as one object striking another; a stream of air passing over a hole, or past a flexible reed; the scraping or plucking of a string; etc.  An elastic medium which transmits the energy from one location to another. This is usually air although sound energy is readily transmitted through other media such as water, steel, or glass. Another characteristic affecting the quality of the sound heard is the boundaries affecting the way the energy is reflected, refracted, diffracted, or absorbed. A receptor which is affected and therefore detects the energy being transmitted by the medium. In human hearing this involves the ear and its component parts as well as the nervous system which processes and stores the information provided by the ear. 
Five fundamental physical qualities can be identified in most sounds:
Frequency Amplitude Spectrum Acoustic Envelope Duration