The process of quantitatively determining one or more properties of acoustic noise. In noise assessment and control studies, knowledge of the physical properties of the undesirable sound is the initial step toward understanding the situation and what should be done to reduce or eliminate a noise problem. The instruments and techniques used for measuring noise are of fundamental importance in noise assessment and control. Many measurements may be required to characterize noise adequately because generally it is possible to make a noise measurement only at a particular point in space, while a noise field often has significant spatial variations.