[Analytic study of noise]

This analysis examines the definition, origin, category, acoustic and psycho-acoustic properties and the quantitative and qualitative measurements of noise, allowing one to delineate the problems associated with such a disturbance. There are several definitions of sound, depending on the angle at which one considers the phenomenon: social, acoustic, psycho-acoustic or medical. The acoustic aspect determines its physical characteristics; the psycho-acoustic aspect deals specifically with its effect on the human ear. Noise assumes very different aspects: ambient, stable, fluctuating, intermittent, pulsing. It presents a disturbance depending on different factors: intensity, frequency, length of exposure, mode of arrival, evolution in time, acoustic characteristics. Over and above all these is added a factor of personal sensitivity, varying from one individual to another. Measurement of noise is performed with the help of an instrument called a sonometer, which records the level of the acoustic pressure, i.e. intensity. From this point, one can evaluate the magnitude of auditive disturbance, Leq. Measurement of human hearing has also been established. This is called audiometry. It allows one to assess the auditive value by drawing a graph: the audiogram. AFNOR has established a classification of noises to be found related to social life. Two broad categories: indoor noises, related to the activity in an apartment building and within the lives of its inhabitants, and outdoor noises, linked to traffic noise and its different forms, and to economic and social activity and noise produced by recreational pursuits.