Noise is generally defined as undesired sound which causes irritation, impairs well-being and, depending on the volume and the duration, can even cause damage to health. The ear picks up the sounds and processes the information contained therein. Noise is perceived subjectively, i.e., every individual perceives sounds differently; some are not bothered or only mildly, others are highly irritated. There are various types of noise sources, e.g. street noise, rail noise, industrial noise, leisure time noise and air traffic noise. 

Sound and its properties

Sound arises through vibrations of a sound source and is disseminated in the air as a sound wave. The strength of the sound level (e.g. the sound pressure level) can be determined by measurement. The sound pressure level is measured in decibels (dB). A sound event is manifested as a tiny fluctuation around the atmospheric pressure; this vibration is perceived by the ear. The loudness perception of a sound event is determined by the sound pressure and the frequency. The frequency (number of vibrations per second) represents the height or the depth of a tone. The higher the frequency, the higher the tone (or sound) is perceived. The stronger a sound is, the more people are likely to perceive it as undesired noise.