In acoustics, noise measurement can be for the purpose of measuring environmental noise. Applications include monitoring of construction sites, aircraft noise, road traffic noise, entertainment venues and neighborhood noise. The word "noise" means any "unwanted sound". Environmental noise monitoring is the measurement of noise in an outdoor environment caused by transport, industry and recreational activities. The laws and limits governing environmental noise monitoring differ from country to country. At the very least, noise may be annoying or displeasing or may disrupt the activity or balance of human or animal life, increasing levels of aggression, hypertension and stress. In the extreme, excessive levels or periods of noise can have long-term negative health effects such as hearing loss, tinnitus, sleep disturbances, a rise in blood pressure, an increase in stress and vasoconstriction, and an increased incidence of coronary artery disease. In animals, noise can increase the risk of death by altering predator or prey detection and avoidance, interfering with reproduction and navigation, and contributing to permanent hearing loss. Various cures are available to combat Environmental Noise; Roadway noise can be reduced by the use of noise barriers, limitation of vehicle speeds, alteration of roadway surface texture, limitation of heavy vehicles, use of traffic controls that smooth vehicle flow to reduce braking and acceleration, and tire design. Aircraft noise can be reduced by using quieter jet engines, altering flight paths and considering the time of day to benefit residents near airports. Industrial noise is addressed by redesign of industrial equipment, shock mounted assemblies and physical barriers in the workplace.
Audio Systems and Broadcasting
Noise measurement can also be part of a test procedure using white noise, or some other specialised form of test signal. In audio systems and broadcasting, specific methods are used to obtain subjectively valid results in order that different devices and signal paths may be compared regardless of the inconsistent spectral distribution and temporal properties of the noise that they generate. In particular, the ITU-R 468 noise weighting was devised specifically for this purpose and is widely used for professional audio and broadcast measurements.
Standards
There are a number of standards for noise measurement, each with a different goal or focus, including:
