Noise

Noise is any undesired signal.

Acoustics

By extension, noise is any unwanted disturbance within a useful frequency band, such as undesirable sound waves in a car passenger cabin. The word "noise" is derived from the same Latin root as the word "nausea".

In the Roman times of Julius Caesar, chariots were prohibited from the streets of Rome after nightfall. The Roman laws at that time were basically enacted to restrict vehicle noise and explicitly controlled the night time chariot traffic in residential areas.

In the 13th century, Nuisance Laws were part of English Common Law which recognised the problems with noise. It pronounced noise as a public nuisance which was regarded as a crime or semi-crime.

Electronics

Electrical signals may be contaminated with noise. This noise may be electronic noise which is an artefact of semiconductor construction techniques and cannot be reduced, or the noise may be caused by environmental factors. This type of noise can be the result of poor positioning or screening of signal wiring. This may result in mains frequency or radio frequency pickup contaminating the required signal.

See also: Acoustics, Broadband Noise, Mains Noise, Noise Pollution, Random Noise, Self Noise, Sound, Vehicle Noise.