In the science of acoustics, noise is unwanted sound.
As far as humans are concerned this is a subjective definition: people
vary in their sensitivity to noise; many sounds are agreeable to some
and noisy to others. Blasts or explosions can cause sudden damage to
the ear and prolonged exposure to impulsive
sounds such as those of a pneumatics drill can cause gradual hearing impairment. In general, any sound that is annoying, interferes with
speech, or reduces concentration or work efficiency may be considered
|Decibel levels associated with various common
sources of noise
From a physical viewpoint, sound waves (either in air or vibrations
in solid bodies) that mask required signals or cause fatigue or breakdown
of equipment or structures are noise and should be minimized. In air,
sound is radiated spherically from its source as a compressional wave,
being partly reflected, absorbed, or transmitted on hitting an obstacle.
Noise is usually a non-periodic sound wave, as opposed to a periodic
pure musical tone or sine-wave combination. It is characterized by its
intensity (measured in decibels), frequency,
and spatial variation; a sound level meter and frequency analyzer measure
Noise may be controlled at source (e.g., by a muffler), between it and
the listener (e.g., by sound absorbing material), or at the listener
(e.g., by wearing earplugs).
- In electronics, noise is an unwanted or
interfering current or voltage in an electrical device or system. Its presence in the amplifying circuits
of radios, television receivers, etc., may mask or distort signals.
Unpredictable random noise exists exists in any component with resistance because of the thermal motion of the current-carrying electrons,
and in electron tubes due to random cathode emission. Thermal radiations
and vibrations in the atmosphere also cause random noise. Nonrandom
noise arises from spurious oscillations and unintended couplings between
- In general science, noise is the random
fluctuations that are always associated with a measurement that is repeated
many times over. Noise appears in astronomical images as fluctuations
in the image background. These fluctuations do not represent any real
sources of light in the sky, but rather are caused by the imperfections
of the telescope. If the noise is too high, it may obscure the dimmest
objects within the field of view.