# Noise (spectral phenomenon)

Noise is any type of random, troublesome, problematic, or unwanted signals.
Acoustic noise may mar aesthetic experience, such as attending a concert hall. It may also be a medical issue inherent in the biology of hearing.
In technology, noise is unwanted signals in a device or apparatus, commonly of an electrical nature. The nature of noise is much studied in mathematics and is a prominent topic in statistics.
This article provides a survey of specific topics linked to their primary articles.

## Acoustic noise
### In transportation

* Aircraft noise
* Jet noise, caused by high-velocity jets and turbulent eddies
* Noise and vibration on maritime vessels
* Noise, vibration, and harshness, quality criteria for vehicles
* Traffic noise, including roadway noise and train noise

### Other acoustic noise

* Artificial noise, in spectator sports
* Background noise, in acoustics, any sound other than the monitored one
* Comfort noise, used in telecommunications to fill silent gaps
* Grey noise, random noise with a psychoacoustic adjusted spectrum
* Industrial noise, relevant to hearing damage and industrial hygiene
* Noise pollution, that affects negatively the quality of life

## Noise in biology

* Cellular noise, in biology, random variability between cells
* Developmental noise, variations among living beings with the same genome
* Neuronal noise, in neuroscience
* Synaptic noise, in neuroscience
* Transcriptional noise, in biochemistry, errors in genetic transcription

## Noise in computer graphics

Noise in computer graphics refers to various pseudo-random functions used to create textures, including:
* Gradient noise, created by interpolation of a lattice of pseudorandom gradients
** Perlin noise, a type of gradient noise developed in 1983
* Simplex noise, a method for constructing an n-dimensional noise function comparable to Perlin noise
* Simulation noise, a function that creates a divergence-free field
* Value noise, created by interpolation of a lattice of pseudorandom values; differs from gradient noise
* Wavelet noise, an alternative to Perlin noise which reduces problems of aliasing and detail loss
* Worley noise, a noise function introduced by Steven Worley in 1996

## Noise in electronics and radio

* Noise (signal processing), various types of interference
** Noise (electronics), related to electronic circuitry
*** Ground noise, appearing at the ground terminal of audio equipment
** Image noise, related to digital photography
** Noise (radio), interference related to radio signals
*** Atmospheric noise, radio noise caused by lightning
*** Cosmic noise, radio noise from outside the Earth's atmosphere
** Noise (video), "snow" on video or television pictures

## Noise in mathematics

* Any one of many statistical types or colors of noise, such as
** White noise, which has constant power spectral density
** Gaussian noise, with a probability density function equal to that of the normal distribution
** Pink noise, with spectral density inversely proportional to frequency
** Brownian noise or "brown" noise, with spectral density inversely proportional to the square of frequency
* Pseudorandom noise, in cryptography, artificial signal that can pass for random
* Statistical noise, a colloquialism for recognized amounts of unexplained variation in a sample
* Shot noise, noise which can be modeled by a Poisson process
* Noise-based logic, where logic values are different stochastic processes
* Noise print, a statistical signature of ambient noise, used in its suppression

## Other types of noise

* Electrochemical noise, electrical fluctuations in electrolysis, corrosion, etc.
* Phonon noise, in materials science
* Seismic noise, random tremors of the ground

## Measures of noise intensity

* Noise figure, the ratio of the output noise power to attributable thermal noise
* Ambient noise level, the background sound pressure level at a given location
* Noise power, with several related meanings
* Noise spectral density, N$_o$ measured in Watt/Hertz
* Noise temperature, temperature that would produce equivalent semiconductor noise