Noise

Noise

Overview
In common use, the word noise means any unwanted sound
Sound
Sound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations.-Propagation of...

. In both analog and digital electronics, noise
Noise (electronics)
Electronic noise is a random fluctuation in an electrical signal, a characteristic of all electronic circuits. Noise generated by electronic devices varies greatly, as it can be produced by several different effects...

 is random unwanted perturbation to a wanted signal; it is called noise as a generalisation of the acoustic noise ("static") heard when listening to a weak radio
Radio
Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...

 transmission with significant electrical noise. Signal noise is heard as acoustic noise if the signal is converted into sound (e.g., played through a loudspeaker
Loudspeaker
A loudspeaker is an electroacoustic transducer that produces sound in response to an electrical audio signal input. Non-electrical loudspeakers were developed as accessories to telephone systems, but electronic amplification by vacuum tube made loudspeakers more generally useful...

); it manifests as "snow
Noise (video)
Noise, in analog video and television, is a random dot pattern of static displayed when no transmission signal is obtained by the antenna receiver of television set and other display devices...

" on a television
Television
Television is a telecommunication medium for transmitting and receiving moving images that can be monochrome or colored, with accompanying sound...

 or video
Video
Video is the technology of electronically capturing, recording, processing, storing, transmitting, and reconstructing a sequence of still images representing scenes in motion.- History :...

 image.
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Quotations

A sound does not view itself as thought, as ought, as needing another sound for its elucidation, as etc.; it has not time for any consideration--it is occupied with the performance of its characteristics: before it has died away it must have made perfectly exact its frequency, its loudness, its length, its overtone structure, the precise morphology of these and of itself.

John Cage (1955), quoted in Classic Essays on Twentieth-Century Music, ISBN 0028645812

Music has no subject beyond the combinations of notes we hear, for music speaks not only by means of sounds, it speaks nothing but sound.

Eduard Hanslick, quoted by Wolfgang Sandberger (1996) in the liner notes to the Juilliard String Quartet's Intimate Letters. Sony Classical SK 66840.

You know the sound of two hands clapping; tell me, what is the sound of one hand?

Hakuin Ekaku (1686-1769). The phrase is a Kōan|Kōan, an irrational comment used in Zen|Zen Buddhism in order to assist practitioners in reaching enlightenment.

Could we not imagine that noise...is itself nothing more than the sum of a multitude of different sounds which are being heard simultaneously?

Jean-Jacques Rousseau, Dictionnaire de Musique (1767)

If a tree falls in a forest, and no-one is around to hear it, does it make a noise?

Source unknown, but apparently originating in the twentieth century; a 1910 physics book asks "When a tree falls in a lonely forest, and no animal is near by to hear it, does it make a sound? Why?" Charles Riborg Mann, George Ransom Twiss, Physics (1910), p. 235. See also: If a tree falls in a forest|If a tree falls in a forest.
Encyclopedia
In common use, the word noise means any unwanted sound
Sound
Sound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations.-Propagation of...

. In both analog and digital electronics, noise
Noise (electronics)
Electronic noise is a random fluctuation in an electrical signal, a characteristic of all electronic circuits. Noise generated by electronic devices varies greatly, as it can be produced by several different effects...

 is random unwanted perturbation to a wanted signal; it is called noise as a generalisation of the acoustic noise ("static") heard when listening to a weak radio
Radio
Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...

 transmission with significant electrical noise. Signal noise is heard as acoustic noise if the signal is converted into sound (e.g., played through a loudspeaker
Loudspeaker
A loudspeaker is an electroacoustic transducer that produces sound in response to an electrical audio signal input. Non-electrical loudspeakers were developed as accessories to telephone systems, but electronic amplification by vacuum tube made loudspeakers more generally useful...

); it manifests as "snow
Noise (video)
Noise, in analog video and television, is a random dot pattern of static displayed when no transmission signal is obtained by the antenna receiver of television set and other display devices...

" on a television
Television
Television is a telecommunication medium for transmitting and receiving moving images that can be monochrome or colored, with accompanying sound...

 or video
Video
Video is the technology of electronically capturing, recording, processing, storing, transmitting, and reconstructing a sequence of still images representing scenes in motion.- History :...

 image. High noise levels can block, distort, change or interfere with the meaning of a message in human, animal and electronic communication.

In signal processing
Signal processing
Signal processing is an area of systems engineering, electrical engineering and applied mathematics that deals with operations on or analysis of signals, in either discrete or continuous time...

 or computing it can be considered random unwanted data
Data
The term data refers to qualitative or quantitative attributes of a variable or set of variables. Data are typically the results of measurements and can be the basis of graphs, images, or observations of a set of variables. Data are often viewed as the lowest level of abstraction from which...

 without meaning; that is, data that is not being used to transmit a signal, but is simply produced as an unwanted by-product of other activities. "Signal-to-noise ratio
Signal-to-noise ratio
Signal-to-noise ratio is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. It is defined as the ratio of signal power to the noise power. A ratio higher than 1:1 indicates more signal than noise...

" is sometimes used to refer to the ratio of useful to irrelevant information in an exchange.

In biology, noise can describe the variability of a measurement around the mean, for example transcriptional noise
Transcriptional noise
A primary cause of the variability in gene expression occurring between cells in isogenic populations . A major source of transcriptional noise is likely to be transcriptional bursting although other sources of heterogeneity, such as unequal separation of cell contents at mitosis are also likely...

 describes the variability in gene activity between cells in a population.

In many cases, the special case of thermal noise arises, which sets a fundamental lower limit to what can be measured or signaled and is related to basic physical processes described by thermodynamics
Thermodynamics
Thermodynamics is a physical science that studies the effects on material bodies, and on radiation in regions of space, of transfer of heat and of work done on or by the bodies or radiation...

, some of which are expressible by simple formulae.

In some fields, noise means unwanted information or data that is not relevant to the hypothesis or theory being investigated or tested.

Acoustic noise


In relation to sound, noise is not necessarily random. Sounds, particularly loud ones, that disturb people or make it difficult to hear wanted sounds, are noise. For example, conversations of other people may be called noise by people not involved in any of them; any unwanted sound such as domesticated dogs barking, neighbours playing loud music, portable mechanical saws, road traffic sounds, or a distant aircraft in quiet countryside, is called noise.

Acoustic noise can be anything from quiet but annoying to loud and harmful. At one extreme users of public transport
Public transport
Public transport is a shared passenger transportation service which is available for use by the general public, as distinct from modes such as taxicab, car pooling or hired buses which are not shared by strangers without private arrangement.Public transport modes include buses, trolleybuses, trams...

 sometimes complain about the faint and tinny sounds emanating from the headphones or earbuds of somebody listening to a portable audio player
Portable audio player
A portable audio player is a personal mobile device that allows the user to listen to recorded audio while mobile. Sometimes a distinction is made between a portable player, battery-powered and with one or more small loudspeakers, and a personal player, listened to with earphones.-History:Portable...

; at the other the sound of very loud music, a jet engine
Jet engine
A jet engine is a reaction engine that discharges a fast moving jet to generate thrust by jet propulsion and in accordance with Newton's laws of motion. This broad definition of jet engines includes turbojets, turbofans, rockets, ramjets, pulse jets...

 at close quarters, etc. can cause permanent irreversible hearing damage.

Regulation of acoustic noise


Noise regulation includes statutes or guidelines relating to sound transmission established by national, state or provincial and municipal levels of government. After a watershed passage of the U.S. Noise Control Act of 1972[1], the program was abandoned at the federal level, under President Ronald Reagan, in 1981 and the issue was left to local and state governments. Although the UK and Japan enacted national laws in 1960 and 1967 respectively, these laws were not at all comprehensive or fully enforceable as to address (a) generally rising ambient noise (b) enforceable numerical source limits on aircraft and motor vehicles or (c) comprehensive directives to local government.

Acoustic noise in film sound


For film sound theorists and practitioners at the advent of talkies c.1928/1929, noise was non-speech sound or natural sound, and for many of them, noise (especially asynchronous use with image) was desired over the evils of dialogue synchronized to moving image. The director and critic René Clair
René Clair
René Clair born René-Lucien Chomette, was a French filmmaker.-Biography:He was born in Paris and grew up in the Les Halles quarter. He attended the Lycée Montaigne and the Lycée Louis-le-Grand. During World War I, he served as an ambulance driver. After the war, he started a career as a journalist...

 writing in 1929 makes a clear distinction between film dialogue and film noise and very clearly suggests that noise can have meaning and be interpreted: "...it is possible that an interpretation of noises may have more of a future in it. Sound cartoons, using "real" noises, seem to point to interesting possibilities".
Alberto Cavalcanti uses noise as a synonym for natural sound
and as late as 1960, Siegfried Kracauer was referring to noise as non-speech sound.

Audio noise


In audio, recording, and broadcast
Broadcasting
Broadcasting is the distribution of audio and video content to a dispersed audience via any audio visual medium. Receiving parties may include the general public or a relatively large subset of thereof...

 systems audio noise refers to the residual low level sound (usually hiss and hum) that is heard in quiet periods of programme.

In audio engineering
Audio engineering
An audio engineer, also called audio technician, audio technologist or sound technician, is a specialist in a skilled trade that deals with the use of machinery and equipment for the recording, mixing and reproduction of sounds. The field draws on many artistic and vocational areas, including...

 it can also refer to the unwanted residual electronic noise signal that gives rise to acoustic noise heard as "hiss". This signal noise is commonly measured using A-weighting
A-weighting
A Weighting curve is a graph of a set of factors, that are used to 'weight' measured values of a variable according to their importance in relation to some outcome. The most commonly known example is frequency weighting in sound level measurement where a specific set of weighting curves known as A,...

 or ITU-R 468 weighting
ITU-R 468 noise weighting
ITU-R 468 is a standard relating to noise measurement, widely used when measuring noise in audio systems. The standard defines a weighting filter curve, together with a quasi-peak rectifier having special characteristics as defined by specified tone-burst tests...


Noise reduction with distance


Sound intensity follows an inverse square law with distance from the source; doubling the distance from a noise source reduces it by 6 dB. This is also called the Rule of 6. This is based on the fact that the equation to calculate noise attenuation at a distance , knowing the SPL at distance is given by,
where d is the distance. If the distance is doubled, the equation simplifies to , which equals 6.02 dB (or approximately 6 dB).

Electronic noise


Electronic noise exists in all circuits and devices as a result of thermal noise, also referred to as Johnson Noise. It is caused by random variations in current
Electric current
Electric current is a flow of electric charge through a medium.This charge is typically carried by moving electrons in a conductor such as wire...

 or voltage
Voltage
Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...

 caused by the random movement of charge carriers (usually electrons) carrying the current as they are jolted around by thermal energy. Thermal noise can be reduced by reducing the temperature of the circuit. This phenomenon limits the minimum signal level that any radio receiver can usefully respond to, because there will always be a small but significant amount of thermal noise arising in its input circuits. This is why radio telescopes, which search for very low levels of signal from space, use front-end low-noise amplifier
Low-noise amplifier
Low-noise amplifier is an electronic amplifier used to amplify possibly very weak signals . It is usually located very close to the detection device to reduce losses in the feedline. This active antenna arrangement is frequently used in microwave systems like GPS, because coaxial cable feedline is...

 circuits cooled with liquid nitrogen
Liquid nitrogen
Liquid nitrogen is nitrogen in a liquid state at a very low temperature. It is produced industrially by fractional distillation of liquid air. Liquid nitrogen is a colourless clear liquid with density of 0.807 g/mL at its boiling point and a dielectric constant of 1.4...

.

There are several other sources of noise in electronic circuits such as shot noise
Shot noise
Shot noise is a type of electronic noise that may be dominant when the finite number of particles that carry energy is sufficiently small so that uncertainties due to the Poisson distribution, which describes the occurrence of independent random events, are of significance...

, seen in very low-level signals where the finite number of energy-carrying particles becomes significant, or flicker noise
Flicker noise
Flicker noise is a type of electronic noise with a 1/ƒ, or pink power density spectrum. It is therefore often referred to as 1/ƒ noise or pink noise, though these terms have wider definitions...

 (1/f noise) in semiconductor devices.

Visual noise


Noise is also present in images. Electronic noise will be present in camera sensors, and the physical size of the grains of film emulsion creates visual noise. This kind of noise is referred to as "grain."

Noise is also used in the creation of 2D and 3D images by computer. Sometimes noise is added to images to hide the sudden transitions inherent in digital representation of color, known as "banding". This adding of noise is referred to as "dithering." Sometimes noise is used to create the subject matter itself. Procedural noise (such as Perlin noise
Perlin noise
Perlin noise is a computer-generated visual effect developed by Ken Perlin, who won an Academy Award for its use in the motion picture Tron...

) is often used to create natural-looking variation in computer generated images.

Vibrational noise


The Earth ground and the built environment are subjected to permanent vibrations commonly referred to as seismic noise but nowadays preferably called Ambient Vibrations
Ambient Vibrations
Various types of vibration sources are always producing so called Ambient Vibrations on the Earth ground . These vibrations are mostly surface waves propagating on the surface. Low frequency waves are generally called microseisms and high frequency waves are called microtremors...

. These vibrations have natural (ocean waves, wind...) and anthropogenic (traffic, machines...) origins depending on the considered frequency range. These vibrations may be disturbing for people (housing close to railway tracks...) and even cause solidian noise (acoustic noise created by particular vibrations of solids like rooms) but they are also used (recorded) to characterize the structures (civil engineering structure, underground) they are shaking in terms of dynamic properties and eventually physical properties.

Noisy genes


The activity and regulation of our genes are also subject to noise. Transcriptional noise refers to the variability in gene activity between cells in genetically identical populations (even identical twins are non-identical). Noise in gene activity has tremendous consequences on cell behaviour, and must be mitigated or integrated. Noise impacts upon the effectiveness of clinical treatment, with resistance of bacteria to antibiotics demonstrably caused by non-genetic differences. Variability in gene expression may also contribute to resistance of sub-populations of cancer cells to chemotherapy. In certain contexts, such as the survival of microbes in rapidly changing stressful environments, or several types of scattered differentiation, noise may be essential.

See also

  • Association of Noise Consultants
    Association of Noise Consultants
    The Association of Noise Consultants is a UK based organisation of companies that are engaged in the business of acoustics, noise and vibration consulting.-Overview:There is a great range of specialisations within the ANC...

  • Background noise
    Background noise
    In acoustics and specifically in acoustical engineering, background noise or ambient noise is any sound other than the sound being monitored. Background noise is a form of noise pollution or interference. Background noise is an important concept in setting noise regulations...

  • Noise and vibration on maritime vessels
    Noise and vibration on maritime vessels
    Noise and vibration on maritime vessels are not the same but they have the same origin and come in many forms. The methods to handle the related problems are similar, to a certain level, where most shipboard noise problems are reduced by controlling vibration....

  • Noise (music)
  • Noise pollution
    Noise pollution
    Noise pollution is excessive, displeasing human, animal or machine-created environmental noise that disrupts the activity or balance of human or animal life...

  • Silence
    Silence
    Silence is the relative or total lack of audible sound. By analogy, the word silence may also refer to any absence of communication, even in media other than speech....


External links