Noise 41415 225629970 2008-07-14T17:13:58Z 217.187.184.94 \m {{this|noise as in sound|Noise (disambiguation)}} In common use, the word '''noise''' means unwanted [[sound]] or [[noise pollution]]. In [[electronics]] noise can refer to the electronic signal corresponding to acoustic noise (in an audio system) or the electronic signal corresponding to the (visual) noise commonly seen as '[[Noise (video)|snow]]' on a degraded [[television]] or [[video]] image. In signal processing or computing it can be considered [[data]] without meaning; that is, data that is not being used to transmit a [[Signaling (telecommunication)|signal]], but is simply produced as an unwanted by-product of other activities. In [[Information Theory]], however, noise is still considered to be [[information]]. In a broader sense, film grain or even advertisements in web pages can be considered noise. Noise can block, distort, or change the meaning of a message in both human and electronic communication. In many of these areas, 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 at the molecular level described by well-established [[thermodynamics]] considerations, some of which are expressible by relatively well known simple formulae. === Acoustic noise === When speaking of noise in relation to sound, what is commonly meant is meaningless sound of greater than usual volume. Thus, a loud activity may be referred to as ''noisy''. However, conversations of other people may be called noise for people not involved in any of them, and noise can be any unwanted sound such as the noise of dogs barking, neighbours playing loud music, road traffic sounds, chainsaws, or aircraft, spoiling the quiet of the countryside. 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 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" ('The Art of Sound' (1929)). Alberto Cavalcanti uses noise as a synonym for natural sound ('Sound in Films' (1939)) and as late as 1960, Siegfried Kracauer was referring to noise as non-speech sound ('Dialogue and Sound' (1960)). === Audio noise === {{Main|Colors of noise}} In audio, recording, and [[Broadcasting|broadcast]] 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]] it can also refer to the unwanted residual [[noise (electronic)|electronic noise]] signal that gives rise to acoustic noise heard as 'hiss'. This signal noise is commonly measured using [[A-weighting]] or [[ITU-R 468 noise weighting|ITU-R 468 weighting]] === Electronic noise === {{Main|Electronic noise}} [[Noise (electronic)|Electronic noise]] exists in all circuits and devices as a result of thermal noise, also referred to as [[Johnson Noise]]. Semiconductor devices can also contribute [[flicker noise]] and [[generation-recombination noise]]. In any [[electronic circuit]], there exist [[random]] variations in [[Electric current|current]] or [[voltage]] caused by the random movement of the electrons carrying the current as they are jolted around by thermal energy. Lower temperature results in lower [[thermal noise]]. This same 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 [[stars]], use [[front-end]] [[low-noise amplifier]] circuits, usually mounted on the [[parabolic reflector|aerial dish]], and cooled with [[liquid nitrogen]]. == See also == *[[Association of Noise Consultants]] *[[Noise regulations]] == External links == {{wiktionary}} {{wikiquote|Sound}} *[http://www.who.int/docstore/peh/noise/guidelines2.html Guidelines for Community Noise, World Health Organization, 1999] *[http://www.aercoustics.com/ Aercoustics Engineering Limited]. ''Consultants in Acoustics, Noise and Vibration'' *[http://www.lindos.co.uk/cgi-bin/FlexiData.cgi?SOURCE=Articles Audio Measuring Articles - Electronics] *[http://www.ieee.li/pdf/viewgraphs_mohr_noise.pdf Mohr on Receiver Noise: Characterization, Insights & Surprises] *[http://www.ieee.li/pdf/viewgraphs_noise.pdf Fundamentals of Electrical Noise] *[http://www.sengpielaudio.com/calculator-noise.htm Noise voltage - Calculation and Measuring of Thermal Noise] *[http://osha.europa.eu/topics/noise Noise at work] European Agency for Safety and Health at Work ([[EU-OSHA]]) [[Category:Noise]] [[Category:Noise pollution]] [[Category:Sound]] [[af:Geraas]] [[ca:Soroll]] [[cs:Hluk]] [[da:Støj]] [[de:Geräusch]] [[es:Ruido (sonido)]] [[eo:Bruo]] [[ko:노이즈]] [[id:Derau]] [[it:Rumore (acustica)]] [[he:רעש]] [[lt:Triukšmas]] [[nl:Ruis (signaal)]] [[ja:ノイズ]] [[no:Støy]] [[nn:Støy]] [[pl:Szum akustyczny]] [[pt:Ruído]] [[ru:Шум]] [[simple:Noise]] [[sk:Hluk]] [[sl:Šum]] [[fi:Melu]] [[sv:Brus]] [[uk:Шум]] [[zh:噪声]]