Noise

This article is about noise as an unwanted acoustic phenomenon. For other uses, see Noise (disambiguation).
NASA researchers at Glenn Research Center conducting tests on aircraft engine noise in 1967

Noise is a variety of sound. It means any unwanted sound. 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 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 sometimes complain about the faint and tinny sounds emanating from the headphones or earbuds of somebody listening to a portable audio player; at the other the sound of very loud music, a jet engine at close quarters, etc. can cause irreversible hearing damage. At intermediate levels there are a range of deleterious health effects from noise. This "intolerable corruption of human space" can be called noise pollution.[1] A claim made by Luigi Russolo in his article, The Joys of Noise is that noise has become so prominent that pure sound no longer exists.[2]

Roland Barthes also observes that noise can be perceived either physiologically or psychologically. We perceive noise physiologically when we "hear" it. On the other hand, when we "listen" to a noise we are doing this psychologically.[1] When we perceive a physiological noise we subconsciously feel the vibrations of the noise (sound) waves with our particles in our physical body whereas psychological noise refers to noise that is perceived when our conscious awareness shifts its attention to that noise rather than letting it filter through our subconscious where it goes unnoticed.

Sound intensity follows an inverse square law with distance from the source; doubling the distance from a noise source reduces its intensity by a factor of four, or 6 dB.

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.

Underwater noise is one of 11 Descriptors of Good Environmental Status according to the EU's Marine Strategy Framework Directive.[3]

Recording and reproduction noise

White Noise
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In audio, recording, and broadcast systems audio noise refers to the residual low level sound (usually hiss and hum) that is heard in quiet periods of programme. This is also known as white noise according to the Merriam Webster Definition.[4] There is a similar phenomena to "white noise" which emanates not only from audio recording equipment but from everything and more particularly, musical instruments (whether they are acoustic or electric). These noises are "impurities." When an instrument plays a pitch, even the most beautiful sounding instruments, there is noise (consisting of impurities) projected. Henry Cowell claims that technological advancements have brought machines closer to diminishing these unwanted noises, but have not been completely successful thus far.[5]

In audio engineering 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 or ITU-R 468 weighting.

Interfering noise

Interfering noises (or interfering sounds) are sounds with a negative sound quality, that is, the sound event leads to a hearing event, which is perceived as unpleasant, disturbing and interfering. This sound event usually releases negative associations as regards the suitability of the product and it is on the whole perceived as not matching the product.

Definition

A noise can be characterised as interfering, if it fulfils at least one of the following conditions:

There is a multiplicity of parameters which play a role in the definition of sound quality. The definition considers the psychologically important distinction between disturbing and function sounds. Function sounds are sounds such as the often desired full sound of an engine. In addition, there is trend in the automotive industry that a complete acoustic insulation is not desirable from the point of view of the customer.

Emergence of interfering noises

Interfering noises are a result of a relative motion at contact points. For the occurrence of interfering sounds two conditions must be fulfilled together:

A cause of interfering sounds occurring predominantly in the car interior is the relative motion of different construction parts to each other. Motion is usually caused by the vibration of the car when driving. Interference sound develops at contact points. If two parts touch one another or rub against each other, then interference sound can develop. Therefore the search for the core causes of interfering sounds is closely related to the search for relevant contact points.

All critical contact points can be isolated and marked on the basis of factors such as previous experience, surveys by quality-specialists from car manufacturing and surveys by specialists of interference acoustics. Here, additionally, construction designs, pictures, drafts (and whatever is otherwise available) are used, in order to represent the problem visually. Videos from previous experience are particularly important thereby because they address the audiovisual part of the human brain and are therefore particularly efficient to make specialists aware of problems.

Characterization of the interfering noise level

An interfering noise doesn't necessarily have to be loud. A mosquito can produce considerable disturbing sound, although it is comparatively quiet with a volume of only approx. 30 dB(A). An orchestra, by contrast, might produce very pleasant sounds, even if its volume amounts to nearly 90 dB(A). The final of an opera can be just as loud as heavy motorway noise. People differentiates unconsciously between good and bad sounds. Each sound signals a message, which, if perceived as disturbing, can then become the problem. It is thus the human mind and not the hearing, which decides whether a noise is felt as disturbing or pleasant. The human hearing can rather be seen as registering the pressure waves and frequencies of sound just like a physical measuring instrument. Stick-slip noises rank first in the hit-list of the most interfering sounds. Examples are sounds such as squeaking, creaking and grinding sounds.

See also

References

  1. 1 2 Listening Roland Barthes. The Responsibilities of Farms: Critical Essays on Music, Art and Representation. NY: Hill and Wang 1985.
  2. ↑ [The Art of Noises: futurist manifesto Luigi Russolo Audioculture page 11, 2004.
  3. ↑ "Our Oceans, Seas and Coasts". europa.eu.
  4. ↑ http://www.merriam-webster.com/dictionary/white%20noise,
  5. ↑ The Joys of Noise Henry Cowell. Audioculture 2004 page 22

Further reading

External links

Look up noise in Wiktionary, the free dictionary.
Wikiquote has quotations related to: Sound
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