NOISE

Sound is an essential form of human communication. However, unwanted sounds, or noise, can lead to a variety of medical problems, including deafness and elevated blood pressure; there is also evidence for an increased pulse rate. There is some evidence suggesting that environmental noise may affect the learning ability of children.

Sound waves are generated by vibrations moving through the air, and they are perceived through a complex interaction of vibrations hitting the inner ear. External vibrations are translated, through bones, into additional vibrations, which are then picked up by hair-like structures in the inner ear. These vibrations are further translated into neurologic signals, which are registered in the brain and received as intelligible information.

Noise can be normal sounds that get in the way of being able to perceive wanted sounds. Sound is measured in units called decibels, and the human ear is well-designed to perceive and interpret sounds at low decibel levels and across a wide spectrum of vibration. Sounds that are too loud, however, can damage the ability of the ear to make sense of what is perceived. A graphic measurement of what one can hear is called an audiogram, and hearing loss can be traced on audiograms. There is some hearing loss that is considered normal with aging, called presbycusis. Additional hearing loss and other physiological damage, may result from excessive loud noise.

There is some controversy as to what level of sound is too high, particularly in workplaces. It is thought that the maximal tolerable noise level for an eight-hour workplace exposure is about seventy-five decibels. The current allowable standard is eighty-five decibels. The standard was decreased from the previous ninety decibel level after a hard-fought battle to try and prevent a significant number of cases of hearing loss. At eighty-five decibels, hearing protection and noise monitoring becomes mandatory. There are several ways that noise can be reduced, either through changes in noise-making equipment itself, or by providing personal protective equipment to individuals who must work in noisy environments. The two basic types of personal protection are earplugs and earmuffs. Earmuffs, which can be put on and taken off more easily, are useful where the noise may be intermittent, such as at airports. Earplugs are more practical for people who spend considerable continuous periods of time in noisy environments.

In addition to noisy workplace environments, there are certain general environments where noise may be a particular problem. Among these are subway systems, where passengers may be intermittently exposed to high noise levels, and in communities located near airports. Over time there has been a considerable effort to diminish the noise around airports, both through the use of quieter engines and through changes in flight paths. In some extreme situations, homes have been bought and people moved out of flight paths near airports to help reduce the risk and annoyance associated with such noise.

Arthur L. Frank

(see also: Hearing Disorders; Hearing Protection; Occupational Safety and Health )

Bibliography

Moller, A. G. (1992). "Noise as a Health Hazard." In Public Health and Preventive Medicine, 13th edition, eds. J. M. Last and R. M. Wallace. Norwalk, CT: Appleton and Lange.

noise / noiz/ • n. 1. a sound, esp. one that is loud or unpleasant or that causes disturbance: making a noise like a pig in a trough | what's that rustling noise outside the door? ∎  a series or combination of loud, confused sounds, esp. when causing disturbance: dazed with the heat and noise | vibration and noise from traffic. ∎  (noises) conventional remarks or other sounds that suggest some emotion or quality: Clarissa made encouraging noises.2. technical irregular fluctuations that accompany a transmitted electrical signal but are not part of it and tend to obscure it. ∎  random fluctuations that obscure or do not contain meaningful data or other information: over half the magnitude of the differences came from noise in the data.• v. [tr.] (usu. be noised about) dated talk about or make known publicly: you've discovered something that should not be noised about. ∎  [intr.] poetic/lit. make much noise.

noise Any signal that occurs in an electronic or communication system and is considered extraneous to the desired signal being propagated. Noise can be introduced, for example, by external disturbances and may be deleterious in a given system since it can produce spurious signals, i.e. errors.

The noise immunity is a measure of the magnitude of external disturbances that a digital circuit can tolerate without producing errors. Logic values are represented electronically by two different voltage levels. Any noise introduced into logic circuitry by external disturbances is added (or subtracted) from the real digital logic signal. The noise margin is the maximum noise voltage that can be added or subtracted from the logic signal before a threshold voltage for a logic state is passed. See also impulse noise, white noise, Gaussian noise.

noise loud outcry; †rumour; loud or harsh sound XIII; †agreeable sound XIV; †band of musicians XVI. — (O)F. noise outcry, disturbance, noisy dispute :- L. nausea sea-sickness, NAUSEA.
Hence (or — OF.) vb. XIV. noisy XVII.

noise A signal that conveys no useful information (e.g. background sound that makes it difficult to hear a conversation). If the useful signal comprises data that are being recorded, random (white) noise can be reduced by summing the recorded signals; incoherent noise is effectively damped out and the coherent signal is enhanced, thus improving the signal-to-noise ratio.