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NASA researchers at Glenn Research Center conducting tests on aircraft engine noise in 1967 Noise Research Program on Hangar Apron - GPN-2000-001457.jpg
NASA researchers at Glenn Research Center conducting tests on aircraft engine noise in 1967

Noise is unwanted sound considered unpleasant, loud or disruptive to hearing. From a physics standpoint, noise is indistinguishable from desired sound, as both are vibrations through a medium, such as air or water. The difference arises when the brain receives and perceives a sound. [1] [2]


Acoustic noise is any sound in the acoustic domain, either deliberate (e.g., music or speech) or unintended. In contrast, noise in electronics may not be audible to the human ear and may require instruments for detection. [3]

In audio engineering, noise can refer to the unwanted residual electronic noise signal that gives rise to acoustic noise heard as a hiss. This signal noise is commonly measured using A-weighting [4] or ITU-R 468 weighting. [5]

In experimental sciences, noise can refer to any random fluctuations of data that hinders perception of a signal. [6] [7]


Sound is measured based on the amplitude and frequency of a sound wave. Amplitude measures how forceful the wave is. The energy in a sound wave is measured in decibels (dB), the measure of loudness, or intensity of a sound; this measurement describes the amplitude of a sound wave. Decibels are expressed in a logarithmic scale. On the other hand, pitch describes the frequency of a sound and is measured in hertz (Hz). [8]

The main instrument to measure sounds in the air is the Sound Level Meter. There are many different varieties of instruments that are used to measure noise - Noise Dosimeters are often used in occupational environments, noise monitors are used to measure environmental noise and noise pollution, and recently smartphone-based sound level meter applications (apps) [9] are being used to crowdsource and map recreational and community noise. [10] [11] [12]

A-weighting is applied to a sound spectrum to represent the sound that humans are capable of hearing at each frequency. Sound pressure is thus expressed in terms of dBA. 0 dBA is the softest level that a person can hear. Normal speaking voices are around 65 dBA. A rock concert can be about 120 dBA.

Recording and reproduction

In audio, recording, and broadcast systems, audio noise refers to the residual low-level sound (four major types: hiss, rumble, crackle, and hum) that is heard in quiet periods of program. This variation from the expected pure sound or silence can be caused by the audio recording equipment, the instrument, or ambient noise in the recording room. [13]

In audio engineering it can refer either to the acoustic noise from loudspeakers or 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

Noise is often generated deliberately and used as a test signal for audio recording and reproduction equipment.

Environmental noise

Environmental noise is the accumulation of all noise present in a specified environment. The principal sources of environmental noise are surface motor vehicles, aircraft, trains and industrial sources. [14] These noise sources expose millions of people to noise pollution that creates not only annoyance, but also significant health consequences such as elevated incidence of hearing loss and cardiovascular disease. [15] Urban noise is generally not of an intensity that causes hearing loss but it interrupts sleep, disturbs communication and interferes with other human activities. [16] There are a variety of mitigation strategies and controls available to reduce sound levels including source intensity reduction, land-use planning strategies, noise barriers and sound baffles, time of day use regimens, vehicle operational controls and architectural acoustics design measures.


Certain geographic areas or specific occupations may be at a higher risk of being exposed to constantly high levels of noise; regulation may prevent negative health outcomes. Noise regulation includes statutes or guidelines relating to sound transmission established by national, state or provincial and municipal levels of government. Environmental noise is governed by laws and standards which set maximum recommended levels of noise for specific land uses, such as residential areas, areas of outstanding natural beauty, or schools. These standards usually specify measurement using a weighting filter, most often A-weighting. [17] [18]

United States

In 1972, the Noise Control Act was passed to promote a healthy living environment for all Americans, where noise does not pose a threat to human health. This policy's main objectives were: (1) establish coordination of research in the area of noise control, (2) establish federal standards on noise emission for commercial products, and (3) promote public awareness about noise emission and reduction. [19] [20]

The Quiet Communities Act of 1978 promotes noise control programs at the state and local level and developed a research program on noise control. [21] Both laws authorized the Environmental Protection Agency to study the effects of noise and evaluate regulations regarding noise control. [22]

The National Institute for Occupational Safety and Health (NIOSH) provides recommendation on noise exposure in the workplace. [23] [24] In 1972 (revised in 1998), NIOSH published a document outlining recommended standards relating to the occupational exposure to noise, with the purpose of reducing the risk of developing permanent hearing loss related to exposure at work. [25] This publication set the recommended exposure limit (REL) of noise in an occupation setting to 85 dBA for 8 hours using a 3-dB exchange rate (every 3-dB increase in level, duration of exposure should be cut in half, i.e., 88 dBA for 4 hours, 91 dBA for 2 hours, 94 dBA for 1 hour, etc.). However, in 1973 the Occupational Safety and Health Administration (OSHA) maintained the requirement of an 8-hour average of 90 dBA. The following year, OSHA required employers to provide a hearing conservation program to workers exposed to 85 dBA average 8-hour workdays. [26]


The European Environment Agency regulates noise control and surveillance within the European Union. [27] The Environmental Noise Directive was set to determine levels of noise exposure, increase public access to information regarding environmental noise, and reduce environmental noise. [28] [29] Additionally, in the European Union, underwater noise is a pollutant according to the Marine Strategy Framework Directive (MSFD). [30] The MSFD requires EU Member States to achieve or maintain Good Environmental Status, meaning that the "introduction of energy, including underwater noise, is at levels that do not adversely affect the marine environment". [30]

Health effects

Earplugs can be used to protect the user's ears from loud noises. Bouchon d'oreille preforme.jpg
Earplugs can be used to protect the user's ears from loud noises.

Exposure to noise is associated with several negative health outcomes. Depending on duration and level of exposure, noise may cause or increase the likelihood of hearing loss, high blood pressure, ischemic heart disease, sleep disturbances, injuries, and even decreased school performance. [31] There are also causal relationships between noise and psychological effects such as annoyance, psychiatric disorders, and effects on psychosocial well-being. [31]

Noise exposure has increasingly been identified as a public health issue, especially in an occupational setting, as demonstrated with the creation of NIOSH's Noise and Hearing Loss Prevention program. [32] Noise has also proven to be an occupational hazard, as it is the most common work-related pollutant. [33] Noise-induced hearing loss, when associated with noise exposure at the workplace is also called occupational hearing loss.

Hearing loss prevention

While noise-induced hearing loss is permanent, it is also preventable. [34] Particularly in the workplace, regulations may exist limiting permissible exposure limit to noise. This can be especially important for professionals working in settings with consistent exposure to loud sounds, such as musicians, music teachers and audio engineers. [35] Examples of measures taken to prevent noise-induced hearing loss in the workplace include engineering noise control, the Buy-Quiet initiative, [36] [37] creation of the Safe-In-Sound award, and noise surveillance. [38]

Literary views

Roland Barthes distinguishes between physiological noise, which is merely heard, and psychological noise, which is actively listened to. Physiological noise is felt subconsciously as the vibrations of the noise (sound) waves physically interact with the body while psychological noise is perceived as our conscious awareness shifts its attention to that noise. [39]

Luigi Russolo, one of the first composers of noise music, [40] wrote the essay The Art of Noises. He argued that any kind of noise could be used as music, as audiences become more familiar with noises caused by technological advancements; noise has become so prominent that pure sound no longer exists. [41]

Henry Cowell claimed that technological advancements have reduced unwanted noises from machines, but have not managed so far to completely eliminate them. [42]

Felix Urban sees noise as a result of cultural circumstances. In his comparative study on sound and noise in cities, he points out that noise regulations are only one indicator of what is considered as harmful. It is the way in which people live and behave (acoustically) that determines the way how sounds are perceived. [43]

See also

Related Research Articles

Noise pollution Excessive, displeasing human, animal, or machine-created environmental noise

Noise pollution, also known as environmental noise or sound pollution, is the propagation of noise with ranging impacts on the activity of human or animal life, most of them harmful to a degree. The source of outdoor noise worldwide is mainly caused by machines, transport, and propagation systems. Poor urban planning may give rise to noise disintegration or pollution, side-by-side industrial and residential buildings can result in noise pollution in the residential areas. Some of the main sources of noise in residential areas include loud music, transportation, lawn care maintenance, construction, electrical generators, explosions, and people.

Occupational noise is the amount of acoustic energy received by an employee's auditory system when they are working in the industry. Occupational noise, or industrial noise, is often a term used in occupational safety and health, as sustained exposure can cause permanent hearing damage. Occupational noise is considered an occupational hazard traditionally linked to loud industries such as ship-building, mining, railroad work, welding, and construction, but can be present in any workplace where hazardous noise is present.

The permissible exposure limit is a legal limit in the United States for exposure of an employee to a chemical substance or physical agent such as high level noise. Permissible exposure limits are established by the Occupational Safety and Health Administration (OSHA). Most of OSHA's PELs were issued shortly after adoption of the Occupational Safety and Health (OSH) Act in 1970.

Earmuffs Ear-protecting headgear worn over ears to protect from cold or loud noise

Earmuffs are clothing accessories or PPE designed to cover a person's ears for hearing protection or for warmth. They consist of a thermoplastic or metal head-band, that fits over the top or back of the head, and a cushion or cup at each end, to cover the external ears.

In acoustics, noise measurement can be for the purpose of measuring environmental noise or measuring noise in the workplace. Applications include monitoring of construction sites, aircraft noise, road traffic noise, entertainment venues and neighborhood noise. One of the definitions of noise covers all "unwanted sounds". When sound levels reach a high enough intensity, the sound, whether it is wanted or unwanted, may be damaging to hearing. Environmental noise monitoring is the measurement of noise in an outdoor environment caused by transport, industry and recreational activities. The laws and limits governing environmental noise monitoring differ from country to country.

Noise control

Noise control or noise mitigation is a set of strategies to reduce noise pollution or to reduce the impact of that noise, whether outdoors or indoors.

Sound level meter

A sound level meter is used for acoustic measurements. It is commonly a hand-held instrument with a microphone. The best type of microphone for sound level meters is the condenser microphone, which combines precision with stability and reliability. The diaphragm of the microphone responds to changes in air pressure caused by sound waves. That is why the instrument is sometimes referred to as a sound pressure level meter (SPL). This movement of the diaphragm, i.e. the sound pressure deviation, is converted into an electrical signal. While describing sound in terms of sound pressure metrics, such as Pascals, is possible a logarithmic conversion is usually applied and the sound pressure level is stated instead, with 0 dB SPL equal to 20 micropascals.

Health effects from noise

Noise health effects are the physical and psychological health consequences of regular exposure to consistent elevated sound levels. Noise from traffic, in particular, is considered by the World Health Organization to be one of the worst environmental stressors for humans, second only to air pollution. Elevated workplace or environmental noise can cause hearing impairment, tinnitus, hypertension, ischemic heart disease, annoyance, and sleep disturbance. Changes in the immune system and birth defects have been also attributed to noise exposure.

Occupational hazard Hazard experienced in the workplace

An occupational hazard is a hazard experienced in the workplace. Occupational hazards can encompass many types of hazards, including chemical hazards, biological hazards (biohazards), psychosocial hazards, and physical hazards. In the United States, the National Institute for Occupational Safety and Health (NIOSH) conduct workplace investigations and research addressing workplace health and safety hazards resulting in guidelines. The Occupational Safety and Health Administration (OSHA) establishes enforceable standards to prevent workplace injuries and illnesses. In the EU a similar role is taken by EU-OSHA.

Noise-induced hearing loss Medical condition

Noise-induced hearing loss (NIHL) is hearing impairment resulting from exposure to loud sound. People may have a loss of perception of a narrow range of frequencies or impaired perception of sound including sensitivity to sound or ringing in the ears. When exposure to hazards such as noise occur at work and is associated with hearing loss, it is referred to as occupational hearing loss.

Ear protection Index of articles associated with the same name

Ear protection refers to devices used to protect the ear, either externally from elements such as cold, intrusion by water and other environmental conditions, debris, or specifically from noise. High levels of exposure to noise may result in noise-induced hearing loss. Measures to protect the ear are referred to as hearing protection, and devices for that purpose are called hearing protection devices. In the context of work, adequate hearing protection is that which reduces noise exposure to below 85 dBA over the course of an average work shift of eight hours. When sounds exceed 80 dBA, it becomes dangerous to the ears. The National Institute for Occupational Safety and Health (NIOSH) has standards that show how long a person can be in different loudness levels before the person reaches their maximum daily dose and becomes damaging to their hearing. These standards can give individuals an idea of when hearing protection should be considered. The maximum daily dose with the corresponding decibel level is shown below.

Physical hazard Hazard due to a physical agent

A physical hazard is an agent, factor or circumstance that can cause harm with contact. They can be classified as type of occupational hazard or environmental hazard. Physical hazards include ergonomic hazards, radiation, heat and cold stress, vibration hazards, and noise hazards. Engineering controls are often used to mitigate physical hazards.

Buy Quiet is an American health and safety initiative to select and purchase the lowest noise emitting power tools and machinery in order to reduce occupational and community noise exposure. Buy Quiet Programs are examples of noise control strategies. Buy Quiet is part of the larger Hearing Loss Prevention Program, and is an example of Prevention Through Design, which seeks to reduce occupational injury through prevention considerations in designs that impact workers.

Safe-In-Sound award

The Safe-in-Sound Excellence in Hearing Loss Prevention Award is an occupational health and safety award that was established in 2007 through a partnership between the National Institute for Occupational Safety and Health (NIOSH) and the National Hearing Conservation Association (NHCA). In 2018, the partnership was extended to include the Council for Accreditation in Occupational Hearing Conservation (CAOHC).

Occupational hearing loss

Occupational hearing loss (OHL) is hearing loss that occurs as a result of occupational hazards, such as excessive noise and ototoxic chemicals. Noise is a common workplace hazard, and recognized as the risk factor for noise-induced hearing loss and tinnitus, but it is not the only risk factor that can result in a work-related hearing loss. Also, noise-induced hearing loss can result from exposures that are not restricted to the occupational setting.

Engineering controls are strategies designed to protect workers from hazardous conditions by placing a barrier between the worker and the hazard or by removing a hazardous substance through air ventilation. Engineering controls involve a physical change to the workplace itself, rather than relying on workers' behavior or requiring workers to wear protective clothing.

Hearing protection device

A hearing protection device, also known as a HPD, is an ear protection device worn in or over the ears while exposed to hazardous noise to help prevent noise-induced hearing loss. HPDs reduce the level of the noise entering the ear. HPDs can also protect against other effects of noise exposure such as tinnitus and hyperacusis. There are many different types of HPDs available for use, including earmuffs, earplugs, electronic hearing protection devices, and semi-insert devices.

There are unique occupational health issues in the casino industry. The most common are from cancers resulting from exposure to second-hand tobacco smoke, and musculoskeletal injury (MSI) from repetitive motion injuries while running table games over many hours.

Safe listening Avoiding hearing damage from intentionally heard sounds

Safe listening is a framework for health promotion actions to ensure that sound-related recreational activities do not pose a risk to hearing.


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Further reading