Noise is unwanted sound judged to be unpleasant, loud or disruptive to
hearing. From a physics standpoint, noise is indistinguishable from
sound, as both are vibrations through a medium, such as air or water.
The difference arises when the brain receives and perceives a
In experimental sciences, noise can refer to any random fluctuations
of data that hinders perception of an expected signal.
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.
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 or
ITU-R 468 weighting.
2 Recording and reproduction
3 White noise
4 Environmental noise
5 Regulation of noise
5.1 United States
Noise in the workplace
6 Health effects from noise
7 Literary views
8 See also
10 Further reading
11 External links
NTi Audio sound level meter measuring noise amplitude in decibels
Sound is measured based on the amplitude and frequency of a sound
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 (dB) are expressed in a logarithmic scale.
On the other hand, pitch describes the frequency of a sound and is
measured in hertz (Hz).
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
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.
Main article: White noise
Problems playing this file? See media help.
White noise is energy randomly spread across a wide frequency band
containing all notes from high to low. It is called "white" noise as
it is analogous to "white" light which contains all the colors of the
Main article: 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. 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. 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.
Regulation of noise
Certain geographic areas or specific occupations may be at a higher
risk of being exposed to constantly high levels of noise; in order to
prevent negative health outcomes, regulations may be set. 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.
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.
The Quiet Communities Act of 1978 promotes noise control programs at
the state and local level and developed a research program on noise
control. Both laws authorized the Environmental Protection Agency
to study the effects of noise and evaluate regulations regarding noise
Noise in the workplace
In the US, the National Institute of Occupational Safety and Health
(NIOSH) provides recommendation on noise exposure in the
workplace. 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. This
publication set the recommended exposure limit (REL) of noise in an
occupation setting to 85 dBA for 8 hours. However, in 1973 the
Occupational Safety and Health Administration
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.
European Environment Agency
European Environment Agency regulates noise control and
surveillance within the European Union. The Environmental Noise
Directive was set to determine levels of noise exposure, increase
public access to information regarding environmental noise, and reduce
environmental noise. Additionally, in the European Union,
underwater noise is a pollutant according to the Marine Strategy
Framework Directive (MSFD). 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".
Health effects from noise
Health effects from noise
Health effects from noise and Noise-induced hearing
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. There are also causal relationships between noise and
psychological effects such as annoyance, psychiatric disorders, and
effects on psychosocial well-being.
Noise exposure has increasingly been identified as a public health
issue, especially in an occupational setting, as demonstrated with the
creation of NIOSH's
Hearing Loss Prevention program.
Noise has also proven to be an occupational hazard, as it is the most
common work-related pollutant. Noise-induced hearing loss, when
associate with exposures from the workplace is also called
occupational hearing loss.
While noise-induced hearing loss is permanent, it is also very
preventable. Particularly in the workplace, regulations may exist
depicting maximum allowed levels of noise. This can be especially
important for professionals working in settings with consistent
exposure to loud sounds, such as musicians, music teachers and sound
engineers. Examples of measures taken to prevent noise-induced
hearing loss in the workplace include engineering noise control, the
Buy-Quiet initiative, creation of the Safe-in-
Sound Award, and noise
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.
Luigi Russolo, one of the first composers of noise music, wrote
the essay The Art of Noises. He argues 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.
Henry Cowell claims that technological advancements have reduced
unwanted noises from machines, but have not managed so far to
completely eliminate them.
Impulse noise (audio)
Noise Awareness Day
Noise and vibration on maritime vessels
Noise in music
Sound level meter
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Look up noise in Wiktionary, the free dictionary.
Wikiquote has quotations related to: Sound
Wikimedia Commons has media related to Noise.
Guidelines for Community Noise, World Health Organization, 1999
Audio Measuring Articles – Electronics
Mohr on Receiver Noise: Characterization, Insights & Surprises
Noise voltage – Calculation and Measuring of Thermal Noise
Noise at work European Agency for Safety and Health at Work (EU-OSHA)
Noise Control Techniques"
Mountain & Plains ERC: A NIOSH Education and Research Center for
Occupational & Environmental Health & Safety
US National Institute for Occupational Safety and Health, – Noise
European noise laws
Addressing Wind Turbine Noise[permanent dead link]
Noise Pollution Clearing House
Introduction to the fundamentals of acoustic engineering
Noise (physics and telecommunications)
Class of noise
Additive white Gaussian noise
Additive white Gaussian noise (AWGN)
Johnson–Nyquist noise (thermal noise)
Quantization error (or q. noise)
Channel noise level
Circuit noise level
Effective input noise temperature
Equivalent noise resistance
Equivalent pulse code modulation noise
Impulse noise (audio)
Noise spectral density
Noise, vibration, and harshness (NVH)
Carrier-to-noise ratio (C/N)
Carrier-to-receiver noise density (C/kT)
Eb/N0 (energy per bit to noise density)
Es/N0 (energy per symbol to noise density)
Modulation error ratio (MER)
Signal, noise and distortion (SINAD)
Signal-to-interference ratio (S/I)
Signal-to-noise ratio (S/N, SNR)
Signal-to-noise ratio (imaging)
Signal to noise plus interference (SNIR)
Signal-to-quantization-noise ratio (SQNR)
Contrast-to-noise ratio (CNR)
List of noise topics
Colors of noise
Radio noise source
Colors of noise