Noise
Unwanted sound measured in decibels, regulated for health and environment.
Noise is sound, chiefly unwanted, unintentional, or harmful sound considered unpleasant, loud, or disruptive to mental or hearing faculties. From a physics standpoint, there is no distinction between noise and 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. Acoustic noise can be deliberate, like music or speech, or unintended. The term also applies to a random or unintended component of an electronic signal, which may be inaudible to the human ear and require instruments for detection, as well as to intentionally produced random signals like white noise or pink noise. In audio engineering, noise refers to the unwanted residual electronic signal that produces acoustic noise heard as a hiss, commonly measured using A-weighting or ITU-R 468 weighting. In experimental sciences, noise denotes random fluctuations of data that hinder signal perception.
Sound is measured by amplitude and frequency. Amplitude, the force of a wave, is measured in decibels (dB) on a logarithmic scale, indicating loudness or intensity. Pitch, describing frequency, is measured in hertz (Hz). The primary instrument for measuring airborne sound is the Sound Level Meter; other devices include Noise Dosimeters for occupational settings, noise monitors for environmental noise, and smartphone applications for crowdsourced community noise mapping. A-weighting filters sound spectra to represent human hearing capability, with sound pressure expressed in dBA. The softest audible level is 0 dBA, normal speech is around 65 dBA, and a rock concert can reach about 120 dBA.
In recording and broadcast systems, audio noise is the residual low-level sound—such as hiss, rumble, crackle, and hum—heard during quiet periods, caused by equipment, instruments, or ambient room noise. Noise is often deliberately generated as a test signal for audio equipment. Environmental noise, the accumulation of all noise in a given environment, primarily comes from motor vehicles, aircraft, trains, and industrial sources, exposing millions to noise pollution that causes annoyance and health consequences like hearing loss and cardiovascular disease. Urban noise, while generally not causing hearing loss, disrupts sleep and communication. Mitigation strategies include source reduction, land-use planning, noise barriers, time-of-d
- Measurement unit
- Decibels (dB) for amplitude; hertz (Hz) for frequency
- Principal environmental sources
- Surface motor vehicles, aircraft, trains, industrial sources
- Key European regulation
- Environmental Noise Directive; Marine Strategy Framework Directive (MSFD)
- Occupational exposure limit (NIOSH)
- 85 dBA for 8 hours with 3-dB exchange rate
- Occupational exposure limit (OSHA)
- 90 dBA for 8 hours average
Lore & Background
Regulation of noise exists at national, state, and municipal levels. NIOSH recommends an exposure limit of 85 dBA for 8 hours with a 3-dB exchange rate, while OSHA maintains a 90 dBA average. In Europe, the Environmental Noise Directive determines exposure levels and reduces environmental noise, and the MSFD treats underwater noise as a pollutant. Health effects of noise exposure include hearing loss, high blood pressure, ischemic heart disease, sleep disturbances, and decreased school performance. Noise-induced hearing loss is permanent but preventable through engineering controls, the Buy-Quiet initiative, and hearing protection, though studies show hearing protection devices without proper selection and fit testing do not significantly reduce risk.
Reader's Guide
Noise is a pervasive environmental and occupational factor with significant implications for public health. Its measurement and regulation are grounded in physics—amplitude in decibels and frequency in hertz—but its perception and impact are subjective and physiological. The distinction between noise and desired sound is made by the brain, not by the physical wave. Regulatory frameworks in the United States and Europe aim to limit exposure, particularly in workplaces and communities, to prevent hearing loss and other health effects such as cardiovascular disease and sleep disruption. The use of A-weighting in standards reflects human hearing sensitivity. Despite regulations, noise remains the most common work-related pollutant, and prevention efforts like the Buy-Quiet initiative and Safe-In-Sound award seek to reduce risks. The legacy of noise research and regulation is a growing recognition that noise is not merely an annoyance but a measurable hazard requiring systematic control, from engineering solutions to land-use planning.
Did You Know?
- NIOSH recommends an occupational exposure limit of 85 dBA for 8 hours with a 3-dB exchange rate, while OSHA maintains a 90 dBA average.
- Underwater noise is classified as a pollutant under the European Union's Marine Strategy Framework Directive.
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