Noise

• 1. Introduction

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  Noise, from a physics standpoint, is identical to any other sound: both are just vibrations moving through a medium like air or water. What separates noise from music or speech is not the vibration itself but what the brain does with it once it arrives. A normal speaking voice measures around 65 dBA, while a rock concert can reach roughly 120 dBA, and the softest sound a person can hear sits at zero dBA. Somewhere between those numbers, a sound crosses the line from tolerable to harmful, from background hum to a measurable public health hazard. How do scientists and governments decide where that line falls? And why did a literary theorist and a composer of noise music end up asking a very similar question about the very same sounds?

• 2. Measuring a Sound

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  Sound is measured along two dimensions: amplitude, which describes how forceful the wave is, and frequency, which describes its pitch. Amplitude is expressed in decibels on a logarithmic scale, while frequency is measured in hertz. A-weighting adjusts a sound's decibel reading to reflect what the human ear can actually perceive at each frequency, producing a figure expressed in dBA.

  The main tool for measuring sound in the air is the sound level meter, though noise dosimeters are typically used in workplaces and noise monitors track environmental and community noise. More recently, smartphone-based sound level meter apps have let researchers crowdsource maps of recreational and community noise.

  That same A-weighting standard would go on to define how loud is too loud, in settings as different as a factory floor and a residential neighborhood.

• 3. Noise in the Studio

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  In audio recording and broadcasting, noise usually means the low-level sound audible during the quiet stretches of a program, and it comes in four recognizable types: hiss, rumble, crackle, and hum. This residual sound can come from the recording equipment itself, from the instrument being recorded, or simply from ambient sound in the room.

  Engineers measure this unwanted electronic signal using A-weighting or the ITU-R 468 weighting standard. Rather than being treated only as a flaw to eliminate, noise is also generated on purpose and used as a test signal to check how well recording and reproduction equipment performs.

  Noise does not always mean an accident. Engineers sometimes generate it deliberately as an intentional random signal, such as white noise or pink noise, each spanning a different shape of frequency spectrum. In electronics more broadly, noise can also describe a random or unintended part of a signal with no audible effect at all, detectable only with instruments, and in experimental science the same word covers any random fluctuation in data that obscures the signal researchers are actually trying to see.

  Outside the studio, that same accumulation of unwanted sound carries consequences that go well beyond a hiss on a recording.

• 4. The Cost of Environmental Noise

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  Environmental noise adds up from surface motor vehicles, aircraft, trains, and industrial sources, exposing millions of people to sound that does more than annoy. Depending on how long and how intensely a person is exposed, noise has been linked to hearing loss, high blood pressure, ischemic heart disease, sleep disturbance, injuries, and even reduced school performance; researchers have also found causal relationships between noise and psychological effects such as annoyance, psychiatric disorders, and diminished psychosocial well-being.

  Even at levels too low to damage hearing directly, urban noise still interrupts sleep, disrupts communication, and interferes with daily activity. Available strategies to bring noise down include reducing it at the source, planning land use around noisy zones, installing noise barriers and sound baffles, restricting certain activities to particular times of day, controlling how vehicles operate, and designing buildings with architectural acoustics in mind.

  Those health findings are exactly what pushed governments in the United States and Europe to start writing noise into law.

• 5. Writing Noise Into Law

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  Regulation exists because noise exposure is not spread evenly. Certain geographic areas and occupations carry consistently higher risk, and environmental noise laws typically set maximum recommended levels tailored to specific land uses, such as residential neighborhoods, areas of outstanding natural beauty, and schools.

  The United States passed the Noise Control Act in 1972 to coordinate federal research on noise, set emission standards for commercial products, and raise public awareness of the issue. The Quiet Communities Act followed in 1978, funding noise control programs at the state and local level. Both laws gave the Environmental Protection Agency authority to study noise and evaluate regulation.

  The National Institute for Occupational Safety and Health set a recommended workplace exposure limit of 85 dBA over eight hours in 1972, using a rule where every 3-decibel increase in volume cuts the safe exposure time in half; under that rule, 88 dBA is only considered safe for 4 hours, and 94 dBA for just 1 hour. The Occupational Safety and Health Administration instead required an 8-hour average of 90 dBA starting in 1973, and a year later began requiring employers to run hearing conservation programs for workers exposed to 85 dBA averages.

  In the European Union, the Environmental Noise Directive works to measure noise exposure and give the public more information about it. The Marine Strategy Framework Directive goes further, treating underwater noise as a pollutant and requiring member states to ensure that "the introduction of energy, including underwater noise, is at levels that do not adversely affect the marine environment."

  None of these regulations, though, guarantee that the protective equipment built to meet them actually works.

• 6. Preventing the Damage

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  Noise has been identified as the most common work-related pollutant, and the resulting hearing loss, when tied to workplace exposure, is classified specifically as occupational hearing loss. NIOSH has responded by building a dedicated Noise and Hearing Loss Prevention program, alongside measures such as the Buy-Quiet initiative and the Safe-in-Sound award, both aimed at encouraging quieter equipment and better prevention practices in the workplace.

  OSHA requires hearing protection on the job, but without individual selection, training, and fit testing, hearing protection devices do not significantly reduce the risk of hearing loss. One study followed more than 19 thousand workers, some of whom regularly wore hearing protection and some of whom never did, and found no statistically significant difference in their risk of noise-induced hearing loss.

  That gap between having protective equipment and actually being protected left room for an entirely different kind of thinking about what noise is in the first place.

• 7. How Thinkers Have Heard Noise

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  The literary theorist Roland Barthes drew a line between physiological noise, which is merely heard, and psychological noise, which is actively listened to, arguing that the first is felt as vibration in the body while the second draws conscious attention. Composer Luigi Russolo, in his essay The Art of Noises, argued that any sound could become music as audiences grew used to the noise produced by new technology, until pure sound effectively ceased to exist.

  Composer Henry Cowell later observed that technological progress had reduced unwanted noise from machinery without ever fully eliminating it. Researcher Felix Urban, comparing sound and noise across cities, found that noise regulation is only one signal of what a culture labels harmful, more a marker of local custom than a fixed acoustic threshold.