Largest urban noise monitoring system

The largest urban noise monitoring network is operated by Bruitparif (FRA) in the city of Paris and its suburbs. As of February 2021, Bruitparif has 150 permanently installed noise sensors in the French capital.

The sensors used by projects like Bruitparif combine a microphone (or array of microphones) with a small low-power computer (these days it's typically a Raspberry Pi). Once a second, sound picked up by the microphone is sent to the computer, which analyses the volume, frequency distribution, and sometimes the direction of origin, before transmitting these measurements to a central server. This means that no-human ear ever listens to the recordings directly, and that they aren't stored anywhere.

Bruitparif was founded in 2004 as an initiative of the Regional Council of the Île-de-France. In the years since its inception, it has established a model that is now being emulated by many other European cities. In 2016, Bruitparif developed by "Méduse" ("Jellyfish") sensor, which combines an omnidirectional microphone with an array of three directional mics, which allows researchers to pinpoint the origin of loud noise sources or track moving ones.

Long-term exposure to anthropogenic (human created) noise has been shown to cause a range of health problems including stress, fatigue, cardiovascular disease and, of course, hearing loss. People who live near airports or busy roads, for example, report more frequent headaches, have more minor accidents and the World Health Organization has ranked noise pollution (specifically traffic noise from cars) as the second most significant public health threat in developed nations after air pollution.