Bangalore: In a step to make cities quieter, the European Union requires member states to create noise maps of their urban areas once every five years. Rather than deploying costly sensors all over a city, the maps are often created using computer models that predict how various sources of noise, such as airports and railway stations, affect the areas around them.

Nicolas Maisonneuve of the Sony Computer Science Laboratory in Paris, France, says that those maps are not an accurate reflection of residents' exposure to noise. To get a more clear picture, Maisonneuve's team has developed NoiseTube, a downloadable software application, which uses people's smartphones to monitor noise pollution. "The goal was to turn the mobile phone into an environmental sensor," says Maisonneuve.

The application records sound picked up by the phone's microphone, along with the GPS location. Users can label the data with extra information, such as the source of the noise, before it is transmitted to NoiseTube's server.

The sample is tagged with the name of the street and the city it was recorded in and converted into a format that can be used with Google Earth. Software on the server checks against weather information, and rejects data that might have been distorted by high winds. Locations that have been subjected to sustained levels of noise are labelled as dangerous. The data is then added to a file, which can be downloaded from the NoiseTube website and displayed using Google Earth.

Currently the software works on only a handful of Sony Ericsson and Nokia smartphones as it has to be calibrated by Maisonneuve's team to work with the microphone on any given model. "We are currently working on a method to automatically calibrate microphones," says Maisonneuve.

Amrit Kaur of the Awaaz Foundation, a non-governmental organisation based in Mumbai, India, that is fighting noise pollution in the city, says that NoiseTube has empowered us to offer citizens a real tool to bring a change in their living conditions.