In the early days of the COVID pandemic, a group of researchers in France started a project called “The Silent Cities Project” to collect soundscape and noise data. In November 2022, they shared their story and their methodology in a webinar. The team included Dr. Samuel Challéat, Dr. Amandine Gasc, Dr. Jeremy Froidevaux, Dr. Nicholas Farrugia, and Nicolas Pajusco.
As most of us know, cities around the world became more quiet during the COVID-19 shutdowns. And it wasn’t just cities, as we learned during our Soundproofist interview with Artash Nath about ocean noise. This event was also a rare opportunity to analyze and quantify our sonic environment.
Origins of the sonic research
The project began in early 2020. During that time, movement within cities or between other cities was seriously curtailed. The team started with small idea about economic impact that grew into something even larger. They wanted to create a global set of baseline recordings to use for data analysis and machine learning. Ultimately, these recordings were collected from 37 countries across four continents.
Their preferred recording equipment included Openacoustics Audiomoth (which can record audible and ultrasonic sounds) and Wildlife Acoustics SM4 (a high-quality recorder used for nature recordings). They set parameters for the audio settings and other consistency requirements for the recordings. By the end of the project, they would collect and analyze over 2 million recordings.
What they analyzed
The research team divided the recordings into 10-second segments and filtered the files from 100Hz to 20kHz to remove low-frequency noise. They used a number of indices, including decibel levels, acoustic complexity, and a “normalized different soundscape index,” which is a ratio between biophony (the sounds of living organisms) and anthrophony (human-generated sounds). The recordings were annotated manually by hundreds of participants, and they were tagged using 527 different labels. The sites were also classified by geolocation, climate, population density, and pandemic confinement measures.
The database
The team built a database that cross-references details such as location data, lockdown measures, types of sound (geophony, biophony, or anthrophony), and duration. The data will be available for others to use in various projects, and they’re also looking for a permanent site for it.
Learn more about this impressive project in their 90-minute presentation.
Silent Cities Webinar Nov 2022.mp4 from Wildlife Acoustics on Vimeo.