Bryan Pijanowski wants to capture the sounds of the world on a single day, and he needs your help.

On Earth Day, April 22, Pijanowski hopes to enlist thousands of people in recording a few minutes of their everyday surroundings with his Soundscape Recorder smartphone app.

All those sonic snippets could create an unprecedented soundtrack to life on Earth — and as they accumulate, year after year, scientists could use them to measure patterns and changes in our sonic environments.

"I've been on a campaign to record as many ecosystems as possible," said Pijanowski, a soundscape ecologist at Purdue University. "But there's only so many places in the world I can be. I thought about how I could get more recordings into a database, and it occurred to me: We have a couple billion people on this planet with smartphones!"

Pijanowski's work typically takes him to places like the Sonoran desert or old-growth rain forests in Borneo, where he analyzes recordings to learn more about ecosystem health and dynamics: relationships between biodiversity and forest canopy structure, or how natural communities recover from wildfire.

With the Global Soundscape project and its Soundscape Recorder app, now available for iOS and Android devices, the emphasis is on cities and towns and suburbs, and our relationships to their sonic character.

After making a recordings with the app, people are asked a short series of questions about what they heard and how they feel. The recording is then uploaded to the Global Soundscape database. "If we make this part of the Earth Day culture, something everyone goes out and does, we can begin to characterize those sounds and compare them from year to year," said Pijanowski.

"We should get a sense of whether and how we're making this a noisier planet, which I think we're doing," Pijanowski continued. "And it should increase awareness of sounds. Hopefully it will make people stop and listen."