Earshot reads the streets, railways, runways and venues around a spot from OpenStreetMap. Each one has a typical sound level and a daily rhythm: rush hours on main roads, music after 10 PM near bars, loudspeakers at dawn and dusk near places of worship, the school run on weekday mornings.
Sound fades with distance and drops further behind the first row of buildings. Every source is added up hour by hour. Day is 7 AM to 10 PM and night is 10 PM to 7 AM, the same split the WHO uses for its guideline limits of 53 dB by day and 45 dB at night.
It is an estimate, not a measurement. Traffic volume, building layout and one-off events change what you actually hear, which is why reports from people who live there matter.