Doppler effect calculator (sound)
Enter the source frequency, the speed of sound and both speeds to get the heard frequency. A familiar case is an ambulance siren rising as it approaches and dropping as it leaves.
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Processing and privacy: The result is calculated inside your browser and your data is not sent to any server.
How to use it
- Enter source frequency, speed of sound in the medium, observer speed (positive toward source) and source speed (positive toward observer).
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
f' = f × (v + vₒ) / (v − vₛ), where v is the speed of sound, vₒ is the observer speed (positive toward the source) and vₛ the source speed (positive toward the observer).
Example
Inputs: Source frequency = 440 Hz, Speed of sound in the medium = 343 m/s, Observer speed (positive toward source) = 0 m/s, Source speed (positive toward observer) = 30 m/s. Result: Observed frequency: 482.173 Hz; Frequency shift: 42.173 Hz; Change: 9.585%.
Limits and caveats
- It assumes motion along the line joining source and observer and still air with no wind.
- Light and astronomical objects need the relativistic Doppler formula instead.
Questions about this tool
How do I enter a source moving away from me?
Use a negative speed, so a source leaving at 30 m/s is entered as −30.
Which speed of sound should I use?
In air at 20 °C about 343 m/s; it rises by roughly 0.6 m/s per degree.
Why is the pitch higher on approach?
The source catches up with its own waves, so the crests bunch up and the wavelength reaching you is shorter.