Doppler Effect Calculator
The shift you actually hear, source and observer separately.
Work out Doppler Effect. The shift you actually hear, source and observer separately. Names the counter-intuitive bit rather than hiding it.
Positive if approaching, negative if moving away.
Positive if you are closing on it.
Frequency you actually hear
1,095.85 Hz
Higher by 95.85 Hz — 9.58%
Source motion and observer motion are not symmetric, which is the subtlety that gets missed. A source approaching at 30 m/s and an observer approaching at 30 m/s give different shifts, because a moving source compresses the waves themselves while a moving observer merely runs into them faster. The familiar ambulance effect is not a gradual slide but a sharp drop as it passes, because the shift depends on the component of velocity along the line of sight — which reverses over the moment of closest approach. This is the classical form, for sound. Light needs the relativistic version, where only the relative velocity matters and the source-observer asymmetry disappears entirely.
How the Doppler Effect Calculator works
Enter the source frequency and both velocities for the frequency you actually hear. Source motion and observer motion are not interchangeable — the page handles them separately because the physics treats them differently.
Also known as: doppler shift calculator · frequency shift calculator · ambulance siren pitch calculator · doppler effect formula
Frequently asked questions
What is the Doppler effect formula?
f' = f(v + vₒ)/(v − vₛ), with observer velocity positive towards the source and source velocity positive towards the observer.
Why are source and observer motion not symmetric?
Because a moving source compresses the waves themselves, changing the wavelength, while a moving observer merely encounters existing waves more often. Thirty metres per second of each gives different shifts.
Why does an ambulance pitch drop so sharply as it passes?
Because the shift depends on the velocity component along the line of sight, and that reverses over the moment of closest approach. The change is abrupt rather than gradual.
What happens at the speed of sound?
The formula diverges — the waves pile up into a shock front rather than a frequency. That is a sonic boom, and it is why this page refuses the calculation instead of returning a number.
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