What sign convention does it use?

You set directions explicitly. "Toward" means moving toward the other party (which raises the pitch), "away" lowers it, and "stationary" contributes nothing. The math uses f′ = f (v + v_o) / (v − v_s) with the signs chosen from your selections.

Why did I get a shock-wave warning?

If the source moves at or faster than the wave speed, the term (v − v_source) is zero or negative and the classical formula no longer applies — the source is breaking the sound barrier, producing a shock wave such as a sonic boom.

Can I use it for light?

It uses the classical (non-relativistic) Doppler formula, which is accurate for sound and for slow-moving sources. The relativistic Doppler effect for light at high speeds needs a different equation.

Doppler Effect Calculator

When a sound source and a listener move relative to each other, the perceived frequency changes — higher as they approach, lower as they part. This is the Doppler effect. Enter the emitted frequency, the wave speed (343 m/s for sound in air by default), and how fast the observer and source are each moving toward, away, or staying still. The calculator applies f′ = f (v + v_observer) / (v − v_source) and reports the observed frequency, the frequency shift, and the observed wavelength. If the source reaches or exceeds the wave speed the denominator breaks down (a shock wave), which the tool flags. Everything is computed locally in your browser.

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Emitted frequency (Hz)Wave speed (m/s)

Observer

Source

Observed frequency

1095.85 Hz

Frequency shift: +95.85 Hz
Observed wavelength: 0.3130 m

How to use

Enter the emitted (source) frequency in hertz.
Enter the wave speed (343 m/s is the default for sound in air).
For the observer and the source, choose moving toward, moving away, or stationary, and enter each speed.
Read the observed frequency, the shift, and the observed wavelength, and copy the result.

Frequently asked questions

What sign convention does it use?: You set directions explicitly. "Toward" means moving toward the other party (which raises the pitch), "away" lowers it, and "stationary" contributes nothing. The math uses f′ = f (v + v_o) / (v − v_s) with the signs chosen from your selections.
Why did I get a shock-wave warning?: If the source moves at or faster than the wave speed, the term (v − v_source) is zero or negative and the classical formula no longer applies — the source is breaking the sound barrier, producing a shock wave such as a sonic boom.
Can I use it for light?: It uses the classical (non-relativistic) Doppler formula, which is accurate for sound and for slow-moving sources. The relativistic Doppler effect for light at high speeds needs a different equation.

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