EARS & WAVES

← Sound phenomena

Doppler effect.

Why a siren drops in pitch as it passes you: hear cars, a train and a race car go by, and see how much the pitch falls at each speed.

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Listen as they pass

Tap an example: the sound drives past from left to right every few seconds; tap again to pause. Headphones help you follow it across.

How the Doppler effect works

Sound travels as waves at about 343 metres a second. When the source comes towards you, each wave starts a little closer than the one before, so the waves arrive bunched up and the pitch is higher. As it moves away they arrive stretched out, and the pitch is lower.

Heard from the roadside, a horn stays high while the car approaches, slides down as it passes, and stays low as it leaves. The faster it goes, the bigger the drop: about one and a half semitones at 50 km/h, more than eight at 300 km/h.

Facts that often get mixed up

  • The pitch does not slide all the way in: it stays high while the source comes towards you and drops as it passes. The slide you hear is the angle changing.
  • The driver hears no change at all: they move with the sound.
  • Christian Doppler described the effect in 1842. In 1845 Buys Ballot tested it with trumpeters on a train near Utrecht: musicians by the track heard the note about a half-tone higher as it came, and lower as it went.
  • The same effect measures speed: police and weather radar, Doppler ultrasound of blood flow, and the redshift that shows galaxies moving away from us.
Speed (a 440 Hz horn)Heard as it comesHeard as it goesThe drop
30 km/h451 Hz430 Hz0.8 semitone
50 km/h459 Hz423 Hz1.4 semitones
100 km/h479 Hz407 Hz2.8 semitones
200 km/h525 Hz379 Hz5.7 semitones
300 km/h581 Hz354 Hz8.6 semitones
Why does a siren sound lower after it passes?

While it comes towards you its sound waves arrive bunched up, so the pitch is higher; once it moves away they arrive stretched out, so it is lower.

Does the driver hear the change?

No. The driver moves with the siren, so the waves reach them evenly; only the people it passes hear the drop.

Does it happen with light too?

Yes. Light from things moving away shifts towards red, and from things coming closer towards blue; that is how astronomers know the universe is expanding.

Mixes

Pick what you need. One tap to start, change anything and save it as your own.

Focus timer

Work in waves.

The Pomodoro rhythm: focus with calm sound in your ears, then take a real break. A soft bell marks every change, so you never watch the clock. Every fourth break is a long one.

25:00Focus · 1 of 4

Sound while you work

Breathe

Slow your breathing down.

Follow the circle and the sound: it rises as you breathe in and falls as you breathe out. Choose a rhythm, or set your own, and pick what plays underneath.

Ready

Sound while you breathe

Noise generator

Any color of noise, from deep brown to bright violet — and everything in between.

Brown noise
Spectrum · 20 Hz – 20 kHz

Sound science

The colors of noise

Same randomness, different tilt. Each color shifts energy between low and high pitches — here is what that sounds like.

White

0 dB / octave

Equal energy at every frequency. Because we hear in octaves, it sounds bright and hissy — the classic "TV static".

Pink

−3 dB / octave

Equal energy in every octave, so it sounds even to the ear. Steady rain, rustling leaves. A favorite for focus.

Brown

−6 dB / octave

Deep and warm, like a distant waterfall or a plane cabin. Masks voices and traffic without any hiss.

Grey

Equal-loudness curve

Shaped around how our hearing works, so every pitch seems equally loud. Balanced and soft.

Blue

+3 dB / octave

The mirror of pink: more treble than bass. Airy, crisp, like a light spray.

Violet

+6 dB / octave

Mostly treble, like hissing water. Sometimes used to mask high-pitched ringing.

Calm

Gentle tones to settle into: singing bowls, a slow warm drone, wind chimes tuned so every note fits.

Frequencies

Famous tones on pages of their own: hear them side by side, with honest facts.

Sound phenomena

How sound bends, shifts, rings and fools the ear, and why space is silent: hear it for yourself.

Nature

Rooms & travel

Animals & countryside

A purring cat, whales and dolphins, a nightingale in the dark, cowbells on a summer pasture. Wonderful in stereo.

For babies

Womb sounds are what a baby heard for nine months: a deep rush of blood flow, and the heartbeat.

Hearing and speaker tests

Check your ears, headphones and speakers, each test on a page of its own with a live picture.

Ear Age · 60 seconds

Test your ears.

Our ears lose the highest pitches first, and it starts early. Find the highest tone you can still hear and see the typical age for it.

  • Headphones on, quiet room
  • Set a comfortable volume on the 1 kHz tone
  • Don't turn it up when a tone disappears — that's the point
20,000Hz

Can you still hear it?

Hearing age test →

More ear tests

Check your headphones, find the deepest bass your setup can play, or play any pitch you like.

Headphones check

Left & right

Each ear should get its own side. It matters for 8D, binaural beats and every stereo sound here.

Headphones on, then tap a side.

Bass test

How low can you go?

Deep tones from 200 Hz down to 20 Hz, the bottom of human hearing. Mostly it tests your speakers or headphones.

Tone generator

Any pitch, 20 Hz – 20 kHz

Hz

Start quiet: high tones and square waves get tiring fast.

Take it to bed

An app without the app store.

Add Ears & Waves to your home screen and it opens like any app — full screen, with its own icon. Everything it needs is saved on your device, so it keeps playing on a plane, in a tent or with Wi-Fi off.

Preparing offline mode…
  • Works offlineNo streaming. Sound is computed on your device, forever.
  • Screen offKeeps playing with the phone locked. The timer fades it out gently.
  • PrivateNo account, no ads, no cookies. Your mixes stay on your device.
Deep sleep