Sound & Wave Generator
Hear a tone and watch its wave at the same time. Slide the frequency to change the pitch, slide the amplitude to change the loudness, and read the wavelength and time period live.
Frequency decides pitch and amplitude decides loudness. Frequency is the number of cycles per second in hertz, and the wave equation is v = f λ with time period T = 1/f. Sound travels at about 343 m/s in air at 20 °C, so a 440 Hz note has a wavelength of 343 ÷ 440 = 0.78 m.
Controls
Press play first — browsers only allow sound after a tap.
Oscilloscope
The real signal going to your speaker, drawn 60 times a second.
Learn by doing
Three quick experiments — tap, listen, and read what changed.
Pitch comes from frequency
Same loudness, different frequency. The higher one sounds higher — the wave has more cycles in the same time.
Loudness comes from amplitude
Same 440 Hz note, different amplitude. The pitch stays exactly the same; only the height of the wave changes.
Quality comes from harmonics
All four of these are 440 Hz, yet they sound different. A sine is one pure frequency; the others add extra whole-number multiples (harmonics).
Every part of a wave, labelled
Exactly the diagram you are asked to draw in the exam — and it updates with your sliders.
Wave equation v = f λ
Fill any two boxes; the third is worked out.
| Medium | Speed of sound |
|---|---|
| Air at 0 °C | 331 m/s |
| Air at 20 °C (use this) | 343 m/s |
| Water (25 °C) | 1,493 m/s |
| Sea water | 1,531 m/s |
| Wood (oak) | 3,850 m/s |
| Steel | 5,960 m/s |
| Vacuum | 0 — sound cannot travel |
Echo, reflection and resonance
An echo is sound reflected back. It travels to the wall and back, so the distance is halved.
d = (v × t) ÷ 2
Resonance
When you force an object to vibrate at its own natural frequency, the vibration grows very large. That is resonance: a tuning fork sets an identical fork singing across the room, a radio picks out one station, and soldiers are told to break step on a footbridge. In a closed pipe or a stretched wire the natural frequencies are fixed by the length, which is why a longer tabla or a thicker string gives a lower note.
Two close notes
Play two tones only a few hertz apart and listen to the loudness rise and fall.
What the two waves add up to
Top: the two tones on their own. Bottom: their sum — the envelope swells and fades, and each swell is one beat.
Why beats happen
Two waves of nearly equal frequency keep drifting in and out of step. When crest meets crest they add (constructive interference) and the sound is loud; a moment later crest meets trough, they cancel (destructive interference) and the sound almost dies away. One loud–soft cycle is one beat.
beat frequency = |f₁ − f₂|
A tabla player or a guitarist uses this: they tune a string against a reference note and tighten it until the beats slow right down and vanish — then the two frequencies are equal. Beats can only be heard clearly when the difference is below about 10 Hz.
The whole sound spectrum
Below 20 Hz is infrasound, above 20,000 Hz is ultrasound. Humans only hear the strip in between — many animals hear far more.
Hearing-range check
A safe, fun demo: the frequency steps up and you say when it disappears.
Can you still hear a tone?
Who hears what
| Animal / source | Range it hears (or makes) |
|---|
Ranges are typical published figures and vary between individuals.
Where ultrasound is used
- Hospital scans — a baby or a kidney stone is imaged by reflected ultrasound.
- SONAR — ships find the depth of the sea and shoals of fish.
- Cleaning spiral tubes, jewellery and electronic parts.
- Detecting cracks inside metal blocks without cutting them.
- Bats and dolphins use echolocation — the same idea, built in.
Where infrasound shows up
Elephants and whales call to each other over kilometres with infrasound, because low frequencies bend around obstacles and travel much further. Earthquakes and volcanoes also produce it — some animals seem to sense a quake before people do.
Sa Re Ga Ma — in hertz
Tap a key to hear it. Music is just carefully chosen frequencies, and the ratios between them are simple fractions.
| Sargam | Western | Frequency | Wavelength in air | Time period | Ideal ratio to Sa |
|---|
Frequencies use modern equal temperament (A = 440 Hz). The ratios in the last column are the ideal whole-number ratios the interval is built on — equal temperament comes within about 1% of each one.
Why these numbers?
Modern tuning fixes A4 = 440 Hz and divides each octave into 12 equal steps, so every semitone multiplies the frequency by 21/12 ≈ 1.0595.
f = 440 × 2n/12 where n is the number of semitones away from A4.
Double the frequency and you get the same note one octave higher — Sa at 261.6 Hz and Sa at 523.3 Hz sound like “the same note”. Our ears judge pitch by ratios, not differences, which is why the frequency slider on this page is logarithmic.
Simple ratios sound sweet
| Interval | Sargam | Ratio |
|---|---|---|
| Octave | Sa → Sa′ | 2 : 1 |
| Perfect fifth | Sa → Pa | 3 : 2 |
| Perfect fourth | Sa → Ma | 4 : 3 |
| Major third | Sa → Ga | 5 : 4 |
| Major sixth | Sa → Dha | 5 : 3 |
When the ratio is simple, many harmonics of the two notes line up exactly and the pair sounds pleasant (consonant). When it is awkward, the harmonics clash and produce fast beats — which is what we call a dissonance.
Sound you can see
Sound is a longitudinal wave of compressions and rarefactions travelling through a material. This page turns that invisible wave into something you can hear, watch and measure.
Press play
Browsers only start audio after a tap, so the first click is what switches the sound on.
Slide the frequency
Low numbers give a deep sound, high numbers a shrill one. Watch the cycles squeeze together.
Slide the amplitude
The wave gets taller and the tone louder — but the pitch does not move at all.
Read the physics
Wavelength, time period, beat frequency and the nearest musical note are all worked out for you.
The five words you must know
Amplitude — the greatest distance a particle moves from its rest position; decides loudness.
Wavelength (λ) — crest to crest, or compression to compression.
Frequency (f) — cycles per second, measured in hertz; decides pitch.
Time period (T) — time for one full cycle, T = 1/f.
Speed (v) — how fast the wave travels, v = f λ.
The wave equation
v = f × λ T = 1 ÷ f
In air at 20 °C, v ≈ 343 m/s. So a 440 Hz note has λ = 343 ÷ 440 = 0.78 m and T = 1 ÷ 440 = 2.27 ms. Notice that if the frequency doubles the wavelength halves — the speed belongs to the medium, not to the note.
Hearing range, infrasound, ultrasound
A healthy young person hears roughly 20 Hz to 20,000 Hz. Below that is infrasound (elephants, whales, earthquakes); above it is ultrasound (bats, dolphins, medical scans, SONAR). The upper limit drops with age — most adults lose everything above about 15–16 kHz.
Beats
beat frequency = |f₁ − f₂|
Two nearly equal tones interfere, so the loudness rises and falls. 330 Hz with 334 Hz gives 4 beats every second. Musicians tune by slowing the beats until they stop.
Echo and SONAR
d = v t ÷ 2
The sound goes to the reflector and comes back, so halve the total journey. An echo needs the reflector at least 17.2 m away, because the ear cannot separate sounds closer than 0.1 s. The same formula gives the depth of the sea in SONAR, using v ≈ 1,531 m/s in sea water.
Sound needs a medium
Sound is a mechanical wave — it needs particles to pass the vibration along, so it travels fastest in solids, slower in liquids and slowest in gases, and cannot travel through a vacuum. That is why the bell in an evacuated jar falls silent, and why space is quiet.
Sound & Wave Generator — your questions
What is the difference between pitch and loudness?
Pitch is how high or low a sound seems, and it depends only on frequency — more cycles per second means a higher pitch. Loudness is how strong it seems, and it depends on amplitude, the greatest distance a particle moves from its rest position. Changing the amplitude of a 440 Hz tone makes it louder but never changes its note.
What is the range of human hearing?
A healthy young person hears roughly 20 Hz to 20,000 Hz. Sound below 20 Hz is infrasound, produced by elephants, whales and earthquakes; above 20,000 Hz is ultrasound, used by bats, dolphins and medical scanners. The upper limit drops with age, and most adults can no longer hear anything above about 15 to 16 kHz.
What is the wave equation v = fλ?
The speed of a wave equals its frequency multiplied by its wavelength. In air at 20 °C sound travels at 343 m/s, so a 440 Hz note has λ = 343 ÷ 440 = 0.78 m and T = 1 ÷ 440 = 2.27 ms. Double the frequency and the wavelength halves, because the speed belongs to the medium, not to the note.
Why can't sound travel through a vacuum?
Sound is a mechanical wave made of compressions and rarefactions, so it needs particles to pass the vibration along. With no particles, there is nothing to carry it. That is why an electric bell inside a jar falls silent as the air is pumped out, and why space is silent. Sound travels fastest in solids, slower in liquids and slowest in gases.
Why must a wall be at least 17 metres away to hear an echo?
The ear cannot separate two sounds less than 0.1 s apart. The sound travels to the reflector and back, so d = v × t ÷ 2 = 343 × 0.1 ÷ 2 = 17.2 m. Anything closer and the echo merges with the original sound, which is why you hear echoes in a large empty hall but not in a bedroom.
What are beats in sound?
When two tones of nearly equal frequency are sounded together they drift in and out of step, so the loudness rises and falls. One loud-soft cycle is a beat, and the beat frequency is the difference between the two frequencies: 330 Hz with 334 Hz gives 4 beats per second. Musicians tune a string by slowing the beats until they stop.
Where is ultrasound used?
Ultrasound is used for hospital scans, for SONAR to measure sea depth and find shoals of fish, for cleaning spiral tubes, jewellery and electronic parts, and for detecting cracks inside metal blocks without cutting them. Bats and dolphins use the same idea naturally, a technique called echolocation.