Pitch and Volume

Not all sounds are the same. A tiny bird goes tweet up high; a big lion goes roar down low. A whisper is barely there; a firework makes you jump. So every sound you ever hear has two things you can change about it — and they are nothing to do with each other.

Think of it like a sound having two dials. One dial goes from low to high. The other dial goes from quiet to loud. You can twist each dial on its own without touching the other. Over the next few pages we'll take the two dials apart, one at a time, and see that the same secret — a wobble — is behind both.

Dial one: high or low is called pitch

Every sound is made by something wobbling back and forth — a string, a drum skin, the air in a whistle, even the little folds in your throat when you hum. How high or low the sound is depends on one thing: how fast that wobble goes.

A faster wobble makes a higher sound.
A slower wobble makes a lower sound.

A short, tight guitar string flicks back and forth very fast and squeaks high. A long, loose one lolls back and forth slowly and rumbles low. This highness or lowness — the setting on the first dial — is called the pitch.

Dial two: loud or quiet is called volume

Now the second dial. How loud or quiet a sound is has nothing to do with how fast the wobble goes — it depends on how big the wobble is. How far the string swings, how much the drum skin bulges.

A bigger wobble makes a louder sound.
A smaller wobble makes a quieter sound.

Pluck a guitar string ever so gently and it barely stirs — a tiny wobble, a quiet note. Give it a good hard twang and it swings wide across the fret — a big wobble, a loud note. Notice you didn't make it wobble any faster, so the note stayed the same pitch. You only made the wobble bigger. That loudness is called the volume.

Two dials, four kinds of sound

Here is the important bit. Because the two dials are completely separate, you can set them in any combination you like. That gives four family-groups of sound:

High and quiet — a mosquito whining somewhere across the room.
High and loud — a referee's whistle blown right in your ear.
Low and quiet — a big dog grumbling softly in its sleep.
Low and loud — thunder rolling, or a marching bass drum.

Every sound in the world sits somewhere on these two dials at once. "High" tells you nothing about "loud", and "loud" tells you nothing about "high". Keep that in your pocket — it's the thing most people get muddled about.

Pitch and volume are different dials. Loud does not mean high.

Pitch (high or low) is set by how fast the wobble goes — faster wobble means higher pitch.
Volume (loud or quiet) is set by how big the wobble is — bigger wobble means louder, not higher.

A tiny mouse can squeak high but very quietly. A huge drum can boom low but very loudly. High and loud are two different things.

Try both dials yourself

This is one wobbling string, drawn so you can see the wobble. Twist the two dials and watch what each one changes on its own:

Slide pitch and the wave squeezes into more, faster wobbles — the sound climbs from LOW to HIGH. The wave stays the same height.
Slide volume and the wave grows taller — the sound swells from QUIET to LOUD. The number of wobbles doesn't change.

Try making it high-and-quiet, then high-and-loud, then low-and-loud. See how the two dials never get in each other's way?

A slide whistle is the best toy for hearing pitch by itself. It's a tube with a little plunger you pull in and out. Blow into it and it makes a note — then pull the plunger and the note swoops up, push it and the note slides back down. Wheee-oooo!

What's actually happening? Blowing sets the air inside the tube wobbling. A short plug of air wobbles fast, so you get a high note; a long plug of air wobbles slowly, so you get a low note. Pulling the plunger makes the tube longer and the note drops. A guitarist does the very same trick by pressing a finger down to shorten the string — shorter string, faster wobble, higher note. Long and low, short and high: that's how nearly every instrument picks its pitch.

How instruments change their pitch

Musicians spend their whole lives twisting the pitch dial, and there are really only three tricks they use — all of them just ways of changing how fast something wobbles:

Make the wobbling part shorter. Press a guitar or violin string against the neck and only a short piece is left to wobble — it wobbles faster, so the note goes higher. That's why sliding your finger up the string raises the note.
Make the string tighter. Turn the tuning peg to pull a string tighter and it wobbles faster — higher. Loosen it and it sags and wobbles slowly — lower. It's how you tune a guitar before you play.
Make the tube longer or shorter. In a recorder, flute or trombone the air is what wobbles. A long tube of air wobbles slowly (low notes); a short tube wobbles fast (high notes). Covering more holes on a recorder makes the wobbling air-tube longer, so the note drops.

And to twist the other dial — the volume — the player simply puts in more effort: blow harder, pluck harder, hit harder. That makes a bigger wobble, so a louder sound, without changing the pitch at all.

Here's a handy rule of thumb: big slow things make low sounds; small fast things make high sounds. Once you notice it, you'll hear it everywhere.

A giant bass drum has a huge, heavy skin. Something that big can only wobble slowly — so it thumps out a deep, low BOOM you feel in your chest. A mosquito, on the other hand, has teeny wings that flap fantastically fast — hundreds of times a second — so those fast little wobbles come out as a thin, high whine by your ear. Same idea sorts the animals: a big elephant trumpets low, a tiny bird tweets high. And the strings of a piano tell the same story — the fat long ones on the left growl low, the short thin ones on the right tinkle high. Big and slow means low; small and fast means high.