The Third Property of Sound: How Strong Is the Vibration?
Whisper someone's name, then call it across a courtyard. Same word, same voice — totally different effect. What you changed is intensity, the third of the four properties that describe every sound.
You already know that sound is a vibration traveling through the air. There are four independent questions you can ask about any vibration. How fast does it vibrate? That is pitch. How long does it last? That is duration. How strong is it? That is intensity — what everyday language calls volume or loudness. (The fourth question, what the sound is made of, is timbre: the subject of the next lesson.)
A lullaby only works quietly; a victory fanfare only works loudly. Before you can use that power on purpose, you need to see where it comes from.
Amplitude: The Size of the Vibration
Pluck a guitar string gently and watch it: it shivers in a narrow blur, and you hear a soft note. Pluck the same string hard: it swings in a wide arc, and the note rings out loud. In both cases the string vibrates at the same speed — that is why the pitch does not change. What changed is the width of the movement. That width is called the amplitude.
The rule is direct: more energy in, wider vibration, louder sound. This is why a drummer lifts the stick higher for a loud hit, why a pianist drops the key faster for a bigger tone, and why you push more air to sing louder. Intensity is energy made audible.
Same frequency, different amplitude — the tall wave is the loud one.
Science measures sound intensity in decibels (dB). A whisper sits near 30 dB, a normal conversation near 60 dB, and a full orchestra can pass 95 dB. You will never need to count decibels to make music, but the scale confirms what your ear already knows: sounds range from barely there to overwhelming.
The harder the strike, the wider the skin swings — and the louder the sound.
Loud Is Not High: Intensity and Pitch Are Independent
Everyday language sets a trap here. We say "turn the volume up" or "the music is too high", and that word high collides with the high of pitch. In music they are two separate dimensions. A note can be:
- high and soft — a violin harmonic floating at the edge of silence;
- high and loud — a trumpet call;
- low and soft — a cello murmuring under a melody;
- low and loud — a bass drum at full force.
Pitch is the speed of the vibration; intensity is its size. You can change either one without touching the other. A singer proves it with every swell on a held note: the pitch stays perfectly still while the sound grows.
Any pitch can be played at any intensity — the two properties never constrain each other.
From Intensity to Dynamics: How Music Writes Loud and Soft
Composers refuse to leave intensity to chance. A musical surprise only works if the orchestra whispers first; a finale only feels triumphant if it rises above everything before it. So notation developed dedicated signs for intensity, called dynamics. The two foundation words are Italian: piano for soft, forte for loud — yes, the piano is literally named "soft-loud", because, unlike the harpsichord before it, its touch could play both soft and loud. You will learn to read these signs, and the whole family built around them, in the lesson on piano and forte.
For now, keep the chain in mind: amplitude is the physics, intensity is what you hear, dynamics are how music writes it down.
Intensity in Action: Three Musical Examples
Haydn, Symphony No. 94, "Surprise" (1791). The slow movement opens with a tiptoeing, quiet theme — then the full orchestra detonates a single fortissimo chord. Audiences have jumped in their seats for over two centuries. The joke is built from pure intensity contrast — nothing else changes.
Ravel, Boléro (1928). One melody repeats for about fifteen minutes while the orchestra grows from a nearly inaudible snare drum to a roaring full ensemble: one enormous, slow-motion crescendo across the entire intensity axis.
Your own keyboard. Choose any key and play it five times, from the softest sound you can produce to the loudest. The pitch cannot change, however hard you strike. Five identical notes, five different intensities: that is this whole lesson under your fingers.
Common Mistakes About Loud and Soft
- "Louder means higher." No — loudness and pitch are independent. Playing louder increases the amplitude of the vibration, not its speed, so the note stays exactly as high or as low as before.
- "Hitting the piano key harder plays a different note." It plays the same note with more intensity. The string is struck harder and swings wider, but it still vibrates at the same frequency.
- "Intensity is fixed by the instrument." Every instrument — and your voice — commands a wide intensity range. A trumpet can murmur; a guitar can shout. The player decides, not the instrument.
Practical Tips for Training Your Intensity Control
- Play the five-level game. On a piano or any instrument, play one single note at five clearly different levels, from almost nothing to full sound. If two neighboring levels sound identical, slow down and exaggerate the contrast.
- Practice the steady-pitch swell. Sing a comfortable note and grow it from a hum to full voice while keeping the pitch frozen. Record yourself and listen back: at first, the pitch tends to creep upward as you get louder.
- Map a piece. Listen to any recording you love and draw its intensity curve on paper — where it whispers, where it peaks. You are training the same ear you will soon use to read dynamics.
FAQ
Is intensity the same thing as volume? In everyday use, yes: volume is the common word for perceived intensity. Strictly speaking, intensity is a property of the sound itself, while volume often means a playback level on a device. Musicians usually say a sound is loud or soft.
Does playing louder change the pitch of a note? No. Loudness comes from amplitude, the size of the vibration, while pitch comes from frequency, its speed. You can change one without changing the other — which is exactly what a swell on a single held note does.
What is the amplitude of a sound? Amplitude is the width of the vibration that creates a sound — how far the string, drum skin, or air column swings from its resting position. Larger amplitude means a louder sound; smaller amplitude means a softer one.
Summary
- Intensity is how loud or soft a sound is — the third of the four properties of sound.
- It depends on amplitude: the wider the vibration, the louder the sound.
- Intensity is independent of pitch and duration: any note can be played at any level.
- In written music, intensity becomes the dynamics: piano for soft, forte for loud.
You can now hear how high a sound sits, how long it lasts, and how strongly it arrives — but when a violin and a flute play the same note at the same intensity, something still tells them apart: timbre, the color of sound.