What a note is actually made of - and what makes two notes sound different.
Back to the Music MapTry it
Start the tone: the wave then travels across the picture, the same way it travels through the air.
Heavily slowed down: in reality this whole picture fits into 20 thousandths of a second. Faster than a screen can show or an eye can see.
What do you notice?
What keeps repeating in the picture while the tone runs?
What it's called
Vibration – a back-and-forth movement that repeats itself the same way – for a note, many hundreds of times a second.
Why
This is what a note looks like when you record it: a movement that keeps repeating itself. The line in the middle is rest, top and bottom are the turning points - just like a swing.
A note is air wobbling back and forth very fast. A plucked string nudges the air next to it, that air passes the nudge along, and your eardrum ends up wobbling in the same rhythm. That is all there is to it.
There are exactly three things you can change about that wobble: how fast it goes, how far it swings, and what shape it has. Those become pitch, volume and timbre - and this page covers the first and the third.
Volume only comes up in passing: it already has its own slider in the settings panel, and it is the only one of the three that says nothing about the note itself.
Why is sound at the very top of the Music Map?
Everything that follows in music - notes, intervals, scales, chords - is a statement about sounds. Once you know what a single note is made of, the rest reads as a continuation rather than a new set of rules.
Quick check
After you pluck it, a string swings less and less far. What mainly changes?
Try it
Drag the slider while the tone is running. The waves move closer together, because more of them fit into the same 20 thousandths of a second.
9 waves in 20 ms
What do you notice?
What happens to the waves in the picture as the tone gets higher?
What it's called
Frequency – how many times something swings back and forth in one second, counted in hertz (Hz).
Why
How fast the wobble goes is the pitch. It is counted in hertz: 440 hertz means 440 times back and forth in one second. Faster means higher - there is nothing more to it.
Double the frequency is exactly one octave up - the same note, just higher. That is why 110, 220, 440 and 880 hertz are all an A.
Why the slider moves through an octave at the same speed at the top and at the bottom: the ear hears ratios, not differences. From 110 to 220 Hz is an octave, from 770 to 880 Hz not even a whole step – although both are 110 Hz apart. That is why every octave takes up exactly one third of the slider.
Quick check
A note vibrates 330 times a second. Where is the same note one octave higher?
Try it
Tap both: the same note, one octave higher. Watch how much of the string is still vibrating in the picture.
What do you notice?
How much of the string is still vibrating when you fret at the 12th fret?
What it's called
Scale length – the vibrating length of the open string, from nut to bridge – about 63 to 65 cm (roughly 25 inches) on most guitars.
Why
A shorter string vibrates faster, in exact inverse proportion: half the length, double the frequency. That is why the 12th fret sits exactly halfway between nut and bridge, and the note there is the octave of the open string – 110 Hz becomes 220 Hz, like the jump on the slider above.
It is also why the frets get closer together towards the body: every fret shortens the string by the same fraction – just under 6 percent of what is left –, not by the same distance.
Thickness and tension decide how high a string sounds when open – that is why the low strings are thicker, and why you tune with the tuning pegs. While playing, the only thing you change is the length: that is what the frets are for.
Quick check
Only a quarter of the string is vibrating. How much faster than the open string?
Try it
Tap them in order: every overtone is a note of its own, each higher than the last. On the guitar: rest a finger very lightly right above the fret wire, don't press, pluck, let go.
What do you notice?
Where does the string stand still while it vibrates?
What it's called
Overtones and harmonics – overtones are the parts a string vibrates in at the same time – halves, thirds, quarters. A harmonic is an overtone you let ring on its own.
Why
A string never vibrates only as a whole. At the same time it vibrates in two halves, three thirds, four quarters – every part shorter, so higher: twice, three times, four times as fast as the open string. These overtones always ring along, you just don't hear them separately.
Rest a finger very lightly on a spot where an overtone stands still – a node – and you stop every vibration that doesn't stand still there. What is left is the overtone. The nodes of the first overtones sit at the 12th, 7th and 5th fret.
That is why the harmonic at the 7th fret doesn't sound like the note you fret there. Both are an E, but the harmonic is three times the open string (330 Hz), while the fretted note sounds an octave lower (165 Hz). The harmonic is a fifth above the octave.
What a fifth is: IntervalsCloser to the nut there are more: just before the 4th fret, five times the open string (two octaves and a major third). And every node has a twin – the one at the 7th fret is also at the 19th, the one at the 5th also at the 24th. Many people tune with harmonics: the 5th fret of one string against the 7th of the next. It isn't perfectly exact – the overtones are pure, the frets are equal-tempered; the difference is a fiftieth of a semitone.
Quick check
Both at the 7th fret of the A string: once fretted, once as a harmonic. Which one was the harmonic?
Try it
All four run at the same frequency. Start the tone and switch between them - the pitch stays, everything else changes.
What do you notice?
What stays the same when you switch the shape – and what changes?
What it's called
Timbre – how a note sounds, regardless of how high or loud it is.
Why
Same pitch, different sound: that is timbre. It lives in the SHAPE of the vibration - it is how you tell a guitar from a trumpet, even when both play the same A.
The bars show what is inside the shape: every shape is a fundamental plus overtones, each at its own strength – the same overtones as on the string, just mixed artificially. The sine has none, the sawtooth all of them, square and triangle only every other one. Which overtones ring along, and how strongly, makes the timbre.
Why all four sound equally loud: without balancing, the square would be clearly louder than the sawtooth, and switching would first sound like a jump in volume. The page balances the energy of the four shapes – whatever still sounds different is timbre. That square and sawtooth still seem more present is part of it: the ear is especially sensitive to high overtones.
Quick check
A piano and a violin both play the same A at 440 Hz. What makes the two sounds different?
Try it
A sine tone, for comparison: no string, only the fundamental.
Tap all four – the same note, and yet four sounds. On the guitar: the open high e string, plucked over the 12th fret, over the sound hole and close to the bridge.
What do you notice?
Which one sounds brightest, which one most hollow – and which one doesn't sound like a guitar at all?
What it's called
Overtone spectrum – which overtones a sound contains and how strong each one is – its fingerprint.
Why
A sine tone is a single tone without overtones. A string, on the other hand, always vibrates in many parts at once – that is why it never sounds like a sine, but like a string.
Where you pluck decides which overtones ring: an overtone with a node at the plucking point stays silent. Over the 12th fret you hit the node of every even one – they are missing, the sound turns hollow and soft. Close to the bridge there is hardly a node nearby, the high overtones stay strong: bright, almost metallic.
Guitarists use this all the time: softer over the fretboard, sharper at the bridge – without changing strings.
The bars are calculated, not measured: an ideal string, judged by the force with which it pulls on the bridge. On a real instrument the body, the string material and the decay shape the sound as well – the high overtones die away faster than the low ones, which is why a plucked note gets softer as it rings out.
Quick check
You pluck at one third of the string, measured from the bridge. Which overtone is missing?
Try it
The lowest note is the open low E string, the highest the high e string at the 24th fret.
What do you notice?
How much of the hearing range do the guitar's notes need?
What it's called
Hearing range and pitch range – what the ear can hear – roughly 20 to 20,000 Hz – and what an instrument can play.
Why
The guitar's fundamentals reach from 82 Hz to 1319 Hz – a narrow strip in the middle of the hearing range.
Its overtones reach far beyond, into the thousands. They make the sound bright – and they are why you can recognise a guitar even from a phone: its speaker hardly puts out anything below about 300 Hz, yet from the overtones the ear works out the missing fundamental.
The upper limit drops with age: many adults hardly hear anything above 15,000 Hz. For the guitar that matters little – what counts in its sound lies far below. The slider above runs from 110 to 880 Hz: three octaves, right in the middle of where the guitar plays.
Quick check
The hearing range reaches from 20 to 20,000 Hz. Roughly how many octaves is that?