# Why does the same note sound different on a piano and a guitar?

> Both instruments play nearly the same set of frequencies. The recipe and the timing are what differ.

https://learnfold.app/wait-how/same-note-different-sound/ · Updated 2026-10-30

A piano and a guitar playing the same A share the same basic frequency and nearly the same family of harmonics stacked above it. The difference is in the proportions and in the timing. Each instrument sets its strings moving differently and passes the sound through a different body, so the harmonics come out in different strengths, and each note starts, fades and changes over time in its own way. Your ear reads both.

## What is a note actually made of?

Pluck a string and it doesn't just swing back and forth as one arc. It vibrates at its lowest frequency, called the fundamental, and at the same time at two, three, four and more times that frequency. Those components are the harmonics. Together they repeat at the rate of the fundamental, which is why you hear one pitch rather than a chord.

Real strings bend that rule a little. UNSW's acousticians note that a string's bending stiffness affects its higher modes more than its lower ones, so the overtones are stretched, each sitting slightly sharp of an exact whole-number multiple. They add that pianos, especially small ones, are less ideal in this respect than harps. So the harmonic series on a real piano is a little less tidy than the textbook version.

The music acoustics group at UNSW Sydney describes a sound spectrum as a "sound recipe", a list of how much of each frequency is in the mix. Two notes with the same pitch use nearly the same ingredients. They can still taste very different if the amounts change.

Timbre is the name for that difference, and it is defined in a slightly awkward way. UNSW puts it as the sum of all the qualities that differ between two sounds with the same pitch and loudness. In other words, timbre is everything left over. That should already hint that one number won't capture it.

## Why do the harmonics come out differently?

Start with how the string gets moving. A guitar string is pulled aside and let go. Where you pull it matters a lot. Sandra Carral's work on guitar plucking, summarised for the Acoustical Society of America, explains that plucking at a point where a particular vibration mode has a still point (a node) leaves that mode out. Pluck exactly a third of the way along and the 3rd, 6th, 9th and 12th harmonics go missing. Pluck at a fifth and the 5th, 10th and 15th drop out. As a rule, plucking nearer the bridge sounds brighter.

What you pluck with matters too. A sharp plectrum bends the string into a sharper corner, and Carral notes that this accentuates the higher harmonics, which is why a pick sounds brighter than the flesh of a thumb.

A piano string is struck instead. The hammer is a felt-covered block that stays in contact with the string for a short but real time. In Donald Hall's lecture on piano hammers, the effective hammer mass runs from about 12 grams in the bass to 6 grams in the treble, and in the middle of the keyboard the contact lasts about half of one vibration of the string. That soft, finite push shapes the spectrum. Hall shows that the simplest textbook models of a hammer blow predict spectra that don't match real pianos, and that you have to include the contact time to get close.

Then there's the body. In the piano, the string's vibration passes through the bridge into the soundboard, which Klaus Wogram describes as the part that turns mechanical vibration into radiated sound. It doesn't do that evenly. The board has a series of resonances, it radiates best between roughly 100 and 2,000 hertz, and which resonances a string excites depends on where along the bridge it is attached. So the soundboard tilts the recipe again before the sound reaches you. A guitar's strings drive a much smaller wooden body through its own bridge, which is one more reason the two recipes differ.

## Why the timeline matters as much as the recipe

A spectrum is a snapshot. A note is more like a short film. It begins, peaks, and dies away, and the harmonics don't all rise and fall together.

The piano has an unusual film. In his lecture on coupled piano strings, the physicist Gabriel Weinreich describes the note as starting loud and decaying quickly, then switching to a much slower decay that leaves a quiet tail. He calls this combination "the miracle of the piano tone". Your ear judges loudness mostly from how a sound starts and sustain from how it lingers, so the piano manages to sound both loud and long. Weinreich ties the speed of the decay to how strongly the strings are coupled to the soundboard through the bridge. Strong coupling gives a loud sound that dies fast. Weak coupling gives a quiet sound that lasts.

A guitar note has its own film, and the player can change it. Carral cites measurements showing that a pluck at right angles to the top gives a strong tone that decays quickly, while a pluck parallel to it gives a weaker tone that rings longer. Same string, same note, different envelope.

Switch the recipe and press Play to watch the fade, or scrub through it. Play tone adds optional synthesized audio after a tap; the pitch and all model strengths are illustrative.

## Timbre is more than the harmonic mix

This is the usual textbook answer, and it is only half right. UNSW makes the point directly. You can't look at a harmonic spectrum and say which instrument made it. Their thought experiment is to filter a violin note so its harmonics match a trumpet's. It would still sound like a violin.

There is an equally popular overcorrection, which says the identity is all in the attack, the first fraction of a second. As a 2019 paper by Kai Siedenburg puts it, sound onsets are commonly considered to play a privileged role in identifying instruments. Siedenburg tested that with resynthesised sounds, made with and without their rapid transients. Removing the fast transients at the start barely hurt listeners' ability to identify instruments. Taking the sample from the middle of the note instead of the start hurt a lot more. His reading is that the start of a note matters because of how the harmonics build up in that window, not because of the rapid transients themselves.

The harmonic recipe matters, and so does the way that recipe changes over the life of the note. Neither alone is enough. If you want a single image, think of a face. The spectrum is a still photo of it. The envelope is the way it moves when it talks, and you'd recognise a friend from either, but far more easily from both.

## So what makes a piano sound like a piano?

Put the pieces together. A felt hammer strikes, so the harmonic balance differs from a plucked string. A big soundboard with its own resonances shapes it. The note jumps up and then fades in two stages, loud first and then a long, soft tail. A guitar is plucked, its harmonics depend on where and with what, its much smaller body shapes the sound differently, and its decay follows the plucking direction. Play the same A on each and your ear gets two different recipes and two different films.

Related: [how noise-cancelling headphones work](/wait-how/how-noise-cancelling-headphones-work/), which also comes down to adding waves together, and [what bees see that you can't](/wait-how/what-bees-see/).

## Two-stage fades and two singers

Weinreich's two-stage decay deserves a page of its own, and the sideways version of this whole question is why two people singing the same note sound different. In Learnfold you can select the passage about the decay, ask why, and the discussion is saved for later. Or pick a "Where next?" door and get a new linked page. A sharper question tends to get a sharper answer, so here is [how to write better questions for an AI tutor](/guides/write-better-questions-for-an-ai-tutor/), and [what following your curiosity looks like](/use-cases/follow-your-curiosity-rabbit-hole/) over a few pages.

## Quick answers

**What is timbre?**

Timbre is the quality that lets you tell two sounds apart when they have the same pitch and the same loudness. It depends on which harmonics are present and how strong they are, and on how the sound starts, changes and dies away.

**What are harmonics in music?**

A vibrating string or air column vibrates at a basic frequency and at whole-number multiples of it at the same time. Those multiples are the harmonics. Real strings are slightly stiff, so their upper overtones sit a little sharp of exact multiples, and piano strings show this more than harp strings. The lowest one sets the pitch you hear, and the mix of the others shapes the character of the sound.

**Does where you pluck a guitar string change the sound?**

Yes. Plucking closer to the bridge gives a brighter tone. Plucking exactly a third of the way along the string leaves out the 3rd, 6th, 9th and 12th harmonics, because those modes have a still point there.

**Why does a piano note sound loud and long at the same time?**

A piano note fades in two stages. It starts loud and drops quickly, then settles into a quiet tail that decays slowly. Listeners judge loudness mostly from the start and sustain from the tail, so the note seems to have both.

**Can you tell an instrument from its harmonics alone?**

Not reliably. Acousticians at UNSW point out that you can't look at a harmonic spectrum and say which instrument made it. How the sound changes over time carries much of the identity.

## Sources

1. [What is a sound spectrum?](https://newt.phys.unsw.edu.au/jw/sound.spectrum.html), UNSW Sydney, Music Acoustics (Joe Wolfe's group)
2. [How harmonic are harmonics?](https://newt.phys.unsw.edu.au/jw/harmonics.html), UNSW Sydney, Music Acoustics (Joe Wolfe's group)
3. [Plucking the string: the excitation mechanism of the guitar](https://acoustics.org/pressroom/httpdocs/160th/carral.html), Acoustical Society of America, lay language paper (Sandra Carral)
4. [The coupled motion of piano strings](https://www.speech.kth.se/music/5_lectures/weinreic/weinreic.html), Five Lectures on the Acoustics of the Piano, KTH and the Royal Swedish Academy of Music (Gabriel Weinreich)
5. [The hammer and the string](https://www.speech.kth.se/music/5_lectures/hall/hall.html), Five Lectures on the Acoustics of the Piano, KTH and the Royal Swedish Academy of Music (Donald E. Hall)
6. [The strings and the soundboard](https://www.speech.kth.se/music/5_lectures/wogram/index.html), Five Lectures on the Acoustics of the Piano, KTH and the Royal Swedish Academy of Music (Klaus Wogram)
7. [Specifying the perceptual relevance of onset transients for musical instrument identification](http://oops.uni-oldenburg.de/3951/), Journal of the Acoustical Society of America (Kai Siedenburg, 2019), University of Oldenburg repository