This is actually question my daughter posed and I’m pretty stumped. She asked how, if two people with (let’s say) perfect pitch sing a song, how is it possible that we can still tell who is singing when the notes would be identical?
Note: I know absolutely nothing about music, but figured this was the best place to ask for her.
Edit: Wow, many of these answers are incredible! I had no idea this would receive such in depth and thoughtful feedback. I have learned a huge amount. I was not exaggerating above when I said I know nothing about music (I don’t even know what pitch is – just quoted my daughter on that) and I’m grateful to those of you who took the time to help me learn.
In: Biology
Timbre of the voice is what makes it sound different. I’d suggest starting more research there!
So basically everyone has vocal chords but they’re all shaped a little different. Because of that little difference it makes the frequencies slightly different. And our bodies are also different so the way the sound resonates in my mouth before it comes out is different.
The sound isn’t just the exact pure tone of the pitch they’re singing in. Every instrument and voice has a distribution of frequencies around the main pitch, known as its *timbre*. A piano, for example, is very concentrated around a specific pitch, while a drum is more spread out (which makes piano a better instrument for expressing detailed harmonies, but also makes it sound much more dissonant if you play a note that’s a bit off).
One of the components of a musical note is its *timbre* (pronounced TAM-bur). Timbre is all the sounds associated with the source that *aren’t* part of the pure tone.
Instruments (and the human voice – hereafter I’ll just say instrument, but it works the same either way) don’t produce a pure tone. The instrument creates the root frequency, the pitch you’re trying to make, and also overtones. Take a guitar string: it will vibrate at a particular frequency, and it will also vibrate at exactly twice that, and exactly thrice, and exactly four times, and etc. The shape of the instrument and what it’s made of and the size and shape and material of the main source of vibrations (lips, reeds, vocal cords, etc.) all change which overtones get amplified and which get diminished. Your ears can hear the differences in these overtones, although your brain filters it from your conscious perception of the sound unless you focus on it.
With a human voice, this includes the size and shape of your mouth and lungs and sinuses and skull and thickness of your skull and jaw and tongue and so on and so forth. All of these things change the overtones in subtle ways, so that even when the root pitch is the same the pitches around it won’t be.
Timbre also includes all the unique sounds that come from the instrument: things like key clicks or valve movements or breath noises or little scratchy bits in your voice, etc.
Edit: “That’s not how you pronounce ‘timbre!'”
[It is in American English.](https://en.m.wiktionary.org/wiki/timbre) It is at the very least *one* correct pronunciation in English. Yes, I know it’s borrowed from French but this comment isn’t in French, it’s in English. I don’t expect everyone on the internet to understand English, but if you’re reading this in the original that means you understand English. Some 60% of the English lexicon comes directly from French so if you’re gonna get upset every time someone pronounces a French word “wrong” in English you’re not going to get very far.
A voice is an instrument. While some sound similar (some even sound almost identical), subtle differences like size, materials, shape, make them sound different. Those are odd terms to use when describing people, but a 110 lb woman is going to sound different than a 300 lb woman singing the same note. The shape of their mouth, the way they push the air out, all make a difference.
It’s like if I have a trumpet and a flute play the exact same melody. They’re both wind instruments, but they sound different enough that you can differentiate them.
Something nobody else has really touched on in depth: Waveforms.
So in really basic electronic music, you’ve got sine waves, sawtooth waves, and square waves. Every note is literally just a pulse of air at a given frequency. It’s why car engines, which are literally just exploding aerosolized gasoline, make audible notes.
There are videos you can search (I’d link one but I can’t right now) that show the relationship between frequency and pitch.
**So what does that have to do with a sine wave?**
Well the waveform is what the sound wave actually looks like. A square wave is completely no noise, then immediately completely 100% energy, then back to complete silence. A sawtooth wave is like a square wave at first, but instead of staying at 100% energy it trails to zero over time. A sine wave is just a very rounded (sinusoidal) square wave so the energy changes are smoother.
And all of those waves have different timbres, or tones.
But if we layer a sawtooth wave with a sine wave, or we decide to cut a huge divot in the top of a sine wave, you’ll get different tones still. Playing with these waveforms is precisely how electric keyboards attempt to synthesize other instruments.
Okay so now we can step away from the electronic sounds, and go back to the natural world. Horns, car exhausts, and the human throat all have characteristics that make their own wave form. There are so many things that can affect which frequencies are highlighted and which frequencies are subdued. You can choose to manipulate those with tongue placement and mouth shape, or bell shape and pipe length or construction material.
Timbre is the key thing here along with the overarching concept of tone. It’s also why any two different instruments (a violin and a saxophone, for example) can play the same note at the same pitch and be easily distinguishable.
The architectural and performance variables of the instrument play an intrinsic part in the “sound”. A saxophone — being made of metal, having a reed, and requiring air flow and key fingering — will undoubtedly create different tones than a violin — being made of wood, having strings, and requiring vibration via bow and manual input on the finger board.
All good answers.
For a five year old I’d say that a saxophone and a flute can play the same note, but they have unique shapes to their bodies causing a difference in sound. Humans also have different shapes to their bodies causing them to sound different when singing the same note.
Edit for a more complete answer to address harmonics and overtones:
Imagine having a palette of only red paints. They are all the same color (or note) but are different shades (or spectrums) of the red paint note. You can mix the lighter red shade with the darker red shade and you’ll still get a red. The color of red that a person can sing is based on their unique blending of red shades. They sing these shades based on how their body is built.
Another thing I marvel at this subject is how it takes special instruments and shapes to make music and sounds yet even a tiny speaker can recreate that special timbre.
When someone sings a note at a certain frequency (let’s say 400 Hz) it’s not just that frequency playing, it’s actually a bunch of frequencies which are whole number multiples of 400 Hz (which is called the *fundamental frequency*). So in addition to 400 Hz, you also have 800, 1200, 1600, etc, which are called *overtones*. The reason that this happens has to do with the fact that the ends of a string (or vocal cord, etc) that vibrate have to be still, a condition which can be satisfied by whole number multiples of the fundamental frequency as visualized [here](https://upload.wikimedia.org/wikipedia/commons/c/c5/Harmonic_partials_on_strings.svg). Notice how for all of the depicted frequencies, the ends of the “string” do not vibrate, meaning that it is a valid frequency for that string.
These overtone frequencies tend to get quieter and quieter the higher you go relative to the fundamental frequency, but how loud a particular overtone is relative to the other frequencies is determined by the shape and composition of the thing that is vibrating. Each person’s vocal cords and voicebox and mouth are going to be shaped a bit differently, and so different overtones will be emphasized, leading to a different sound.
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