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
I think there’s a better and more interesting answer than the ones posted here, even though they’re all good explanations.
The “note” a singer, or any other instrument makes, is a frequency. Literally “how **frequently** does the sound oscillate?”
With a guitar, it’s “how frequently does the guitar string oscillate?” Meaning vibrate. If you watched a guitar string in slow-motion, you’d be able to see it vibrating after it was plucked. You can kinda see it even without slo-mo, it’s just a blur.
With your voice, it’s flaps of skin in your throat that are vibratring.
If someone sings an A#, that means their vocal chords are vibrating 466 times per second. Everyone singing an A# at the same time is vibrating their vocal chords 466 times per second.
But sound is MORE than just a frequency, which you know if you think about it. It’s also an “amplitude.” Which means “loudness.” We could both be singing A#, but I might sing louder than you. Same note, two different volumes.
But sound also has a SHAPE! Which is SUPER COOL! Let’s look at the “purest” tone, which is called a [Sine Wave.](https://www.wisc-online.com/assetrepository/getfile?id=3768&getType=view&width=0&height=0)
That is a real simple wave and because it’s so simple it would make a very pure tone if you listened to it. But **pitch** is **just** frequency. A wave with a different **shape** but the same **frequency** would be the same pitch, but could sound very different.
Let’s look at a different kind of wave. What’s called a [Saw Wave.](https://qph.fs.quoracdn.net/main-qimg-41c43d0e532ac48adf72c485e31c5e33-c)
You can see why it’s called a saw wave, right? Looks like the teeth of a saw!
Well, this makes a VERY different sound. It sounds…actually it sorta sound the way it looks! It has an *edge*. It’s not as pure as the sine wave. When you listen to any bowed instrument, the sound you’re hearing is a Saw Wave, because that’s the actual physical motion of the string!
[Watch this!](https://preview.redd.it/5azm0uox03y21.gif?format=mp4&s=ea49e13ee62118531858184d756c3b8047f810a2)
(the preview might not be working)
https://preview.redd.it/5azm0uox03y21.gif?format=mp4&s=ea49e13ee62118531858184d756c3b8047f810a2
You can see it there. The bow is pulled across the string. At first, the friction of the bow catches the string and pulls it smoothly back. That’s the “ramp up” of the saw wave. Eventually the tension in the string overcomes the bow’s friction, and the string ‘snaps’ back. Which is the sharp, straight-down line of the saw wave. But the bow is still pulling, so the string gets caught again and the cycle repeats.
Saw Waves and Sine Waves are still pretty simple though. The waves produced by the human voice look *weird* and *messy.* [Look!](https://i.stack.imgur.com/lhC4Y.gif)
If you look on the graph, everything from the 1 hash, to the 8 mark is ONE cycle. That is a complex wave and it’s still way simpler than the human voice. The human voice looks more like [this.](https://www.researchgate.net/profile/Jody_Kreiman/publication/281119746/figure/fig6/AS:668580781752330@1536413488325/Waveform-showing-extreme-aperiodicity-phrase-finally-by-a-female-English-speaker.png)
THAT is why two people singing the same note are recognizably different. They’re vocal chords are vibrating VERY complexly. So complex, it’s almost unique! When you recognize someone’s voice, you’re recognizing the unique properties of the SHAPE of the wave their vocal chords make. That shape is based on the physical shape of their vocal chords and their throat and even their mouth which is helping shape the sound as it comes out.
The **rate** at which their skin flaps vibrate might be the same, but because their skin is floppy and weird shaped, it doesn’t just go smoothly up and down like a guitar string. It waggles all over WHILE going up and down and that is what singers and musicians call “timbre.” Timbre means “The way your skin flaps waggle around while you vibrate them.”
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