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
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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