So if an A is 440hz, why does a piano playing an A sound different than a violin, a guitar, or someone’s voice making that same A 440 note? It’s obvious that the pitch is the same on each instrument but each instrument has a distinct sound. I’ve never heard an A on a piano and thought, is that a piano or a cello. Why can we distinguish between instruments?
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A cello string vibrating at 440hz is also vibrating at a bunch of other frequencies like 220 and 110 just to start, nice even multiples or fractions of 440. and thousands of others as well. The shape of the instrument amplifies some frequencies and mutes other so you get in the end an unique “signature” made of the combination of all these waves. Even two cellos would have slightly different sounds an expert might be able to tell apart. A piano has a different sized string, different shapes, and of course is not played with a bow, so it will have a very different signature. If you took a cello string and a piano string and just stretched them across a couple of nails on a 2×4, they would sound much more alike.
Another good example of the weirdness of timbre is when you breathe helium. Your voice sounds high pitched and squeaky. But if you sang a 400Hz note after breathing helium, it’s still going to be mostly 400Hz. But just like a cello, your vocal chords are also vibrating at 800Hz and 1600Hz etc. The helium does not alter the frequency of your voice. It alters which frequencies are amplified. so you are still singing 400hz but the 800 and 1600 hz tones are amplified more. That’s a different Eli5 but for simplicty think of helium as changing the instrument and not the note.
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