I understand how a single sound wave works, but I’m picturing the track on a vinyl record. How is a needle riding a single soundwave playing back all of those uniquely different sounds?
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When two waves collide, they just add together. You just get one bigger more chaotic wave. No matter how many you add together you never get anything but *one* big chaotic wave.
So then if you reproduce that *one* wave, you’re reproducing all of those sounds. You’re not reproducing the direction they were traveling in, but that normally doesn’t matter – it sounds the same to your ear.
It’s because any specific sound, of any shape, can be represented by some sum of all the different fundamental (perfect sine wave) frequencies. You are making one wave, but you can also decompose it into component sine waves. This is called the Fourier Transform, and it’s an underpinning of like half of all physics.
It’s not really a generalization, because it’s also true that only that specific combination of pure frequencies will create that specific wave.
For some intuition, you should find a “Fourier Transform animation”, where progressively small circles draw out whatever shape they want. Each circle represents the addition of another frequency to the sum, and the more frequencies you add, the more precisely you can approximate the shape.
All the waves just add together, because I’m the end is just compression of air. There’s not two different air mediums to carry sound to your eardrums, and when it gets there, you don’t have multiple eardrums.
The truly amazing thing isn’t how they add together. It’s how your brain can take them back apart. That part is complex and still not very well understood. We know that it happens, we have clues about the way it works, but it’s really only modern neural networks that would come close to replicating the ability synthetically.
Sound waves simply describe the motion of air molecules at acoustic frequencies. Lower frequencies make the molecules wiggle slower. Higher frequencies make them wiggle faster.
Hold a laser pointer in your hand. As you draw the dot from left to right across the wall in front of you, large slow arm movements yield a nice sine wave with maybe two or three peaks before you run out of wall. Now, imagine the laser pointer is taped to one of those old electric razors that buzzed like crazy and made your hands tingle if you held it too long.
Repeating the same manoeuvre, sweep the draw the dot across the wall, lifting waving your arm up and down while holding the “lazor.” The dot follows a similar path as before, with the exception that the razor’s higher frequency vibration is recorded as well. The dot merely represents how a the motion of single object may be seamlessly influenced by multiple sources, which superimpose their influences simultaneously and harmoniously onto the same object.
So it is with air molecules and whatever adds energy to their motion.
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