If sound is simply vibrations, how can we hear competing sounds at the same time? What stops them from mushing together to make one sound like what happens when you mix paint together?
If sound is simply vibrations, how can we hear competing sounds at the same time? What stops them from mushing together to make one sound like what happens when you mix paint together?
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Sound coming from different angles and distances gets processed slightly differently in such a way that your brain can distinguish. Think of a red and blue checkerboard, it WOULD be purple if everything was mixed, but the light doesn’t do that on the way to your eye
Our ears and brains are really, REALLY good at doing exactly that. The reality is that they do all kind of mash together, then the super computer inside your skull separates them again.
If the sounds occupy different frequencies, they don’t really interfere. Similarly, when you drop a big rock in the water, you can see big waves it makes and the little ripples at the same time. The little ripples have a high frequency, the big waves have a low frequency.
If two or more sounds are happening with a similar frequency, then it can become muddled and mushed, just like paint. This is why you can understand one person talking just fine, have a much harder time if two people are talking at once, and 8 people talking at once just becomes an indistinguishable babble.
Sometimes they do “mush together”, the careful application of which is basically how noise cancelling headphones work.
Consider a small pile of stones on the floor. Zoom out slightly and you see that floor is actually half way up a small mound of dirt. Zoom out slightly and see that small mound of dirt is actually at the bottom of a hill. Zoom and slightly and see that small hill is actually the side of a valley. Zoom out slightly and see that valley is actually within a mountain range. Your ear drum – which is, remember, capable of movement on a single axis – is capable of recognising the small stones on its way from the bottom of the mountain up to the top.
Unlike our eyes that only work with about three light sensors our ears have much more capable tuned little sensors that can tell our brain what frequencies make the sound, their relative levels, and the phase between them. So the brain can deconstruct and get a lot of information out of that.
Think of your ears as very sophisticated stereo microphones and your brain is the best channel mixer available. Those two devices can easily discern two frequencies, so can your ears and brain. To a degree, this needs to be trained and practiced, but the hardware is easily capable of discriminating different frequencies at the same time. We can also detect timbre, so even two sounds at the same frequency but emitted from different sources can be distinguished.
Have you ever listened to the first violins play together? Then, one violin playing solo. You can easily tell the difference. That is because, while the frequencies AND the source are basically the same, they are coming from different angles and the human hear is (not as good as dogs) somewhat directional. It might be hard to hear only one violin in the first violins, though trained musicians usually can, we are capable because our brains and ears are so sensitive to it.
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It’s called auditory stream segregation—our brains group sounds together or separately based on location, frequency (high/low), timbre (tone color), and some other factors. This is why you can focus on one person talking in a room that’s filled with people talking, which is called the “cocktail party effect”
Imagine you’re in a pool. The surface isn’t perfectly smooth, there’s a bunch of little waves and perturbations on the surface. It’s “noisy”. Then your friend cannonballs into the water, and the waves from that make their way over to you.
All those little waves on the surface haven’t gone away, but you can very clearly see the waves that your friend made going through the water.
Sound is the same. Sound waves pass through each other and are still recognizable even when there is other noise.
But sometimes everything does get mushed together if it’s too noisy. Imagine you’re in the ocean instead and it’s very choppy water. The waves your friend makes by jumping in immediately get swallowed up in the chaos and after a moment you can’t really see them. It’s too noisy and loud. That’s your friend trying to talk to you at a rock concert.
Sound is vibrations, but vibrations can stack to make different shapes, and a part of the ear, called the cochlea (like a little snail shape, with hairs) helps our brain decode the shape back into its constituent frequency parts by resonating at different frequencies that get turned into electrical signals.
Our brains are pattern recognition machines.
While one sound pattern is happening, other patterns are happening around it, at the same time, each one distinctly separate. Sometimes the sounds do have overlap, like the same frequency happens at the same time.
If we just had one moment of time like this to hear what’s happening, with 2 or more overlapping layers of identical sounds, that would be nearly impossible to distinguish what’s happening.
But luckily, we usually have the benefit of knowing what each pattern sounded like before and after that brief confusing moment.
We have other inputs helping us, such as sight, which lets our brain connect the dots and let us understand what was most likely heard from each source of sound. For example, watching someone’s lips while they are talking in a loud environment might help you hear what they are saying better even if you can’t “read lips” too well normally.
Sound vibrations combine two important features: amplitude AND frequency.
If you “listen” to only a nanosecond of a vibration you can maybe determine the amplitude of the sound wave at that moment in time compared to your calibrated zero-level, but there is no way to tell what frequencies are possibly at play if you’re only going off that amplitude versus your baseline amplitude. See this overly-zoomed example where it’s hard to even venture a guess what multiple competing frequencies might be at play on the graph of the math function.
But if you listen to a long-enough clip – relative to the (inverse of) frequencies you’re investigating – then monitoring the evolution of the amplitude makes things more discernable. See this nicely-zoomed version of the same example where you can see three-and-a-bit “big” waves, each with a lop-sided shape and lots of littler waves on top. In this case it is possible to see the wider patterns and “subtract them out” as seen here.
I’m answering as a physicist acknowledging that you asked with a biology flair, so I’m focusing on the sound itself and not the ear as I’m not expert in that.
We can distinguish “simultaneous sounds”, because they have unique interference patterns. This is means that any combination of simultaneous sounds are basically new sounds that we can distinguish from individual ones. We know there is “something else”, because it is different from what we would hear if we heard just one note or one person talking. They don’t really “compete” to be heard, rather they just combine to form something new.
Similarly to colors, when you combine colors, you get something new each time: one does not erase the other and what registers is the sum of the components.
Whether you can effectively distinguish between component sums or components that appear as sums of components depends on the quality of the sounds used, the quality of the mixing and how good the instrument is in distinguishing (for bio this probably means genetics basically).
>What stops them from mushing together to make one sound like what happens when you mix paint together?
They do mix together like paint and that is how we can tell the difference.
Depending on what paints we mix together our eyes see a certain color. Most paint colors are not made from just a single color or even a couple of colors but are made up of different levels of a bunch of colors.
Sound is very much like that where our ears/brain identify different mixes of vibrations as different sounds.
Think about musical instruiments. A violin plays a single note but that isn’t a single vibration. It is a bunch of vibrations that get mixed together and our brain identifies it as a violin.
You can have a bunch of different instruments all take turns playing the same note and each one will sound different because they have a different profile of sounds mixed together.
As others have answered our brains are also good at separating out sound profiles so you can also distinguish different subgroupings at the same time like a lawnmower and a telphone both at the same time.
It’s called a complex sound wave. The wave that hits your ear is a mathematical combination of all sound around you.
Cool thing is when waves of different frequencies come they form a new more complex wave consisting of these base frequencies. No information is actually lost in these waves and you can mathematically separate a complex wave into its base frequencies using something called a fourier transform. This is how computer handles signals.
But our ears do essentially the same thing. Differents parts of the ear vibrates at different frequencies and are thus able to separate out the complex sound wave into its base components, like a real life fourier transform.
It’s called the Superposition Principle:
> The superposition principle, also known as superposition property, states that, for all linear systems, the net response caused by two or more stimuli is the sum of the responses that would have been caused by each stimulus individually.
Note that although Fourier Transforms are deeply rooted in this principle, the human brain does not perform a Fourier Transform. The human brain performs a Wavelet Transform using wavelets very close to the Morlet Wavelet. In other words, the human ear isn’t so much a simple frequency analyser as it is an active non-linear filter.
you can separate those sounds back into individual frequencies with a Fourier transform.