eli5 How does the brain separate out frequencies it’s hearing so that we can make out different instruments in a song? It seems like some insanely complex analysis behind the scenes??
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At the ear level, there are hair cells which bend in response to sound. They’re arranged in a way where lower frequencies will stimulate one area of hair cells and higher frequencies another. This signal is then transduced to the brain to the auditory cortex, where frequencies are then encoded. From what I remember the auditory cortex separates high and low frequencies by location though with all things with the brain it’s pretty complex.
Your ears can also do something called the attenuation reflex, where a muscle in your ear contracts which stiffens the tympanic membrane, which can minimize the amount of high intensity sound that gets transmitted to your inner ear.
At the ear level, there are hair cells which bend in response to sound. They’re arranged in a way where lower frequencies will stimulate one area of hair cells and higher frequencies another. This signal is then transduced to the brain to the auditory cortex, where frequencies are then encoded. From what I remember the auditory cortex separates high and low frequencies by location though with all things with the brain it’s pretty complex.
Your ears can also do something called the attenuation reflex, where a muscle in your ear contracts which stiffens the tympanic membrane, which can minimize the amount of high intensity sound that gets transmitted to your inner ear.
At the ear level, there are hair cells which bend in response to sound. They’re arranged in a way where lower frequencies will stimulate one area of hair cells and higher frequencies another. This signal is then transduced to the brain to the auditory cortex, where frequencies are then encoded. From what I remember the auditory cortex separates high and low frequencies by location though with all things with the brain it’s pretty complex.
Your ears can also do something called the attenuation reflex, where a muscle in your ear contracts which stiffens the tympanic membrane, which can minimize the amount of high intensity sound that gets transmitted to your inner ear.
The brain does not know the instruments. That part is learned: frequencies like x, y, z combined are a flute, etc.
Hearing scientist here.
Sound is a type of wave. Waves have some interesting properties that mean you can combine two waves of different frequencies (pitches) together to get a more complicated wave. But, you can also take a complicated wave and work backwards to figure out what frequencies made it up.
The part of your ear that turns physical waves into electrical signals headed for the brain is called the cochlea. It’s structured so that the high frequency waves can only get into the start of it before getting stopped, but low frequency waves can get further in before getting stopped. This means the cochlea can tell what pitch the sound is by how deep the wave travels. This lets the brain figure out what pitches it’s hearing, and in what amounts.
Now, the other side of this is that a given instrument actually plays multiple notes at the same time (even if they’re only trying to play a single note) and these extra notes are what gives the instrument its tone. Our brains are really good at spotting the patterns that make up these different sounds, a bit like an acoustic fingerprint.
Some sound engineering can make this easier. By putting, say, the guitar through the left channel, the keys through the right, and the singer equally in the two, it makes it easier for us to separate out the different sounds because our two ears are hearing different mixes. If something is happening in both ears, we know it’s the singer, but if it’s only in the left then it’s the guitar. (It’s not usually that extreme, but that’s the basic idea.)
So yeah, there’s a mix of how our ears work mechanically, some maths, our pattern recognition, and good sound design.
Hearing scientist here.
Sound is a type of wave. Waves have some interesting properties that mean you can combine two waves of different frequencies (pitches) together to get a more complicated wave. But, you can also take a complicated wave and work backwards to figure out what frequencies made it up.
The part of your ear that turns physical waves into electrical signals headed for the brain is called the cochlea. It’s structured so that the high frequency waves can only get into the start of it before getting stopped, but low frequency waves can get further in before getting stopped. This means the cochlea can tell what pitch the sound is by how deep the wave travels. This lets the brain figure out what pitches it’s hearing, and in what amounts.
Now, the other side of this is that a given instrument actually plays multiple notes at the same time (even if they’re only trying to play a single note) and these extra notes are what gives the instrument its tone. Our brains are really good at spotting the patterns that make up these different sounds, a bit like an acoustic fingerprint.
Some sound engineering can make this easier. By putting, say, the guitar through the left channel, the keys through the right, and the singer equally in the two, it makes it easier for us to separate out the different sounds because our two ears are hearing different mixes. If something is happening in both ears, we know it’s the singer, but if it’s only in the left then it’s the guitar. (It’s not usually that extreme, but that’s the basic idea.)
So yeah, there’s a mix of how our ears work mechanically, some maths, our pattern recognition, and good sound design.
Hearing scientist here.
Sound is a type of wave. Waves have some interesting properties that mean you can combine two waves of different frequencies (pitches) together to get a more complicated wave. But, you can also take a complicated wave and work backwards to figure out what frequencies made it up.
The part of your ear that turns physical waves into electrical signals headed for the brain is called the cochlea. It’s structured so that the high frequency waves can only get into the start of it before getting stopped, but low frequency waves can get further in before getting stopped. This means the cochlea can tell what pitch the sound is by how deep the wave travels. This lets the brain figure out what pitches it’s hearing, and in what amounts.
Now, the other side of this is that a given instrument actually plays multiple notes at the same time (even if they’re only trying to play a single note) and these extra notes are what gives the instrument its tone. Our brains are really good at spotting the patterns that make up these different sounds, a bit like an acoustic fingerprint.
Some sound engineering can make this easier. By putting, say, the guitar through the left channel, the keys through the right, and the singer equally in the two, it makes it easier for us to separate out the different sounds because our two ears are hearing different mixes. If something is happening in both ears, we know it’s the singer, but if it’s only in the left then it’s the guitar. (It’s not usually that extreme, but that’s the basic idea.)
So yeah, there’s a mix of how our ears work mechanically, some maths, our pattern recognition, and good sound design.
The brain does not know the instruments. That part is learned: frequencies like x, y, z combined are a flute, etc.
The brain does not know the instruments. That part is learned: frequencies like x, y, z combined are a flute, etc.
Not a complete answer, but a significant portion of your brain is actually busy filtering all the “data” it gets from your senses. If it didn’t, you would constantly be overloaded with a lot of useless information. So a large part of what you see and hear isn’t actually preceived consciously. A by product of that is: for it to filter effectively, the brain needs a way to separate and categorise stuff, so it knows what to filte rout and what to keep in.
Coincidentally most “data” we receive from our senses has an intensity factor to it by ehich it can categorise stiff. Like how loud a sound is, or how fast it vibrates the air. How hot or cold a surface is. How many particles of a specific odor reach your nose.
I’m no neuroscientist, but I suspect it uses these diffwrent intensities to categorise it. Think of a sorting machine sorting objects by size. Bigge robjects go through bigfer chutes, smaller ibjects go through smaller chutes.
For your hearing: instead of the size, it measures how hard certain hairs in your ears vibrate. And instead of the chute it sends a stronger or weaker electrical pulse to your brain. Multiple sounds simply send multiple signals at once, and activate different braincells.
[I’ll scratch this parts if it turns out completely wrong.]
As for a fun side note from my personal life:
As someone diagnosed with aspergers, my brain is wired slightly differently than the avergae brain. I notice I’m more sensitive to sound in certain situations.
Rubbing together paper towels doesn’t really make much of sound, but I get an uncomfortable itch even from a fair distance away when someone uses a paper towel.
I also go to church and when we sing together I can still pick out many individual voices at once, and pinpont their exact origin. In a crowd of 400 I can still pick out about a dozen indivuals nearer to me. All while hearing the “crowd” sound and accompanying music as well. Not sure how rare this is, as I suspect conductors are often capable of this as well.
Side effect for me is that hanging around in crowds gets tiringvfor my brain and I often need some alone time after an hour or two. I also noticed that a few drinks of alcohol make this ability dissapear, which is handy when I want to hang around longer at parties.
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