How can the human ear (the brain, really) clearly discern more than one sound at a time?

Question

I understand how sound is generated by pressure waves vibrating the eardrum. And this makes perfect sense to me when a single sound is generating that vibration. But when multiple sounds are vibrating the eardrum at the same time (like when listening to music with different instruments and vocals) how does the brain tease those differing vibrations apart so we can hear the individual inputs…as opposed to them mixing all together into one sound; The equivalent of mixing a bunch of different paint colors together and ending up with brown.

In: Biology

Answer 1

ELI5: When sounds are added together a completely new sound wave is constructed that is an amalgamation of both waves.

Think of waves in a pool. If you have one person making the waves at one end of the pool using the same amount of energy every time, then you’ll see one set of waves moving across the pool in an orderly fashion.

But what if two people are say… 10 feet apart and both make the same type of wave. Do you still see one wave in the pool? No. You see places where the waves add together, and places where the waves cancel each other out. This “addition” of both the waves together is actually a unique wave in itself. This is how sound works as well. Each individual sound “adds” together to make a new, unique, sound wave. Our brains are just good at picking out one sound in that sound wave. (Computers are also very good at it.)

ELI’mOlder: What you want to look up is related to Fourier Transform. It’s a math… thing… but you don’t actually need to know the math. Watch this video from where I linked it (at 50s).

You only need to watch until ~2:00.

A fourier transform is the way we program computers to separate sounds, or rather, the way we program the computer to be able to identify certain individual sounds in a sound amalgamation.

Our brain does the same thing, and that’s how we can pick out a “single” sound among an array of others.

Also, the sound “addition” is also how a single speaker with a single moving component can produce many different tones at once (aka music!)