How is it possible that your brain can turn a sound wave (say 3000mhz) and it can sound like a voice, car, or an alarm?

Question

I just can’t wrap my head around it. Is it just crazy brain things, a difference in number of waves, or some other thing? How is it possible that a speaker can replicate all sounds?

In: 24

Answer 1

The sounds you hear are never just a pure wave. If you were to record them, using a microphone, and look at the graph of pressure over time, you would never see a basic sine wave. Every real sound is a combination of many of those waves.

To visualize this easier, imagine it like one of those wave pools that have many pusher plates, like [this one](https://youtu.be/pir_muTzYM8). They can create the most basic kind of wave by just going back and forward at regular intervals, but they can also activate independently at different times and create different waves with different frequencies and different offsets that all mix together in the pool. Those are like the sounds around you, all mixing together in the air, which, when interacting with your ear, will come together as one singular, complex wave. As a sidenote, your eardrum works the same way as those pusher plates on the pool, just in reverse. The differences in pressure push the drum in and out, and your brain registers it.

There’s a mathematical operation called a Fourier transform that makes it possible to take in a complex wave and break it down into every single simple wave that made it. Your brain does the exact same thing, just unconsciously and extremely quickly. That way, it can separate all the sounds from everything around you and tell the dog barking apart from the fan going in the background.

The actual “sound signature” of each object exists because they, themselves, produce a complex wave instead of a simple one. They have a frequency and an amplitude (which we perceive as the pitch and the loudness respectively), but they have a distinct shape. That’s how a violin and a flute can be playing at the same pitch and the same volume but still sound completely different. [Here](https://www.researchgate.net/figure/Waveforms-of-different-instruments-at-a-particular-frequency_fig1_305333971) is a graph visualizing the difference for a couple instruments. A tuning fork is built specifically to get as close as possible to the pure sound, to a basic sine wave with the specific frequency it’s tuned to.