Something absolutely amazing is how our cute little ears separate out distinguishable sounds from all of the noise hitting them. I don’t mean this in a poetic way. On the street with all the noises of the cars and birds and wind and kids, you can hear all of those things individually. This is absolutely amazing.
It’s amazing because the only thing which actually hits your eardrum is a single wave. Each sound producing thing on the street sends a wave of sound outward, and they are all trying to enter your eardrum at the same time. This is a messy process. They don’t all take it in turns, or go in in different regions, instead they all pile up on top of each other into one big wave which is a combination of all of these individual sources.
It’s like if you have two people each holding and end of a really long piece of rope, long enough that they can’t see each other. They only way they can communicate is by sending waves down the rope by flicking it up and down. If at one end someone starts moving the rope up at down at a regular rate, so that nice clean waves get sent down the rope, the person at the end can easily see these waves and look up in their special wave-to-English dictionary what their friend is trying to communicate.
This is exactly the same situation as listening to a pure tone (say middle C) except that the rope is the air in between the speaker and your eardrum (which of course are the two people).
Real sounds are rarely pure tones. Instead of one of the friends with the rope wiggling it up and down at a regular rate, it’s like he moves it frantically all over the place, with little or no regularity. This is the wiggly, crazy looking waveform you tend to see on your screen if you record something on a computer.
When you have multiple sounds at once it’s even more complicated: it’s like having multiple people competing to move the rope up and down at the same time. Of course, at each point in time they will all disagree about where the rope should be, so they’ll end up taking an average of where they each want it. If two people think it needs to be up high, and one of them thinks it needs to be low, than it’ll end up somewhere in between (but somewhere toward the high end, as there are two who want it there).
In the same way, when you are on the street, or at a concert or in any situation in which there are lots of separate sounds, all of these waves are fighting to move your eardrum around. What ends up going into your ear at each instant is an average of all of these waves. Amazingly your brain is then able to separate all of these sounds apart from each other, even if you have never heard that type of sound before! You can isolate the people talking from the birds, or the piano form the orchestra. If you are at some funky concert with a bizarre instrument made from, I dunno, linen and pork-chops, chances are you can isolate that even though your brain doesn’t know a priori what waveforms from that instrument “look like”.
There are exceptions though. If sounds are similar enough it is hard to distinguish them without practice: for example, sometimes it’s almost impossible to hear which is the cello and which the violin in a string quartet, if they are playing the same notes. Your brain is naturally good at telling stuff apart, but you can train it to be even better with practice. I guess this is true for other senses too: foodies and wine-snobs (Winies? What’s the proper term for one of them? Oh yeah… oenophiles) practice to be able to distinguish finer graduations of taste than the built-in functionality affords.
One of the things I had trouble with when I started listening to classical music was that it all sounded the same. I found it really hard to distinguish the instruments in the orchestra, which may have been why I was so into piano concertos. Everyone can hear the piano. At some point I must have practiced enough that my brain could start to distinguish things, and suddenly it sounded a lot more like music.
One of the wonderful things about music is that we can switch between listening via concentrated focusing, and letting it all pour into our ears in one gloriously messy, arguing, intricate river of sound.
