I'll bet you didn't know that your ears are lying to you. Oh yes. They only let us hear a small range of sound, the stuff between 20 and 20-thousand cycles per second (or "hertz"..a kilohertz is a 1000 of those cycles, usually abbreviated "KHz"). So there are lots of sounds out there you can't hear...right now. They could be wonderful, but you'll never know, thanks to your lying ears.
Why should you care?
Well, if you're a musician, or voice actor, a recording engineer, or just recording audio for podcasts and videos, this knowledge is crucial. Here's why.
Our ears still lie to us EVEN when the sound IS in that 20-20KHz range, the bastards. Some sounds seem louder to us than others even when they are at the same volume, like a baby's cry (around 3 KHz - this will really blow your mind - or maybe you'll just find it boring).
Rooms, those big boxy things we normally spend a lot of time in, change how a sound....well....sounds. If sound were like light, your typical bedroom would be kinda like a house of mirrors; but you wouldn't be able to SEE the mirrors! Put a little candle in just the right place in that room, and it gets reflected by so many mirrors that is seems like a search light.
But if you move that same candle to a different spot, you might not be able to see it at all. You also should know that just about every room in the world has a different mirror set-up.
Now imagine that someone asked you use that first room to create a very specific color and intensity of light bulb. Maybe they want it for something kinky, I don't know. But their specs say it needs to be "a soft red, and very subdued." Now remember that we can't see the mirrors. We set to work adjusting the controls on our bulb-maker until we get one that puts out a nice, soft red light with just the right amount of "subdued."
You confidently take your light to the client, who puts it into a socket in his room, and suddenly it's really bright, and now a kind of fire-engine red! What happened to the bulb? It looked great in your room. Nothing happened to the bulb. It is as it was when you made it. But the mirrors in the client's room (the ones you can't see) are different from the ones in yours, and they cause the light to be reflected differently, making it APPEAR different.
Which one is right? Neither! Hah, you're starting to get angry at me now, aren't you? But it's true, and it's just like audio. Until you can find a room with no mirrors, or at least with the biggest ones removed or shifted to eliminate the worst of the reflection problems, you literally CAN'T know what the bulb's light really looks like.
How Does This Translate To Audio?
Well, if my room tends to amplify bass frequencies, my ears would tell me that there was too much bass in a song when there really wasn't! So I might respond by turning the bass down on the equalizer (EQ) too much before I burn the song to CD. In that room, it sounds fine because the bass is being artificially boosted by the room itself.
But as soon as I take it my buddy's room, which is larger, or my car (which in the case of home recording may ALSO be larger:)), I might find there is no bass left at all in the recording!
The only real way to deal with all of this ear-lying nonsense is to know a little something about HOW they lie, which means you gotta get familiar with EQ and all that stuff about Hertz and crying babies. That way, you'll at least know how to get a much more accurate picture of the truth, and your sound will sound good in ALL rooms, not just yours. If you are of a mind to dive deeper into the world of EQ and frequencies, a great place to start would be our article What is Equalization, Usually Called EQ?