Dog on a leash theory . . .
This is more of a newbie explanation on the behavior of compressors. For anyone interested. I call it my "dog on a leash theory of compression":
The dog is like the audio signal. It wants to run off and do it's own thing. Chase squirrels, smell poo, etc. Sometimes it will jerk suddenly, like when it sees a cat or rabbit, and other times it will just gradually try to make you walk/run faster because your two legs are too slow for him. This is what makes him unique, and gives him the qualities of a dog. On the other hand, you the owner want him to express himself, but you also want to maintain some control over him.
Imagine that you are walking Fido towards a brick wall that is several feet in front of you.
The leash is your compressor. It keeps your dog under controll, moreless. Depending on it's slack and the elasticity of it's fiber, it puts you in the driver's seat of how much leaway your dog has to roam (how loud your audio signal will get).
Now you have control over this by what kind of leash you use. You can put your dog on a really short leash made of inelastic fiber, which will basically give him no breathing room to "be a dog" and to express himself. Or you can put him on a longer leash with more elastic fiber. This will give him more breathing room, but you have to be on your toes, because you're sacrificing some control over him.
Attack/Release:
The elasticity of the leashe's fiber is like the attack control on the compressor. A shorter attack time on an audio signal means you aren't giving the signal "very much slack" so to speak. Audio signals will be under tighter control, and won't be as dynamic. As soon as they try to get too loud, the compressor (or the leash) will keep it in tighter check.
A longer attack time is like using a more elastic material on the leash. You still maintain control as long as your dog doesn't stretch the leash's material beyond it's breaking point -- something that happens to my old socks and underwear a lot -- But he still has a little more freedom for sudden jerks, like if he sees a squirrel, he can at least start to chase it for a few seconds before the elastic starts to "snap back" and gain control over him. In audio terms, this would make for a punchier sound (longer attack time).
Ratio:
The ratio of the leash (compressor) would be how much "snap back" the leash has once it exceeds it's elasticity. Let's suppose there is 8 feet of slack available before the leash's elastic starts kiciking in and pulling him back. 8 feet is now your "threshold." Now let's suppose he jerks away from you suddenly to the distance of 12 feet. That's 4 feet beyond your threshold.
The ratio will determine how much beyond this threshold he gets. A 2:1 ratio on the leash/compressor would pull him back to 10 feet in front of you. Divide the distance he runs beyond the threshold (4 feet) by 2, and you get two feet beyond the threshold, or 10 feet. A 4:1 threshold would ensure that he only gets 1 foot beyond the threshold (4 divided by 4), so he would only get as far as 9 feet in front of you.
Limiter:
Now getting back to the brick wall that you are walking towards: This is like the limiter. It's your last barier of protection, really. Let's suppose your dog sees a squirel run by, and he jerks suddenly away from you to chase after it. Perhaps he jerks so fast that the leash slips out of your hand, or maybe even snaps it. The brick wall ahead of you insures that he won't get beyond that point. At the last second, the squirrel may swerve to the left or to the right, but the wall is there, and the dog won't be able to get past it. Maybe it will even hurt his head (hard clipping) if he runs in to it hard enough. Perhaps it will have a cushion placed on it to soften the blow (soft clipping). But the brick wall is there as your last line of defense to make sure he doesn't get away from you.
And in the audio world, you can set the elasticity of the leash (attack time), as well as it's recovery time (release). You can set the exact point at which the leash will become firm, tighten and start pulling him back (threshold), and when all else fails, there is a brick wall in front of you (limiter) . . . and you can even decide how far ahead of you to place the brick wall (the limiter's threshold).
