More Compression

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barryh

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Ok, I've been reading alot about compression over the past few months and bought one of them Behringer Composer things to play around with. I was finally actually able to make some productive use out of it last night recording some bass tracks. (It really seemed to smooth out my farcical slapping "technique").

But this I'm still not sure of:
I know that the compressor reduces the gain of a signal that's above the "threshold". Does it also increase low level signals, which some of the stuff I read seems to suggest? Does this question make sense even? (I can never be sure!)

-Barry
 
I think Chessrock sums it all up perfectly in the other thread just below.

I hope he won't mind me posting his reply in that thread, but it really is an exceptional analogy. You can tke this to the bank...or the dog park if it suits you...

"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)."
 
Wow, I like a good analogy and that was a great one. The scary thing thing is that I pretty much actually understood it. I'm still not sure about one thing, though. But instead of trying to word the question, maybe someone could tell me if the following statement from my "composer" manual is a typo or something. It says:

"As it is the desired effect of a compresser to increase a low level signal, generally the threshold is set low"

This just doesn't fit with everything I think I've learned about compressors/leashes...I thought the compressors were all about reducing as opposed to "increasing". Maybe I should just ignore that sentence and move on.

Thanks!!!
Bow-wow-wow-yippie-O,
-Barry
 
By turning the loud signals down, you are, in effect, raising the volume of the quieter signals, but a compressor doesn't actually raise the volume of quieter signals. It just seems to....does this make sense?
 
I can't think of any dog analogies for this one.

But try this: Think of the loud parts: an aggressive snare hit, or a sudden burst of energy from the singer . . . which we refer to as "transients" or "sudden jerks" on the leash in dog terms. These are small moments that are louder than the rest of the signal.

If you leave these signals the way they are, then you'll be forced to turn your volume down, for fear that these transients will pop up out of nowhere and blow your speakers (or worse yet, your ear drums). This means you'll have to strain a bit to hear the otherwise quieter parts.

When you use a compressor to tame these sudden jerks in volume, then you are allowing for a more consistant volume. Now you can turn your volume up nice and loud without fear of the sudden jerks doing any harm. The quieter parts are still technically the same volume, but since you are now able to turn your main volume up, they are now louder,

Think of the name: "compressing." That's what you're doing. You're compressing the audio signal to keep it consistant in volume. Volume is all relative. By making louder parts quiet, you are making the quieter parts louder (in relation) and vice-versa.
 
Good answers - this is just a little bit of further elaboration or restatement, since it can be confusing to a beginner.

"Compression makes loud parts softer and soft parts louder" is a bit of an oversimplification, and not entirely accurate.

As has been stated, when you compress a signal you are making some or all of the signal SOFTER. If your threshold is set high, it will only decrease the level of the very loudest parts. If the threshold is set very low, everything will come out at a lower level.

Attack time also figures into this: if the attack time is long, the faster transients will pass through unaffected and undiminished in volume. A very short attack time will capture/attenuate all or most of the transients.

Your ratio determines how much the signal is diminished once it crosses the threshold. For example, a 5:1 ratio means that if the original signal increases 5 db, after engaging the compressor that same signal will only increase 1 db. When you get up to ratios of 20:1 or more, it is considered limiting, since almost any increase in volume will produce a negligeable change after compression. Usually limiters are set with a high threshold, otherwise you would be removing all dynamics from the material.


If you look at the controls on your compressor there is usually one called "make-up gain". This is where the "soft parts louder" comes in. After using a compressor to compress (or limit) audio material, you end up with a "softer' result and less total dynamic range. The makeup gain lets you then raise the entire result - the entire track gets louder by the amount of makeup gain you apply.

BUT...since you have first applied compression, the loudest parts are now closer in dynamics to the softest parts. This not only creates available headroom to raise the entire track, but gives this result: the very loudest parts are actually raised back (with makeup gain) to THE SAME level as they were before (assuming they were at or near max volume), but since the softest parts are now closer in level to the loudest parts, they are dragged up in volume to a higher level than they were originally. This makes the average level of the track sound hotter, as well as keeping the softer parts from being overwhelmed or hidden by other tracks in the mix.

I've probably just made things more confusing. Sorry! :(
 
Damn, two good anwers in a row. You're on a roll, tonight. The force is strong in you. I get the feeling you're not the typical newb. Look, there's this other newb by the name of Tyler something or other. I want you to be his mentor. Just look around for all the really intelligent comments. Those will be his. You can sort of be his obi-wan. I'll be your Yoda. Alright? :) :)

Seriously, though. Good posting.
 
awww... you're makin' me blush!

So, how many posts do I need before i shake the Newbie handle, anyway?
 
Posting does not a newbie make. Intelligence makes you a senior member, it does.
 
octoruss said:
Posting does not a newbie make. Intelligence makes you a senior member, it does.
Click to expand...

Guess you can just call me "Newbie-For-Life" then! :D
 
>>>>I've probably just made things more confusing. Sorry

Um, no. Those last couple of posts really cleared some things up for me in a *big* way, in way that the manuals/books I've reading haven't. Big ol' light bulb is on. Big ol' light bulb!

Thanks,
-Barry
 
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