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Compression: "Common Knowledge" Questions Dynamics Processors (HW)
Old 14th August 2008
  #31
Gear Nut
 

A lot of this is obvious, but just stick with it for a second and hopefully I can illustrate that compression does have the effect of "flattening" or reducing the dynamic range of your pre-compression EQ. I'm not saying this is a bad thing, sometimes you want the compressor to work like this, just trying to explain what is happening.

Compression reduces the dynamic range of whatever signal is feeding it. There's a lot of different reasons you might want to do this, one of them is that it lets you turn things up to the point that, were they not compressed, they would start clipping. Let's say that's our goal for compressing this particular signal.

So lets say you boost 15 dB at some frequency, doesn't matter which one. That will probably become the loudest part of the signal, for this exercise let's assume this is what happens. So now this boosted frequency is what will trigger the compressor whenever the signal gets too loud...BUT the signal is NOT ALWAYS triggering the compressor. Now think about what happens.

Your signal is going along fine, no compression, your EQ curve is perfectly intact, and then it hits a big peak. Since we established earlier that your EQ boost made the frequency you're boosting the loudest part of the signal, that is what is triggering the compressor. In other words, if you DIDN'T have the compressor, the EQ would have made the boosted signal so hot it would have clipped.

But the signal didn't clip...so what happened? Since the uncompressed EQ curve would have caused clipping, and clipping didn't happen, the EQ curve MUST HAVE been changed! Specifically, while the compressor was acting, the boosted frequency was turned down. This means while the compressor is acting on your EQ, it's reducing the dynamic range of your EQ. So while an uncompressed EQ would yield a 15dB boost, and clipping, the compressor, when active, makes it a smaller boost but doesn't allow the signal to clip. An EQ curve that has 10dB from highest boost to lowest cut would visually appear FLATTER than an EQ curve with 15dB from highest boost to lowest cut. That's how a compressor flattens EQs.
Old 14th August 2008
  #32
I find EQ's work best without compression. They do like expansion. I like dynamics, lots of them. I'm weird.

Jim Williams
Audio Upgrades
Old 14th August 2008
  #33
Lives for gear
 

Quote:
Originally Posted by TheBSper View Post
That's how a compressor flattens EQs.
Again, you are correct regarding the Flattening of the EQ over time.

However, Like I said, if you take a constant tone, boost one frequency so that there is no change over time, just a solid, consistant tone with a bump at 1k, the Compressor WILL NOT affect the frequency makeup. it will compress the entire signal the same amount and all frequencies will simply be turned down by the same amount.

It is very content-dependent.

If you have a very complex source material, like drums, then if you had a very boosted frequency that happens to get exacerbated when a cymbal hits, the compressor will clamp it down and might be able to release before the snare hits, leaving the snare unaffected, and ultimately, making the EQ seem flatter "Over Time".

But again, DURING that moment when the compressor clamps down on the track when the cymbal hits, everything around the cymbal is getting turned down too..

So what might be more accurate to say is.
"Simply compressing the signal will NOT affect pre-compression EQ, but the act of a compressor turning on and off over a given amount of time may appear to flatten the EQ depending on the source material."

Think of it this way- if you boost 20hz by 1000dB on a flute track and throw a compressor on there, it wont make a difference because there is no 20hz material in a flute track to affect the compressor..

You are still boosting that frequency range by a TON, but the compressor is not affected by, nor affects it.

only if, somehow, over time that flute track happens to approach a sound close to that frequency, it will get magnified, compressed, and look possibly like nothing ever happened. but again, that is ONLY over the TIME domain.
Old 14th August 2008
  #34
Gear Nut
 

Quote:
Originally Posted by DarkEcho View Post
"Simply compressing the signal will NOT affect pre-compression EQ, but the act of a compressor turning on and off over a given amount of time may appear to flatten the EQ depending on the source material."
Right on, that's what I was getting at. You're also right that it won't have the same effect on a constant tone, but since most (if not all) of what we deal with in our day-to-day compression work is complex signals I wanted to make sure I got my point across.

Good stuff, this thread really makes you wrap your head around the interactions between different signal processing.
Old 14th August 2008
  #35
Lives for gear
 

Yeah, definitely. I am still trying to wrap my head around how EQ after a compressor more behave differently..

As you said, usually never are we dealing with constant tones, but I was just using it as a demonstration for the "single-instance" argument.

if you were to boost a certain frequency of a track, whenever the instrument being played enters that frequency area, it will get magnified by the shape of the bell and if you have a compressor after that, then the compressor might flatten out the EQ work you did..

I think maybe this is why compressors are so hard for people to understand, because they are soooo source dependant, it's hard to explain much of anything..


Even EQ is very source dependant..

I mean, if you boost 500hz on a piano, if you are playing the very top keys, you probably wont hear as much of the effect as if you move down the board to the notes around A440 that actually have their most powerful frequency/fundamental AT the boosted area.

So EQ isnt just tone shaping, its tone shaping changes depending on the notes being played...

AKA: Just turning up the higher frequencies wont make the bass sound "trebly", given, there are probably going to be overtones and harmonics produced by the bass that reach those frequencies, but the as you start to move up the fretboard to notes that have a fundamental in the boosted range, you will suddenly have a significant increase in volume. Where you were just boosting as "garnish" to the bass, you are not boosing the bass notes themselves.
Old 14th August 2008
  #36
Gear Nut
 

Exactly, which is why so much of this business is experience. There's just so many different ways sounds and gear can interact that it takes a long time and lots of trial and error to get a good grasp on everything. That being said, a post way back around the beginning of this thread suggested doing corrective EQ then compression then creative EQ, and I kind of agree.

I usually do moderate EQ before compression and anything crazy (kick drums, stuff that can have HUGE boosts and cuts) after. Otherwise the compressor can limit the extreme range of dynamics that I'm trying to get by having such a drastic EQ.
Old 15th August 2008
  #37
Lives for gear
 
Unclenny's Avatar
Quote:
Originally Posted by synthoid View Post
If that's so, then the makeup gain doesn't affect the signal in any way except how loud it is.
I'm thinking that makeup gain imparts more of the character of that particular compressor.


Sugarland Rain
Old 15th August 2008
  #38
Quote:
Originally Posted by synthoid View Post
Hmm? We agree that the compressor applies gain reduction when the input is too hot -- above the threshold. The question is, what does the makeup gain do? I am under the impression that in most compressors, it is simply an amplification stage at the output of the compressor -- provided as a handy way of restoring overall power levels in light of the gain reduction applied by the compressor.

If that's so, then the makeup gain doesn't affect the signal in any way except how loud it is.

But maybe you are saying that in some compressors the makeup gain is integrated in a different way into the circuit?

-synthoid


Anything I've seen called a "compressor" has make up gain. A lot of people will say that that amplifier has some color or mojo or whatever. But, I find that the ratio and the action of the compressor are what impart the coloring of the sound.

Do the experiment - instead of using the make-up gain, boost it on the return to the board. If you have iron in the signal path (output on the compressor or input on the console) then you might hear a slight difference. But that's from the transformer.




-tINY

Old 15th August 2008
  #39
Lives for gear
 
synthoid's Avatar
 

Quote:
Originally Posted by tINY View Post


Anything I've seen called a "compressor" has make up gain. A lot of people will say that that amplifier has some color or mojo or whatever. But, I find that the ratio and the action of the compressor are what impart the coloring of the sound.

Do the experiment - instead of using the make-up gain, boost it on the return to the board. If you have iron in the signal path (output on the compressor or input on the console) then you might hear a slight difference. But that's from the transformer.




-tINY

Now it sounds like you're saying the same thing I thought I was saying all along, haha, which is that the makeup gain is simply a gain stage. So I think we're in agreement!

-synthoid
Old 15th August 2008
  #40
Gear Guru
 
u b k's Avatar
 

Quote:
Originally Posted by DarkEcho View Post
If a loud sound happens at the same time as a 10db quieter sound, the compressor will turn them both down equally, and the quieter sound will still be 10db quieter than the loud sound, but they will both be quieter than they originally were.

it's not that simple. what matters is how those two sounds relate over time as the comp is doing its thing. if the sound that's 10db louder gets 13db louder over a given period of compression, then it will be compressed more than the quieter sound. the easiest way to hear this is to mix a tom fill too loud then strap a comp across the mix; if you set it up right, it won't sound like the whole song being ducked on the fill, it'll just pin the fill back into the music.

with the possible exception of the atomic squeezebox, compressors are most definitely *not* the equivalent of a fast hand on a fader riding the gain.

attack time has a big impact on the perception of freqs, esp. high freqs, as do the ratio and the amount of gain reduction... all depending on the character of the comp in general. with a lot of comps, the more you dig in the more it attenuates the highs; with others, the more it excites them.

then there's the detector and what it's sensitive to. there are comps like the 525 which react veerrryy touchy to low mids and so they tend to spread the sound out, while something like a 33xxx will react more to the vocal range and tend to sound squishier in that range the more you dig in.

this is why you can feed the same signal to 30 different comps and when you crank a certain freq first you'll get somewhere between 25-30 different sounds on the other end.


gregoire
del
ubk
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