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Understanding Compression Dynamics Processors (HW)
Old 16th December 2010
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Understanding Compression

I'm going to throw this up as I think it will be a helpful post. It's not totally comprehensive, but it's a good start.

1. What is dynamic processing?

A dynamic processor is something that outputs a signal, where the level of the outgoing signal is based on the level of the incoming signal. In other words, a loud signal coming in will come out differently than a quiet signal coming in.

2. What are the basic types of Dynamic Processors?

Compressors - the most common - the louder the signal is coming in, the less level it provides going out. In a compressor, a target level is set - called the "threshold" - and any signal coming in that exceeds that level will be reduced. The higher the level is above the threshold, the more reduction is done. More on this later.

Expanders - the quieter the signal is coming in, the less level it provides going out. In other words - it makes quiet signals even quieter. Much like a compressor, the threshold is set at a certain level. Any signal that does NOT exceed that threshold is reduced, and the quieter the signal, the more reduction is done.

Limiters - limiters are like super compressors. The idea is to ensure that the level does not exceed the threshold. Because this amount of compression is extreme, a limiter relies on certain functions and design that regular compressors do not have.

Gates - gates are like super expanders. Anything that does not exceed the threshold is reduced to inaudible. Again, because gates are extreme, they often require a slightly different design than a regular expander.



Now - I'll focus primarily on Compression, because that's going to be the most commonly used dynamic processor.

----------------------------------------------------

COMPRESSION

Every signal you hear is compressed. ????? Yes, every signal you hear is compressed.

Bare with me. Imagine you have a rapper in front of a microphone. The rapper raps, you record. You play it back. You haven't used any processing - you're just playing back the raw vocals.

You are listening to a signal that has gone through at bare minimum 3 stages of compression - and more likely than not - it's closer to 6.

The microphone capsule gains tension as the rappers voice pushes it - in other words - it pushes back - and the more the rapper's voice pushes in - the harder the capsule diaphragm pushes back. In other words, the louder the signal hitting the capsule, the more reduction the capsule does to the signal. That's compression! (It's mild compression, but it's still compression).

Along the way through the microphone, you may hit a tube. Tubes have a non-linear response to voltage - the response is quite curved, and also changes the frequency balance of the signal. This is called saturation - which will tend to "round out" a signal, by reducing the loudest peaks. Compression! And before leaving the microphone, the signal may hit a transformer as well, which will saturate in a similar way. (more compression).

The preamp is going to have multiple stages of saturation - and often times, the more gain you give something - the deeper that saturation curve goes. In other words, the more you drive the signal at the preamp, the more compression the signal experiences.

Then the sound has to actual come out the speaker cones. Well, those speaker cones are going to build up tension when pushed further. See where this is going? This is called "cone compression".


Ok - so this is a bit of a simplification - but there's a point here. The point is that "compression" is always part of the signal. Some mics have less of it, some have more - same with speakers, tubes, transformers, etc. And they all do it in different ways. With tubes, people will talk about their saturation curves and THD (total harmonic distortion - or frequency alterations). With mics people will refer to how it "grabs" a sound - or more specifically - the sound's shape. These all add up to really the most important ideas:

Frequency and Shape!

Instead of thinking of a compressor that compresses - think of it as something that changes the shape of a sound. If you start listening for "shape" the mysteries of compression will reveal themselves to you, and fairly quickly.

Setting a compressor is like setting a mold for the signal to fit into. The threshold determines where the compressor starts working, the ratio is how hard it's going to work, the attack is another way of saying how sharp will the transient sound be, and the release is how much tail or sustain do you want to emphasize.

Yikes! Time out!

What the hell is a transient? A transient is a very fast signal - in other words the "attack" of the signal. Drums have transient attacks. Strings have gradually risinng attacks. So the attack control on the compressor is really like saying - how much emphasis on the attack of the signal do you want? Do you want the attack to be really rounded out and diminished? Set the attack low. Do you want the attack to be prominent and stick out? Set the attack high. Of course, this works directly in conjunction with the threshold. Try it yourself, set the threshold low, and the attack short. Suddenly, the attack sound of your snare is gone. Set the threshold low and the attack long. Suddenly the punch of your kick is very round and bouncy. Set the threshold high and the attack short. Now the snare is a little fatter and rounder, and not quite as s***** (but possibly a little duller). Set the threshold high and the attack long - the change is hardly noticeable, the attack is just a little bit "rounder."

How to achieve maximum punch?

There is a thin line between a transient sound, and a sustained sound. A sound that holds for any noticeable amount of time is sustaining. A sound that moves by too quickly to register as it's own moment is transient. But transients can vary in length. A transient can be half a millisecond. It could also be ten milliseconds. And those won't sound the same. A big factor in punch is how long that transient exists. A quick transient sounds "s*****" - but a long transient sounds "punchy." You want to find the point that makes the transeint exist as long as possible before "flattening out" or becoming a sustained sound. Only your ear can tell you where that point is.

Good samples are already shaped to have that kind of impact - and any additional compression may soften that. Of course, punch has a lot to do with frequency as well - but that's for another thread.

Now what about the release? The release is super elusive. It deermines how long it takes for the compressor to let go. If the release is too short for the signal you are going to get a disjointed sound shape which usually results in distortion. If it's too long, your signal never really returns to its natural shape, and you generally lose tone. So the idea is to find a point that emphasizes the sustain (which is where most of the signals tone lives) properly.

Lastly, when the attack and release are set in a way that seem to argue - the compression can become very audible. You either hear the decent or the acent of the signal level. This is called pumping. It's generally annoying, but can sometimes be used an effect.

----------------------------------

So, rather than think of a compressor as something that effects the "level" of a signal. Think of it as something that effects shape. Why? Because level can be controlled with the volume fader more accurately and transparently. A fader doesn't really control shape, unless you are being extremely meticulous. Conversely, compression will always effect the shape of the sound it is working on.

Once you start hearing shape, you will understand compression.
Old 16th December 2010
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Old 16th December 2010
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storyville: singlehandedly saving the hip hop forum.
Old 16th December 2010
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Quote:
Originally Posted by ncoak View Post
storyville: singlehandedly saving the hip hop forum.
All in a days work?
Old 17th December 2010
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Quote:
Originally Posted by ncoak View Post
storyville: singlehandedly saving the hip hop forum.
Lets ****ing hope so.
Old 17th December 2010
  #6
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Excellent post! We could use more like this from the seasoned vets.
Old 17th December 2010
  #7
great post

Would love to hear you do one on EQ
Old 18th December 2010
  #8
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Quote:
Originally Posted by phillysoulman View Post
Lets ****ing hope so.


btw, thanks storyville
Old 18th December 2010
  #9
Gear Head
 

Thank you for that. We need more posts like this. It's amazing how much people use compressors simply because they think it's necessary without even knowing why.
Old 18th December 2010
  #10
T1M
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i hate to be the one to say it but...

tl;dr
Old 18th December 2010
  #11
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Quote:
Originally Posted by ncoak View Post
storyville: singlehandedly saving the hip hop forum.
heh So True.
Old 18th December 2010
  #12
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illacov's Avatar
 

Quote:
Originally Posted by Storyville View Post
All in a days work?
What up Story!

Compression is very easy to misunderstand and abuse, so posts like this are very helpful.

You have to know the basics of compression before you can truly begin to understand its important in the creation of modern and old school music alike.

These posts should give people a definitive insight into your new service Story!

Peace
Illumination
Old 18th December 2010
  #13
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Storyville's Avatar
Quote:
Originally Posted by rexall75 View Post
Thank you for that. We need more posts like this. It's amazing how much people use compressors simply because they think it's necessary without even knowing why.
EXACTLY. People use compression, because they know other people are using compression - and what never gets communicated is that all sound has shape and frequency balance. Compressors and eqs primarily serve for adjusting those to the shape and frequency balance that you WANT. But if you don't have the end game in sight you probably don't get the most out of compression and eq.
Old 19th December 2010
  #14
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Quote:
Originally Posted by Storyville View Post
EXACTLY. People use compression, because they know other people are using compression - and what never gets communicated is that all sound has shape and frequency balance. Compressors and eqs primarily serve for adjusting those to the shape and frequency balance that you WANT. But if you don't have the end game in sight you probably don't get the most out of compression and eq.
Do you generally compress or EQ first, and why?
Old 19th December 2010
  #15
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Quote:
Originally Posted by T1M View Post
i hate to be the one to say it but...

tl;dr
That's your problem. This guy is offering some great lore. On top of that, his writing style is clean and efficient. If this is "too long" and you're not willing to invest a little time in reading it, especially if you don't already know that much about compression, I dunno man.


"You can have anything. Anything for which you are willing to struggle." - Eric Thomas

Blake

EDIT: Thanks Storyville! Great post :D
Old 19th December 2010
  #16
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Great post as usual Story !

And yes, the other part is now to understand when to apply it...the "what for ?".

And that usually comes from experience and/or feedback for the beginners...
Bigger transient on drums, or crushing them a little more is usually appreciated nowadays.

Bigger transients also bring sounds forward in the sonic scenery...

Things like that might be a motivation to apply compression or not.. Since I am still self taught, it took me (or is taking me rather) about 3 years to understand and I'm not even close to the better results.

The whole thing about mixing is that even when you know all the concepts, picking the moment when they apply the best and getting your ears to know when you should/ "might want to" apply them is quite difficult..
Old 19th December 2010
  #17
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Quote:
Originally Posted by CRACKPIPE View Post

File:Mercedes-Benz CL203 CLC180 Kompressor Heck 1.JPG - Wikimedia Commons

the only "compressor" most of my "rapper" clients are familiar with.......hahah
this is a great thread! It's so clear that I wish more people would not read it so I will still have a job! cheers!
Old 19th December 2010
  #18
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Quote:
Originally Posted by Twig View Post
File:Mercedes-Benz CL203 CLC180 Kompressor Heck 1.JPG - Wikimedia Commons

the only "compressor" most of my "rapper" clients are familiar with.......hahah
this is a great thread! It's so clear that I wish more people would not read it so I will still have a job! cheers!
Don't worry about having a job - this is the music business....

Just kidding(?)

Anyway, the point B.A.S.E made is right on the money. My (apparently too long) article is to illuminate a concept. The real skill comes from knowing when the sound is shaped correctly, or being able to hear how a sound SHOULD be shaped. If I could teach this from an article I'd deserve a prize.

Then, there comes in the bigger picture - because dynamics, frequency balance, and space are all tied together in one mighty Jenga tower. Being able to work that relationship is conceptually difficult, and in practice even harder to master.

@yosemitisam - to answer your question in a way that illustrates the point I am getting at: I eq and compress exactly at the same time. If I use an eq, I am also effecting the shape, if I use a compressor, I am also effecting the tone. So even if I only compress, I am in effect also eqing. Compressing something generally changes the tone - it eqs the signal. EQing will highlight or supress certain frequency bands which will be more present in certain parts of the sound.

For example - if I eq up a lot of treble in a kick drum - the attack sound of the kick becomes pronounced. Similarly, if I use an expander to turn the sustain of the kick down, the attack sound will also become pronounced.
Old 19th December 2010
  #19
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Quote:
Originally Posted by Salty James View Post
great post

Would love to hear you do one on EQ
I'm going to let this one marinate for a moment, but eventually I'll write something on EQ.

However, I wouldn't mind hearing your thoughts on EQ, or dynamic processing for that matter.
Old 19th December 2010
  #20
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Hey Mate, thanks for that. I also recently read what you wrote about Reverb. Both have been very helpful. You have a unique way of explaining and I like the way you convey your understandings.

Have you thought about doing any teaching? You seem to have a gift in it.
Old 19th December 2010
  #21
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Quote:
Originally Posted by Storyville View Post
Don't worry about having a job - this is the music business....

Just kidding(?)

Anyway, the point B.A.S.E made is right on the money. My (apparently too long) article is to illuminate a concept. The real skill comes from knowing when the sound is shaped correctly, or being able to hear how a sound SHOULD be shaped. If I could teach this from an article I'd deserve a prize.

Then, there comes in the bigger picture - because dynamics, frequency balance, and space are all tied together in one mighty Jenga tower. Being able to work that relationship is conceptually difficult, and in practice even harder to master.

@yosemitisam - to answer your question in a way that illustrates the point I am getting at: I eq and compress exactly at the same time. If I use an eq, I am also effecting the shape, if I use a compressor, I am also effecting the tone. So even if I only compress, I am in effect also eqing. Compressing something generally changes the tone - it eqs the signal. EQing will highlight or supress certain frequency bands which will be more present in certain parts of the sound.

For example - if I eq up a lot of treble in a kick drum - the attack sound of the kick becomes pronounced. Similarly, if I use an expander to turn the sustain of the kick down, the attack sound will also become pronounced.
I never understood exactly why EQ and compression affect each other but that makes sense. So for example, if you have a fast attack compressor which dampens the articulation, that will by necessity lower higher frequency information in that sound (like if you fast compress a kick it will compress the knocking information around 1k). Or in a way, you could use an EQ to scoop out 800 - 1k and that would have a similar effect to a fast attack compresor. Is that the idea?

edit: I'm going to further guess that that leads to your final answer to the question, which would be, "whatever is appropriate in the situation, based on that principle as well as other things you glean from years of experience mixing."
Old 19th December 2010
  #22
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Quote:
Originally Posted by Edward Shnapper View Post
Hey Mate, thanks for that. I also recently read what you wrote about Reverb. Both have been very helpful. You have a unique way of explaining and I like the way you convey your understandings.

Have you thought about doing any teaching? You seem to have a gift in it.
Thank you. I teach as a guest instructor at a high school from time to time. And, fun slightly embarrassing fact, I used to be a Hip Hop dance teacher. Good times....
Old 19th December 2010
  #23
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Quote:
Originally Posted by yosemitesam View Post
I never understood exactly why EQ and compression affect each other but that makes sense. So for example, if you have a fast attack compressor which dampens the articulation, that will by necessity lower higher frequency information in that sound (like if you fast compress a kick it will compress the knocking information around 1k). Or in a way, you could use an EQ to scoop out 800 - 1k and that would have a similar effect to a fast attack compresor. Is that the idea?

edit: I'm going to further guess that that leads to your final answer to the question, which would be, "whatever is appropriate in the situation, based on that principle as well as other things you glean from years of experience mixing."
Yes, but of course it's not really that simple. The kick drum example is easiest because there's not much high content in the sustain of the kick - but in other instruments you can have all sorts of frequencies popping around all sorts of places. Using an EQ will have shape changing effects, shape changing effects will have tone balancing effects. However, they are not interchangeable. There is a vector where they have the same effect, but also areas where you will get distinctly different results.

the final final answer is "whatever sounds best." But that's one of those GS answers that's ultimately true, and not very helpful.

My final answer would be this - as a corrective measure I will generally Eq first, and compress second - if either are needed. However, once I put the compressor on, I might find the tonal balance changing and made retweak my eq - or possibly even add another eq to the chain after. If the shape of the sound more distinctly needs correction I may address that first.

But, there are cases where I compress before Eqing. JJ Boogie from Arrested Development, who's on this forum from time to time, sent me a mix he was having difficulty with. One of the problems was the kick. It just didn't have a lot of low end to it. Simply eqing up the low end made the kick soft and blurry - no good. To fix this, I compressed the kick, being very choosy about my attack and release settings. The goal was to bring up the sustain of the kick without chopping down the attack. Once I got that in place THEN I eq'd up the low end. Because I had more sustain present in the kick drum, the low end eq had a more dramatic effect.
Old 19th December 2010
  #24
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Great post. Can you do one of eq.
Old 20th December 2010
  #25
Understanding Compression

To see what the compressor does to your sound tonaly run a 1k tone into it, compress it in various ways. Listen to what comes out.
Old 20th December 2010
  #26
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Great post Storyville. thumbsup

Hip-hop aside, which uses a lot of compression generally speaking for that "slamming sound", my only advices to people is to not use them as a crutch. In other words (in situations where the genre doesn't necessarily demand that in your face sound) don't use compression because you're too lazy to do the automation.

With good "classic" R&B vox (depending on the song) if the vocal sounds great I try really hard *not* to compress it, to work out the performance levels with automation or clip gain and let it breath. In those cases there is often a little mild compression on the input signal anyway.

Great stuff Storyville. Newbies in particular just destroy their recordings with compression it seems.
Old 20th December 2010
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Cool thanks man!

Do you have an opinion on opto compressors? A local engineer who I took some lessons from seems to swear by the Massey CT4 and I'm curious what makes it different from, say, the stock compressor plug-in in Logic.
Old 20th December 2010
  #28
Quote:
Originally Posted by yosemitesam View Post
Cool thanks man!

Do you have an opinion on opto compressors? A local engineer who I took some lessons from seems to swear by the Massey CT4 and I'm curious what makes it different from, say, the stock compressor plug-in in Logic.
For what it's worth, opto compression is REALLY hard to emulate digitally, IMO. That's not to say the opto-style plugins don't sound good (many do), but analog opto compression is very complex and I've yet to hear a plug that recreates it accurately in terms of the time constants.

In general, opto compression is slow-ish...certainly slower than VCA (dbx, Distressor, SSL, etc) and way slower that FET (1176, et al). It tends to work in a program-dependent way, meaning, what you put into it affects the way it works, in a more complex way than the usual "louder-makes-more-compression". Also, because of the photo cell, the time constants are not linear. For example, an opto comp set to quick release will begin to loosen its grip pretty fast, but the photo cell takes time to fully discharge, so the last bit of the reduction tends to have a slower release (try to imagine a photo bulb on a photography camera; it flashes bright and instant, than slowly fades).

Anyway, not to be a total party-pooper, but you'll have a hard time really learning the subtleties of compression styles (especially opto!!) via plugin. They're just not quite there yet. On the other hand, you can figure out plenty about attack and release, ratio, threshold, and all that other stuff, so please don't take my comment as dismissive.

EDIT/ADDENDUM: just occurred to me it's sorta useless to answer like I did without giving some direction as to HOW opto compression might be used.

So, consider what I said about its being slower. You wouldn't find yourself using it to add sustain or loudness to drums. You wouldn't use it to tame an aggressive and spitty rap vocal. On the other hand, it can be great for smoothing out things like bass guitar and dynamically-sung vocals (often in conjunction with a second, faster compressor to catch the peaks). I sometimes use an LA2A to add a subtle attack to the front of a snare; it allows the transient to poke through and clamps down nicely on the body of the drum, emphasizing the stick nicely. Gives a very nice, 70s-L.A. vibe.

Of course, there are a lot of factors that go into choosing, and in addition to the compressor's gain reduction action, some consideration must be made for its general tone. In those cases, you may finding yourself choosing a slow-ish compressor for something that might require faster reduction, but the tonality just kinda works and you either make the compromise or combine the slow-ish comp with a second, faster one. But that's sorta getting away from the nuts and bolts of this thread, so I'll digress.

Best of luck to ya
Old 20th December 2010
  #29
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To springboard off of Ben's post:

I normally record hip hop vocals with a dbx 163x (modded) to an ART Pro VLA (opto). The VLA would be set to fast attack, longer release. It helped to gel the vocals a bit and give them a nice taste of oomph.

The VLA by itself wasn't really what I would call a first compressor for hip hop vocals, then again I really wasn't a fan of it for vocals on its own period.

I liked it better as a second unit for smoothing.

I remember that we dug the ART Tubepac pretty hard for overheads when you needed a nice dose of trashy/splashy drums.

I also think that Optos have some nice qualities for running mixes through but the compressor's behavior is really going to dictate where you place it. I sort of dug the VLA on kick and snare during tracking, set with a slower attack and fast release. Doing say a good 6 db of reduction, but also with a mult in case I didn't like the sound (normally I keep the compressed version though).

I really wanna try out the Joe Meek stuff and see how their Optos sound by contrast. I've had some recent opportunities to hear a much faster version of an opto compressor at work and they sound very very nice.

Great thread!

Peace
Illumination
Old 20th December 2010
  #30
Quote:
Originally Posted by yosemitesam View Post
Cool thanks man!

Do you have an opinion on opto compressors? A local engineer who I took some lessons from seems to swear by the Massey CT4 and I'm curious what makes it different from, say, the stock compressor plug-in in Logic.
whenever i use a logic compressor i find it hard to hear what it does and as a result i end up with to much comrpession going on. on the other hand, when i use one of my outboard compressors during tracking or mixing (RNC, RNLA, LA-610's comp) i can really hear what the compressor does and it's much easier. even when using the liquid mix compressors it's a bit harder to set the parameters than on outboard, but better than using plug-ins.
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