Old 04-30-2012, 09:06 AM   #1
Boddrick
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Default A couple of conceptual compression questions

Hi guys n' gals,

Compression, for the most part, makes a lot of sense to me. I get how it works. Compress the dynamics of a sound to give it less volume variation. That's useful for raising the average volume to a much higher level, amongst other things (this is what you'd call 'limiting', right?).

But there are a couple of gaps in my understanding, which I wanted to figure out if someone's got a minute.

First of all, the attack setting. For the purposes of limiting (if I'm using that term correctly), which seems to be the main use of compression, I can't imagine why you'd ever use an attack of anything but 0ms. I mean, if you don't compress the sound immediately, you might well have a noise that peaks in volume almost instantaneously, giving you clipping before the compressor kicks in. The only use I can think of for a longer compressor attack is sidechained compression, where you could use it to change the character of the 'pumping' (assuming a kick is the source).

Secondly, I hear people say things like "put a compressor on the snare". That confuses me. A snare only lasts for about half a second at most. Surely all you'd do by compressing that is give it a weird square-shaped volume envelope? I mean in some electronic tracks, you might want a snare like that, but I get the impression that's not what people are talking about. Can a compressor somehow help snares and stuff like that pop out of the mix?

As ever, any help from you lovely people will be met with grateful hugs and kisses. And if that's not your thing, a manly fist-bump can be arranged.

Cheers!
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Old 04-30-2012, 09:26 AM   #2
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Good questions, actually. Attack is useful if you actually want that initial transient to pop a little bit, but you still want to tame the overall effect of the instrument. For instance, I like to have a longer attack time on a drum buss compressor so the kit as a whole still has some snap to it. I can then raise the overall level by having it lightly (or heavily) compressed without destroying the punch. Same with certain vocals. Too fast an attack will make it mushy. And keep in mind that there are many different styles of compressors too (hardware and plugin versions too!). Some are completely tweakable, others are totally affected by the input signal.
Do I qualify for the hugs, kisses, or at least the many fist-pump yet?
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Old 04-30-2012, 09:33 AM   #3
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I'm putting in a plug for Mike Senior's book: Mixing Secrets for the Small Studio. Great resource, and extremely practical.

Here is a teeny-tiny excerpt that might help answer your question re drum compression:

Quote:
Fast attack, fast release. .....[removed for copyright protection]... Result: Less drum transient.

Fast attack, slow release......[removed for copyright protection]... Result: More consistent performance.

Slow attack, slow release......[removed for copyright protection]...Result: Less drum sustain. (It’s worth noting here that, although compression is normally associated with reducing dynamic range, in this case it might easily increase it.)

Senior, Mike (2011-02-25). Mixing Secrets (Kindle Locations 3518-3520). Elsevier Science. Kindle Edition.
BTW, if you do decide to get this book, I recommend a hard copy. I have both the Kindle version and hard copy, and the Kindle version doesn't do a great job on the images and side bar notes.
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Old 04-30-2012, 10:22 AM   #4
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There are so many uses, creative and practical, for compression.
What's also interesting is the use of compression on recordings over the decades, a very worthwhile read on a free afternoon.
There's a ton of info in books and on forums. eg.

http://www.gearslutz.com/board/showw...limiter-basics

http://www.soundonsound.com/sos/dec0...ompression.htm

http://www.soundonsound.com/sos/jan0...s/advanced.asp

Then investigate paralell compression further to control fulness and dynamics in your mixes.
Have fun, it's an amazing topic!;-)
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Old 04-30-2012, 11:21 AM   #5
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Quote:
Originally Posted by Boddrick View Post
Hi guys n' gals,
The only use I can think of for a longer compressor attack is sidechained compression, where you could use it to change the character of the 'pumping' (assuming a kick is the source).

Secondly, I hear people say things like "put a compressor on the snare". That confuses me. A snare only lasts for about half a second at most. Surely all you'd do by compressing that is give it a weird square-shaped volume envelope?
1. Slow attack-fast release can add bounce and "pump" to tracks without sidechaining. Say (for example) you have a bassline with distinct notes but the sound is smearing together - slow attack allows the notes to ring out and then the fast release squashes the sound inbetween while allowing the compression to open back up in time for the next note.

2. Compression on snares generally are for emphasizing the reverb tail, the ringing out as opposed the the initial "thwack". I use parallel compression for this usually. You could add a slow attack comp on the track to pop out the transient and and a fast attack-slow release comp on the parallel to bring out the rattle of the actual snares and the room sound.
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Old 04-30-2012, 11:34 AM   #6
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Please take this advice: the best way to know what a compressor does is using it. The theory may not help here, some compressors are very unique. Listen and memorize what happens when you move a control, learn that behavior and then apply it to your tracks while mixing/producing. Seriously, spend time listening, you won't regret it
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Old 04-30-2012, 11:50 AM   #7
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Quote:
Originally Posted by richie43 View Post
Do I qualify for the hugs, kisses, or at least the many fist-pump yet?
I think for that answer you might even qualify for a super-exclusive, one-time-only KISS BUMP! Who knows what that might be but look forward to it. That was a very useful answer, thanks man.

Hugs and kisses to all involved actually, those are all great answers. I should've guessed that compression would be an entire topic in itself. It seems like fast/slow compression attack/release is a really powerful tool actually, so I'll read up on it and get cracking with the practice.

Thanks muchly!
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Old 04-30-2012, 11:51 AM   #8
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Quote:
Originally Posted by Mercado_Negro View Post
Please take this advice: the best way to know what a compressor does is using it. The theory may not help here, some compressors are very unique. Listen and memorize what happens when you move a control, learn that behavior and then apply it to your tracks while mixing/producing. Seriously, spend time listening, you won't regret it
I hear that! Now that these guys have given me a nice breakdown of the general idea, playing around with a compressor myself will be a lot more productive.
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Old 04-30-2012, 02:38 PM   #9
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The deeper you dive and the more you experiment, the more experienced you get with it, you'll see that compression is way more than a one trick pony. It's a super-versitile utility/effect that when used properly in all its various contexts can mean the difference between a demo and a hit!
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Old 04-30-2012, 02:55 PM   #10
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Also, read this thread if you have some time spare - pretty interesting - particularly UBK and Dr Frankencopter's posts (with clarifications from Paul Wolff)

http://www.gearslutz.com/board/so-mu...mpression.html
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Old 04-30-2012, 05:57 PM   #11
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Quote:
Originally Posted by timlloyd View Post
Also, read this thread if you have some time spare - pretty interesting - particularly UBK and Dr Frankencopter's posts (with clarifications from Paul Wolff)

http://www.gearslutz.com/board/so-mu...mpression.html
Really interesting thread, thanks for posting the link.


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Old 05-01-2012, 02:56 AM   #12
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Quote:
Originally Posted by Wolffman View Post
Really interesting thread, thanks for posting the link.


Cheers
there is a line 'tho which is very confusing for a noob like me:

"
This is a misunderstanding of what attack time is. Attack is not the amount of time it takes for a comp to 'grab' once threshold has been crossed, attack is the amount of time it takes the comp to reduce the gain by Xdb. X is fluid and, while the official spec is 10, I've spoken to designers who prefer 6 and one who prefers 8."


I hope this concept is valid only for opto compressors...
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Old 05-01-2012, 03:29 AM   #13
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Quote:
Originally Posted by Cresta View Post
I hope this concept is valid only for opto compressors...
Why? Afaik, it applies to all basic compressor types. The attack stage begins immediately, as soon as the input crosses the threshold*. Attack speed (using "time" is a little confusing), describes how long it takes for the compressor to reduce the input by 10dB (standard, as mentioned, apparently some designers spec their speed relative to a different amount of attenuation).

Think of the attack stage as a switch that's being smoothed by a low-pass filter if it helps. The switch flips when the input signal goes above the threshold, and depending on how it's filtered, will take a certain amount of time to stabilise. This is why you sometimes see the term "time-constant", as it refers to the filter time-constants of the attack and release stages.

* the only caveat to this, is where a compressor has a built-in amount of "pre-comp" delay, which literally describes the delay between the moment the input crosses the threshold, and when the attack stage begins. Also, some compressors have user-variable pre-comp (i.e. ReaComp). It can be used to let transients through completely unaffected, before letting the attack stage begin.

Though, it's certainly possible that a designer could link the attack speed to a pre-comp delay, which could have the effect of making a comp sound like it dealt with fast-attack and transients much more transparently than others But, afaik that would fall into the category of individual design choices, not a characteristic of a certain basic topology. Could be wrong about that though!! If so, I hope for a nudge in the right direction
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Old 05-01-2012, 04:33 AM   #14
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Compression-the sound of Rock'n'Roll!
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Old 05-01-2012, 05:34 AM   #15
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Quote:
Originally Posted by timlloyd View Post
Also, some compressors have user-variable pre-comp (i.e. ReaComp). It can be used to let transients through completely unaffected, before letting the attack stage begin.
It actually works the other way around in ReaComp, as descibed in the ReaEffects manual:

Pre-comp
Allows the compression to gradually begin a specified number of milliseconds before the threshold is reached.

the number field seems to accept negative values though.
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Old 05-01-2012, 05:41 AM   #16
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Thanks Tim for the explanation
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Old 05-01-2012, 05:52 AM   #17
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Quote:
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It actually works the other way around in ReaComp, as descibed in the ReaEffects manual:
Thanks for the correction! Shows how much I use ReaComp
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Old 05-01-2012, 06:32 AM   #18
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Another important use for compression is tone shaping. I think of it as fast atk/rls-times generating a brighter/edgier/more distorted sound. Slow times does the opposite. Of course this is dependant on the actual comp used, as they all have different tonal characateristics, but generally this is the case. It might seem counter-intuitive as far as atk-times goes, since shorter attack times also "bury" the transient - wich is usually harmonically complex and "bright". I still argue that fast attack times give rise to distortion - that is increased harmonics - more edge.

A good starting point for figuring stuff out is high ratios, fastish release and low tresholds. This will give you a great starting point, at least for understanding how the attack setting alters the transient part of the sound.
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