Myth #4: Compression reduces dynamic range

How many times have you read this particular nugget of wisdom? And sometimes it’s true. But not always. Indeed sometimes it’s important that it’s not true.

Imagine a mix in which kick, snare, and cymbals/overheads feed a drum bus. The intuitive thinking goes something like this: if I slap a compressor on this bus and compress it, by definition I’m going to be pushing down the loudest stuff and as a result the dynamic range will be reduced. That’s what compression does, right?

Yes, and no.

Yes, a compressor can and does push down on the loudest stuff. But no, that doesn't mean the dynamic range is automatically reduced.

Yes, a compressor can and does push down on the loudest stuff.

But no, that doesn’t mean the dynamic range is automatically reduced, and here’s why: if your attack is slow enough, the bulk of the transients will still come screaming through even though the detector is simultaneously screaming at the gain circuit to ‘TURN IT DOWN!’ Then, if your threshold is low enough and your ratio is high enough, what does get pushed down gets pushed down so far that the resulting signal is much quieter than it would have been if you hadn’t compressed it at all.

The result of those two factors: the loud stuff is just as loud (albeit for a shorter time) and the quiet stuff is quieter. Which is to say that your dynamic range is now increased as a result of the way you applied the compression.

Engineers exploit this reality every day on their drum buses; the classic trick is to take a comp set to a medium or high ratio, slowest attack, fastest release and dig in hard. With a deft set of hands and ears, the result is a track that, on its own, is an unusable series of fast, dead-sounding thumps and pops that herald each drum hit in a highly exaggerated but uniformly level manner. This track is then blended in parallel, usually quite subtly, and the result is a palpable increase in the perceived impact, punch, warmth, and consistency of the drum sound.

So yes, compression generally does reduce the dynamic range, but it doesn’t have to, and sometimes it does exactly the opposite to wonderful effect.

Myth 5: Compression makes sounds bigger

This final myth is very personal to me.

I had the pleasure of attending an early Mix With the Masters seminar hosted by one of the acknowledged masters of mixing and, in particular, artful compression, Michael Brauer.

At one point the group was talking about compression, and someone asked Michael what he’s listening for when dialing in one of his elaborate compression schemes (if you haven’t read up on his multi-bus and five-compressors-as-one-vocal-comp techniques, you should; even if you never try them your brain will appreciate the novel approach).

pushing a sound into a compressor is like pushing an object into a stretched rubber band

This is my interpretation of what he said (and I’m OK repeating it here because I’ve since read it in interviews he’s done): pushing a sound into a compressor is like pushing an object into a stretched rubber band. The harder you push the object, the more the rubber band pushes back. Michael listens for the point where there’s a musical push-pull movement and the comp feels springy and flexible.

Not pushing enough results in too little resistance – no interesting movement. But push too far and the rubber band loses its elasticity and becomes stiff – the sound loses its life. What’s more, when you push too hard into a compressor the sound becomes small.

When he said that last bit, I remember jolting upright in my seat because I’d never previously felt like I had a masterful grasp of when to stop laying in with a compressor. I had become pretty adept at using ratio and release to control the transparency or audibility of the effect, and I was starting to feel confident in knowing what kind of attack served the sound in the mix. But where to park that threshold was still a mystery to me and had been for a long time. This nugget of insight felt like the key to solving that puzzle.

if I was squeezing a sound and it got thicker, I thought that was the same as making it bigger

When I got back to my room in the States I immediately laid into my compressors and started listening not just for snap and swing but also for size. I became obsessed with running every track I had – every sound and bus, even my FX – through the different comps in my rack and plugin folder. I relentlessly tweaked them in all kinds of ways – aggressively, musically, invisibly, whatever – constantly level matching and bypassing the comps to listen for one thing and one thing only: how big or small the sound became in the context of the full mix.

What I heard was a revelation. I realised I had been confounding ‘density’ with ‘size’. That seemingly small syntactic error had huge ramifications, both on my productions and on my experience of creating them. This mistake explained why I never knew when to stop digging in with a compressor.

Here’s what that mistake looked like: if I was squeezing a sound and it got thicker, I thought that was the same as making it bigger. I was enamoured with the ‘grr’, the ‘hair’ and the urgency that compression added to my sounds. When I bypassed and that density went away, I was resolute that the compressor was improving things.

Wrong.

The problem with making density your primary compression benchmark is that you can keep going as far as the comp will let you; if urgency is a drug, compressors are the dealers of the stuff. And they have no conscience; they’re happy to dose you up as often and as hard as you’re willing to go.

Ultimately you don’t want every sound to be as dense as possible

But mixing is a game of balances. Of relentless trade offs and compromises. Ultimately you don’t want every sound to be as dense as possible; instead, you want it to be as dense as necessary to transmit the emotion… and no denser.

That means attuning your ears to the proportionate spaces around each tone like the curves and twists of the pieces in a jigsaw puzzle, filling up the spectrum where necessary while preserving enough dynamics to allow the sounds, and with them the entirety of your mix, to breathe – to have air around the elements such that you feel the impact when those spaces contract and the sounds collide.

Everything in a mix must be shaped with complete awareness and respect for every other piece in the puzzle… or it won’t fit. It won’t assemble into the vivid picture that the song wants to be – a gripping story the listener wants to surrender to from start to finish.

Gregory Scott is an engineer, producer and the owner of Kush Audio.

If you enjoyed this column you might find our book ‘The Secrets of Dance Music Production’ a helpful resource for similar articles.

10th September, 2015

Comments

  • Really interesting article. I’ll need to come back and read Myth 5 again tomorrow to fully understand it, but that myth was the most interesting idea: “mixing is a game of balances, of relentless tradeoffs and compromises.
    You don’t want every sound to be as dense as possible”.

    Something to consider. Nice one!

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  • Amazing article! Thank you!

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  • Here I went thinking this was another dumb article on compression, after reading countless articles that basically re-write the manual for every compressor out there. This was great though. It really got me thinking about compression differently. A few ideas were only vaguely acknowledged in the back of my head until now, like the attack and release happening all the time once over the threshold.

    Nice analogies and reference to density too. I’ll definitely be listening differently now.

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  • As soon as I see Gregory Scott’s name on an article I know I am in for a good read and always learn something. I love the studio tours here at attack but I am starting to really look forward to the articles by Mr. Scott …. not sure on my favorite section at this point. Mr. G Scott should really write a book on Studio Technologies.

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  • Exactly what I have always felt, but only subconsciously… Yeah, so many people don’t get compression, I hear it all the time. Myth 5 is so big. I was beginning to believe people who say “it sounds big aye?”, when it really just sounds more dense; squished of its (potentially big) life… Anyway, I couldn’t have put it into better words than Mr. Scott. Good article!

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  • Your explanation of ratio is backwards. For every 3dbdb of input over threshold you get 1db of output over threshold. The way you said it 3:1 would be more gentle than 2:1.

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  • Was literally just about to say what Pete said. It should be said “for everly 3dB the input signal passes the thresold, only 1dB will be allowed to pass by the compressor”. This article is great though!

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  • *threshold

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  • i loved this article but i was over here thinking i was losing my mind over what he said about ratios. glad someone else noticed that.

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  • Crap not to be a stooge, but also noticed this wording “if your attack is slow enough, the loudest bit of that transient will come screaming through before the detector tells the gain circuit ‘TURN IT DOWN!” I think saying that it will come through before the detector tells it to turn down, confuses people back to thinking that “Attack is the time it takes for a compressor to begin compressing once a signal crosses over the threshold” maybe worded like this “if your attack is slow enough, the loudest bit of that transient will come screaming through in the time that it takes the compressor to ‘TURN IT DOWN!” to the targeted gain amount” fits the point of myth #1 better.

    Only pointing these out because i like this article so much and really wanna share it with everyone who i know struggles with years of people/the internet explaining how compression works in a slightly wrong way.

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  • Peter, Kellen and others on our Facebook page,

    Thanks for raising this. Gregory has corrected the column above to what it should have said.

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  • Yeah, thanks to everyone for giving me my best facepalm moment of 2015!

    Compression guru my ass, LOL!

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  • Love it this article! One of the best I’ve seen about comps. Greg, why don’t you do a video tutorial series about compression techniques?, that would be epic!

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  • This is a fantastic article! I teach students at university and those compressors always are most mysterious creatures for them. It’s that mix-up of time and attenuation levels that gets everyone (and got me too for ages).

    A possible explanation for the attack/release confusion maybe that engineers learn the concept of attack and release in relation to sound shaping envelope in synthesizers, where those parameters are related to time… So automatically they transfer the idea to compressor when they see those settings on the box/screen. But it is not like that.

    When using a compressor I have a vision of a particularly attentive and fit engineer with his hand on a sprung lever. The second he hears a signal louder then the set threshold he presses the lever down… The louder the sound – the harder he presses and holds it till the signal starts decreasing, then he starts releasing… Note, all of it is above the threshold. Time comes into it in some way, but it’s the pressure of the signal that is more important and how quick is the engineer… Cause if he is set a bit ‘slow on the uptake’ – those fast drums transients peaks will certainly get through unattended…

    Oh and good point from Kellen above about drums transients – that one sentence got me a little confused too. Otherwise this is excellent. And the bit about the rubber band and the sound getting “bigger grrr” was an epiphany for me too. I will put it into our course reading and get on fixing my mixes!

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  • So refreshing to finally have an article to give my students as “post class reading / revision” that actually is the truth! I always feel a little cocky telling them that some books / online articles / etc… have it wrong, but this article will be my backup proof from now on!

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  • Lovely article – and I thought I was going to get to call-out the bit about “if your attack time is slow…” :-).

    Comment about not applying gain reduction until the threshold is reached ignores knee settings – a soft kneed comp will apply GR before the threshold.

    GR meters dancing above the threshold simply reflect that more or less level is hitting the key, so more or less level is being output – so you’ve got more or less gain reduction in terms of absolute level, but not in terms of reduction ratio (release knee notwithstanding).

    Not picking – just a couple of points that could cause some confusion down the line.

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  • After reading the article, I believe Scott needs a hug. Someone please give him one. 🙂

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  • oops. “Mr. Scott”, as he is the teacher here.

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  • Interesting. I’ve lived long time with that springy and flexible thing but that size part is kinda new.
    Also the attack part was new. I really thought there is delay. I was left wondering how soft and hard knee option in plugins affect that 2/3 timing.
    Thank you. Great article.

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  • Great Article!

    I would add one side note here that your Myth Busting descriptions are only fully true for Analog compressors because there was no escaping the limitations of the Physical components used.

    Digital (plugin) compressors are not restricted by the same physical limitations and many use the Myths you describe as the Laws in their design. This includes most of the top manufactures and complicates defining things quite a bit. It also allows for many incredibly powerful tools that are impossible to create in the analog realm.

    Michael Brauer’s description is right on point and defines the Art of compression as opposed to the use of compression.

    Cheers!
    Mike

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  • Where’s the proof??? Show us some math at least. Or is this just another completely subjective piece of tripe that ‘seems right’ because of the way it is written? Are there any standards left in the ‘pro’ audio world anymore?

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  • Sorr y- I wasn’t through when I hit submit. There is no account taken here of the knee, or the compression ratio and the interaction of the two at the onset of compression – at the very least. I hope the students who read this question it instead of taking it as ‘gospel’

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  • John Paterno: myths 1-4 are fact, only 5 is subjective. I’m unclear whether you actually read the whole article, it doesn’t seem so.

    You ask (albeit rhetorically) whether there are any standards left in the pro audio world; ironically, there is no agreed upon standard for exactly how to measure (or even define) attack, and to the best of my knowledge there never has been.

    It doesn’t matter what the ratio and/or knee are, attack is what it is. A steeper ratio and harder knee (e.g.) simply means that, with an attack of Xms, more compression will be applied within those Xms than would if the attack were slower and the knee softer. Same attack, same signal, different GR occurring in the same slice of time.

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  • I read it. Twice. There is no description of the methods you used to come up with these conclusions. There is no ‘academic’ method here at all. How are you testing these assumptions? What is your method? How are you measuring it? You are creating a definition of attack but not backing it up with any rigorous proof, thus creating your own myth in the process. – but trying to pass it off as fact. Kinda like Donald Trump. My issue is not that you have an opinion on how it works, but that you are stating things as ‘facts’ when you can’t even narrow in on a number. ‘Roughly 2/3rds’?? Is that a fact?…

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  • You ask “‘Roughly 2/3rds’?? Is that a fact?…”

    I’m hoping that’s a rhetorical question, if not the word ‘roughly’ should give you the answer, but I get the feeling from your approach you are not looking for answers but an argument.

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  • I’m looking for the relevance in practical terms and application, and why the ‘smoking gun’ hype-riduculousness in the tone of the presentation. The RC time constant, and T, are phenomenon that designers have had to deal with since they coupled a resistor and a capacitor together.

    For those interested in what he’s really talking about – which he failed to mention – from Wikipedia ‘RC Time Constants’ :

    T is the time required to charge the capacitor, through the resistor, by ≈ 63.2 percent of the difference between the initial value and final value or discharge the capacitor to ≈36.8 percent. This value is derived from the mathematical constant e, specifically 1-e^{-1}, more specifically as voltage to charge the capacitor versus time

    Charging V(t) = V_0(1-e^{-t/ \tau}) [1]
    Discharging V(t) = V_0(e^{-t/ \tau})

    So yes, this phenomenon exists, but to say the rest of the world is wrong in practical usage is pretty arrogant at best. He’s not ‘demolishing a myth’, he’s focusing on the minutia that even real designers do not worry about by the time their product hits the shelves. Is it something designers struggle with? yes. That’s precisely WHY there is no standard definition. Does it affect the practical application and end use. No. ‘Completely and utterly incorrect’? Seems to me it is more splitting hairs.

    In full disclosure, it’s been a long time since my college electric engineering classes, so I consulted a couple of designer friends who pointed me in the right direction with this ‘roughly 2/3rds’ business. But I at least have tried to explain where that number comes from here, even if the author did not.

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  • “Seems to me it is more splitting hairs.”

    Wow, just wow! Your lack of self awareness is astounding.

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  • Give it a rest , Ness. No need to be a jerk.

    Besides, aren’t our ears the most important things when it comes to audio engineering? As valid as the maths surrounding compression are, we should always remember to challenge ourselves with questions like ” Does this sound good?” Which seems to be Greg’s point, hence myth 5. Of course that’s subjective so no point debating what “good” means.

    Good article, Attack. I’d be stoked to read Greg’s opinions on EQ or EQ vs compression in mastering in future.

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  • Thnx mr Gregory Scott for the subject, that to Michael Brauer for the rubber “thing” and thank you John Patterno for the capacitors, also i would like to say thank you to Mike who has left the comment and explained a bit in his video about this subject when it comes to analog and digital compressors and why this can not be applied to every digital comp.

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  • Great article! I am not sure if I understood the following correctly :

    “Any time the gain reduction meter is increasing (i.e., the comp is reducing the gain of the signal), the compressor is attacking.
    Any time the gain reduction meter is decreasing (i.e., the comp is restoring the gain of the signal), the compressor is releasing.”

    Do you mean that, for every db of gain reduction added over threshold, the attack time dictates how fast the compressor is adding it ? ie. a 20ms attack time would affect how fast a compressor goes from a -5db of gain reduction to a -10db one ?

    I always thought that once the threshold was crossed, there was some sort of linearity in the amount of gain reduction applied (with the ratio affecting the GR with, well I guess, some sort of look-ahead technology).

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  • Great info…in the comments too.

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  • Very interesting, but I don’t think having a faulty understanding of exactly when the attack kicks in really changes how anyone will use a compressor. Slower attack times = more transients get through. That applies whether the attack time controls how fast the compressor starts working or how fast it achieves 2/3 of the desired gain reduction.

    I understand from an electrical engineering standpoint the difference is important. But from a “let’s creative beautiful music” standpoint, it doesn’t really change how I use a compressor when I reach for it.

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  • @ Joe Gilder: indeed the creative process isn’t hindered by not knowing this (as you have proven numerous times). But in my opinion insight in the technical processes behind the compression will sometimes get you where you want to be faster.

    It helped me dealing with my drum tracks and it felt “right” to me for understanding the technical side.

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  • brilliant article! would love to see one in a similar vain on gates/expanders. lately I’ve been using them a lot in my productions and they seem a lot more relevant than compressors oddly enough

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  • I still dont have any idea how to use a compressor, but I feel a lot smarter

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  • Nothing new, every compressor spec sheet will tell you this.

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  • Thank you Greg.

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  • I was always taught to set a fast attack for parallel compression. As a matter of fact there is an article by Bruce Aisher for Attack Magazine where his suggestion is, “attack time should be as fast as possible”.

    Can we clear this up?

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  • awesome article, helped me a lot..thanks!

    any chance of getting an article on WHEN to use compression? or anyone have any good links?

    thanks again!

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  • @ John Paterno Maybe give it a rest. Greg’s definition of attack is spot on.

    He doesn’t need to follow the “scientific method” (LOL) to give his explanation, as he is not investigating some phenomenon, just reporting on the facts — namely, the standard practice of compressor makers. It’s not like you need to measure it to verify it’s true, you can always ask any electrical engineer working in analog compressors or VST programmer modelling them.

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