(This is part 6 of a 6-part series by staff engineer Justin Colletti. Check out part 1 on bass management, part 2 on high frequencies, part 3 on bus compression, part 4 on panning for width, part 5 on depth, and part 6 on getting better balances.)
Setting compressors is usually one of the last skills that engineers get truly comfortable with.
If you listen to seasoned pros when they’re being honest, most will readily admit that they couldn’t really hear compression in reliable detail—much less use it with easy confidence—until they’d been in the audio game for years.
The mix bus compressor has a uniquely potent ability to intimidate the bejesus out of new mixers, probably because there seems to be the most at stake: “Only the sound of your entire mix!!“
And so, most new mixers will take one of three approaches when they first start mixing with a bus compressor:
1. They’ll be very cautious, pick up a tip from a favorite veteran mixer, and just go with those settings for years—even if they aren’t sure they’re really hearing what the mix bus compressor is doing.
2. They’ll be so cautious that they don’t want to use a bus compressor at all.
3. They’ll throw caution to the wind and hammer the bus comp like crazy because they’re convinced that’s what some of the biggest pros are doing, really.
A Better Way
These are actually decent enough places to start.
If a certain technique works reliably for someone whose work and mixing style you love, maybe it’ll work for you too. Just make sure you’re copying someone whose mixes you actually like and can relate to.
(Internet forums, random blogs and comments sections of websites generally not usually going to be your best bet for this.)
There’s also no rule that says you need bus compression at all. Your mastering engineer is always happy to help if your mix needs a little bit of extra “glue.” And remember that some styles of music may even sound better with minimal, or no bus compression at all.
It also is true that many great mixers do throw caution to the wind. In certain genres, some of them may compress more than you’re “supposed to.”
Ultimately, great mixes require two things: Fearlessness and Experience. Without experience, fearlessness won’t get you great-sounding mixes. But it is a great way to learn.
Still, there’s a better way to make sure that your bus compressor is doing what it should. And that’s to understand what it’s doing inside and out.
And that’s what this post is all about. Toward the end, I’ll even share a surefire step-by-step approach to get great mix bus compressor settings every time.
Why Use a Mix Bus Compressor At All?
It’s rarely wise to do anything in a mix just because you’re “supposed to.” So before you even turn on your mix bus compressor, you should have a sense of what you’re trying to accomplish with it.
In my mind, there are five things you can use a mix bus compressor to obtain more of: “Excitement”, “Glue”, “Control, “Shape”, and “Loudness.”
These are related qualities, and there will be tradeoffs between them. (More on that in a minute.) But as a mixer, you should focus mainly on just two of them: “Glue” and “Control”.
If you want “Excitement”, focus on getting that primarily from your mix itself! Try fader rides. Try effects. Try digging in hard with compression on one instrument, or on a specific sub group.
Likewise, if you want to adjust the “Shape” (or “Envelope”) of specific sounds, focus on doing this instrument-by-instrument or group-by-group.
And if it’s overall “Loudness” you’re after? Forget about it! This is not the time for that. This is the time for mixing. Any monkey can make it louder. (Though some better than others, admittedly.)
So be sure your priorities are straight, and that you’re focusing is on making the song sound as interesting and as authentic as possible. That is you mission.
Getting a little bit of extra excitement, shape and loudness out of a bus compressor is certainly possible, but it should be a bit of an afterthought. This is also precisely the kind of things that a mastering engineer is best suited to help you with in the end. You have bigger fish to fry.
Glue and Control
So what are “Glue” and “Control”, the two most important things to seek in a mix bus compressor?
“Glue” is the sense that sounds somehow gel together. Like they exist in the same world and breathe the same air. Mix bus compression is not the only—or necessarily the best—way to achieve this, but it can help.
“Control” is both tonal control and dynamic range control. A compressor can help make sure that song sections flow well into one another. A bus compressor can also ensure that you can be a bit visceral, playful and bold with your fader moves, knowing that your compressor will help to reign you in a bit if you do as humans do and take a good thing just a little too far.
Also remember that some styles of music may sound great pushed hard, while others may sound even sound better with little or no bus compression at all. So know and learn the style that you’re mixing in. References and experimentation help.
I’d only recommend that you don’t turn on a mix bus compressor just because you’re “supposed” to. Turn it on because it’s become a helpful and proven part of your workflow, turn it on to achieve something in particular, or turn it on because you want to experiment with one and see what it does to a mix.
How to Set a Mix Bus Compressor: The Basics
The one thing most mix engineers will agree on is that your mix bus compressor shouldn’t do a lot. But just how much is “a lot”? Here’s the most common advice you’re likely to find on that topic:
A) Use low ratios, like 1.5:1 or 2:1
B) Make sure your bus compressor isn’t clamping down all the time, and that it has a chance to recover between beats
C) Compress by 1 dB, or maybe 2 dB on the mix bus
These are a decent guidelines to start with. They’re especially useful if you’re having trouble hearing what bus the compression is doing, as they help you err on the side of too little rather than too much, which is wise. No one, not even iZotope, has yet developed the “de-compressor”!
But how about something a little more specific? You’ll find a more advanced version of this checklist just a bit further on.
When to Fire it Up (This is the most important part.)
Mastering engineers are “supposed” to advocate caution with bus compression, but I have to admit that some mixers will get a great sound while pushing the bus compressor somewhat hard.
In his Mix it Like a Record video, GRAMMY-winning mix engineer Charles Dye suggests that you can get away with more compression—up to 3-4 dB in some sections with fairly high ratios, like 3:1 or 4:1—as long as you put your bus compressor on at the beginning of your mix session and then mix into your compressor.
So many of the best mixers I know will do something like this: They’ll patch in their bus compressor fairly early on and mix into it. Not only will the bus compressor respond to you, but you will respond to it. If you take just one strategy away with you today, let it be this.
I’d even go as far as to suggest that you should never put on a mix bus compressor at the very end. What’s the point of that amyway? All you’re doing is changing the mix that you thought you had just “finished”! So either put it on before the halfway point of your mix, or leave it off.
Assuming that you care enough about your work to make sure it goes to a great mastering engineer for a final QC, this is one of the things they do best, anyway. We’re always happy to obsessively work on things the last little extra 10% of glue, shape, excitement and loudness with fresh ears, on a system especially suited to that task. You have more crucial things to do.
I’d recommend that you should spend your precious focus and energy on obsessing about making the mix sound great. Make bold choices. Strike great balances. Make it interesting. That’s where you’re going to have the most impact.
So if you are going to put a bus compressor on at the end, I ‘d suggest you do it for one of two reasons: Do it because you’re experimenting with bus compression to hear what it does, or do it because you’re mastering a track for somebody else.
How to Set a Mix Bus Compressor: In Detail
As promised, here’s that easy step-by-step approach for finding mix bus settings that work every time.
You can use this technique on each and every song, or you can use it to establish a “default” approach that you tweak as necessary.
Once you’ve done this enough times on any one compressor, you may not even need to go through the steps anymore:
1) Start with a slow attack (maybe 50-100ms) and fast release (maybe 0.2 to 1.0ms). The exact numbers aren’t important.
2) Set your ratio to anywhere between 1.5:1 and 4:1. Go lower if you’re looking for more transparency and more dynamics, and higher if the track is more aggressive, or begs for more control or a more “processed” sound.
3) Ultimately, you’ll want to bring down the threshold so you’re that you’re compressing by anywhere from 1-4 dB during the loudest sections. While you’re dialing in your settings however, it may be useful to temporarily over-compress your mix. If you’re just starting to master the skill of bus compression, don’t be afraid to listen with 10dB of gain reduction or more as you dial in your settings! It can be a good learning experience.
4) Now, make the attack time faster and faster until you just barely start to loose the impact and articulation of your most dominant transient instruments. (Usually kick and snare.)
5) From here, if you want more vibrant and aggressive impact, back off a little bit toward a slower attack time. If you want a “smoother”, more processed, or more controlled sounding mix, push the attack a touch faster instead.
6) Next, make your release time slower and slower until the gain reduction meter has just enough time to recover to zero between dominant beats. (Usually kick and snare once again.)
7) From here, if you want more aggression, excitement and loudness out of the track, you can set the release time a bit faster. If you want things to sound smoother and more controlled, set it a bit slower instead. (The “auto” release can also be very nice on some compressors, and there is no shame in using it if it sounds good.)
8) Adjust your threshold, ratio and attack to taste. Try to compress 0-1 dB for a more organic sound, as much as 3-4dB for something more processed or aggressive. These are just guidelines. Use your ears.
9) Make sure that you’re mixing into your compressor, occasionally taking note of how much it’s clamping down. Consider backing off on the threshold if you’re compressing “too much”.
How do you know when it’s “too much”? Listen for “pumping”, “breathing”, “graininess” or a mix that just sounds kinda small and flat and irritating, not matter what you do.
If in doubt, try not to compress by more than 3-4dB on the loudest sections of a heavy or very processed song. 2dB of compression is plenty for the loudest sections of more acoustic or dynamic genres. And often, all you need is 1dB, just for a little glue.
But hey — if it sounds good, it is good! This is just one well-proven place to start, and a great way to develop and master your own approach.
Bonus: Attack and Release Settings in Detail
The effect of different attack and release settings is probably the last thing most engineers learn to hear clearly. This goes double when it comes to something as subtle as a compressor on the mix bus. It may be helpful to think about it this way:
Attack time affects “Shape”: Faster attack settings will smooth out transients and give more control and “sheen”. Slower attack settings will increase “impact” of the attack, which some folks refer to as “punch”.
Release time affects “Excitement”: Faster releases will give you more grit, aggression and “pump”. Slower release times will smooth out a track, and may seem to set it back slightly from the speakers.
Ultimately, there are really just 4 main combinations:
1. Slower Attack, Faster Release
(Good for strong impact with lively spring in the step. Can be too aggressive and “pumping” if taken too far.)
2. Faster Attack, Faster Release
(Good for smoothing out sharp transients, but still lively. Can loose too much life and impact if taken too far.)
3, Faster Attack, Slower Release
(Good for extra control and smoothness. Can sap the life out of a mix if you take it too far.)
4. Slower Attack, Slower Release
(Good for control of “macro dynamics”. Can be very useful and subtle, or can be completely ineffective.)
Putting it All Together
Here are two more simple guidelines that will allow you to synthesize all these ideas and wind up in the right place:
1: For a more organic feel, try low ratios like 1.5:1 or 2:1 and compressing no more than 1 dB. (Maybe 2). Use slower attack settings, and release times allow your compressor to just barely reach full recovery between beats.
2: For a more processed sound, try higher ratios like 3:1 or 4:1 and compressing up to 3-4dB in the loudest sections. Know that faster attack times will smooth out your mix, while faster release times will give you more “grit”, “pump” and aggression. Slower release times can make things smoother, but can get counter-productive quickly if you take it too far and don’t let the compressor recover at all.
One could write a whole book about compression and feel like they’ve just barely done it justice. The sounds is something that’s hard to put into words, and at first, it can be a real challenge to even hear it reliably and assuredly.
Ultimately, there are two great ways to learn to really hear your mixbus settings: 1) Experiment, and 2) Listen to your mixes in an an environment where you can really hear every last detail.
If you’ve made it this far and you’re interested in the latter, then you’re welcome to sit down with me, Joe or Roman and hear your mixes in the super-revealing mastering room at JLM anytime!
It can be quite a stunning and memorable experience if you’ve never been in a space like this before. (Fun too, we think!)
And if you can’t make it down, we’re always happy to assist from afar, helping to ensure that your tracks have just the right balance of glue, shape, control, loudness and excitement in the end.