# Looking for some Learning...



## immortalgropher (Feb 16, 2010)

And I want one of you guys to write about it! We're all professionals, but we can still use re-freshers and knowledge and this happens to be an area of knowledge I am not so strong in and think it would be a great article to add to the site .

Mix buss compression is something I don't particularly delve in and I want to learn more about the following:



What is mix buss compression?
How has it been used in the past compared to today's usage?
What are the benefits and challenges?
How should one approach mix buss compression?
Maybe throw in a screenshot or two as well for a visual reference showing general settings and such.
Any takers?


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## Phillyduke (Oct 2, 2010)

all 80's SSL consoles had compression built into the output buss which, apparently, everyone overused. Started taking this final compression out of the mastering eng's hands. I'll usually have a multi-band compressor inserted into the outbus in Cubase before printing...among other inserts.....Duke


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## ngarjuna (Mar 29, 2010)

Mix bus compression is one of those things that people don't usually approach in a singular way; everyone has their own conception of what they're looking to achieve and what will get them to that point. That said, I can tell you how I approach it; probably a lot of people approach it differently, though.

First off: Mix bus compression really just refers to placing a compressor on (or utilizing one that's built into) the 2-bus. As Phillyduke pointed out this became especially popular in the era when a world class, famous compressor was built into a world class, famous console and, thus, readily available for bus duty without having to patch anything. I'm under the impression that using a compressor on the 2-bus was somewhat less common prior to that console but that's before my time, honestly.

Goal: To achieve a little extra "glue" between parts. It's not for leveling per se and it's not for catching transients (I prefer the precision of careful automation for both of those tasks in the land of DAWs). To me, the glueing that takes place is the primary benefit of mix bus compression.

-Don't work your mix up and then slap a compressor on the 2-bus. If adding a compressor to your whole mix actually makes it sound better....that implies some less than great things about the mix itself! A mix bus compressor should be part of the mix, I would even go so far as to say "from start to finish". Obviously you can (and might want to) rough some levels in before you start adjusting your compressor.

-Low ratios. Remembering that the idea here is not to smash, it's to glue. 1.5:1 - 2:1 is usually where mine sit (mostly depending on the compressor I'm using). Some people like 4:1 for the task; there's nothing wrong with that either (not really my style personally).

It's hard to make any kind of general statements about attack and release as this is hugely dependent on a number of factors: program material, compressor model, end goals, etc. Also keep in mind that compressors especially (although it's true of most gear) don't always have accurate labels; what they call 1ms might be considerably faster or slower than it's labeled, particularly on emulation plugins which seek to model the behavior of hardware above accurately labeling everything. Also, not every compressor has variable/labeled attack and release times; some of these make for very good bus compressors too. If I had to generalize, I would probably say:

-Slow-ish attack. Your transients should, by and large, be shaped individually as needed. There's no reason to clobber them further with a fast attack on the master bus. That said, be sure to experiment a bit until you find your sweet spot. Slow-ish attack is a good general starting point but sometimes I will speed it up to suit the material better.

-Medium to slow release. You don't want it to pump on you (unless you do, in which case that might be a little different than more common uses of mix bus compression but it's still valid). As above, definitely experiment until you get a feel for where you like it.

-A good rule of thumb is to adjust threshold slowly; you want to shave maybe .5dB - 3dB max. Your compressor may or may not have metering which will show you an accurate picture of your gain reduction; that's okay because the actual numeric amount isn't what counts, use your ears here. You're looking for the spot where things are starting to really come together and sound cohesive but somewhere before the point where you start to crush your transients and heavily impact your transients.

-There are lots of compressors which can be used for a mix bus compressor; they all have a very different vibe to them so keep that in mind as you're dialing in. My go to is usually an SSL style compressor (although I've been beta testing a new Nebula compressor which is quite likely to become my go to mix bus comp forever more, a classic Neve unit) [I prefer Cytomic's The Glue for software SSL style compression, never heard another SSL style plug that comes so close]. But there's no real right or wrong here; you can get great mix bus compression out of a very wide variety of software and hardware units.

-Parallel compression works on the mix bus too. Sometimes, instead of a mix bus compressor, setting up parallel busses works even better; one channel crushed to hell and the other with no compression at all. I don't personally use this as often because I find it difficult to set my attack/release/wet-dry levels so early in the mix. But it's an option for sure. If your mix bus compressor already has a dry/wet adjustment even better, that's something you can tweak as you're mixing.

-Others like using compression serially in stages. This is not something that I do so I can't give you much advice but some swear by it, using one compressor to adjust/shape on louder parts of the signal and another adjusting/shaping lower parts. Sometimes this is accomplished by using a compressor and limiter in series (keeping in mind that a limiter is really just a compressor pushed past the 8:1 or 10:1 setting by literal definition).

-If you're doing it right, disabling/bypassing your mix bus compressor should sound worse than it does with the compressor engaged. This is definitely worth checking, especially if you mixed into it (as I suggested that you do) to avoid falling for compensation on the part of your auditory processing. In this case, everything should sound a bit more separated and less cohesive than with the comp engaged.

Now there is a potential downside to this: you want enough dynamic range left in the material so that the mastering engineer (even if that's you [don't master your own mixes! but that's for another discussion...]) has some room to play. It's really important that you leave some headroom here, not only in terms of the actual level but also some room to compress as needed. Mix bus compression is NOT meant to replace the mastering stage. Even if you're going to master your own mix, separate that from the mixing process; leave yourself some headroom and take your premaster and master it. Using your mixing master bus compressor is not really a great plan. So in a nutshell: don't push it too far. Mix bus compression, when performed correctly, is usually going to be a very gentle and somewhat subtle process.


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## spacedout (Dec 17, 2007)

Great post, ngarjuna! :T


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