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Mix bus compression

Pro tips for a tighter mixdown

2021 Jun 05     
2 Bit Thugs

Used correctly, bus compression can help the various elments in a mix gel together better. Chris Lyth has some ideas to get you startedā€¦

Mix bus compression (also sometimes called master bus compression) refers to adding a compressor to your main stereo mix. This technique adds power, swing, polish and cohesion to your mix.

While electronic music doesn’t technically require the same amount of compression as acoustic music does, mix bus compression plays an important part in the overall mix dynamic, and compression is used in a very different way in electronic music than it is in, say, country & western. 

You will read articles saying to leave mix compression to the mastering engineer – and admittedly, there is a some general wisdom in this. However, compression can be so integral to the sound of electronic music that it strays from being a technical process into being a creative one. 

The sonic difference between starting your mix with a compressor and putting one on at the very end is huge. Putting a compressor on at the very end of a mix can significantly change the balance and undo a lot of good work. When applied at such a late stage, compression should only really be used in a very gentle fashion, just to tidy up the odd peak here and there.

So, while opinions may vary, I’m standing firm and saying the best strategy is to begin your mix with the mix bus compressor in place, and mix through it. This has a number of advantages: your mix will tend to gel together better, and it makes mixing feel like a more organic process. All your mixing decisions will be informed by the individual parts reacting to the compressor. Done correctly, you can quickly carve out a vibey and exciting mix and it allows you to back off a little with the compression applied to individual channels.

Which compressor to use?
The type of compressor you use, and the specific model, will of course make a huge difference to the overall sound of your mix.  Every compressor works and sounds differently, and the various different designs (FET, tube, VCA, optical) all have their own behavioural and tonal characteristics. As a result, a 10ms attack time (for example) set on one compressor will sound different to the same setting on another. Some compressors, such the SSL G-Master Bus, may be bright and clean; others, such as those from Tube-Tech, will sound rich and warm.

You'll need to work out for yourself which you prefer, but here are a few great bus compressor plug-ins to check out…

1. API 2500 
The API has a very contemporary-sounding aesthetic and comes equipped with a comprehensive feature set that makes it a great choice for punchy compression with character. Waves and UAD both do great clones.

2. SSL G-Master Bus Compressor 
Probably the most famous mix bus compressor of all time: it’s simple to use, sounds great and is stunningly adept at getting the job done. Again, Waves and UAD both offer versions of this.

3. Logic Stock Compressor 
A very comprehensive unit that can yield great results. Sounds great and is massively underrated. 

4. Klanghelm MJUC Variable-Tube Compressor 
An absolute steal at 24 Euros. Gives a range of tones from rich and highly coloured to clean, fast and punchy, and combines vintage tones and state-of-the-art features brilliantly. Just buy it. 

5. Softube Tube-Tech Mk II 
Fast, smooth, rich and colourful, and sounds superb when used subtly on house and disco-type material. 

NB: There are, of course many other compression plug-ins available, not to mention dozens if not hundreds of rackmount options. The five listed above, though, are plug-ins I've had good experiences with personally.

Turn on, tune in…
Whichever compressor you're using, tuning it specifically to your track will yield results far better than arbitrarily picking a preset. A good way to do this is to get the basics of your track up and running – drums, bass and a few synths, for example – and then follow the steps below…

1. Add your chosen compressor and place it on your main L&R output. 

2. Mute your bass channel for now and let the drums and synths play.

3. Set your compressor’s ratio to between 2:1 and 4:1.

4. Set the attack to the fastest setting and the release to its slowest.

5. Now we are going to be deliberately extreme for a moment, in order to really hear what the compressor is doing. Pull down your threshold till you are reaching around -8dB to -10dB of gain reduction.

6. Slowly dial back the release time until you hear the compressor starting to 'pump'. Tune the release so that the compressor is pumping rhythmically in time with your track. 

7. Start to raise your attack time until you can hear the kickdrum punch through again. Around 10ms-30ms is a ballpark figure. You want to hear the thump of the kick clearly.

8. Now un-mute the bassline. You will probably have to pull back the level on your bass fader a little, to compensate for the massive over-compression. 

9. Find your compressor side-chain and engage the high pass/low cut, setting it to between 50Hz-70Hz This will allow deep bass to pass through and the compressor will be mainly triggered by the kick. 

10. Dial back the threshold setting to a more sensible level, so that it’s now only knocking off 1dB-3dB of reduction.

Your compressor is now tuned specifically to your track. This works well in kick-heavy genres as it adds push and pull to the groove.

You may find that as you add more elements to your track, you need to adjust the settings a little. More often than not, it will be the threshold setting, either adding more gain reduction to tighten up the mix, or loosening off the compression to allowing the mix to breathe. Do remember that if you apply too much compression, your music will start to sound strained, distorted and a bit lifeless. A little really does go along way!

When setting attack and release times, most of the work should be done by ear. However, keeping an eye on the swing of a compressor’s VU meter can be useful, as it responds to the most fundamental aspects of your track. The aim here is to get the VU needle to pulse in time with your track. Too slow a release time, and the needle barely moves. Every track is different and will need different settings – it’s all very much about feel. 

Set up a test track, play around with all the settings and get to know your compressor intimately. Really dig in and push the process to extremes, and learn the different functions and sweet spots of your chosen one. 

And remember…

Music is a form of expression, and when it comes to making electronic music, compression is part of that expression. So it would be remiss of me to say 'never to do this' or 'always do that' – the above is just a gentle guide with some ideas and observations. No one else makes music like you, so no one else will use compression exactly you do. 

So as always, experiment – and if you love the way it sounds, then it’s absolutely correct!

Words: Chris Lyth






Tags: mix bus compression, master bus compression, SSL, Tube-Tech, Logic, Klanghem, Tube-Tech, Waves, UAD, API 2500