In the age of MP3 files compression often sounds like a dirty word, but when we talk about compression during the mixing process we actually mean something entirely different.
Where audio data compression essentially chops out elements of a song, compressing tracks in your DAW is simply a way of sculpting a sound.
In very broad terms, compression can help add punchiness to your instruments and increase the perceived loudness of a track, and let’s face it, most of us prefer listening to music loud!
But aside from just affecting the dynamic range of a track, compression has a lot of other creative uses which you can utilize to add an extra dimension to your mixes.
What Is Sidechaining/Sidechain Compression?
Once you get to grips with the basics of compression then the next step is to explore sidechaining. Essentially sidechain compression is a way of using the output of one track to affect the compression on another track.
While initially, this does sound complicated it is actually a very simple process that most DAWs allow you to do with just a couple of clicks.
Insert a compressor plug-in onto the track you want to be affected and you will usually find an option to sidechain within the compressor itself, often in the top corner.
Click on this and simply select the track that you want to influence the compressor, hit play and lower your threshold until the compressor kicks in.
Sidechain Compression (4 Use-Cases & Examples)
1. The Pumping/Ducking Effect
This sidechain compression technique manipulates the ducking effect in moderate to extreme ways, in order to achieve dynamic movement and pulsing in a chosen instrument.
By sidechaining any element with the compression on one or more of your other instruments you will create a ducking effect as the chosen trigger activates.
This creates the ‘pumping’ effect that you often hear in modern dance and electronic music.
The compressor is placed on the channel “Pad Synth”, with the sidechain mode activated.
The top channel titled “Kick Trigger” signals the sidechain compressor to activate each time the sound source plays. This channel is muted as it is merely there to act as a trigger.
Threshold is pulled down to a level where the “Pad Synth” starts pumping (sidechaining).
Compressor settings are adjusted so that the movement ‘grooves’ with the beat. This requires some playing around with (and is subject to taste).
Tweak the parameters from subtle to the intense and you’ll get a feel for how sidechain compression can really add another dimension to your composition — have fun!
2. Separating Kick and Sub-Bass
In bass-heavy music such as dubstep and drum and bass, the kick drum and sub-bass play dominant roles in the makeup of the mix.
A little ‘hack’ that many producers employ is to use sidechaining to quickly duck the sub-bass out whenever a kick triggers. This can create a sense of separation, and in many cases, help to remove chances of the kick and sub-bass conflicting with each other in the lower frequency spectrum.
In other words, it allows more space in the mix for the kick drum to cut through without competing with the bass and muddying up the low end.
The aim is generally for this to not be noticeable to the listener, and is used purely as a mixdown trick.
3. Creating Space for Vocals
Aside from intense ducking effects, sidechain compression can also be a handy tool for subtle reductions in order to clear room for vocals. Say for example you are mixing a hard rock track, you may be trying to find space for vocals over the top of a distorted riff or chord progression and you run the risk of one or the other getting lost in the mix due to frequency masking (where your vocals and guitars occupy similar frequencies on the spectrum and therefore fight each other for space and lose clarity).
There is a certain amount that can be done by EQ’ing your tracks and removing troublesome frequencies in the guitar that may be stopping the vocals come through.
A next step could be to automate a reduction in the guitar’s volume, making space for the vocalist. This can also prove useful in certain situations.
A 3rd thing to try is putting a sidechain compressor on your lead guitar that is triggered by your vocal track. Warren Huart refers to this as a “quick, poor man’s easy way to mix lead guitar and vocal”, and it’s easy to hear why.
Manual automation is usually what one would reach for in this circumstance, as it allows you pinpoint precision over volume boosts/attenuation. Using a sidechain compressor, however, can be a great way to get ‘in the ballpark’, and don’t be surprised if you actually achieve some cool results you wouldn’t have gained by doing manual fader rides!
Long story short, this technique allows you to be creative with your mixing, whether you opt for a longer attack and release time to create more of an obvious ‘swelling’ effect, or alternatively go for a much shorter time to nudge the guitar down a few db as soon as the vocals begin.
Try using this if your track transitions from a full, intense intro into a vocal-dominant verse. The reductions in your guitars will allow the vocals and guitar to sit right without losing any perceived impact.
4. Multiband Sidechain Compression
Whilst most compression plugins will reduce the overall level of the track it applies to, multiband compression enables you to target entire frequency bands. This can be a really effective way to achieve space.
Again let’s use the example of guitars and vocals both competing for clarity in the midrange.
We know we can sidechain the vocals to control the guitar’s volume, but maybe we just need a little extra breathing space for the vocals and don’t necessarily want to affect the lower and higher frequencies of the guitars.
Using a multiband compressor means you can scoop out just the midrange frequencies of the guitars, which may be all you need to get that extra clarity in the vocals.
Similarly, you may find you do need a bit of compression on the higher frequency content of the guitar, the great thing about multiband is you can set a different threshold on both frequency ranges, meaning you could have a more extreme reduction in the mids and just a slight reduction in the highs.
Using a multiband compressor gives you an added level of customization that a normal compressor won’t, enabling you to be super granular in the frequencies you choose to automate out.
Pre vs Post-Fader
If you want to really dig deep into sidechain compression then you need to think about routing your input track to an auxiliary or bus track to then be fed to your compressor.
It’s easy enough to simply sidechain one track to another but try creating a send to a new bus track, set your send to ‘pre-fader’, then sidechain the bus track to the compressor and set the bus to ‘no output’.
This ensures that the signal being sent to the bus will not be heard in the mix, but will still be able to be fed to your compressor.
Setting your send to pre-fader means that the signal being received by the bus track (and then the compressor) is sent before the actual channel fader rather than after it.
You can raise and lower the level of the channel but the compressor will still react the same as it will be unaffected by the volume of your channel output and instead be affected by the signal you have sent to your bus track.
Imagine you have reached the end of your mix, your track is balanced well and sounds great but just as you are about to bounce it down you decide you want to lower the level of the kick drum.
If you reduce its level with the channel fader, this will affect the way the compressor behaves and you’ll have to adjust your settings accordingly. If you have used a pre-fader send then you can increase and lower the levels as much as you please via your fader without changing how much your destination track is compressing.
It can take a while to fully get your head around the idea of pre vs post-fader sends but once you do it will really open up doors for you when it comes to mixing and can be really useful with other effects as well.