'Sidechaining' was traditionally a technique used in radio so that the volume of the music was automatically reduced whenever the DJ spoke. If you listen to almost any presenter-led radio station you will hear this effect in use - the engineer isn't manually ducking the fader every time they anticipate that the DJ is going to talk. This would be a difficult job! A compressor is placed on the music and the DJ's mic is set as the sidechain input, so that the music's volume is reduced every time the DJ talks. In this scenario, the voice is the trigger or source signal.
Over the last few decades, as dance music (and music technology in general) has developed, engineers began to use sidechain compression in more musical ways. Perhaps the most common use of this technique is where a compressor is set up to 'duck' specific instruments whenever the kick drum is played, in order to make the kick stand out and ensure that people can hear it to keep the beat. However, sidechain compression can be used for all sorts of creative solutions (and is) in all sorts of musical genres.
I've recently altered the way I work with sidechain compression due to the purchase of one plugin: Kickstart from Cableguys (in partnership with Nicky Romero). This plugin can be applied to any track or bus and automatically generates a source signal that directly effects the audio running through that track.
Not only that, but it allows you to choose the type of envelope or 'modulation curve' that effects the sound from a range of awesome presets (which is great for customising the groove). It also features a handy mix dial to alter how much the signal is effected, from very subtle to totally extreme!
However, I still utilise sidechain routing for particular tasks within my projects, or if I'm trying to achieve a particular sound.
Sidechain from the off
At the start of my projects I like to set up a sidechain straight away. In fact, where possible, it's great to work with templates and build a sidechain source into it from the get-go to save time and effort in each project. For an in-depth look at working with templates in Logic, check out the first part in my series of posts on the topic.
The traditional way of achieving this in Logic was to send the kick signal (or whatever you wanted to be the sidechain source) to a bus. Then, apply a compressor to the channel you wanted to sidechain, for example, bass, and choose the bus as the sidechain input. It's a good idea to change the output of the bus itself to 'No Output', so that the kick signal (or, again, whatever you've used as the source) isn't duplicated through the bus. This approach, though, has some limitations and inconsistencies that I prefer to avoid.
For example, if you change the volume of the source signals during a mixdown, this can alter how much the compressor responds to them and, in turn, affect the balance of the mix. Say you reduce the volume of the kick - the amount of kick signal reaching the compressor will be reduced and the sidechain compression will also be reduced. Furthermore, if you solo the instrument that's being compressed, you'll need to also solo the kick for it still have an effect. Annoying, especially when you want to hear the effect of the compression in isolation.
I prefer to use an audio sample. I place the sample on each beat of the bar (or whichever beats I want to trigger the sidechain - read on for more on this) and loop it for the entire track. Many people use a kick sound, although it could be anything with a good attack. I prefer using a hi-hat sample as it has a fast attack and short decay, which can create a tighter sound when triggering the compression.
I can then use the compressor itself to dial in the amount of attack or release I want. Nice.
Sidechain tracks don't look very pretty, so I prefer to hide the channel. You can reveal hidden tracks by selecting 'H' in the top left of the Arrange, or hitting 'Ctrl + H'. Then select 'H' on the track and click the 'H' on the top left again (or 'Ctrl + H') to hide these tracks again. Fear not, they'll still be running in the background and can be revealed at any time. As an aside, this is also really useful for reference tracks.
When two is better than one
I sometimes even set up 2 sidechain sources for specific scenarios. In breakdowns or sections with a very different feel (most commonly when the drums cut out) I often don't want instrument parts to be compressed by the sidechain signal, or at least not as much. It can sound inappropriate to have instruments pumping when there aren't any drums playing, especially when it's a poignant breakdown or interlude.
Why don't I just stop the sidechain source for these few bars? This can create a subtle volume increase (sometimes significant) as the instrument is no longer being ducked by the signal. Not only is this distracting for the listener, but it can throw the mix balance. So why don't I just automate the volume? The compressor is still acting on the sound when its settings have been carefully optimised for the sidechain effect, so it can sound really unnatural. An example would be a fast attack that sounds strange when not being sidechained.
Although it requires more organisation, I tend to duplicate the track (which is really easy in Logic anyway by hitting the duplicate track button as shown below) and simply reduce the volume fader in balance with the sidechained version. With this method the two tracks are independent but sound consistent, so I get the best of both.
This approach has now changed slightly as the Kickstart plugin has altered my workflow. It's now easy to automate the 'mix' of Kickstart (i.e. the amount it effects the sound with sidechain) and reduce or increase the sidechain effect depending on the arrangement.
Tighten your sound
As mentioned previously, sidechaining is most commonly used from a functional perspective, frequently to create more room for the kick drum in the mix by ducking the volume of the bass (or any other instrument) whenever the kick plays. Besides the usual pumping action, it also has a myriad of other uses.
Another functional use is on effects such as delays and reverbs in order to further tighten the overall mix. It's always a good idea to EQ your effects to ensure that any unnecessary low-end is removed to avoid muddiness in the mix. However, it can also be very effective to apply sidechain compression to these effects to duck them whenever a kick or snare hits, for example, as this can tighten your mix even further.
Improve the groove
Another great tip that I've had a lot of joy with can seem a little counter-intuitive when you first consider it. I picked this up from a video with either Deadmau5 or Steve Duda, I can't quite remember it was so many years ago, but all that matters is that it works! You can sidechain compress claps and snares with a kick drum (or whichever signal you prefer, as long as it hits at the same time as the kick). This may sound strange, but it can really add to the sense of groove, particularly for House or any four-on-the-floor-based genres.
This method works really well if the claps/snares are offset slightly (and I mean slightly) from the main beat. For more information on this approach, stay tuned as I'll be writing a post specifically on How to Mix Claps in EDM.
On top of these mix uses, there are also more creative ways to use sidechaining - check them out in this related post.
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