In Part 1 of this series, we discussed the basic concept of side-chaining along with a couple of the most common applications. In this segment we'll learn about more specialized uses of side-chaining and how to set up your system for side-chaining.
One very common side-chaining technique is especially useful for broadcast mixing, commercial voice-overs, or to blend background worship music with a spoken message without losing clarity. The background music, group mix, or master instrumental mix can be side-chained to the vocal/dialogue track so the music drops automatically when the vocalist or speaker is active. You'll want to use a low threshold, high ratio, and a fast attack on your compressor. The release can be set to a longer time allowing the backing tracks to swell more naturally back to their previous level when the voice stops.
UnGating - Triggering the Bass in Lockstep with the Kick
Another method uses a side-chained compressor set as a gate, so the signal is only allowed to pass when the trigger track is active. This is popular in pop styles where the kick drum is central to the entire mix. To utilize the UnGating technique, you'll probably want to use fast attack and decay settings to get the most percussive effect. This can be a really powerful technique when used on massive synth bass sounds in contemporary pop music. You can also run an LFO synth part blended and tuned to fatten up the kick itself (or even tune the kick to every note for a special effect).
Get the Mix Really Pumping
One method that is especially popular in EDM styles is to side-chain the entire mix to the kick drum and set the compressor to achieve an audible pumping effect when the kick hits. This can make the mix literally surge along with the kick for a dramatic effect. Use a slightly higher ratio compared to the vocal separation technique, along with a slightly lower threshold and slightly longer release. There are no wrong answers here; you are manhandling your mix with the compressor, so subtlety is not the goal. Play with the settings until you like it.
Selective Frequency Compression with Side-Chaining
You can also use side-chaining to tame frequencies that are out of control the same way studio engineers and mastering facilities have done for decades, by using a graphic EQ or channel EQ to tell the compressor what to squash. De-essing (reducing vocal sibilance) uses this same principle. Begin by running the output of the channel you want to process into your compressor and back to another channel or group on the board. Run a cable from an auxiliary send on the source channel and into a parallel (control) channel. Then connect the output of the control channel to the side-chain input on your compressor. Now anything you boost on the control channel will trigger the compressor. Use the control channel EQ to boost whichever frequencies are overbalanced in the source track and the source track will be automatically compressed whenever those frequencies occur.
You can use this method to control vocal sibilance (ess sounds), excessively bright cymbals, obnoxious rhythm instruments with too much midrange in the wrong places, or warm up a bass guitar with too much high end clatter to blend well into the mix. Theoretically you can use multiple compressors rigged this way to control several different frequency bands just like a multi-band compressor. If you're mixing in a Digital Audio Workstation (DAW) you most likely will have a dedicated multi-band compressor that makes it even easier to set up.
Setting up the System for Side-Chaining
In the digital realm (DAW), you have as many compressors available as your system resources permit. But if you want to use side-chaining for live music you'll need some outboard compressors. Many companies now offer multi-channel compressor/gate units that are great for this and typically quite reasonable to acquire. Make sure you obtain units with side-chain inputs. You'll want to use a separate buss, group, or auxiliary send for each trigger source. Then run the output into the side-chain input of the compressor. Insert the compressor into the channel or group you want to control. Carvin Audio's Concert Series Mixers have convenient channel insert jacks to facilitate this. Specialty insert-Y cables make it easy to set up this type of configuration since you have only one cable running from the mixer to the compressor.
Once you get a chance to employ side-chaining in a couple of real-world situations you'll begin to see how powerful it can be. Before long you'll imagine new ways to control one channel with another via side-chaining and discover an entire world of creative solutions and techniques to add to your sound repertoire. Have you ever tried side-chaining? How did you put it to work for you?