The most common application of a sidechain compression effect in contemporary music production is to use the kick drum as a sidechain source to trigger compression on the bass. When the kick hits, it cuts through the low end of the mix better because the compressor on the bass attenuates simultaneously. In this excerpt from Start to Finish: Ill Factor - Episode 8 - Vocal Production Pt. 2, ill Factor demonstrates another handy sidechain compression application, this one for vocals and enhance your vocal effects.
But first, he shows how he electronically doubles the lead vocal.
Doubling vocals, Improve your vocal effects
As the excerpt begins, he’s planning on using Waves Doubler 4 plugin to thicken up Jared Evan’s vocal. He explains that, yes, you can put Doubler on the vocal track as an insert. While he sometimes configures it that way, he’s using it as a send effect, placing it on a Return track in Live. It's a very good way to enhance your vocal effect.
One of the advantages that parallel configuration is that you can route other tracks to the effect, as well as your vocal effects. That saves CPU resources compared to using individual inserts on multiple tracks.
Once he gets Doubler set, it thickens up the sound of the voice nicely.
Once he’s happy with Doubler 4’s effect on the vocal or vocal effect, he turns his attention to the quarter-note, ping-pong delay that’s on it. He’s feeling like it’s getting in the way of the vocal a little. Here’s where he brings in the sidechain compressor.
He puts an instance of Live’s Compressor on the Return track after the delay and sets it for sidechain compression input, with the lead vocal as the source. That means that whenever Jared’s vocal is present in the signal, it will reduce the delay level. The amount of attenuation depends on how he sets the Threshold, Ratio and other compressor parameters. At the end of a word or a phrase, the delay will come back in at full volume.
Ill Factor’s sidechain compressor setting for the vocal delay.
It’s the same concept as a compressor on the bass with the kick as the sidechain compression source. You want to make one part stick out from another that’s in a similar frequency range and could be masking it a little. The delayed signal from a vocal will be exactly in the same range as the lead vocal itself. If they’re overlapping at all, it could reduce the clarity of the lead. Ill Factor plays the section with and without the sidechain compression. It definitely helps the vocal and vocal effects come through more.
How a Sidechain Works
Sidechain compression may sound complex, but it’s not. In most compressors, the incoming signal gets duplicated. One part goes to the output and the other to the detector circuitry. The detector uses the incoming signal to trigger the compressor based on the settings of the threshold, ratio and so forth.
The signal sent to a compressor gets duplicated, with one part going to the detector and the other to the processor and eventually the output.
If the compressor has an external sidechain compression feature, like Live’s Compressor has, you can use an external signal to go to the detector instead. That’s the Sidechain compression. In Live, you can choose any track or bus as a sidechain compression source.
Live’s Compressor also has a sidechain EQ. You can use that to modify the signal going to the detector and vocal effect for example, whether it’s from an external source or the track you’re compressing. That can come in handy if you only want part of the signal to trigger compression.
With the sidechain compression active, the signal from the sidechain compression source goes to the detector, while the audio signal goes straight into the processor.
One reason for that sidechain compression filter is to cut out bass. At a given amplitude level, bass frequencies exert more energy, and therefore will exceed the compressor’s threshold more than higher frequencies. If you don’t want as much compression, whether you’re sending an external sidechain compression or the source track to the compressor, you’d filter out some of the low-end.
Sometimes you might do the opposite. In Episode 6 of this series, ill Factor wanted to use a kick drum as an external sidechain compression source, but the song only had a stereo drum part with snare and hi-hat. So he used the sidechain compression filter to roll off everything over 145Hz, which effectively eliminated the snare and hat from the sidechain compression signal.
Worth a Try to Sidechaining vocal effects
In Live, the Gate plugin also features a sidechain compression, which gives you some intriguing possibilities. You can use it to change the track’s rhythm to match another part in the session, which can be a terrific way to make parts groove with each other more.
You put a gate on the source track and set it to be triggered by the sidechain compression from another track that’s rhythmic in nature. The gate will open and close based on the rhythm and your settings. It doesn’t have to close all the way to create the effect.
Here’s an example. In this piece, there’s a percussion part that we’ll use as the sidechain compression source for the gate. It’s fed to two tracks, the bass and a synth pad, to change them rhythmically and integrate all their feels.
First, here’s the original:
Here’s the same part with the gates on the synth pad and bass turned on. The settings are a little exaggerated for demonstration purposes.
The settings for the gate on the keyboard.
Getting the results you want when using a sidechain compression gate like this usually requires some experimentation to find the ideal setting. The Threshold is critical, as are the Attack, Hold and Release controls.