Noise gates are among the oldest audio-production tools. They mute a signal falling below a certain level, called the threshold, to remove unwanted noise. Most modern noise gates include a sidechain input (also known as a key input). That's used to control the gate with a separate signal. In this article, I'll discuss a variety of musically creative ways to use noise gates and sidechains.
Acoustic kick drum tracks rarely have the depth and low end heard on modern commercial recordings. To beef up a kick drum track, use a synth or signal generator to create a low-frequency sine wave and insert a gate effect on its output. Route the kick drum to the sidechain input as well as to the main mix or drum submix. The sine wave will now be triggered by the kick drum signal. Set the gate effect's hold and release controls to fairly low values to keep the duration of the sine wave short, and you will have a nice, fat low end to beef up the kick drum (see Web Clip 1). The pitch of the sine wave can make a big difference, so experiment.
You can also use gates to add punch to a snare drum track. Subgroup a copy of the overhead mic tracks to a bus with a gate, and route the close-miked snare track to the gate's sidechain input. Adjust the threshold so that the gate is triggered by the snare hits but not by the lower-level leakage in the snare track. Because the original overheads are intact on separate tracks, you can add further processing to the overhead subgroup to flatter the snare. I often convert the overhead subgroup to mono, add heavy compression, and then blend it back in panned to the center.
Gates can tighten up sloppy performances by making parts start and end in sync. Web Clip 2 illustrates a sloppy piano part and tight bass part playing similar patterns. A gate on the piano track, with the bass track feeding the sidechain, tightens things up nicely. The gate's hold and release settings are crucial in determining the feel of the gated piano part.
A similar sort of controlled gating will tidy up vocal backing tracks. Group the background-vocal tracks in a submix and insert a gate. Then use the backing track with the best timing as the sidechain input to improve the timing of the whole ensemble. You can also use this technique to keep a bass track locked to a kick drum track.
FIG. 1: A phaser is inserted between two gate effects. The different settings on the two gates allow the phaser-processed portion of the signal to be shorter than the nonprocessed part.
Insert a gate on a chord, pad, or ambient track and gate that track using a rhythmic pattern or loop for the sidechain. You'll get the precisely controlled rhythmic chopping effect often found in dance music. For rhythmic variation, use a copy of the rhythm track for the sidechain source and shift it in time by a musical subdivision — a 16th note, for example. Don't feed the copy to the main output, of course. For tonal variety, use two gates with different settings and insert a phaser or other effect between them (see Web Clip 3 and Fig. 1).
For some novel panning effects, try two gates in parallel. Start with a mono loop and assign the output to separate buses panned hard left and right. Insert a gate on each bus, set one gate for a slow attack and quick release, and set the other gate for a fast attack and slow release. You get a stereo loop with an intriguing pan envelope.
You can go well beyond the clichéd gated-reverb effect of the '80s when processing a reverb with a gate effect. For instance, bus a drum loop to a reverb followed by a gate whose sidechain is fed by the same loop. That produces a tight reverb envelope following the natural accents of the drum loop. The gate's hold and release controls dramatically affect the length of each burst of triggered reverb (see Web Clip 4).
As you can see, gate effects are useful for more than cleaning up noisy tracks. Whenever a track seems a little lifeless, try some creative sidechain gating. You may be surprised by the results.
Eli Krantzberg is a Montreal-based drummer, vibraphonist, bandleader, and home-studio owner.