All too often producers overlook – or sometimes disregard – the value of the lowly noise gate and its cousin, the expander.

Originally designed to help eliminate hiss, rumble and other unwanted recording artifacts, the noise gate has quite a few creative uses once you understand what’s going on under its hood.

In this tutorial, we’ll take a closer look at the underlying principles that govern this type of effect.

How a gate works

The first concept to grasp is that gates and compressors affect the same aspect of sound: Volume.

What’s more, they both do the same thing to the volume – reducing the amplitude of a signal based on its dynamically changing loudness.

The crucial difference is that a compressor attenuates (lowers) the volume of a signal when it gets too loud, whereas gate lowers the volume of a signal when it gets too quiet.

Huh?

Well, that’s the reason the gate was invented in the first place.

Since hiss and noise are quieter than the sound of the instrument being recorded, by using a gate on an instrument, only the ‘intentional’ sounds pass – everything else (the quiet stuff) is lowered in volume, thus reducing unwanted noise in a track.

Gate parameters

The parameters of a gate are much more straightforward than those of a compressor, so users don’t have to concern themselves with things like and ratio, knee, or peak/RMS modes.

Almost every gate includes the following set of parameters: Threshold, attenuation amount (range), attack, hold, and release.

The diagram above shows these parameters in context.

Other options include “flip” mode and sidechaining, which are capable of some really unique effects when applied correctly.

Threshold. The threshold parameter determines the volume below which the signal will be attenuated.

That is, when the signal drops beneath the threshold, the gate kicks in.

Attenuation. Sometimes called “range” this is the amount that the signal will be attenuated when the threshold is crossed, activating the gate.

Extreme amounts cut the signal off entirely.

Smaller amounts cause the gate to function as an “expander” – a fancy term for a gentler gating effect, since it ostensibly expands the overall dynamic range of a signal.

Attack. As with compressors and synths, the attack parameter determines how quickly process begins – lowering the signal after it falls below the threshold.

Hold. Since the dynamics of even a sustaining note can vary slightly, the hold parameter allows the gate to remain open at full volume for a specific duration after the threshold is crossed, ignoring those subtle variations.

With the hold value set to zero, gating can sometimes create undesirable “chattering” effects when the threshold is set too close to the signal’s lowest volumes.

Release. This parameter determines how long it will take for the gate to return to its normal state when the signal passes back above the threshold.

Flip. Some gates, like the one in Ableton Live (pictured above), have a flip switch that inverts the behavior of a gate, allowing signals to pass only when they are below the threshold.

While this implies that the gate will perform similarly to a compressor, the end result is rather different and much less refined.

Sidechaining

Without a sidechain function, the gate is a largely utilitarian tool – useful, but not particularly glamorous.

Add a sidechain and the gate becomes one of the coolest toys in an electronica producer’s arsenal.

Here’s why.

As with the compressor, a sidechain allows a second signal to determine when the gate opens and closes.

So, you could take a sustaining signal like pads or vocals, then use a drum loop as the sidechain input.

This screenshot (at right) from Live shows a gate configured with its sidechain controlled via a track that contains drums.

In this instance, every time a drum crosses above the threshold, the sustaining part is heard.

Between drum hits, the sustaining sound is cut off.

The end result is that the sustaining sound pulsates in perfect time with the drum loop.

Adjusting the sidechain gain and/or gate threshold can fine-tune the results so that only the loudest drum hits open the gate – or vice versa.

Tinkering with the attenuation, attack, hold and release parameters will modify the overall character of the gating, with effects ranging from a slight rhythmic quiver to “chopped up” audio.

For even more precise control – if your sequencing software allows it – you can use a softsynth’s channel as a sidechain input.

In this manner, every time you play a note on the designated softsynth, the gated sound will be heard.

This will allow you to sequence more complex, tightly controlled rhythms than a drum loop permits.

If you’ve never played with a sidechained gate before, we strongly urge you to drop what you’re doing right now and go try it out.

And we’ll be back in a few weeks with another groovy production lesson…