In Noise Gates – Part 1 we discussed some of the various uses of the noise gate in live audio mixing. In this installment we’ll look a little closer at the various noise-gate controls and their respective functions.
The most common parameters found on the typical noise-gate are Threshold, Ratio (sometimes called Range), Attack, Release, and Hold. Additionally, the better noise-gates come equipped with variable EQ filters in the detection circuit (more about that later). I will attempt to briefly describe these control parameters and their uses.

The Threshold control is used to set the level desired to start to onset of the processing. In other words, when the audio signal falls below the level set by this control, gating begins to occur. It is very important to set this control low enough to open the gate when the instrument is played but high enough to prevent the gate from false-triggering (by adjacent sound sources). This takes some experimentation to get it just right.

As I alluded to earlier, the better gates provide adjustable EQ filters in the detection circuit side-chain to further aid in deciding what sounds the gate responds to (and which sounds it ignores) by effectively tuning out frequencies outside of the sound source frequency range. This does not change the sound of the source, but instead, only changes what the noise gate detector circuit “hears”. Personally, I would never buy (or use) a noise gate that was not equipped with this feature, as my experience has shown that false triggering is very likely to occur without proper tuning of the detection circuit. If gates are constantly false-triggering, the result is often worse than not gating at all.

The Ratio (or Range) control determines how much residual signal passes when the
gate is “closed”. In other words, it can be set to gate the source signal 100% when it falls below the desired threshold, or it can be set to allow a certain percentage of the source to bleed past the gate. I equate it to a door that is able to shut tightly (with no sound leakage) or shut loosely (allowing some measure of leakage to pass). This is largely a matter of taste, and often based on the nature of the source being gated. Sometimes it is more desirable to allow some leakage (downward expansion) to occur because it sounds more natural than hard gating – some experimentation is in order here as well.

The Attack control determines how quickly the noise gate responds to the source level
falling below the established threshold. In other words, the Attack control determines how quickly the gate opens up to allow sound to pass through. If set to open too slowly, the sound source can sound chopped and unnatural. If it is set to open too quickly, sometimes pops or clicks can be generated. As with all of the noise parameters, it’s imperative to “use your ears” and experiment to find the best results.

Conversely, the Release control determines how quickly the gate closes after being triggered. In some cases (think drums) it is sometimes helpful to shorten the decay of the sound source, in order to “tighten” the sound. Other times it’s important to make sure that the gate closes slowly enough to allow for sustained notes to completely fade before the gate closes. (This control works in close conjunction with the next described parameter).

The Hold control is closely linked to the Release control in that it determines how long it holds the gate open before allowing it to begin closing (at the Release rate). Again, this one is determined by the nature of the sound source. Some sounds will need to “hold” before closing, but other things will not require much (if any) Hold time – EXPERIMENT!!!!!!

Have fun!!

-Michael Grosso CCFL technical director / audio engineer

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