How to use Noise Gates

Noise Gates (or Gates as they are usually called) are pieces of outboard equipment used in PA systems that for some people are mysterious and complicated. I will post a series of articles about these pieces of kit and what they are used for.
Firstly, a gate behaves like it sounds. It electronically shuts a gate across the audio signal going through it so nothing is let through. When a 'key' signal operates the gate, it is opened to let the signal through and when the key is removed, the gate closes again and the signal removed. All of these are configurable to a certain extent depending on what unit you are using.
The key signal can be internal (derived from the audio signal itself) or it can be external (comes from whatever you plug into the back of the unit) but we will assume that all our keying is internal.
The threshold control says at what level the key signal will open the gate, so let us assume we have a Tom from a drum kit through a microphone plugged into our gate. Our gate is set to internal key and the threshold is set to -40db. Somebody hits the drum and very shortly after they hit it, the signal passes -40db and the gate is opened. After the hit, the drum sound fades away and after dropping past the -40db position, the gate is closed again and the remainder of the sound is cut off. This is the most basic operation of a gate.
Now we have looked at the operation, what do we use them for? The two most common uses of gates are 1) To shorten the sound of a ringing (usually) Tom Tom and 2) To remove latent noise on a channel (such as an electric guitar). We will look at the second example first because it is the most simple.
For many electric guitars, because of a love of old technology, valves and single coil pickups, lots of guitar rigs have excessive noise when the guitar is not being played. Left uncontrolled, it is at best annoying and at worst unprofessional. Add a gate into the channel and you can control the threshold at which this noise is removed by the gate. You might efectively tell the gate to remove anything below -40(ish) db so that when the guitarist actually plays, assuming they never play anything really quietly, the gate will open and when they stop, it will close again.
The same basic setup applies to the Tom Tom but there are problems that you might find with Tom Toms and even with guitars that require slightly more complicated setting up which I will cover in my next post.