Noise Gate
Noise Gates are devices that attempt to minimize noise in the signal. Most focus on muting the signal while you are not playing. They detect the volume level of the inbound signal and compare it to a threshold value which can be dialed in for your guitar, playing style, and setup. If the signal is below the threshold, it is expanded (opposite of compressed), reducing its volume. In some cases, devices known as expanders and noise gates are the same thing; but in practice devices marketed as expanders are usually more configurable similar to, or even a feature of, a compressor. Noise gates typically feature a fixed, high expansion ratio, causing any signal level below the threshold to be silenced.
Using a noise gate is a good idea any time your rig produces audible noise and possibly hum while you are muting your guitar. Most of the time the source of the noise is the nature of electric pickups, and if heavily distorted, compressed, and/or amplified create fairly loud noise relative to signal volume. In Rock and Djent, where the guitars are often highly distorted but also need to abruptly rest, noise gates help create greater contrast between rests and accents. But they can be used in any style that seeks to exterminate inherent noise from pickups or other devices during rests.
Contents
Visualization
I find the best way to visualize how the gate works is to picture a hinged gate that uses a spring to stay closed. Imagine the audio stream from your guitar is a parade of animals. As they approach the gate, they push against it and if they are strong enough they are able to get through. When you stop playing, your guitar is still outputting noise from your pickups, which can be visualized as small bugs. These bugs cannot open the gate themselves and instead go into the ground, never to be seen or heard from again. However, they will get through if they accompany some animals - the gate cannot filter the bugs out of the parade; it can only open and shut.
Common controls can be explained this way as well. Decay for instance could be described as a shock absorber on the gate preventing it from closing abruptly, letting smaller and smaller amounts of small animals and bugs through. A variable expansion ratio can be described the same way - if the animals cannot fully open the gate, only some ratio of them are allowed to get through.
Advanced Gate Features
Basic noise gates feature a fixed, high expansion ratio, so that any signal lower than the threshold is essentially muted. Advanced gates may feature
- Different thresholds for "opening" and "closing" the gate, preventing jitter
- Smaller or adjustible expansion ratios
- Different inputs for detecting the level vs. the signal that is actually affected
- Hold parameter to prevent the gate from "closing" on momentary low signal
- Decay parameter for a more natural-sounding fade when the gate closes
Noise Suppressors vs. Noise Gates
Some devices are lumped together with noise gates but don't actually use the gating method above. Instead these noise suppressors or removers analyze the signal and attempt to remove noise from it rather than muting or dampening the entire signal. I am very wary of these devices - high settings leave clearly audible artifacts in the signal.
Signal Chain Placement
I like to place my noise gate first in my chain (or behind the wah pedal only). I don't want any devices between the guitar and the gate from compressing or adding noise to the signal, which makes the gate's job that much more difficult.
The only exception to this is with gates like the ISP G-Rack and chained Decimator II's, which feature multiple inputs. This allows it to be placed first in the signal chain to detect the guitar signal and determine whether the gate should engage or not and last in the chain for actually gating the signal. This is the best scenario, as everything in the chain is adding noise and any distortion/compression stages in the chain are amplifying that noise. The gate at the end of the chain mutes as much of that as possible, leaving only downstream devices like the power amp to add noise, which is actually far lower than the noise that a saturated distortion pedal or pre-amp produces.
A facsimile of this setup can be done with multiple gates.
Dialing it in
How you dial in the gate depends on how you intend to use it. For metal players (especially djent), the main use is to go quickly from power chords or palm mutes to full mutes, being able to quickly switch from raucous distortion to silence. For softer lead players, the main use is simply to reduce the noise when not playing. There is no need to quickly switch on/off, as the tone itself likely has delay and reverb. Rather, the bigger fear is for the gate to kill a sustaining note unnaturally rather than letting it decay.
These are the basic scenarios with everything else falling between these extremes. For metal tightness, setting Hold or Decay settings very low or to 0 allows the gate to completely close quickly. If the expansion ratio is adjustible, it should be set rather high. If the gate has a single threshold value, it should be set high enough to easily kill any noise when the guitar is muted, but not so high that it prevents more subtle playing like a hammer-on from nothing from sounding. Also, make sure sustaining notes aren't outright killed. It's best to test the settings with the softest part of any song you want to play. If the perfect threshold setting is difficult to find, and it seems like the gate sometimes jitters on/off for playing that is right on the border, you may want to use a small Hold setting - like 10-40 ms. This will stop the gate from jittering on mild fluctuations of the signal level, but it will also increase the time it takes for the gate to activate, losing some "tightness".
If the gate has separate open/close thresholds, I find its best to set the open threshold about 2-6 db higher than the close threshold. This prevents jitter while allowing you to keep Hold at 0 ms. But start by keeping them at the exact same setting and dialing them in the same way as you would normally with a single threshold gate. Once you've found the sweet spot, move them in opposite directions. Then test to make sure Open Threshold isn't so high that it won't open for more subtle playing, and make sure the Close Threshold doesn't kill sustaining notes completely pre-maturely but still closes as soon as you mute the guitar.
For more subtle gating, use higher Decay settings. This helps particularly on leads where you are likely to sustain notes until they decay completely, with the gating sounding more natural. Also, if the lead tone has delay and/or reverb, this helps to mask the gating mechanism as well, getting a cleaner sound. Otherwise, your main concern is to use as low of a threshold value as possible - you want the gate to close when you mute your guitar, but that's the only time it should.
Multiple Gates
As mentioned above, every piece of gear in your chain will add noise, and compression/distortion stages will amplify it. Placing the gate at the front of the chain makes it easier to dial in; however, it is only muting the signal from the guitar, not all the noise created by downstream devices. Placing the gate at the end of the chain makes it very difficult to dial in effectively, as well as sounding artificial as it kicks on/off.
To counter this issue, some use multiple gates, one in the front and one in the back. Some use even more, bracketing compressors, distortion pedals, or the amp's pre-amp with pairs of noise gates. This is much easier to do in modelers where all of those gates are free, in comparison to real-world units where each additional gate is going to add significant cost to the rig.
The same advice applies to dialing multiple gates as it does one.