Noise Gates
A Guide to Noise Gates in PA Systems
A Noise Gate is to an expander much as a limiter is to a compressor. Essentially it is an expander that mutes the signal when it falls
below the threshold, rather than simply reducing the gain. A downward expander with a ratio
higher than 8:1 is effectively acting as a noise gate.
What it is
Usually a noise gate is a 19" 1U box with knobs or buttons (and more
often than not a couple of LED meters) on the front. Some compressors
have a noise gate function included in the channel facilities.
What it does
A noise gate mutes the signal when it falls below a threshold (the threshold is generally user-determined).
How it works
It senses the input level, and closes the channel when the input level falls below the threshold. It can have controls for:
• Threshold.The level below which the signal is muted.
• Attack. How quickly the gate opens
once the signal reaches the threshold. On most sounds (particularly
percussive sounds), the attack should be very fast to avoid cutting off
the beginning of the sound.
• Release. Certain important parts of
the sound (decaying resonance & natural reverb tails) may fall below
the threshold. If the gate is closed too soon, the cut off may be
audible (& unnatural).
• Filter. If a noise gate is used on a
small rack-mounted tom, low-frequency sound from the kick drum may
exceed any usable threshold. A filter enables the user to tune out (or
sometimes tune in) a frequency range, so that the gate only opens when
sounds in a particular frequency range exceed the threshold.
• Stereo/Mono. Most multi-channel noise
gates allow coupling of each pair of channels for stereo use. If gating
is applied to left and right channels independently, drop-out of one or
other side can result whenever the signal on one side is above and on
the other side below the threshold.
How do you use it?
If all else fails, read the manual!
Noise gates are usually connected on channel inserts.
Expanders and noise gates can have a disastrous effect if set up
badly, and are at best problematic in live performances: spill from
other
instruments or from monitors can make it impossible to set effective
thresholds. With care they can deal with very situation-specific
problems (for example, buzzing from a bass guitar can be silenced
between songs by careful use of a noise gate with a filter). However,
they are most commonly used on drums, either to reduce spill between
drums, or to reduce the ringing of undamped toms. In this application,
they are usually used on channel inserts.
To use a noise gate on a drum:
1. Set the channel gain.
2. Set the attack and release to their fastest settings.
3. While the drummer hits that drum (and only that drum), raise the threshold until the drum starts to cut off.
4. Reduce the threshold a couple of decibels, so that the beat always exceeds it.
5. Increase the release time gradually, so that the drum is able to ring on a little after each beat.
Although the cut-off will still be audible, this will be much less
noticeable when the whole kit is being used and the whole band is
playing. A little reverb on the drum will help make the cut-off less
noticeable during solos.
Other than on drums, leave well alone.
Do you need one?
If the drums are well tuned and damped (or if ringing toms are an
intentional part of the drummer's sound), you probably don't need one.
Otherwise, one channel for the kick drum and one for each tom can be
useful. Most compressors include a basic noise gate on each channel, which is useful if you need to gate and
compress the same signal (kick drum is sometimes a good candidate for this).
What sort do you need?
One that has at least all the controls described above. Four channels
is usually enough (which might mean you need more than one unit).
- Source (astralsound.com)
