It may be the Nora Batty of the recording studio but don't let the noisegate's

unglamorous image put you off. Professional studio engineer Trevor Curwen shows

it's capable of a few neat tricks to liven up your tracks...

Noisegates are found in every studio and PA rig in the country, where they quietly

go about performing their nominated task of separating wanted sound from

unwanted background noise. However, as well as cleaning up, gates can also do

plenty of creative jobs, including some you would more likely associate with a digital

effects unit.

Perhaps with the rise of sophisticated mix automation and the manipulation

available in hard-disk recording systems, the physical rack-mounted noisegate is

not such a crucial tool as it once was, but it's far from past its sell-by date, as the

new Drawmer DS501 proves (10/10, FM108). With this in mind, FM takes the

opportunity to present a rundown of a noisegate's functions and pass on some

creative tips.

Basic operation

A gate's basic function is to remove unwanted noise between the sections of

wanted material. It is usually connected via a mixing desk's channel insert points or

in-line with the sound source so the whole signal passes through it. In live sound

applications gates are used primarily on drums to ensure each individual drum's mic

picks up sound from that drum only. In recording applications, using a gate while

actually recording can be dangerous as you could accidentally gate out part of the

performance. Therefore, gates are more likely used at mixdown

A typical example of a gate's more conventional role is to clean up an individual track of a multitrack recording. If,

say, a recording of a miked up guitar amp has amplifier hiss plus low-level bleed from other instruments, the gate

could be used to shut down the track when the guitar isn't playing so the unwanted sound won't clutter up the mix.

At its simplest, a gate acts as an automatic switch, separating the louder sounds from the quieter ones. You can

set a threshold above which sound is kept, and below which it is rejected. The sound to be treated - known as the

program material - is fed into the noisegate's channel input and the gate will remain closed, effectively silencing

the sound until it rises above the threshold and opens the gate.

The action of the gate is determined by its sidechain circuitry. In normal use this is fed by a split of the signal from

the input, known as the key signal. The circuitry senses the strength of the incoming signal and when the signal

exceeds the threshold, the sidechain circuitry opens the gate.

Open the envelope

How quickly the gate opens and closes and how long it remains open is set by its envelope controls. The attack

control sets how quickly the gate opens after the threshold has been reached. In the majority of cases a fast

attack time will be the norm, but the attack control can also be used as a creative tool; by setting a slow time

sounds will swell in slowly for a 'bowed' effect. The hold control keeps the gate open for a preset time after the

signal has passed the threshold and the decay control sets how quickly the gate closes once the signal has

dropped below the threshold level.



All three envelope controls are usually found on dedicated noisegates but some basic gates, especially those

found in channel strip type units alongside other processing, have more limited control or envelopes that are set

automatically depending on the program material.

A rudimentary gate's sidechain senses level changes alone, but a more fully specfiied gate such as the industry

standard Drawmer DS201 has key filters that can be used in conjunction with the threshold control to prevent

sounds that fall outside a set frequency range from opening the gate. Filtering usually involves rolling off high and

low frequencies to zero in on the wanted sound and eliminate as much of the unwanted sound as possible. It is

only applied to the sidechain key signal and not to the program material, which remains unaffected. By putting the

gate in Key Listen mode, which routes the key signal directly to the output, the effect of the filters can be heard

while you adjust them.

A typical example of using the filters would be when using multiple mics on a drumkit. You may want to gate a

particular drum, say the snare, but are having problems because the hi-hats bleed into the snare mic and are

opening the gate. A gate opens whenever the incoming signal exceeds the set threshold, so reducing the

threshold level goes some way to helping this problem but you run the risk of gating out some of the quieter snare

hits. Hi-hats inhabit a higher frequency range than snares, so bringing the filters into play in this instance and

rolling off the top end will allow you to reduce or eliminate the possibility of a hi-hat opening the gate.

This technique can also be used to separate the kick or snare in a drum loop so it can undergo further processing

or EQ before mixing it back in with the original to change the sound of the loop. If you have no need to use a gate

in a gating role you can use the filters purely to EQ any signal passing through it. To do this, just put the gate in its

Key listen mode. The filters can now be used to merely remove a little top, bottom or both from the signal or to

severely limit its bandwidth.

Finally, the range control determines how much signal can be heard when a gate is closed. For many

applications, setting the range to its extreme setting so that the closed gate totally silences the sound would be

the norm but in some circumstances this may sound unnatural, so the control can be adjusted to ensure the

sound is only attenuated to a set level when the gate closes.

External key

Some of the more unusual effects gates can be used for are achieved by using one signal to gate another. A

gate's sidechain circuitry can be switched, so that instead of sensing the strength of the incoming (internal) signal

entering the channel input it will sense the strength of any external signal plugged into the gate's key input, a

socket usually situated on the rear panel.

With a gate's key source switch set to External mode, any signal present at the key input, aso lng as it is above

the threshold level, will open the gate, making it possible to use this key input as a 'switch' to open and shut the

gate regardless of the characteristics of the program material being put through the unit. This feature can be used

to add an extra element of sound to certain drum hits and is the way to add real gated reverb, if that's your thing .

To add reverb to specific snare hits on a recorded drumkit, a track of the room ambience recorded by a distant

mic is used as the gate's progarm material. A split from the snare drum signal is then patched into the key input

so the gate opens for a burst of ambience every time the snare hits. The sound of the ambience can be shaped

using the envelope controls.

The same basic technique can be used to add some real low end into a weak bass drum sound. This technique

may not be too relevant to anyone sequencing a bass drum as there is always the option of using whatever

sample you wish, but for a live recorded bass drum it's a different matter. The trick is to have a deep continuous

sine wave such as those produced by Akai samplers as the gate's program material and use a version of the

existing bass drum at the key input.

The gate will open every time the bass drum plays, creating a low bass note that, with carefully set hold and

release settings, can be mixed in with the original bass drum.

Ducking

Ducking is another gate function that relies on the key input for its implementation. Everybody who listens to the

radio will hear ducking in action at some time or other when the music is made to drop in level whenever the DJ

speaks over it. This is achieved by having the music as the gate's program material and taking a feed from the

DJ's microphone signal into the key input of the gate. If the gate was set up for normal gating it would open when

the DJ started talking, but in Duck mode the gate's action is reversed so it colses when faced with a key input

signal. The degree to which the gate closes is set by the range control and this can be adjusted to create a subtle

drop in level if required.


From a musical point of view, this can give a rudimentary automation of an instrument's volume. Take the

example where a synth pad is playing as part of a backing track but needs to drop slightly in volume to make

space for vocals. This can be achieved by putting the pad through the gate and feeding a version of the vocal into

the key input. Whenever the vocalist is singing the pad will drop in volume and the gate's envelope controls can

be set so that it fades back up at the end of the vocal phrase.

A similar thing can be done with effects. If the effects returns are fed through the gate, any reverb or delay can be

subdued while the vocal is present only to swell back up at the end of phrases.