Music Production and Technology

The Art of Noise Gates

March 2007

Introduction
Most students of music technology and most musicians are familiar with various audio processors and effects; we all love to play with digital delays and flangers etc. We can "hear" those. They're fun. But there's one processor that sits in our effects rack every day, waiting patiently for it's chance to shine. Waiting to prove to the world that it too can be fun. This piece of audio equipment deserves much more attention than it normally receives and this article will endeavour to do just that. Dear, humble noise gate today is your day. This is your chance to show the world what you can do, so step forward, into the limelight and shine.

What is it?
Noise gates fall into the category of dynamic processors because they change the dynamic content (the volume) of an audio signal. There are some things that noise gates have in common with other dynamic processors - compressors, limiters etc. On the front panel of a noise gate you will find controls named "threshold", "attack" and "release" just as you would see on a compressor. But that is where the similarity ends. Functionally, a noise gate is nothing like a compressor or a limiter.

The function of a noise gate is simple; as the name suggests, a noise gate was originally designed to remove background noise from audio. It does this by only allowing an audio signal to pass through it once it crosses the threshold set by the user. For example, let's say a vocalist produces a level of around -12 decibels (dB) when singing but during the quiet parts of the song we can hear background noise at around -34dB (coughing, the lyric sheet rustling etc.). If we set the threshold to around -24dB then the gate will only "open" when the vocalist sings, thereby muting all the background noise.

Silver Gate - Logic Pro plugin

Drawmer DS201 - dual channel rack mount

Let's take a closer look at the controls

" The 'threshold' control, as mentioned above, sets the gate's sensitivity to the audio signal and determines when the gate will open. The gate opens when audio is above the threshold and closes when audio is below the threshold. This control is usually scaled in decibels (dB).
" The 'attack' control determines how long it takes for the gate to fully open. This is similar to the attack control on a synthesiser's A-D-S-R envelope. In fact, our noise gate could be considered to be an automatic amplitude envelope; we'll discuss this in more detail later.
" The gate's envelope section is completed with a 'hold' control to determine the amount of time the gate stays open, and a 'release' control, to determine how long it takes for the gate to close. All of the gate's envelope controls - attack, hold and release - are usually scaled in milliseconds (ms).
" Another control often found on noise gates is the 'range' control, also known as 'reduction' or 'floor'. This control sets the minimum volume for the audio, thereby allowing some signal to pass through at a reduced volume when the gate is closed. This control is usually scaled in dB and ranges from around -100dB (fully off) to 0dB. At a setting of 0dB no volume change (gating) will take place, even if the audio exceeds the threshold. With this control the gate doesn't have to act as an "on/off" switch for the audio signal and can be used to create more subtle gating effects.
" Sometimes you will see high pass and low pass filters on noise gates. However, these filters are not used to process the signal passing through the gate, instead they are used to process another audio signal called the 'Side Chain Input" (AKA 'Key Input'). This side chain signal can be used as an alternative trigger for the gate. It does not appear at the gate's audio output except for monitoring during the setting up process.

Use of side chaining and frequency conscious gating is where the fun really starts with this wonderful tool. But for now we'll deal with the basics.

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