A gate (also called an expander or noise gate) is a type of dynamics processor used to increase the signal’s dynamic range. Read on for some nuts & bolts theory plus a demonstration on using a gate to remove noise in a guitar track.
Nuts & Bolts
A gate works by attenuating the signal below the threshold. The attack and release parameters work the same as a compressor. The attack controls how fast the gate opens, the release controls how fast the gate closes. Many gates, including the one in my example have an additional parameter called ‘Hold’, this controls how long the gate stays open. Attack and release times are usually related to the type of material being processed. Using a drum kit as an example, generally the attack and release times are set fast to ensure the ‘transients’ get through. The hold time is then set to allow enough of the body of the waveform through the gate. Gate’s will generally have a few more parameters, let’s use the stock D3 Expander/Gate in Pro Tools as an example.
|Range: Defines the amount of gain applied on signals below the threshold. A range of -40 dB means that signals below the threshold are reduced by 40 dB.|
Key Input: Allows for an external signal to be fed into the side chain. For example it is common to use the inside kick as a key input when gating the outside kick as it will have less spill.
Look Ahead: Let’s the side chain examine the input signal slightly before processing takes place. Makes the gate operation less obtrusive.
Side Chain: Used to equalize the side chain signal that triggers the gate. This is often used to filter out unwanted frequencies allowing the threshold to be set lower and thus retaining more of the signal.
The purpose of this gate will be used to remove the low level noise in between the chord hits. This includes the noise of the equipment and the finger movements.The aim is to end up with a clean and punchy guitar track.
|I started the processing by identifying an instance of the noise and looping it.|
I then set the threshold so that the noise was not audible. I tweaked the attack, release and hold time so that the transients and body was able to pass through the gate. I found that I was able to take a bit of edge of the transients by enabling the look ahead and setting the attack around 70 microseconds. I listened to the rest of the track and adjusted settings until the noise was removed. Here are the settings I ended up with.
The video below demonstrates the effect of the gate. Notice how the hiss of the recording gear and finger noise disappears when the gate is engaged on the second repeat? Although not significant by itself, noise of this sort will become apparent on multiple tracks and will take up valuable space in a mix.