Expanders 101

I have been asked recently about expanders and how do I use them in mixing; so I thought I would put together this article to explain a bit of background about expanders as a tool and how they invaluable they can be in the mixing process.

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Before we discuss expanders themselves, it’s important to understand what we’re actually doing to the sound.

Expanders are processors which are able to affect the dynamics of a sound, Dynamics are an essential part of a sound, so having being able to control dynamics is an invaluable asset for mix engineers.

The range/difference between the sound’s loudest and quietest moments is called dynamic range. This is the main element of a sound that is affected by an expander, simply put Expanders particularily push the difference in loudness between quiet and loud sections of an audio track pushing quiet sounds quieter and loud sounds louder.

Expanders are the very opposite of compressors as they expland the dynamic range - for the most part - an engineer would use it to un-do what a compressor has done.

Like compressors, expanders share a very similar concept; with identical controls- what’s fundamentally different is that an expander affects what’s below the threshold.

Ratio.

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Just like compression, is expressed in I/O- with the below ratio (1:2), 20 dB is in below the set threshold will result in 40 dB wirth of falls for output.

Whichever part of the signal below the threshold is pulled down and made quieter.

Most often you will see expander/gate rather than one of them individually. You will get a control to dial the ratio you need for whichever task you want to accomplish ( often between 1:1 and 1:100).

On older hardware, it was switch that toggles a gate into an expander with a fixed ratio.


Attack/Release.

Attack and release on an expander manage changes in gain reduaction - for example attack will slow down a change in gain change from -60 dB to 0 dB and release will do the same in gain change from 0 dB to -60 dB; it’s worth noting that that both the attack and release are independent from the threshold. When the signal goes above the threshold, gain reduction will decrease as fast as the attack will allow, when the signal signal is below the threshold then expansion starts again.

Hold.

Hold can be used in two different manners; much like a compressor- the control will alter the release ratio; however if implemented like a gate then the hold control will pause gain reduction for the set period once the signal drops below the threshold.

In principal, to use an expander while mixing is simple a tool which is much smoother than gates which is a less obstructive with gradual transition between a processed a none processed signal.

Upward Expansion.

One of the most overlooked techniques in mixing is upward expansion; similar to compression and affects louder signal crossing the threshold, but rather than pushing the signal down, sound is pushed up in level- expanding the dynamic range further.

The ratio determines how much the signal is expanded; unlike compressors - in which the ratio is expressed in whole numbers; expanders’ ratio is expressed as a fraction of one.

Usage.

Let’s talk about how you can expansion to get better results.

First Off- (Better-Transients) - much like a transient designer and get more attack on your percussions. Start with mid to fast attack (less attack will get more transients); set a high ratio initially and adjust the makeup.

Expansion (especially multiband) can be used to bring life back to a heavily compressed lifeless drum track - something that wasn’t recorded very well. Expansion can recreate dynamics and tone such track.

I tend to use expansion to highlight and boost unexpected parts of a signal by adjusting attack/release times. For instance reverb tail on a vocal track, I use slower attack time as the expander would be still following the initial transient.

Expansion can be used to bring in body of an instrument by focusing on the lower mids, maybe less harshness on a thin track or less transietns on too much picking in a guitar track.

Your options are many and much like compression; always leave head before it in the signal chain in order to avoid clipping.

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