Expander / upward compression (a guide for dummies)

Hello and welcome to this week's article!
Today we are bringing a new topic on our infinite list of article about compression: upward compression!

What is upward compression?
It's a type of compression that works exactly in the opposite way than the regular one: you set a ceiling, and decide a whole wave signal or part of it (with a multiband compressor / expander) in which the volume will be increased until it reaches the ceiling.
To make it easier: we choose a part of the sound, or the entire sound, and make it louder until it reach a certain level.
The signal is increased within a ceiling or within a range (some expander has the control named "range" in which the upper limit is the ceiling), and it just increases the volume below the threshold (rather than lower it as a regulal compressor would), putting it into "the range".

If we are expanding the entire sound until it reaches the ceiling, the result will be the same of a regular compressor: the loudest parts of the sound will be attenuated, the quietest will be raised in volume, that's why this procedure is more suited when it affects only a certain frequency range.

Why do we do this way instead of just raising the volume?
To have more control over our transient;
in facts, if we have a sound that is too much oriented on the high end and we want to bring out the body whilst at the same time mantain controlled the dynamic range, we can expand the low end of that sound (like in the picture, in which only the low mids, the part coloured in blue, is expanded, while the part in purple is normally compressed).

Why don't we just use an equalizer to boost the part we would like to expand?
Same answer: because we want to control the transient and avoid it to have too much dynamic range, with volume spikes that can end up out of control.

The uses of an expander are several: to reshape the sound of a microphoned guitar or bass that sounds too thick or too thin, to give life to certain frequency areas of the room microphone of a drumkit, or to apply corrections in a band recorded with few or one single microphone.

This leads us to the same dilemma we arrived when talking in general about multiband compression:
is it a compressor? Is it an equalizer? Many producers consider it the magic wand to solve every mix and mastering problem, while others prefer using the basic tools (broadband compression, equalizer, volume) following the rule that it's better to use few simple tools and master them rather than experiment too much with more complex tools with the risk of ruining a mix.

What is your opinion? Do you use multiband compressor and expanders?
Let us know!


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