While there are tons of great mixing tools to choose from, EQ and Compression always seem to steal the spotlight.

We’re practically obsessed with our idols’ favourite frequencies and attack/release times. So much so, that we’ll even just skip past anything else, and straight to the “good stuff” when watching their courses.

One of these often skipped-past and overlooked processes is Expansion.

“Expansion? Never even heard of it…”

Don’t worry, a lot of people haven’t - but you’ve heard of Gating, right? Well, an Expander is essentially just a gate with a lower ratio. If gating is the opposite of limiting, then expansion is the opposite of compression.

While a compressor compresses, or reduces volume when a signal goes above the specified threshold, an expander expands, or increases it.

After the threshold has been surpassed, our familiar attack, release and ratio controls come into play, albeit, now in reverse:

• While attack on a compressor determines how quickly the gain reduction will kick in, on an expander, it determines how long it takes for the expansion “boost” to be applied.
• While release on a compressor determines how long it takes for the compression needle to return back to zero after the signal has gone back below the threshold, for expansion, it determines how long the volume boost will last.
• While with a 4:1 ratio on a compressor, -3dB of gain reduction will be applied for every 4dB that goes over the threshold, with an expander at the reversed 1:4 ratio, +3dB of gain increase will be applied for every 1dB that goes over the threshold.

All of this stuff may seem a little confusing, but it’s definitely more complex in theory than it actually is in practice. On that note, let’s take a look at some of the most common usages for expansion, alongside some basic audio examples:

1. Downwards Expansion (Broadband)

Downwards Expansion is a similar process to gating, and is most commonly used for bleed and noise reduction. While the idea with gating is to essentially mute and eliminate bleed, with an expander, it’s to simply reduce the level of the bleed.

Although totally getting rid of leakage may seem like the more appealing way to go, it’s not the most natural. Simply switching from gating to expansion allows for more realistic results, as if there was just less bleed coming into the microphone to begin with.

Check out the following audio examples and you’ll hear exactly what I mean:

Here’s a raw kick track, with the original bleed intact: 

Here’s the same kick, with Gating used to “mute” the bleed:

Finally, here’s our kick through an Expander. Reducing bleed rather than muting it:

So, with these “classic”, conventional uses of gating and expansion (no fancy internal or external sidechaining being used), it’s clear how expansion can produce less jarring results.

I’ll quickly note that the key to achieving high-quality gating and expansion results is to adjust the attack and release times correctly.

Generally speaking, you’ll want the fastest attack possible. This way the gate/expander reacts to the incoming signal instantly, and won’t chop off any front-end transient. If available, you can also use lookahead to ensure that your gate/expander is foreseeing incoming hits ahead of time and opening up accordingly.

For the release, think of it as a “sustain length” control. While setting a short release will eliminate more bleed, you’ll also shorten the original decay of the kick in the process. Try and set it to where it's rhythmically fading out in time with the song, and not swallowing all of the original low-end punch.

Next, let’s take a look at using downwards expansion in a multi-band configuration for an even greater level of control and customisation.

2. Downwards Expansion (Multi-Band)

Most of the time, when we talk about drum bleed being a “problem”, we’re often referring primarily to excess cymbal bleed.

Given that in rock and metal, applying huge 6-8kHz treble boosts to kicks, snares and toms is key in getting them sounding clicky, present, and upfront, if you have a ton of cymbals washing around in these tracks, they’re prone to getting really harsh and invasive in the process. Multiply this harshness by however many close mics you’re dealing with, and you’ve got a big, ear-piercing problem...

By applying downwards expansion to our drum shell recordings in a multi-band configuration, we’re able to tame the mostly-treble cymbals in between hits, while leaving the original low/low-mid punch and sustain of said shells intact.

Listen to the following examples, and pay attention to the difference in the low-end sustain of the kick:

Our Broad-Band Downwards Expanded kick example from before:

The same kick, but with Multi-Band Downwards Expansion focused above 500Hz (using an internal sidechain set at 60Hz, the kick’s fundamental frequency):

With the broadband variation, our kick’s sustain is being shortened based on our release time. With the multi-band variation however, we’re allowing said sustain to ring out naturally for it’s full duration.

Both options could work fine depending on context. It all depends on the sonic vibe you’re after.

That basically covers Downwards Expansion. Finally, let’s take a look at Upwards Expansion.

3. Upwards Expansion (Broad & Multi-Band)

While typical gating and downwards expansion are all about reduction, upwards expansion is about enhancement.

With our previous examples, we always had the range control of our expanders set to a negative value, meaning any signal that fell below our predetermined threshold was being reduced by X number of dB (the negative range).

This time around, using Fabfilter’s Pro-MB in expansion mode, we’re going to set our range to a positive value. This way, our band is starting from zero (unity), and will expand upwards every time the input signal surpasses the threshold.

Upwards Expansion is essentially good for applying volume (broadband) or EQ (multi-band) boosts to a signal, dynamically. By adjusting our attack and release times, we can determine how quickly the boost will be applied, and how long it will stick around.

Here are some examples of upwards expansion being used to enhance our already bleed-reduced (downward expanded) kick drum from the previous example:

Using Broad-Band Upwards Expansion to enhance the entire front-end transient attack of the kick by +5dB, much like a transient designer would do (first bar with the boost bypassed, second bar with the boost enabled):

Using Multi-Band Upwards Expansion focused at 5kHz and above to enhance the high-end attack of the kick without affecting the lows (first bar with the effect disabled, second bar with the effect enabled, using an internal sidechain focused at 60Hz for improved triggering accuracy):

CONCLUSION: “EXPAND” YOUR TOOLSET!

As you’re probably starting to realise at this point, there are pretty much endless possibilities as to what we can do using Downwards Expansion, Upwards Expansion, or even a combination of the two, in both broad, and multi-bandconfigurations to fix & enhance a mix.

Trying to boost low-end in a drum loop on ONLY the snare? Expansion.

Looking to enhance guitar pick-attack without boosting harshness? Expansion.

Want to reduce cymbal bleed while ALSO enhancing high-end kick attack? Expansion.

The list goes on...

While setting up these kinds of crazy and complicated techniques would have been pretty difficult and time-consuming with the limitations of analog back in the day, nowadays, with all of the amazing routing and side-chaining capabilities of digital, it’s an absolute breeze.

Sure, EQ and Compression may still be fan favourites, but expansion can fix the unfixable - Give it a go in your next mix, and you never know, it might just jump to the top of your list...