Compression Expansion in Mixing – When to Use Expand on a Compressor

99% of the time when we’re using a compressor plugin, we want to use it in its conventional/typical way, meaning we want to tame peaks and reduce the overall dynamic range. How about that other 1% of the time, or using a compressor’s expansion? Let’s talk what compression expansion is, and when to use expansion on a compressor.

Compression Expansion

compression expansion

Expansion on a compressor does the exact opposite of compression, meaning it increases the volume of peaks rather than attenuating them.

This is not to be confused with upward compression which makes the quiet parts of the sound louder without affecting the peaks.

Ableton’s stock compressor (check out my complete overview of the Ableton stock plugins) features an expansion setting:

You’ll see all of the same controls with expansion as compression in threshold, attack, release, etc.

The difference here with the threshold is that when the threshold is met, the volume increases.

The compressor’s attack and release settings still act the same way, determining how quickly the expansion begins and ends, respectively, once the volume hits the threshold.

The auto makeup gain setting is the other exception in terms of how it works.

Typically with normal compression this setting automatically adds back in gain to replace what you’ve taken out by pulling down the peaks.

When expanding the peaks, you’re making the track louder. As such, the auto makeup gain REMOVES gain to ensure the output level is similar to the input level before you boosted those peaks.

When to Use Expand on a Compressor

Dynamic range is natural and a certain amount of it sounds more interesting. When the volume of a sound varies, it is more likely to hold our attention for those changes rather than a flat sausage of sound with zero dynamics which is much easier to tune out.

As such, expansion is useful for adding a little more dynamic range to a track to give it a little more contrast in volume within itself.

A practical example instrument I’ve used expansion on is a tambourine. Typically the rhythm with a tambourine alternates between regular shakes accented by hitting it on quarter notes on the beat.

These hits result in a spike and provide a little contrast with the surrounding shaking rhythm, helping to better establish the rhythm and tempo of the song overall.

When these spikes aren’t prominent enough, I’ll use expansion to push them up and make them a little more noticeable in the performance. In this case, I’ll set the threshold to target those peaks which are above the average level during the shakes.

Ableton’s “Expand” setting tops off at a 2:1 ratio, meaning every dB above the threshold will essentially get doubled.

As such, you need to be careful as it’s easy to seriously boost your peaks more than you intend to, which is why setting the ratio requires a little trial and error to find the sweet spot and get those peaks where you want them.

Expanding can also practically be applied to a vocal track which was recorded with a lot of unwanted background noise. The vocal would still represent the peaks above the noise, so applying expansion would ideally put some more distance between the vocal and the noise.

If that alone didn’t adequately clean up the vocal, further processing like applying a noise gate would be easier with that extra range between the vocal and noise.

While some compressors might not feature an obvious expansion setting, some compressors allow you to set the ratio BELOW 1:1.

While a ratio of 1:1 would result in zero compression, any compression ratio below 1:1 would result in expansion. A compression ratio of 0.5:1 is essentially the same as an expansion ratio of 2:1, so keep that in mind whenever you see a compressor which offers the ability to go BELOW what we think of the minimum/null setting in 1:1.

While needing a compressor for expansion/expanding in general is rare in mixing, you now have a better understand of how it works and a couple examples of instances when you might want to consider it.

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