It’s a creative choice that is up to the producer or engineer. The right choice depends on the goal and finding the best signal path to achieve it.

Several factors influence why an audio engineer would want to place an equalizer before compression, or after it. But before we learn about those situations, it’s important to understand how EQ’s influence on a sound changes when placed in different spots in a signal chain. These different spots usually refer to the compressor’s place in relation to the equalizer, so “Pre-EQ” or “Post-EQ” are common phrases to describe this arrangement.

Compression Before EQ? EQ Before Compression? How Pre- or Post-EQ Affects the Sound.

EQ either emphasizes or deemphasizes different frequencies of a signal. If you boost certain frequencies with an equalizer, you are increasing their dynamic range. If you cut certain frequencies, you are decreasing their relative dynamic range.

These equalization changes (boosts and/or cuts to a signal’s frequencies) affect the overall dynamic range of the signal as a whole. And this is the main reason why a signal will sound different when compressed before or after an EQ application: the compressor is acting on a different signal with, or without, equalization.

Some mastering engineers overwhelmingly prefer EQ before compression, letting the compressor tame some of the frequencies adjusted by the equalizer. Pre-compression EQ definitely feels less responsive in comparison, mainly because the compressor is acting on your carefully applied adjustments, adding another interactive variable that affects your EQ choices.

Other engineers prefer the precision offered by EQ post-compression, where the compressor’s work is taken out of the equation when going for a tone. There is no right or wrong - it’s simply a creative choice.

Examples of Pre- and Post-EQ Compression.

In a world where everything is heard, sometimes it is easier to hear an example rather than read about it. These examples are easy to try on your own - there’s nothing like hearing it yourself.

Acoustic Guitar EQ and Compression

If you place a mic in the soundhole of a guitar, you get boom. You might ask, “Who would place a mic in the soundhole?” They’re out there and some have good creative or technical reasons for doing so. Now, compress that signal. You’ll find the compressor reacts to the loudest frequencies, which are also the boomiest frequencies that tend to congregate in and around the soundhole. This clamps the compressor down when those frequencies are present, leading to pumping or otherwise non-ideal compression artifacts. Placing an EQ with a low cut filter after the compressor in this case doesn’t remove the pumping artifacts (which may or may not be cool).

Now, place the EQ before the compressor. Engage the low cut to remove the boom. Notice the compressor isn’t pumping any longer. This is a common example of pre- or post- EQ compression can be used to settle dynamic sounds in a mix.

Kick Drum or Bass EQ and Compression

Any instrument with a lot of dynamic range can be a challenge for a compressor, if the goal is more transparent processing. In the same manner as the example above, finding peaks in the signal of a bass or kick drum track and removing them before or after compression can give you very different results. Rather than a sweeping low cut filter, using parametric EQ to even out a bass or kick signal can make the compressor more effective, reducing its workload and allowing it to act on a more even signal. Or for more creative options, allowing a compressor to pump rhythmically can be just the ticket and a core element of a track - it’s up to you.

In summary: How to use EQ before or after compression

Hopefully, you now understand how and why EQ affects compression when placed before or after a compressor. Using this knowledge to your advantage, you can make creative choices faster and more effectively.