Which Comes First: EQ or Compressor?

When mixing a new project, usually the first tools the engineer will reach for are EQ and compression. Not only do these processors correct problems with a recording such as low end thumps, and help to narrow dynamic range for a more even-sounding track, but they are also used to shape the tone and balance the individual elements of a mix. But should we use EQ or compression first?

In the analog console days, most consoles were laid out with the EQ first in the chain followed by compression. Today, a lot of mixing is done in the box which allows us to experiment with the order in which we compress or EQ. Let’s take a look at how EQs and compressors interact.

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The relationship between EQ and compression

Before we discuss whether to use compression or EQ first, we need to look at the relationship between the two. EQ and compression have the potential to manipulate the level—or volume—of a sound. However, the way in which they work with level is different. EQ allows the engineer to boost or cut certain frequencies to fix a problem or change the color of the sound. Compression changes the relationship between your loudest points and quietest points, bringing these differences in level closer together. Because both EQ and compression manipulate level, when you place both types of plug-ins on a track whichever plugin comes first will impact the sounds you can get from the plug-ins that follow.  

What is EQ?

All sound is made up of frequencies that we perceive as pitch. In a mix, instruments that have overlapping ranges of pitch, such as higher notes on a bass and lower notes of a guitar, can compete to take up the same sonic space in a phenomenon called frequency masking. Manipulating the frequencies where tracks compete helps to cut muddiness, add clarity to the tone, and enhance separation between instruments. 

In mixing, EQ is used technically to correct problems such as harshness, as well as creatively such as automating a low-pass filter to make something sound distant or underwater. The important thing to remember is that we adjust these frequencies by changing their relative level. 

When we boost the low end for example, what we are really doing is turning up the level on a band of low-pitch frequencies. When we cut 1.5k Hz on a vocal, we are turning the level down on a band of higher-pitch frequencies to cut harshness. For a more detailed look at EQ bands, this article on the Principles of Equalization is a good resource. Check out iZotope’s best articles on EQ for tips and tricks for using EQ.

What is compression?

Compression is a dynamics process that takes the loud parts of your signal and makes them quieter, reducing the dynamic range resulting in a level that’s more even throughout. Most compressors have a threshold control that adjusts when the compressor starts to reduce levels. A lower threshold means the compressor will react and begin compressing at quieter volumes. Anything below the threshold will remain unprocessed. 

Like EQ, compression can be used in technical and creative ways, for example to bring out syllables in a vocal take that we’re having trouble hearing or to add weight to a drum kit. In any case, be intentional about why you’re adding compression and the effect you’re hoping to get out of it, and let that guide your compressor choice. For more tips and tricks for compression, check out iZotope’s best articles on compression.

Adding compression to a signal chain

When considering EQ and compression, It's important to note that a compressor generates extra harmonics. That might mean if you've placed an EQ in your chain first followed by a compressor, you may want to EQ the signal again to get the tone you’re looking for, either by enhancing or attenuating those harmonics.

Listen to how the sound changes when you add a compressor. 

Using compression before EQ 

When compression is used before EQ, some of the compression is undone when we boost frequencies with the EQ. This is because the boosted band of frequencies can be louder than the compressor would have allowed, or than frequencies outside the boosted range. 

In the audio example and screenshots above, we can see and hear how adding compression to a signal adds harmonics not originally present in the signal. However, if too much is added in a certain area, you might find yourself reaching for an EQ to tame some of those harmonics.

The argument for using compression before EQ is that “you’ll have to EQ the signal again anyway,” so why not use just one EQ after compression and call it a day? Well, if there are any technical issues that can be corrected with EQ such as low end thumps, these might trigger the compressor in undesirable ways so it’s best to clean those up before adding more processing.

Using EQ before compression 

Typically, an EQ before a compressor is doing a more technical job than a creative one such as adding presence or clarity. The EQ modifies the degree and focus of the compressor, while the compressor tames the curve of the EQ that came before it. 

Let's listen to what using EQ before compression sounds like. In this example, I’ve added a 12 dB boost at 1kHz to a lead vocal. Notice how the signal sounds less EQ’d after the compression is added. This is because the compressor will kick in as soon as the signal’s level hits the threshold.

Dramatic boosts in EQ mean the threshold is met at a different level than it otherwise would have been without the EQ, causing the compressor to lower the level in response. 

Whether it's EQ or compression first: do what sounds best to you 

My typical vocal chain often starts with a technical EQ for basic cleanup, a technical compressor to round off peaks gently, then a creative EQ for tone shaping, followed by a creative compressor with more aggressive settings for added harmonic characteristics, capped off with a De-esser, but your chain might be different. Whether you're using an EQ before or after the compressor, you should be doing what sounds best for your mix. Trust your ears! 

Once you’ve got some settings you like, try re-ordering the plug-ins to hear what that sounds like and compare how the plug-ins respond to each other. Take note of the amount of gain reduction your compressors show when you experiment with placement as well. It will take some practice, but eventually you’ll find an order of operations that works well for you.