EQ – Pre or Post Compression?

When I was first learning about mixing, I remember spending hours on audio / recording forums sifting through arguments about mixing techniques and whether EQ should sit before or after compression.

I haven’t seen that conversation lately (praise jesus), but I have seen people advocating for some bizarre stuff. Ever since digital processing power became cheaper than analog hardware, processing techniques have grown incredibly complex and are often unnecessarily convoluted.

Sure, try new things, but unless your clients have deep pockets and a sense of adventure, maybe you shouldn’t be spending too much time experimenting with complicated routing; navigating through 3 busses and 3 separate signal chains for one vocal track will get confusing, tedious, and expensive.

So, here’s my two cents about getting a stable, polished sound with EQ and compression in the quickest way possible.

Short answer: use both

Before even adding an EQ to your channel strip, know what you’re trying to accomplish. Are you doing corrections for weird resonances or harshness? Are you coloring the sound? Are you eliminating “dark energy” that’s killing your compressor but isn’t even audible in the mix?

The most compelling reason to use pre-compression EQ is to keep the compressor from reacting to unnecessary frequencies. The most compelling reason to use post-compression EQ is that compression (especially heavy compression) will alter the frequency content, so you’ll need more frequency shaping afterward. These two goals are not mutually exclusive, so why not use both?

The nice thing about using both pre- and post-compression EQ is that you can divide up these tasks sensibly.

For pre-compression EQ, the goal is to use improve the sound quality (derp) while also modifying how the compressor behaves. Follow these quick steps for good pre-compression EQ results:

1. In most cases, use an analyzer to set a hi-pass around the fundamental frequency if necessary.
2. Then use your ears to dial it in. For a harder sound use a higher cutoff frequency and steeper filter order (e.g. 12 decibels / octave). For a softer sound use a lower cutoff and a gentler filter order.
3. Is there any high frequency content that is not useful or rich/musical sounding? Remove it with a lo-pass, using a gentler curve for an open sound or a steeper curve for a confined sound.
4. Pay special attention to the low frequencies. Lower frequencies have more power (i.e. energy) than higher frequencies at equal perceived volumes and can cause a compressor to hit harder, but that same compressor behavior can also create a psychoacoustic sense of warmth without actually adding any extra low frequencies, especially if your compressor is using RMS detection instead of peak.
5. Remove ugly body or room resonances that don’t add something to the track using tight notch filters; you probably don’t want your compressor reacting to these, and you probably don’t want your listeners hearing them either. Pay special attention to the mids and lo-mids in this step.

After compression, the goal of EQ is to color the sound, correct anything undesirable the compressor added (although choosing a more fitting compressor should be considered first), and (if it’s a stereo track) use EQ to adjust the stereo width. Use these steps for quality results:

1. Use an analyzer to check if the compressor is radically changing the frequency content. If so, make sure it’s a sound you want; if not, consider changing your compressor.
2. Do some frequency sweeps (or use your ears) to pick out key ranges that give an instrument its desirable/expensive-sounding characteristics.
3. Do some frequency sweeps (or use your ears) to pick out key ranges that give an instrument its undesirable/cheap-sounding characteristics. You may have done this already in the pre-compression EQ, but it couldn’t hurt checking again.
4. Use what your learned from the previous steps to accentuate or correct the track. Your goal here is balance! You’re creating a lens for this track to shine through and add its particular color to the overall mix.
5. Coordinate these EQs across tracks to fit well together.

Once you’ve completed these steps, go through this checklist to confirm excellent results:

1. Listen for balance, stability, and rhythm; if your compressor’s settings are solid, but you still hear a strange “volume occlusion” or “hard-to-hear” effect, check both ends of the frequency spectrum on your pre-compressor EQ. Excessive low end might be driving your compressor too hard, or a cluttered high end may be making your compressor behave chaotically.
2. Do all of your instruments add their own particular color or vibe to the mix? Do they all live in their own space? Either your arrangement may need some work, or your post-compression EQ could use a tweak.

Other useful thing: use a compressor’s sidechain EQ

I love using a compressor’s sidechain EQ to alter its behavior. Maybe it’s esoteric, but it shouldn’t be.

One use case might look like this: you want a punchy, warm drum kit sound, but the compressor isn’t adding much motion, and adding those warm low mids creates a thick, clumsy sound.

You might try using a compressor with a full 4–6 band sidechain EQ. A compressor’s sidechain EQ alters the signal used to attenuate the output signal. In other words, the input is copied, altered by the sidechain, and used as a keying signal to determine the amount of gain reduction, leaving the input signal unaltered except for the gain reduction. It’s a great way to modify the compressor’s sound.

With a drum kit buss, try adding a gentle boost in the 120–250Hz range. This will get your compressor kicking, creating the psychoacoustic effect of more warmth while preventing the muddiness you get from adding low mids.

You can do a similar thing by adding a boost in your pre-compressor EQ, then cutting in the same range in the post-compressor EQ, but keep in mind that most nice EQs are asymmetrical (boosts usually have a wider Q than cuts), so your results will be imprecise. Imprecise is OK sometimes, though.

Wrap

Thanks for reading! If you have any questions, comments, or hate speech, leave a comment and I’ll do my best to respond.

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Links

MModernCompressor – An awesome compressor with a full 6-band sidechain EQ (and loads more useful features)