How to Use an Elliptical EQ in Mixing and Mastering

TL;DR: An elliptical EQ is a tool used in mixing and mastering to fix phase issues caused by stereo width in the low frequencies. You may have heard it called a mono-maker. That is essentially what it does: it sums stereo information down to mono in the low end, where wide stereo signals cause more problems than they solve. In this guide, I walk you through what an elliptical EQ is and why your low end needs one, even if you are not mastering for vinyl. I also cover the plugin I use (Brainworx bx_digital V3) and the exact filtering settings I apply in my own masters.

What Is an Elliptical EQ?

An elliptical EQ is a type of equalizer used to fix phase issues in the low end. Those phase issues usually come from too much stereo width in the bass and sub frequencies. You may have seen the same kind of tool under a different name. Mono-maker is probably the most common one.

To keep this simple: an elliptical EQ takes wide stereo information in the low end and sums it down to mono. Some elliptical EQs are designed just for the low range, while others can reach up into the midrange and higher. The most common use case is when the lows, and particularly the bass track, lose focus because the stereo image is too wide.

Why Stereo Low End Is a Problem

Elliptical EQs have been used for decades, especially in vinyl mastering. Here is why that matters, even if you never plan to press a record.

When you master for vinyl, a lot of stereo information in the lows becomes a real problem. The phase differences between the left and right channels cause serious issues during the cutting process. At worst, the cutting head can literally skip because the out-of-phase information is too extreme for the groove to handle. That is a physical failure, not a sonic preference.

Even in a purely digital workflow, out-of-phase low end causes problems. It kills your punch. Headroom gets eaten up too, which means less room to push the master loud. And the mix falls apart on any mono system. Club PAs summed to mono, phone speakers, and Bluetooth speakers all expose the problem immediately. If you are not sure how to check for this, see my post on how to use audio meters and analyzers. The correlation and stereo image tools show you exactly what is happening down there.

Bottom line: the low end needs to be tight and focused, not wide. An elliptical EQ is one of the cleanest ways to make that happen.

The Elliptical EQ Plugin I Use: Brainworx bx_digital V3

There are plugins on the market designed specifically for elliptical EQ work. If you already have an EQ with mid/side processing, though, you are good to go. My go-to for this job is Brainworx bx_digital V3.

bx_digital V3 has a dedicated mono section and a stereo section, and you can treat them independently. That is the whole game. Being able to filter the stereo information separately from the mono information is what makes elliptical EQ work possible in the first place.

Other options include FabFilter Pro-Q 4, which I also covered in my post on how to use a dynamic EQ. Any other modern EQ with mid/side capabilities works too. The principle is the same no matter which plugin you reach for.

A Real-World Scenario: When Wide Low End Kills Your Mix

Let me walk you through what actually happens when the low end gets too wide. I often test this on a master from Wamlo, an EDM track. If you look at its stereo image, the low range deliberately has very little stereo information. That is by design, because with EDM you need the kick and the bass locked in the center, tight and focused. A wide low end in that context kills everything.

To demonstrate the problem, I sometimes exaggerate the stereo width on purpose and listen to what happens to the kick and bass. The result is immediate: the more I widen the low end, the less punch and clarity the track has overall. Suddenly the kick stops hitting. Your bass stops anchoring the track. That whole bottom feels loose and weak.

This is not a hypothetical. A very common scenario is when clients send mixes for mastering with stereo bass tracks. Almost every time, those tracks cause phase issues in the low end. The fix is to filter out some of that stereo low-end information, which is exactly what an elliptical EQ is built for.

My Elliptical EQ Filtering Settings: What I Actually Do

Here is how I approach elliptical EQ filtering on a master.

Filter Out Everything Below 20 Hz on Both Mono and Stereo

Mastering engineers often recommend a high-pass filter at around 20 Hz on both the stereo and mono information. There are two reasons for this.

First, the human ear does not really perceive frequencies below 20 Hz. You are not losing anything musically.

Second, just because you cannot hear that information does not mean it is not there. Most of the time there is plenty of sub-20 Hz content, and it eats up a surprising amount of headroom. If you are trying to hit a competitive loudness level, that invisible low-end junk is working against you. See my post on RMS vs LUFS for more on loudness targets and why headroom matters.

Filter the Stereo Information Up to 30 or 50 Hz

Once the sub-20 Hz stuff is gone, the next move is to filter the stereo information up to somewhere between 30 and 50 Hz. This keeps the low-end frequencies mono, which is where you want them anyway. The more stereo information you cut, the more mono the mix sounds down there, and the tighter your low end gets.

Exact cutoff depends on the source material. Some mixes need more aggressive filtering, some need less. Start around 30 Hz and go up from there if the low end still feels loose.

Choose Your Slope Carefully

Most modern EQs let you choose the slope of your filter, which is how steep the cut is at the cutoff frequency. Options usually run from 6 dB per octave up to 96 dB per octave, and some plugins like Pro-Q 4 even offer a brickwall setting.

For most of my masters, I use 6 dB or 12 dB slopes. Gentle filtering usually sounds more natural and keeps the transition smooth, rather than creating an obvious cliff at the cutoff frequency.

Elliptical EQ vs Mono-Maker: Are They the Same?

Not exactly. They do similar jobs, but they are not identical.

Both tools take stereo information in the low end and sum it to mono. The difference is in the control you get. A true elliptical EQ, or a full mid/side EQ like bx_digital V3, lets you choose the slope and the exact cutoff. It also gives you much more surgical control over the whole process. A dedicated mono-maker plugin often just gives you a single cutoff frequency with a fixed slope baked in.

Here is a quick way to see the difference. Set a mono-maker all the way up to 22 kHz. You might notice there is still some stereo information left. That tells you the mono-maker itself has a slope, just one you cannot adjust. An elliptical EQ with adjustable slope gives you more flexibility for different source material.

For quick, set-and-forget mono compatibility, a mono-maker is fine. When you are doing mastering work and every decision matters, an elliptical EQ or a full mid/side EQ gives you the control you need.

Recommendations for Mixing and Mastering

Here is the practical checklist I use:

• In mixing: If your EQ has mid/side processing like bx_digital, put a high-pass filter at 20 Hz on the mono section to kill any unnecessary sub information that is wasting headroom.
• In mastering: Same rule for the mono section. Also apply a 20 Hz high-pass on the stereo information.
• For extra low-end focus: Filter the stereo information up to somewhere between 30 and 50 Hz, depending on the mix. This locks the low end to mono where it belongs.
• Use gentle slopes: 6 dB or 12 dB per octave sounds more natural than steep cuts.
• Watch your volume after filtering: Cutting stereo information in the lows can reduce perceived loudness. If that happens, compensate with the gain knob on your EQ or at the output of the elliptical EQ itself.
• High-end filtering is optional: You can filter some of the very top frequencies if there is unwanted content up there. This depends entirely on the source material. For most mixes, leaving the high end alone is the right call.

One Last Thing: Compensate for Volume Loss

This one catches people off guard. When you filter out stereo low-end information, sometimes the mix feels quieter overall. Even though the visual EQ curve only shows a change in the sub frequencies, the perceived level drops.

That perceived loss of volume is real. Stereo information adds a sense of size and loudness that goes away when you mono the low end. The fix is simple: use the output gain on your EQ, or whatever gain stage comes next, to push the level back up. Your low end will be cleaner and tighter, and the track will still feel as loud as it did before you touched it. For more on setting your levels properly throughout the chain, see my post on what is gain staging.

Key Takeaways

• An elliptical EQ sums wide stereo information in the low end down to mono, fixing phase issues and tightening the low end.
• The problem exists in every workflow, not just vinyl mastering. Out-of-phase lows kill punch, waste headroom, and fall apart on mono systems.
• You do not need a dedicated elliptical EQ plugin. Any EQ with mid/side processing, like Brainworx bx_digital V3, can do the job.
• Apply a 20 Hz high-pass on both the mono and stereo sections to clear out sub-audible junk.
• Filter the stereo information up to 30 or 50 Hz to lock your low end to mono.
• Use gentle slopes (6 or 12 dB per octave) and compensate for any perceived volume loss with gain.

Your Assignment

Before you close this tab, do this: open a mix you are working on and load an EQ with mid/side capabilities on the master bus. Try a 20 Hz high-pass on both sections and listen to what changes (spoiler: probably nothing, and that is the point). Then experiment with filtering the stereo information up to 30, 40, and 50 Hz. Pay attention to how the kick and bass respond at each cutoff. Train your ears to hear what a tighter, more focused low end actually sounds like.

Related Articles

How to Use a Dynamic EQ in Mixing and Mastering. When a frequency is only sometimes a problem, a dynamic EQ is the right tool. Here is how I use one.

RMS vs LUFS: What Is Loudness and How to Measure It. What loudness actually means, why headroom matters, and the streaming platform targets every producer should know.

How to Use Audio Meters and Analyzers. The meters and analyzers I open in every session, including the correlation and stereo image tools I use to spot phase issues.

What Is Gain Staging (And Why Your Mixes Need It). How to manage your levels from the start of a session so every plugin in your chain works at its best.

Mastering Chain Plugin Order. Where each processor belongs in the chain, including where an elliptical EQ fits best.

About the Author

Adrian Milea is a Mixing and Mastering Engineer, Music Producer, and Educator with over 25 years of experience. He has releases on Armada Music, features in DJ Mag, and teaches producers worldwide through his courses at adrianmilea.com.

Until next time, Stay Cool and Make Great Music!
-Adrian Miilea