iZotope Ozone 9 Maximizer Review: Honest Mastering Test

TL;DR: The iZotope Ozone 9 Maximizer is a solid limiter. It doesn’t distort or pump at hot levels, it preserves the stereo image and depth of a mix really well, and the Learn Threshold feature is genuinely useful. But in my tests against the TC Electronic Brickwall Limiter and FabFilter Pro-L 2, the Ozone 9 Maximizer added some harshness at the top end that affected the clarity of the master. Good limiter, but not my first pick for the final stage.

The limiter you use at the end of your mastering chain is one of the most important tools in your whole signal flow. Pick the wrong one and you can undo all the careful work you did earlier. That’s why I’ve been on a long quest testing limiters from across the audio market, and today it’s the iZotope Ozone 9 Maximizer‘s turn.

I’m comparing it against my two reference limiters: the TC Electronic Brickwall Limiter (PowerCore version), which is still my favorite, and FabFilter Pro-L 2, which is another excellent option I trust.

If you’d rather watch the full test with audio examples, here’s the video:

A Quick Tour of the Ozone 9 Maximizer

The interface is clean and straightforward. On the left you have the IRC modes, in the middle you control threshold and ceiling, and on the right you have your input and output meters. Let’s go through what actually matters.

The IRC Modes

IRC stands for Intelligent Release Control, and Ozone 9 gives you several modes to choose from. Hover over each one and you’ll get a quick description, but here’s the short version:

• IRC LL — smooth, thick limiting with low latency for a rich sound
• IRC I — similar character with more latency
• IRC II — clear and sharp limiting that preserves peaks
• IRC III — surgical limiting with profiles like Pumping, Balanced, Crisp, and Clipping
• IRC IV — spectral shaping for reduced pumping and distortion, with three profiles: Classic, Modern, and Transient

From my testing, IRC IV is the one I keep coming back to. It handled the test material the best, and the three profiles inside it give you real flexibility.

The Learn Threshold Feature

This is one of the more interesting features in the Maximizer. When you activate Learn Threshold, you tell the plugin what your target loudness is, hit play, and it automatically adjusts the threshold to hit that target. It’s similar to a feature I found recently when testing the Brickwall Limiter HD Native from TC Electronic.

I’ll show you how to use it properly later in this post, including a small but important tip that could save you from nasty distortion if you forget one step.

Ceiling, True Peak, and Channel Linking

The Ceiling control sets your output level. I always set it to -1 dBFS in my mastering sessions to keep true peaks under control. By default, the Maximizer limits sample peaks, but if you want to handle true peaks properly, activate the True option. Always do this if you’re working at hot levels.

You can also choose how the Maximizer processes your channels with the Transient and Sustain options. Linked, both channels get processed together. Unlinked, they’re processed independently. Personally, I never unlink channels when limiting in mastering. Stereo image stability matters too much.

There’s also a Stereo Independence option, a transient emphasis control, dither settings, and the usual input and output metering you’d expect.

How I Tested the Ozone 9 Maximizer

For this test I used a song produced and mixed by my brother Vlad. I’ve used it across pretty much every limiter test on this channel, which is exactly the point. After listening to the same track through dozens of different limiters, I can hear differences almost immediately.

I matched all three limiters in loudness as closely as possible, set the ceiling to -1 dBFS, and activated True Peak mode on the Maximizer. Then I started in IRC IV with the Transient profile and worked through the song.

How the Ozone 9 Maximizer Actually Sounds

First Impressions: Transient Profile

Right from the start, I’m pleased that the Maximizer keeps the 3D space of the mix almost untouched, and the stereo image stays solid. That’s a good sign. A lot of limiters mess this up, so credit where it’s due.

But as I moved into another section, I noticed the top end started feeling a bit harsh compared to the Brickwall Limiter. So I switched to the Modern profile to see if it would soften things.

Modern Profile

The Modern profile sounds closer to the Brickwall Limiter than Transient does. It’s less harsh on the top end. But even with Modern selected, in the loudest, busiest section of the song, I still heard some harshness creeping in compared to the Brickwall. The Brickwall just sounds more natural to my ears.

Ozone 9 Maximizer vs. FabFilter Pro-L 2

I brought Pro-L 2 into the comparison and ran the same section. Pro-L 2 sounded more natural and less harsh than the Maximizer, and it kept the separation between elements of the mix more under control. Same kind of result as the Brickwall comparison.

I also tested the Transient profile against Pro-L 2 in another section, and the Maximizer added some presence to the master that wasn’t intended at the mastering stage, while Pro-L 2 kept everything natural and transparent. So in that comparison, both the Brickwall and Pro-L 2 came out ahead for me.

The Soft Section Test

This is something I always test now after running into limiters that mess with quieter parts of mixes by making them louder than they should be relative to the loud sections. With the Brickwall in this section I hit about -13.6 LUFS. With the Ozone 9 Maximizer, almost the same. So the Maximizer is well behaved here. It respects the dynamics of the mix and doesn’t artificially pump up quieter sections. Good news.

True Peak Handling

With the ceiling at -1 dBFS and True Peak mode activated, the Maximizer kept true peaks at around -0.9 dBFS. That’s solid. Just remember that in Ozone 9 Maximizer, the “ceiling” parameter is what other plugins call “threshold.” Different plugins, different names for the same thing. Always check before you start.

How to Use the Learn Threshold Feature (And the Tip Most People Miss)

This is the part I promised earlier. Here’s the proper workflow:

1. Find the loudest part of your mix and start playback there
2. Set the threshold to its initial position (0 dBFS)
3. Set your ceiling (I use -1 dBFS)
4. Activate True Peak if you want it on
5. Click Learn Threshold and set your target loudness (let’s say -9 LUFS)
6. Hit play and let the Maximizer adjust the threshold automatically
7. Once it hits your target, deactivate Learn Threshold

Step 7 is the one most people miss. If you leave Learn Threshold on, the Maximizer keeps trying to hit your target loudness even during the softer sections of your mix. When the louder sections come back around, things start distorting because the plugin is over-pushing the signal. So once you’ve hit your target, turn it off. That’s it.

So Should You Use the Ozone 9 Maximizer?

Here’s my honest take.

The Ozone 9 Maximizer is one of the best limiters on the market. It doesn’t distort or pump at hot levels, it keeps the stereo image and depth of mixes almost untouched, the Learn Threshold feature is genuinely useful, and IRC IV with the Modern profile sounds really good. There’s a lot to like.

But in my side-by-side tests, the Maximizer added some harshness at the top end that affected the clarity of the master, especially compared to the TC Electronic Brickwall Limiter and FabFilter Pro-L 2. The Brickwall and Pro-L 2 both sounded more natural and transparent on this material.

To be clear: I’m not saying the Ozone 9 Maximizer makes every mix harsh. This is what I heard on the test material I used. Your mileage may vary depending on your music. Some of that harshness can also be tamed with multiband compression or EQ earlier in your chain.

If the Ozone 9 Maximizer is what you have, you can absolutely make great masters with it. But if you’re shopping for a new limiter and want my pick, I’d still grab the Brickwall or Pro-L 2 first.

Related Articles

• Sonnox Oxford Limiter Review — Another limiter test against the Brickwall and Pro-L 2.
• Mastering Services — If you’d rather have me master your track on the gear I tested here, here’s how that works.
• One Song Mastering Breakdown — Watch me master a real song from start to finish, including the limiter stage.
• Mixing & Mastering Cheat Sheet — A free download to improve your mixes and masters in under 10 minutes.

Ready to Go Deeper?

If you want to stop guessing about which limiter to use and actually understand how to master your tracks the right way, check out my Pro Audio Mastering Course. I walk you through the entire mastering chain step by step, including how to choose and use limiters, how to handle true peaks, how to avoid the mistakes most producers make at the loudness stage, and how to get masters that compete with commercial releases. Whether you’re mastering your own productions or client work, this course will get you there.

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About the Author

Adrian Milea is a Mixing & Mastering Engineer, Music Producer, and Educator with over 25 years of experience. With releases on Armada Music and features in DJ Mag, Adrian has spent decades testing gear, building mastering chains, and helping producers around the world get their music to a professional level. He runs adrianmilea.com where he shares tutorials, gear tests, and courses for serious music producers.

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