Izotope Ozone 12 Review: Stem Processing Comes to Mastering

One of my all-time favourite plugins has just received a significant update. Ozone 12 might look familiar at first glance, but underneath the slightly refreshed interface lies some genuinely revolutionary technology that could change how we approach mastering entirely.

The most obvious visual change is how iZotope have organised the ever-growing collection of modules. Click the add button and you’ll find them sensibly categorised into Core (the original modules), Modern (recent additions), and Vintage sections. It’s a small change, but when you’re working quickly it makes a real difference.

The Mastering Assistant Gets Smarter

The mastering assistant has been completely overhauled, split into Automaster and Custom modes. Automaster works much as before, but Custom mode gives you proper control over the process for the first time. You can now choose which modules to include – finally, I can disable Dynamic EQ without having to work around it afterwards.

More significantly, there’s now an Intensity control that ranges from Subtle to Transformative. Anyone who’s used the mastering assistant will appreciate this – it had a tendency to be rather heavy-handed. The analysis time can now be extended up to 60 seconds, though iZotope still recommend analysing the loudest section of your track.

I tested this on an indie rock track and found the Custom mode much more musical than previous iterations. The assistant picked up EQ moves that actually made sense contextually, rather than applying generic shaping.

Stem EQ: The Game Changer

Here’s where things get interesting. Stem EQ uses AI separation technology to isolate bass, drums, vocals and other elements from a stereo mix, allowing you to EQ them independently during mastering. If you’d told me 20 years ago this would be possible, I’d have laughed.

To demonstrate, I deliberately mixed a track with the vocals sitting 4-5dB too low in the mix. Using Stem EQ, I could bring them forward without affecting the rest of the track. The separation isn’t perfect – you can hear some artifacts if you really push it – but for subtle corrections it’s remarkably effective.

This opens up possibilities that simply didn’t exist before. How many times have you received a mix where the vocal is slightly buried, or the bass guitar is sitting just a bit too prominently? Previously, you’d have to send it back to the mix engineer. Now you can make these adjustments as part of the mastering process.

The implications for mastering engineers are huge. We’re no longer completely at the mercy of the mix balance. Obviously, this isn’t a substitute for proper mixing, but as a corrective tool it’s genuinely revolutionary.

Unlimiter: Undoing the Damage

The Unlimiter tackles another common problem: over-limited source material. We’ve all received tracks that have been squashed beyond recognition, often by novice producers using aggressive limiting presets.

The process is straightforward – play your over-limited material, hit Learn Threshold, and the module analyses where the limiting is occurring. You can then dial in how much transient information you want to restore.

I tested this on a hip-hop track that I’d deliberately mangled with aggressive limiting. The Unlimiter managed to restore a surprising amount of the original punch in the kick and snare. It’s not magic – the distortion artifacts remain – but it gives you much better raw material to work with.

The Delta mode lets you hear exactly what’s being restored, which is mainly transient information from drums and percussion. While it can’t completely undo heavy limiting, it’s remarkably effective at restoring some life to dead-sounding masters.

Bass Control: Beyond the Meters

Bass Control provides visual feedback about the low-end balance and punch in your master. Unlike traditional spectrum analysers, it compares your material against industry standards, showing whether your bass sits within acceptable ranges for balance and impact.

I found this particularly useful when working on material where the bass relationships weren’t immediately obvious. The module shows target zones based on commercial releases, giving you a reference point for how your low-end should sit.

During testing, I artificially boosted the bass on a track until it was completely overwhelming. Bass Control clearly showed the balance meter exceeding the target zone. By pulling back on the Balance control, I could restore a more appropriate relationship between the bass and the rest of the mix.

The visual feedback proved especially valuable when working in my home studio, where acoustic limitations can make bass judgements tricky. It’s not replacing your ears, but it’s providing useful contextual information about how your decisions might translate.

IRC5: Multiband Limiting Arrives

The new IRC5 limiter algorithm represents a significant departure from previous versions. Rather than applying broadband limiting, IRC5 appears to use multiband processing, only limiting frequencies that actually need it.

Comparing IRC5 to IRC2 in Delta mode reveals the difference immediately. IRC2 affects the entire frequency spectrum – you can hear the bass guitar being limited along with everything else. IRC5 focuses mainly on the elements actually hitting the threshold: typically kick drum, snare, and high-frequency content.

The practical result is that you can achieve similar loudness levels with less audible limiting. The meters show IRC5 working less hard than previous algorithms, though as always, your ears should be the final judge. I still found the Modern and Transient algorithms preferable on some material, despite the meters suggesting otherwise.

Real-World Performance

I put Ozone 12 through its paces on both rock and hip-hop material. The Stem EQ proved consistently useful for subtle corrections that would previously have required mix revisions. The Unlimiter handled over-processed material better than expected, while Bass Control provided valuable reference information for low-end decisions.

The updated mastering assistant feels more musical and controllable than before. The ability to exclude modules you don’t want makes it much more practical for professional use.

Final Thoughts

Ozone 12 represents genuine innovation rather than incremental improvement. Stem EQ alone changes what’s possible in mastering, while the other additions address real-world problems we encounter daily.

For mastering engineers dealing with imperfect source material – which is most of us, most of the time – these tools open up new possibilities for improvement without compromising the original vision. The technology isn’t perfect, but it’s remarkably effective within sensible limits.

If you want to see these tools in action on complete tracks, I’ve created detailed walkthroughs mastering both a rock track by So Impartial and a hip-hop track by Who Killed Kenny, demonstrating how these new features integrate into a complete mastering workflow. (see videos above)

While Ozone 12 provides powerful tools for enhancement and correction, the art of mastering still comes down to experience and trained ears. If you’re looking for professional online mastering services that combine technical expertise with musical sensibility, visit mixandmastermysong.com to hear examples of my work and learn more about my approach.