Open Wide: Stereo Widening
The Pros, Cons, and Phasing Pitfalls
Stereo Widening Tools: The Pros, Cons, and Phasing Pitfalls
Stereo widening tools can be incredibly powerful in music production, allowing you to open up the mix, create space, and emphasise key elements. But as with any audio processing, they need to be used with care. Overdo it, and you risk introducing phase issues that can weaken your track, particularly in mono playback.
In this article, I’ll dig into precarious world of stereo wideners—when and how to use them, common pitfalls, and insights from listening and testing some of the most popular plugins available. I’ll also explain why when mastering, I often use wideners sparingly to subtly enhance the dynamics of a mix between verses and choruses, adding depth without sacrificing clarity.
When to Use Stereo Widening
Stereo wideners can add excitement and dimension to:
Choruses: Widening during a chorus can make it feel bigger and more impactful compared to the verse.
Backing Vocals: Spreading backing vocals across the stereo field can help them sit behind the lead vocal without muddying the centre.
Synths and Pads: Stereo wideners can help ambient elements like pads and synths surround the listener, creating an immersive experience.
When NOT to Use Stereo Widening
There are moments when stereo widening can work against you:
Bass Frequencies: Bass should remain tight and central for focus and punch. Widening low-end content can cause phase cancellation, resulting in a weak low end, especially in mono.
Essential Mono Elements: Lead vocals, kick, and snare generally work best in the centre. Widening them can make them lose their power and clarity.
Mastering Overuse: In mastering, excessive widening can make a mix sound detached and hollow. I prefer small, incremental widening changes—just enough to open up the mix during structural transitions like choruses, often paired with a small gain boost (or reduction everywhere else).
Stereo Widener Plugin Tests: Strengths and Weaknesses
It’s essential that the changes a stereo widener plugin makes to your audio does not introduce phase issues or artefacts when summed to mono. So many people consume audible media on their phones, often on a mono bluetooth speaker; not to mention mono radio. I tested several popular stereo wideners and evaluated their performance based on phase coherence, mono compatibility, and sonic impact. Here's what I found:
1. NUGEN Stereoizer
Pros: Extremely precise; adjustable parameters for psychoacoustic control.
Cons: Can introduce noticeable phase cancellation if pushed too hard.
Verdict: Great for subtle enhancements but requires a light touch.
2. Stereo Savage
Pros: Creative modulation options like panning and Haas delays.
Cons: Delay-based widening can cause smearing and phase issues in mono.
Verdict: Fantastic for creative sound design but risky in a mastering chain.
3. AIR Stereo Width
Pros: Simple interface, good for quick stereo enhancement.
Cons: Lacks precise control and can add reverb-like effects that muddy the mix.
Verdict: Suitable for simple widening tasks but not ideal for detailed work.
4. Quad Image (IK Multimedia)
Pros: Multiband stereo imaging with solid mono compatibility in the low-end.
Cons: UI is dated and can be unintuitive for fine adjustments.
Verdict: Effective for complex tasks but with a learning curve.
5. Kilohearts Stereo
Pros: Simple and CPU-friendly.
Cons: Lacks detailed phase controls and transparency at higher settings.
Verdict: Lightweight and easy to use but not as precise as other options.
6. Ableton Live Utility
Pros: Built-in, reliable, and phase-conscious with simple width controls.
Cons: Limited features for advanced imaging.
Verdict: One of my favourites! A solid tool for basic widening without introducing phase issues.
7. Waves S1 Imager
Pros: A classic with mid-side control and width adjustments.
Cons: Delay-based widening can cause phase issues in mono.
Verdict: Great for traditional widening but watch out for phase cancellation.
8. Brainworx ShearSpread / Control 2
Pros: Mono-maker for bass and smart stereo width controls.
Cons: Complex interface can be daunting.
Verdict: A mastering-grade tool with deep flexibility.
9. SSL Fusion Stereo Image
Pros: Subtle and musical widening that preserves the stereo field.
Cons: Hardware-like subtlety—won’t work for drastic widening.
Verdict: Excellent for tasteful, phase-safe widening in mastering.
10. Leapwing StageOne
Pros: Transparent widening with a "depth" feature for adding 3D space.
Cons: Expensive but worth it for its sound quality.
Verdict: A premium choice for precise widening without sacrificing mono compatibility.
11. Ozone Imager
Pros: Free and highly visual, with clear phase metering.
Cons: Pushing it too far can cause harsh stereo artefacts.
Verdict: Great for visualising your stereo field, but don’t max out the settings.
12. Polyverse Wider
Pros: Unique algorithm that avoids traditional phase issues.
Cons: Some transient artefacts when summed to mono.
Verdict: My go-to for stereo enhancement, but I’m noticing transient issues with fast attacks.
Top choices:
Ableton Live Utility, Polyverse Wider, Leapwing StageOne
Why Polyverse Wider Stands Out
Having been my go-to for a few years now, Polyverse Wider uses a unique approach that relies on comb filtering and phase manipulation rather than delay-based or mid-side techniques. It appears to be almost exactly the same algorithm as my previous favourite, Ableton Live Utility (great for ensuring bass mono preservation too). It’s possible I got sucked in by the attractive UI on the Polyverse plugins.
Key strengths of Wider:
Phase Coherence: Wider adjusts phase relationships rather than introducing delay-based offsets, keeping the sound more stable in mono.
No Reverb or Delays: Unlike many wideners that use subtle delays or reverbs to create space, Wider doubles the signal across the stereo field in a phase-friendly way.
Mono Compatibility: When summed to mono, the additional stereo information cancels out cleanly, leaving the mono signal unaffected.
However, after close listening and feedback from a fellow producer, I’ve noticed that fast-attack transients (like snare hits and percussion) can introduce slight artefacts in mono playback on Wider and Utility. Even though the stereo effect itself cancels cleanly, some subtle phase interference seems to occur during sharp, percussive moments.
A Better Choice?
For projects where transient clarity is critical, Leapwing StageOne and SSL Fusion Stereo Image have proven more reliable in maintaining a natural sound without transient artefacts. StageOne in particular excels at transparent widening while adding depth without compromising mono playback.
Final Thoughts
Stereo widening can transform a mix—but only if used carefully. It’s easy to overdo it and introduce phase issues that weaken your track, especially in mono. Plugins like Polyverse Wider can deliver stunning width with minimal impact on mono compatibility, but even the best tools can show their limits with extreme transients. I think my final choice for real detail and perfection in mixes is going to be Leapwing StageOne. Whilst the PolyVerse plugin is great in almost every instance, faster attack transients seem to introduce some undesirable distortion. In many respects, Ozone Imager is actually a better sonic choice, however it doesn’t translate well to mono if using the more extreme settings. I want something whose algorithm entirely cancels itself out on the mono sum. The only plugin that seems to fully achieve that is StageOne.
At this level of detail, some of it becomes subjective. I’d love to know your thoughts—what wideners have worked for you? And have you noticed similar artefacts with phase-based plugins?