Surround mixing on headphones just got serious with OLLO Audio’s S5X€539, olloaudio.com
OLLO Audio is an independent developer of pro audio-focused headphones based in Slovenia. Its latest release is the S5X, a set of analogue, wired headphones boasting clever design and additional software to help you accurately judge surround mixes while listening in stereo.

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To be clear, while surround headphones do exist, the S5X are not the same. Rather they are “tuned for accurate object positioning in virtualised 3D audio”, according to OLLO. But what does that mean in practice, and can they be used for regular stereo mixing?
Before we get to that, a word on the build. The headphones are beautifully constructed in a combination of wood, metal and plastic. They’re an open-backed design with detachable plugs that terminate in a 3.5mm jack, and a 6.3mm adapter is supplied too.
The ear pads are soft, comfortable and replaceable, should they eventually start to wear out. The headband is, of course, adjustable and the phones feel light when worn, comfortable for the invariably long periods of mixing for which they’ll be employed.
OLLO S5X headphones on desk
You can just plug in and go but OLLO’s whole thing here is the idea of calibration. The headphones are designed to be as flat and neutral as possible to give the most accurate picture of a surround mix when downmixed into binaural (stereo) format. The thinking is that most surround content for games, movies and other applications is in reality experienced on stereo headphones rather than elaborate home cinema systems and as such it’s vital to mix it accordingly.
OLLO takes the idea of calibration very seriously indeed. To demonstrate just how seriously, part of your purchase is the company’s USC (unit specific calibration) plugin which you can download after registering. Then you send them the serial number of your headphones and based on their records of the build and analysis of your specific pair, they generate a calibration file which is emailed back to you. You then load this into the USC plugin, which you insert across the master bus in your DAW, and it calibrates the output for your personal pair of cans. The plugin itself is simple, with on/off and gain controls as well as the ability to hold up to eight configurations, should you own more than one pair.
The company is at pains to point out that this isn’t some kind of enhancement, which some other ‘personalisation’ systems use to magically make everything sound punchier. Nor is it they say for audiophiles expecting a similar result. Instead, it’s a very subtle 0.5 – 1dB change in tolerance where required. Since the headphones are already tuned to be as flat as possible, it’s making very minor tweaks based on the physics of your specific pair. It also works with the Waves NX plugin (for virtual room emulation for headphones), though our experience of trying to get Waves’ own software to authorise properly was frustrating to put it mildly.
So what’s happening here is that when working with a surround project the output from your DAW is being downmixed to binaural format for monitoring in stereo, and passed through the USC plugin to best calibrate it for your headphones. This does of course mean turning the plugin off before doing any actual exporting, or it would be included in the bounces. Most modern DAWs provide at least a few options here, like Logic’s Dolby Atmos with its multiple binaural monitoring modes.
OLLO S5X headphones USC plugin
If any of this sounds like a foreign language, it’s likely that this particular model of headphone is not aimed at your workflow. OLLO points towards its S4X model (€449) as a more conventional mixing tool, with a more mid-focused tuning. The S5X is tuned to have less bass and more high-end presence, which the developers say based on extensive testing offers the most accurate results for object positioning in 3D space.
As such, you would lean towards the S4X for more conventional stereo mixing duties. The S5X however is quite remarkable when fed downmixed surround content. Unless you’re a seasoned pro, it still feels a bit like magic being able to move sounds around in three dimensions and have this translated live to a stereo pair of headphones. But they are indeed extremely accurate, their flat response coping very well with the complexities of working in three dimensions.
When listening to regular stereo mixes they are too upper-mid-heavy and lacking bass but this is precisely because they are tuned for a different use. A good test – and a way to gauge their surround performance on a ready-made source – is to play back an album that has been properly mixed for Dolby Atmos, for example, and where the work has already been done.
We try the 2017 mix of R.E.M’s Automatic For The People since we’re intimately familiar with the original and the results are amazing. The talent lies with the people who mixed it of course, but the S5X does an incredible job of revealing all the detail, much of which isn’t even apparent in the original stereo mixes. Whole melodies appear and there’s just an incredible sense of space that elevates the record to new heights.
OLLO S5X headphones on desk
That’s where you’d hope to end up when mixing your own projects for spatial or surround and, with these carefully-tuned dynamic headphones, you can be assured that the monitoring side of things is taken care of. The goal is accurate translation of what’s on the surround speakers into your binaural mix in real time and on that front they certainly deliver. The sound is incredibly detailed, and separation is spectacular.
You may or may not be the type of user who cares deeply about the fine-grained calibration that the USC plugin offers. Either is fine, honestly. And you can use these without it, though it’s part of the purchase price anyway. While most serious reference phones will do a good job of handling a downmixed surround signal for mixing purposes, the specialised flat tuning on offer here really makes a difference and will be invaluable if you’re doing this kind of work with any regularity. OLLO does offer a 30-day money back guarantee with a few caveats, although you’re not likely to need it.
Key features

Reference class, open-back dynamic headphones with flat frequency response
Hand-picked, left/right matched transducers for better instrument separation
Dynamic Neodymium drivers
30 Ohms
Replaceable earpads with outer diameter of 95 mm
Detachable braided silicone cable with OFC core
Specially tuned for handling downmixed surround audio
USC calibration plugin (AU / VST3)
All components user-replaceable
Front-to-back air pressure equalisation
Works with Waves NX

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