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Universal Audio OX

Guitar Speaker Emulation System
By Dave Lockwood

Universal Audio OX

Don’t have a great‑sounding room? Can’t turn your amp up to get the sounds you want? Want to turn down your speaker without sacrificing your tube amp’s tonality? Maybe this changes everything...

SOS Gear Of The Year 2018 Editors PickUniversal Audio describe the OX rather prosaically as an ‘Amp Top Box’. That’s understandable, given that the full description is more like ‘reactive dummy load, stepped speaker attenuator, dynamically modelled digital speaker, microphone and room emulation... with wireless remote control app’!


The OX is designed to accept a speaker‑level input from a tube guitar amp — there’s no amp modelling on board — whilst simultaneously offering a guitar‑speaker output via a variable attenuator, plus a digitally modelled speaker and microphone emulation, with effects, at its line outputs. In a studio setup, you can use the silent setting on the guitar speaker output to hear the exact signal you are recording on the studio monitors, and in a live setup, you can turn your amp up to where you want it, and your speaker down to where FOH wants it, whilst sending your preferred speaker and mic signal to the desk as an analogue line‑level or digital source.

Electric guitarists today have more options than ever before for both recording and live performance, with digital modelling and impulse response‑based speaker emulations having attained a level of authenticity that many players now find completely satisfying. The best ‘reactive’ dummy‑load attenuators now offer a true speaker‑like impedance curve to amplifiers and allow tube amps to be used with their ‘sweet‑spot’ settings without upsetting front‑of‑house engineers or home‑studio neighbours.

UA’s OX enters this market as something of a hybrid, being both attenuator/dummy load and speaker emulator in one box, with French company Two Notes Engineering’s Torpedo Studio dummy load and speaker emulator perhaps being the closest functional equivalent. Rather than use impulse responses — analogous to tonal ‘fingerprints’ of speaker cabinet and microphone combinations — UA have developed their own digital modelling process, which they state allows their emulated speakers to respond dynamically to changing input signals, as a real speaker would.

I have used impulse responses happily and successfully for a number of years now — for me and many other players, IRs changed the landscape of speaker emulation overnight from “meh” to “that actually does sound like a guitar speaker!” Extremely convincing though IRs can be, unless you have a hardware IR loader, you need to monitor something other than the sound you intend to end up with in order to achieve a latency‑free tracking setup, before applying the IR you want as a software process. The OX’s all‑in‑one solution means that the sound you hear as you’re playing is the sound you are recording, with negligible latency (under 3ms).

Of course, IRs have a fixed transfer characteristic — their tonal signature — and whilst you can always tweak them a bit with EQ and room simulation, I’ve never yet been able to get a single IR to fully imitate a real speaker’s whole range of responses. Like many others, I guess, I’ve ended up with a small library of IRs optimised for different pickup settings and levels of drive — when what I really want is something that gives the appropriate response to whatever I throw at it. Given UA’s deep expertise in both classic analogue studio gear and digital emulations of analogue gear, perhaps nobody was ever better placed to look beyond IRs to the possibility of a more dynamic, detailed speaker emulation technology.

Design & Construction

The OX itself is a seriously substantial unit, with a 15 x 5.5 x 8 inch metal housing featuring a stylish, slightly retro, wooden front‑panel trim. At over 14lbs, it feels like it ought to have an amp‑like mains transformer in it, but it actually has a 12V external DC PSU, albeit with a reassuringly robust four‑pin XLR locking connector. I’m guessing that the weight comes from the power soak of the reactive dummy load circuitry. I was delighted to see that there is no fan!

Speaker Volume offers a level‑controlled feed to a guitar speaker whilst Line Out governs the modelled speaker and mic output, with the room‑mic mix independently adjustable.Speaker Volume offers a level‑controlled feed to a guitar speaker whilst Line Out governs the modelled speaker and mic output, with the room‑mic mix independently adjustable.

Despite the deep control available in the remote app, the front panel has just five knobs, and a nice cosmetic touch in the form of a classic amp‑like jewel power light. All the DSP resides in the OX itself, so once you’ve tweaked and stored a few settings that you like, you don’t need to keep the remote control app running. You can store six ‘rigs’ — complete combinations of speaker, mic and effects emulations — selectable from a six‑way rotary switch. Whatever the stored value, the amount of simulated room ambience can always be overridden by a dedicated rotary control. Another six‑way rotary determines the output level to a connected guitar speaker, with ‘none’ and ‘everything’ at the two extremes. Line out and headphone level (plus quarter‑inch socket) complete the simple and intuitive control line‑up.

Over on the back panel we find connections for a speaker‑level input from a tube amp (solid‑state amps are not advised), and a post‑attenuator output to a guitar speaker. A three‑way impedance switch allows the OX to present a 4, 8 or 16 Ω load, which should keep most amps happy. If you accidentally power up an amp without remembering to switch the OX on first, there’s a 16Ω ‘safety load’ that will take care of things while you figure out what you’ve done. It’ll also keep everything safe if you switch off the OX, or it loses power while an amp is connected. A pair of balanced/unbalanced quarter‑inch jack line outputs is where the speaker‑emulated signal and effects appear — the actual speaker output is unaffected — and there are also S/PDIF (RCA and optical) digital outputs, three USB ports and a footswitch connection. The USBs at present do nothing more than provide a route to software updates, but obviously hint at plans for future expansion, as does the presently ‘inactive’ footswitch socket. Actually, the footswitch does do something: connecting a simple make/break switch causes it to temporarily capture and replay a bit of input signal like a looper, which you can then use to audition cab and mic setups without having to keep playing. This seems to be undocumented, and I don’t know if it will survive the footswitch getting a proper function in future, but it’s actually quite useful!

The speaker connection on most combo amps won’t be long enough to reach the OX’s speaker output. To use the attenuator you will need to buy or fabricate a short male‑ to female‑jack speaker lead. Using a locking female jack makes this feel a bit more secure.The speaker connection on most combo amps won’t be long enough to reach the OX’s speaker output. To use the attenuator you will need to buy or fabricate a short male‑ to female‑jack speaker lead. Using a locking female jack makes this feel a bit more secure.

On Test

The reactive dummy load/attenuator seemed like a good place to start testing. After all, the amplified life of the signal starts at the amp; if the amp isn’t behaving normally your chances of creating a convincing speaker emulation are inherently compromised. Dummy loads on most older attenuators tend to be purely resistive, which means their impedance is constant regardless of the frequency of the input signal. This is unlike a real speaker, which will always exhibit a significant amount of ‘reactance’ (variation of impedance with frequency). For an amp to sound and feel like it does when it is driving a speaker, its output stage has to be seeing something that closely resembles the impedance curve of a real speaker. The OX’s attenuator is a real gem, as far as I’m concerned. I felt no desire to start tweaking tone control settings on the amp as I went down the attenuation ranges, and that’s the biggest clue that the OX is keeping the amp happily convinced that it is driving a normal speaker at all settings. It sounds like there is a small amount of ‘voicing’ going on at lower output levels — I confirmed this by recording the low‑level signal and boosting it to the loudness of a recording of the minimally attenuated signal — but it is not at all extreme, and I think it is probably beneficial overall. It seems to give the quietest setting some girth, without which many might perhaps find it unusable. A couple of my amps were more affected by the attenuator than the rest, being a little darker at the highest attenuation setting, but not to the point where I wasn’t happy to use them.

The attenuation settings are stepped. To my ears and in my applications, they are entirely logical increments, but I suspect that, particularly in a live context, some might wish for finer increments at the top of the scale. Of course, most people’s ideal would be a fully variable pot, but that’s not an easy thing to achieve in an attenuator without compromising something else, such as the total range of attenuation available. These increments work for me — for recording, the speaker is off, and for stage, one‑notch‑down is just right for a pair of 6V6s into a single 12.

The App

So far, we’ve been all analogue, all hardware — all ‘real’ if you like. Connecting the two analogue line outs and firing up the app takes us into the OX’s parallel digital world. The app is exclusive to Apple operating systems, being available for iPads (iOS 11) or Mac OS (Sierra onwards) desktops. I’m tempted to say “at the moment”, but there is seemingly nothing to be had from UA on this, so I won’t speculate. If I were a confirmed ‘non‑Apple user’, I’d be disappointed in that situation. That said, one of the factory rigs that the OX ships with so perfectly fitted my tastes that I could still have made great use of this without ever firing up the app, so maybe Android and Windows guys should still check it out.

The OX can process the result of the modelled cab/speaker/mic sound with up to four simultaneous effects. These are derived from the company’s highly respected UAD platform, and on offer are a lovely‑sounding plate reverb, two different EQ types, a delay processor, and an 1176 FET compressor model.The OX can process the result of the modelled cab/speaker/mic sound with up to four simultaneous effects. These are derived from the company’s highly respected UAD platform, and on offer are a lovely‑sounding plate reverb, two different EQ types, a delay processor, and an 1176 FET compressor model.The app interface (see the ‘Wi‑Fi & The App’ box) shows you a graphic of your chosen cabinet and mic setup in a nice‑looking studio live room, with a small mixer in the lower half of the screen. The three mic channels — two close mics and one room mic — feed a stereo master fader, with each mic channel having mute, solo and hi‑pass filter switches, a pan pot, plus the ability to insert an EQ. The master channel sums all three sources and offers four‑band EQ, a lovely 1176 compressor emulation, a sweet‑sounding vintage plate reverb algorithm, and a versatile stereo digital delay with filters and modulation. Each processor opens into a UA‑style, graphic‑heavy, detailed editor. The mix controls on both reverb and delay could be better scaled to give a bit more resolution in the normal working ranges, I feel. One for a software update, maybe.Universal Audio OXUniversal Audio OXUniversal Audio OXUniversal Audio OX

Using the pan controls in combination with the two outputs allows you some track allocation options: you can record the two close mics separately, with or without a little room mixed in, or, my favourite, choose a mono room mic and send it to one output while the two close mics are combined in the other channel. So long as you’ve remembered not to use any of the master effects, recording these two streams separately allows you to vary the amount of room mic in the context of your track when mixing. Personally, I prefer not to have much ‘baked‑in’ room ambience on a guitar signal, and would always rather add it as needed while mixing, but the OX room signals are so ‘just right’ that I find it worth recording them, even in mono, so long as I can give them their own output. Of course, four outputs, with separate close mics and a stereo room, or even three, with separate close mics and a mono room, would have been great. As it is, there are two — and I’ve really got no complaint about that. It is entirely manageable and versatile enough exactly as it is. Working with the OX for a couple of weeks I’m increasingly finding that anything that it won’t do simply pales into insignificance beside what it will.

The digital outputs are 24‑bit, with a fixed 44.1kHz sample rate. In my view, that is more than adequate to capture anything electric guitar related. Others may disagree. In practical terms, I think the only real benefit that a higher sample rate might offer is a lower latency — even the analogue line outs exhibit a small 2.77 millisecond latency because they are outputting a signal from a digital process. Under three milliseconds is insignificant when the rest of your process is entirely analogue, but you might want to bear it in mind if you start combining the line‑out source with a real mic signal. (The throughput from the attenuator to the real speaker is entirely analogue and therefore latency‑free.)

There are plenty of speakers and cabs to choose from — a 1x10, five 1x12s, a 2x10, five 2x12s, a 4x10 and four 4x12s — and any rig can have any combination of cabinet, mics and effects. (See the ‘Speaker Cabinets’ box.) The really interesting thing I found with the speaker cabinets is that the amp/speaker combinations that, in my experience, work best in the real world, tend to work best with the OX, too. And the speaker cabinets I tend to like and use the most are also the ones I prefer in the OX. Of course, this could mean I am just a bit unimaginative when it comes to adventurous pairings of amps and cabs, but it could also mean that the OX’s cabinets are uncannily accurate in their emulations of the real thing.

Some might say that the OX’s range of cabs leans slightly towards the vintage and classic end of the spectrum, but I don’t think of speaker cabinets as hugely genre‑specific. There’s no 4x12 with V30s, for example, but for me the right amp into any of the 4x12s will get me ‘that sound’, with a touch of EQ and compression. And, just as in the real world, even a single‑driver cab can be made to sound huge in a recording with the right amp and appropriate (virtual) miking.

The OX is specified for a maximum input of 150W RMS (200W peak) with a software selection of 50 or 100 Watts setting the basic operating range. As far as I can tell, nothing much happens if you mismatch this setting except that the output gets slightly louder or quieter, depending on which way you are mismatching. I certainly never felt I was anywhere near to clipping anything internally unless I was boosting with EQ a bit too much, or running the compressor output significantly above unity. Tempting as it may be to turn your tube amps ‘up to 11’, you don’t have to work with good attenuators and speaker sims for very long to realise that there are many amps that don’t actually sound that good when pushed to the limit. Most have a ‘best operating range’ where both preamp and power amp are driven to an optimum extent, but very rarely, in my experience, will that be in the top 10 percent of the volume scale.

The other speaker parameter is Speaker Drive — an intriguing process of gradual virtual ‘ageing’, through to level‑induced speaker distress at the top of the scale. The latter includes the phenomenon sometimes referred to as ‘cone‑cry’, which can exhibit as a ‘false harmony’ note or various forms of intermodulation distortion. It’s certainly convincingly authentic, but I can’t say that I particularly like to hear any cone‑cry (I accept that some people do) and personally I’d certainly never let a real speaker exhibit such effects for very long. The ageing effect to be found further down the Speaker Drive scale, however, is very subtle and eminently usable, softening the attack and smoothing the distortion a little, just like a favourite old speaker with a good number of miles on the clock.

Mic Selection

The mic collection includes all the guitar recording ‘standards’ and some other studio classics, too (see 'The Mic Locker’ box). Part of the ‘art’ of guitar recording is mic selection, with another big part being mic placement. Interesting, therefore, that the OX app doesn’t give the user any placement parameter other than on‑ or off‑axis. I have to admit, this slightly bothered me... right up until I actually heard the output from the OX! Now I’m just pleased that mic distance is a parameter I don’t have to think about, and to know that my two mics are always going to be phase coherent. It sounds to me like some of the bass boost of proximity‑effect may have been rolled off from some of the virtual mic signals, as I rarely found myself activating the fixed high‑pass filter in each mic channel. Occasionally I actually wanted a little more ‘weight’ in one or two of the 4x12s, but it was easy to dial it in on one or other of the mics, or the master channel, using the EQ, which offers a choice of graphic (four‑band with high‑ and low‑cut) or Touch (DAW plug‑in style) views. I’ve not used every one of the ‘real thing’ in this mic collection extensively, but the ones I’m very familiar with sound, well, very familiar. Like the speakers, they’re doing just what I would expect them to do in the real world.

The inclusion of a virtual DI box in the ‘mic locker’ is a nice touch. It’s important to remember that this is a post‑amp DI, not an instrument tap that can be used for reamping. What it can be used for is adding a bit of sparkle to a clean guitar sound, or indeed having a speaker impulse response applied to it after recording, so long as the DI box output was recorded to its own track. This can give you the sound of a different cab to blend with or even replace the one you recorded via the OX. If you do want to reamp via the OX you’ll have to record a clean guitar DI and plumb that back through the whole signal chain of amp and OX, as the latter has no line input — it’s a speaker‑level‑input‑only device. It’s been flagged as an issue by some people that there’s no way to get a playback signal into the OX’s headphone output, which would, of course, have made it the ultimate private practice device. I can see the point from the users’ perspective, but with little analogue mixers available now for so little money, I can also see why UA might have made the choice to omit it.

A degree of ‘room sound’ is crucial to making a guitar amp sound and feel ‘normal’ to the player when it is close‑miked — after all, we don’t generally listen to our guitar speakers with an ear two inches from the cone. All too often, however, room simulations on guitar processors sound like a really obvious short‑decay artificial reverb, or a slapback effect. A real tracking‑room ambience is neither of those: it is a supportive, enveloping soundfield that gives dimension and weight to the speaker signal, sounding like it belongs to it, rather than something imposed on it as an effect. The OX room mics, one stereo and two mono ribbons, and one stereo and two mono capacitor models, really deliver this perfectly, as far as I’m concerned (see 'Room Mics' in 'The Mic Locker’ box). The range goes from ‘imperceptible’ to ’too much’, but in between lies the perfect supporting ambience for each of the cabs — the one that makes everything feel easy, natural and ‘normal’, as if you were in the room with the amp.

Of course, the amount of room that makes everything feel great when you are playing is rarely the amount of room you’ll want on the final recorded signal by the time it is in a mix, hence my earlier comments about taking the room mic signal out as a separate output. Having recorded electric guitars almost exclusively on studio monitors for about the last 10 years, I’m lucky enough to have a dedicated hardware room simulator that I use just in the monitoring while tracking, so I can record dry whilst still feeling ‘in‑the‑room comfort’ for playing. If you can’t do that, then separating the dry and room signals on the OX certainly works, but you can’t then use any of the effects on the master bus, as they sit across both outputs. A future option to send a close‑mics‑only signal out of the digital outputs whilst monitoring a room‑rich sound on the analogue outs wouldn’t be too much to ask for, would it?

Each of the room mics can operate in one of two states: a fully ‘live’ mode, or slightly damped, as if there were absorbent baffles in the room and a rug on the floor — a suitable little rug appears under the amps in the graphic when Damp is selected, of course! The audible effect is subtle but all the more useful for that, with Damp mode being generally ‘faster’ and tighter in the bass. There’s a little more than just a tightening of the ambience going on: some of the mics are listed as being in different places in the room, and offer yet more subtle differences to the overall sonic palette.

Better Than The Real Thing?

There’s a persistent myth that electric guitars are super‑easy to record: you just shove an SM57 in front of your speaker cab and away you go. Well, as any guitar player who has just listened to a disappointingly ‘small’, nasal‑sounding playback of their ‘performance of a lifetime’ will tell you, that’s not entirely true. There are as many ways to make a bad‑sounding recording of an electric guitar as there are any other instrument. Electric guitar tone is the sum of all its parts — the player, the amp, the speaker, the room, the mics. ‘Tone is in the fingers’, people love to say. Well it is — but only if tone is everywhere else in the chain, too. The OX takes the most problematic part of the chain for most of us — not many of us have ready access to unrestricted volume in a great‑sounding room — and offers a totally convincing, golden‑ears‑engineer‑miked speaker cabinet solution, using your own amps at any volume setting you choose.

If it did that with just one virtual cabinet and one microphone I and, I suspect, many others would still be very happy. The fact that there’s a range of cabinets and a choice of classic mic emulations is just icing on the cake. All the factory cab and mic combinations are instantly convincing, but there is so much you can tweak if they are not quite right for your tastes or the track: swap out the cabinet for something else; change the mics; go on‑ or off‑axis, more or less ‘roomy’, stereo or mono; or add a touch of EQ or compression. It is all so quick and easy compared with unstrapping your guitar and adjusting things in the physical world. Of course, no time‑saver is worth compromised sound, but there is no compromise here, to my ears. The OX serves up a miked cabinet sound every bit as good as anything I have ever achieved with real mics and cabs, and it does it consistently, with the ability to recall any number of perfectly tailored whole setups. It is a neat single‑box solution, optimised for both stage and studio; simple in its most basic function, yet deep when you want it to be. UA are renowned for their emulations of classic studio hardware of the past; they just might have made another ‘classic’ of their own.  


There are plenty of other ways to record guitars now, but sticking with the scenario of using real tube amps, Two Notes Engineering’s Torpedo Studio unit offers a reactive load, with IR‑based emulation of the whole speaker, microphone, preamp and room‑acoustic signal chain, and is capable of good results. A good stand‑alone reactive load — John Suhr’s Reactive Load, Weber MASS, Fryette Power Station and a number of others now have good reputations — can also be used with a hardware IR loader, or recorded raw to apply IRs in software afterwards.

Wi‑Fi & The App

The OX’s app offers a comprehensive library of modelled cabinet, speaker and mic setups using an intuitive folder structure, but you can swap out any or all of the elements and store your own User setups too. The virtual mics can be set to on‑ or off‑axis, high‑pass filtered, panned, soloed or muted, and blended to taste using the on‑screen faders.The OX’s app offers a comprehensive library of modelled cabinet, speaker and mic setups using an intuitive folder structure, but you can swap out any or all of the elements and store your own User setups too. The virtual mics can be set to on‑ or off‑axis, high‑pass filtered, panned, soloed or muted, and blended to taste using the on‑screen faders.Universal Audio OXThe OX app can be downloaded from UA’s web site, and requires Mac OS Sierra or High Sierra on a desktop, or iOS 11 for iPad. This would appear to exclude users of older‑generation iPads that can’t be upgraded any further, but I have heard of some people successfully running the app under an older OS, so it is certainly worth a try if you are in that position.

The app will only connect via Wi‑Fi, which seems unnecessarily limiting when you’ve got USB ports sitting there doing nothing at present. That said, Wi‑Fi connection was entirely painless — the OX will create its own Wi‑Fi hotspot if it doesn’t see an existing network. It’ll ask for authentication via the password on the back of the unit, and firing up the app and clicking ‘Find My OX’ will bring up the control screen. The OX app will ask you to register the system to your UA account, or create a new one if you don’t have one already. It couldn’t be much simpler. Connecting via your own Wi‑Fi router doesn’t in any way seem to impact on the performance of the app, which is as near instant as you need for the type of adjustment involved, and is probably more convenient because you can temporarily exit the app if necessary, without having to change any settings.

Beyond the studio/mixer view and effects editors lies the file management area. You can save Rig Presets: entire setups of cabs, mics, EQ and effects; and Effect Presets: favourite settings for any one of the reverb, compressor, delay or EQ processes.

A simple and intuitive folder structure allows you to audition the extensive library of factory presets, tweak them and save them as user presets. You can also create other folders, perhaps to save presets by genre or application. You can also tag presets as Favorites, without duplicating them — they just show up in the Favorites folder. It’s mostly very slick, although I did have a couple of issues with intermittently unresponsive Options icons right at the edge of the screen on a Gen 5 iPad. Of course, that is the sort of thing that can be dealt with via a simple app update, and I daresay it will be fixed before too long.

Assign view in the app allows you to choose which rigs are stored in each of the OX’s six Rig slots — the ones instantly accessible via the six‑way hardware switch on the front panel. Whole sets of six can be saved and restored, with the one caveat that if you currently have a rig with unsaved edits, it will be overwritten by recalling another Rig Set. When creating your own Rig Sets, the ‘active’ slot is always the one selected on the front‑panel hardware control, so if you want to listen to a series of rigs before assigning them to slots in Assign View without constantly reaching out to the hardware, I found it best to make temporary assignments to the active slot, before storing them to the slot where I really want them.

Speaker Cabinets

The OX offers a choice of 17 speaker cabinets, selectable within the software app. The actual manufacturer references given below are my opinions, not Universal Audio’s references.

  • 1x10 Black Cha: A small, open‑back vintage 10‑inch speaker with “classic small amp honk”.
  • 1x12 Blue J: A 1950s‑era cabinet and ‘Jensen‑voiced’ speaker, delivering “classic American open‑back 12‑inch speaker tones”.
  • 1x12 GB25: A 1950s‑era open‑back cabinet paired with a Celestion G12 Greenback, described as “a more overdrive‑friendly British speaker”.
  • 1x12 Blu 15: A 15W Celestion Alnico speaker in an open‑back cabinet. Vox AC‑15‑style.
  • 1x12 Black D‑ux: A mid‑’60s‑era Jensen in a ‘blackface’ Fender Deluxe Reverb, open‑back 12‑inch combo cab.
  • 1x12 Black GB30: An open‑back cabinet paired with the heavier‑duty 30W Celestion G12.
  • 2x10 V‑ux: Two 10‑inch speakers in an open‑back ’60s‑era cabinet, which has to be a Fender Vibrolux.
  • 2x12 Two Verb: The classic Twin Reverb pairing of two 12s in an open‑back cabinet. Fender have used a number of different speakers in these over the years, including Jensen, CTS, Oxford and Eminence. This probably models Jensens.
  • 2x12 Black 8H: A custom half‑closed cabinet featuring the high‑wattage aluminium‑capped speakers “favoured by early ’80s metal players” — Altec 417‑8H Series II, I believe.
  • 2x12 Ace Top: Vox AC‑30 2x12, with the famed Celestion Alnico ‘silver’ frame speakers.
  • 2x12 Boutique D65: A custom ported cabinet with classic old Celestion G12‑65 speakers.
  • 2x12 Alnico 50: A closed‑back cabinet featuring two modern, probably Eminence Alnico 50W speakers, offering “smooth and singing single‑note tones when using high‑gain”.
  • 4x10 Bman: The four 10s in an open‑backed cabinet of the Fender Bassman combo offers some highly articulate sounds, with a slightly “scooped mid‑range and extended presence”.
  • 4x12 GB25 Thick: A Marshall 4x12 with original Celestion 25W Greenbacks — “the sound of rock guitar”. This specific vintage cabinet has “extended low mid‑range and bass response”.
  • 4x12 GB25 Punch: As above, but this cab has a “moderately scooped mid‑range delivering a tighter sound”.
  • 4x12 Super 80: A custom ported cabinet with four Celestion G12‑80 speakers. Great for high gain, in my experience, with a “soft treble response, but with an aggressive and forward mid‑range”.
  • 4x12 White 75: A custom ported cabinet featuring “12‑inch white/cream 75W modern British speakers with an extended treble/presence frequency response”. I assume this means Celestion G12H‑75 Creamback.

The Mic Locker


Any close mic, or combination of two different mics, can be used on any cabinet, individually positioned on‑ or off‑axis. The close‑mic signals can also be panned for output routing or a wider image. The manufacturer identifications below are mine, but I have retained elements of UA’s own descriptions, as they refer to the actual specific examples that were modelled.

  • Dyn 57: The Shure SM57 has been an industry standard for recording loud guitar amps since the late ’60s. UA’s model is based on a vintage unit from the ’70s.
  • Dyn 421: Sennheiser’s MD421 has long been a European favourite alternative choice to a 57. This particular model is based on a vintage white unit from 1963.
  • Rib 160: The Beyerdynamic M160 ribbon mic was a favourite of UK‑based recording engineers in the late ’60s. This model is based on a vintage silver unit from that era.
  • Rib 121: The Royer 121 ribbon is truly a ‘modern classic’ for recording electric guitar, with a silky high end and extended bass — great on its own but also a firm favourite paired with an SM57.
  • Con 414: AKG’s C414 solid‑state condenser mic offers a clean, articulate sound, with plenty of high‑end clarity and low‑end punch.
  • Con 67: Neumann’s U67 tube condenser model has a wide frequency range without sounding harsh or bottom heavy, with a gentle upper mid‑range that’s “great for distorted rhythm guitars.”
  • Direct: A speaker‑level DI Box, offering the raw sound of your amp without the filtering effect of a guitar speaker.


The room mics capture the ambience at very specific points in UA’s own high‑quality recording room.

  • Ribbon Stereo: A matched pair of ribbon mics placed in the drum area of the tracking room “with a warm treble response with an overall vintage ’50s and ’60s session vibe”.
  • Condenser Stereo: A matched pair of tube condenser mics placed in the drum area of the tracking room.
  • Condenser Man Mono: A tube condenser mic placed in the left side of the tracking room (when viewed from control room).
  • Condenser 67 Mono: A tube condenser mic placed in the right side of the tracking room by the drum overheads (when viewed from control room).
  • Ribbon 84 Mono: A ribbon mic with an “old‑school recording studio vibe”.
  • Ribbon 121 Mono: A modern ribbon mic that adds “depth and punch without getting in the way of the close mics’ high end”.

Audio Specifications


  • Dynamic Range: 114.5dB (A‑weighted)
  • Frequency Response: 20Hz to 20kHz, ±0.1dB
  • Signal‑to‑Noise Ratio: 114dB (A‑weighted)
  • Total Harmonic Distortion + Noise: ‑110dB at ‑3dBFS
  • Channel Separation: 129dB
  • Output Impedance: 100Ω
  • Maximum Output Level: 20.2dBu (balanced)
  • Output Latency: 2.77ms (122 samples at 44.1 kHz)


  • Format: S/PDIF
  • Connector Type 1: Female Phono (RCA)
  • Connector Type 2: Optical Toslink JIS F05
  • Sample Rate & Word Length: 44.1 kHz/24‑bit
  • Output Latency: 2.57ms (113 samples at 44.1 kHz)


Download | 59 MB

I must admit, I was in two minds about doing audio examples for this — after all, at least half of what you are hearing is the amps and guitars. You'll also be hearing the type of sounds that I tend to prefer, which may not be the type of sounds you want to be making. That said, I was able to dial these in to sound the way I wanted them to with my amps, and I suspect anyone else would be able to do the same with theirs. To my ears, very few of the OX rig presets (well, one actually) come up sounding exactly as I'd want to use them, so expect to do a bit of tweaking and refining to get the best results, just as you would with a conventionally miked recording set up.

I've used a different amp and OX cab for each example, but the mic setups are often similar, because I found combinations that worked and stayed with them, until they didn't. Great though they are, I used none of the OX effects and dynamics in these examples, with just a bit of the low-pass filter on the master channel, usually rolled down to about 8kHz. The SM57 is always paired with a ribbon or condenser mic in these setups, so I've rolled-off some of its top-end, too, using it just for a bit of mid-range solidity. The ribbon or condenser model is always the dominant one of the pair. Speaker Drive varies across the examples between the lowest setting up to about 50 percent. I used no mix EQ or dynamics in the examples. What you hear is the output from the OX's analogue line outputs as a mono track, with a bit of OX room mixed in, and occasionally a touch of mix reverb.

These short examples are all in the context of tracks (except number 4, which is an intro and never gets to the track). Personally, I find it difficult to interpret electric guitar tone out of context — things that sound great on their own don't always sound right in a track. There's no 'metal' example — extreme or otherwise — as that's something I haven't done since I had appropriately great hair, and therefore have no up-to-date real-world reference. But I see no reason why the OX cabs wouldn't be able to deliver what's required.

1. Deluxe clean

  • A late '60s Fender Deluxe Reverb using an OX 1x12 with blue-frame Jensen C12. There's so much detail in there to make me think I'm hearing the real thing rather than a software model.
  • Strat, middle and neck pickup combo.
  • Mics: Shure SM57 and Royer 121, both on-axis, ribbon has HPF activated.

2.  Marshall loud

  • A 'Super Lead' quartet of EL34s paired with OX Celestion G12 'Greenbacks' in a 4x12. What else?
  • To me, this has the 'chewy', articulate quality that is always present in the real thing, but often missing from heavy distortion simulations.
  • Les Paul Custom, bridge pickup. Monitored loud, hence the edge-of-feedback octave split.
  • Mics: Shure SM57 and Royer 121, both on-axis, no HPF.

3. Twin touch

  • Warm, 'touchy-feely' Twin Reverb 6L6s, driven enough to be sitting on the edge between clean and dirty according to the amount of pick attack. OX cab is modern Alnicos in a 2x12.
  • Telecaster, neck pickup.
  • Mics: Royer 121 and Neumann U67, ribbon is off-axis, both have HPF activated.

4. EL84 ratty

  • 'Gnarly' single-ended Cornford EL84 keeps its authentic ragged edginess into an OX Celestion Alnico 'blue'. Most modellers get this too fizzy or too dark, but never 'just right', as it is here.
  • Strat, bridge pickup.
  • Mics: Shure SM57 and Neumann U67, both on-axis, no HPF.

5. Mesa Mark smooth

  • No surprise that a vintage Mark IIB should pair well with the OX's Altec 417 — a popular choice with many early Boogie players.
  • Telecaster, bridge pickup, tone rolled back a bit.
  • Mics: Shure SM57 and Neumann U67, both on-axis, condenser has HPF activated.

6. Princeton dark

  • I love the OX's 1x10. Logically, it pairs beautifully with a '68 Princeton, but I could happily use it on almost anything. Here it is doing dark and woody for smoky jazz, but it will chime and grind, too, when you want it to.
  • Les Paul, neck pickup.
  • Mics: Shure SM57 and Royer 121, both on-axis, no HPF.


  • Excellent reactive load box/attenuator.
  • Sounds like a real, perfectly miked guitar cab.
  • Virtual room mics that sound just right.
  • The app gives a lot of tweakability.
  • The OX can be used without the app.


  • The app is iOS 11, or recent Mac OS, only.
  • Attenuator steps might not suit everyone.
  • No line input for ‘private practice’ backing tracks.


A complete recording system that lets you use your own tube guitar amps at their optimum settings, at any monitoring level you choose. It offers the sounds of multiple cabinets, without requiring a warehouse and a comprehensive mic collection, and directly addresses the weakest link in many home‑ and small‑studio guitar‑recording setups with great virtual rooms.


£1170 including VAT.

Published September 2018