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Universal Audio OX

Guitar Speaker Emulation System
Published September 2018
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...

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Published September 2018