Universal Audio OX Stomp

The dynamic speaker and mic modelling of UA’s popular OX amp‑top box is now available in a compact pedal format.

The OX Stomp takes the dynamic speaker modelling of UA’s OX amp‑top dummy‑load, attenuator and speaker simulator and puts it into what’s now a familiar UA six‑knob, double‑footswitch enclosure. Just to be clear, though, this is not an OX somehow miraculously made smaller: there’s no dummy load, so you can’t plug the speaker output of an amplifier into it. This is a line‑level (or below) device, designed to accept the output of a preamp or guitar‑amp simulator pedal. Don’t UA make some of those, with OX‑derived dynamic speaker simulation already onboard, you might be thinking? You’d be right, of course, and very good‑sounding they are, in my opinion, although the OX Stomp’s wider range of cabs and miking choices offer a lot more flexibility than the onboard choices of the UA amp pedals. There are plenty more really useful applications for this little box, though: most obviously, you can put it after a dummy load/speaker attenuator, with due attention to signal levels, and enjoy most of the functionality of the full‑size OX. You can feed it the output of an ‘amp‑in‑a‑box’ pedal, but preferably one that replicates an output stage rather than just a preamp. And, finally, you can use it with amp‑modelling devices from other manufacturers, many of which may benefit from a more sophisticated and detailed speaker‑sim process, especially those from before the era of really good IR‑based (impulse response) speaker simulation.

Guitar‑speaker IRs are, in effect, just a very detailed frequency response curve derived from a digital recording of a guitar speaker that can subsequently be imposed on the sound of a guitar amp or simulation, and their widespread adoption has had a transformative effect on the usefulness of direct‑recording devices for guitars. The speaker simulation in UA’s original OX product, however, is not IR‑based, but uses a real‑time modelling process that allows it to respond dynamically to varying input signals, replicating the behaviour of real speakers with more detail and accuracy than the static ‘snapshot’ of an IR.

Making Connections

The OX Stomp has a limited number of physical controls on board, with much deeper, detailed control and editing available via the UAFX Control app.Like all the larger format UAFX pedals, the OX Stomp has stereo I/O on unbalanced quarter‑inch TS (tip‑sleeve) jacks, so stereo inputs can be maintained in stereo, whilst a mono input can benefit from the onboard room simulation in either stereo or mono. Recognising that users may want to employ guitar pedals, not just true line‑level devices, as a source, there’s plenty of range in the internal operating level; you just need to be prepared to turn up the output control a long way with lower‑level signals. There’s no level metering on the pedal or in the app, so I just used the position of the output knob when feeding a line input at unity gain as a guide: if I was turning it below halfway to get a sensible externally metered level, there was probably too much going in. In theory, I guess the input level should make a difference to the ‘dynamic speaker modelling’, but provided that I wasn’t too far to either extreme it all just seemed to work as expected. As usual, there’s a USB‑C port for registration and firmware updates only, so no MIDI or digital I/O, and you’ll need to source your own 9V DC external power supply with a current capacity of at least 400mA.

Like the OX amp‑top box, the OX Stomp has a limited number of physical controls on board, with much deeper, detailed control and editing available via the UAFX Control app, but it does still include all the virtual speaker cabinets, microphones and effects of the original unit. Physical controls consist of a level knob for each of the two virtual close mics, plus another (stereo or mono) for the room miking setup, Speaker Drive amount, simulating speaker condition, and an overall output level. In addition, a three‑way switch for each virtual mic allows you to choose Dynamic, Condenser or Ribbon as the mic type.

The OX Stomp is built around the concept of the Rig: a complete setup of virtual speaker cab, two mics, room ambience and effects that can be stored as a preset and activated via the footswitches or the UAFX Control app.

The OX Stomp is built around the concept of the Rig: a complete setup of virtual speaker cab, two mics, room ambience and effects that can be stored as a preset and activated via the footswitches or the UAFX Control app. The Rig knob in the centre of the pedal selects any one of the six presets currently loaded into the pedal as the ‘active Rig’. Given that the OX Stomp has neither motorised pots nor virtual, LED‑ring pots, it will be apparent that the knobs and switches won’t always match the sound of the preset. In fact, they almost never will unless all your presets are basically the same or you’ve just saved the current setup, which you can do either by pressing and holding the active Rig footswitch until the LED flashes, or within the UAFX Control app.

Rigs saved via the footswitch retain their edits in the pedal itself, but don’t get added to...