Universal Audio Apollo X Gen 2

In the latest generation of the Apollo X range, UA have added a host of new features including Sonarworks SoundID integration for both speakers and headphones.

It’s been a surprisingly long time since I last typed the phrase 'Thunderbolt audio interface' at the head of an SOS review. When it superseded FireWire, the new standard seemed to promise everything you could possibly want for audio: high bandwidth, super‑low latency, support for hot‑plugging and daisy‑chaining. But after promising beginnings, the Thunderbolt tide has turned. Mid‑priced interfaces that once boasted Thunderbolt connectivity, such as the Focusrite Clarett and PreSonus Quantum ranges, now employ USB instead.

There’s a long list of factors in play here. Certification has always been problematic, especially for smaller manufacturers. There are no Thunderbolt chipsets comparable to the ubiquitous XMOS range, which offer ready‑made solutions for USB interface design. In the PC world, adoption by motherboard manufacturers has been half‑hearted. And, above all, USB is good enough for most use cases. So much so, in fact, that nearly all audio interfaces are still USB2 devices at heart, and don’t exploit the much greater bandwidth available in USB3 and USB4.

Thankfully, though, it seems unlikely that Thunderbolt will suffer the same fate as FireWire. It now uses the same Type‑C connector as USB devices, and is being developed not as an alternative to USB but as a superset of it. In practical terms, Thunderbolt is becoming ‘USB plus’: not needed or implemented on every device, but a widely available and supported option in higher‑end systems where its special powers make a difference.

One such system is Universal Audio’s Apollo range. UA adopted the new standard as soon as it was practical, and have stuck with it ever since. Late in 2024, they announced what is in effect the fourth generation of Apollos, and they’ve very much kept faith with Thunderbolt. And, more importantly, they’ve also developed a tempting raft of new features.

Bolt From The Grey

Previous refreshes of the Apollo line have been staggered, with the rackmounting and desktop Apollos being updated separately. This time around, UA have reinvented the entire range in one fell swoop, with the only exceptions being the baby Apollo Solo and the two legacy desktop models that cater to PC users without Thunderbolt. There’s also an intriguing new model aimed at the live sound market, which is described in the boxout.

Dubbed the Apollo X Gen 2, the new range is visually distinguished by what UA call a “new look and feel”. I didn’t detect much change in the feel of anything, but the front panels of the rackmount models and the cases of the desktop units have reverted from black to a smart pale grey that recalls the brushed metal look of the very first Apollos, more than a decade ago. There is a total of seven models in the Gen 2 line‑up: the Twin X and Apollo x4 are desktop units, while the x6, x8, x8p, x16 and the new x16D are all 1U rackmounting devices. Like previous generations, all of the Gen 2 models come with external power supplies; the only Apollo that can be bus powered is the Solo, which has not yet been updated. Sadly, you still don’t get a Thunderbolt cable in the box, which would annoy me if I’d just shelled out four figures for a new audio interface!

The integration of UA’s UAD‑2 Powered Plug‑in platform has always been central to the Apollo range, and that’s still very much the case. All the rackmount Gen 2 Apollos are Hexa models, meaning they feature six processing cores, while the x4 has four and the Twin X is available in Duo and Quad configurations. As before, the DSP can host both conventional audio processors and UA’s Unison plug‑ins, which have the ability to reconfigure the input‑stage circuitry in the analogue domain, enabling the emulation of a huge selection of mic preamps, guitar amps and other such devices.

With the release of the Gen 2 models, this built‑in DSP has gained new powers. Thanks to a collaboration with Sonarworks, both Gen 1 and Gen 2 Apollo x interfaces can host corrective EQ and calibration for both loudspeakers and headphones. Other improvements include further refinement of the Apollo Xs’ already impressive audio specs, with even more dynamic range on most analogue I/O and a pretty staggering drop in THD, especially on the headphone amps. Bass management is now supported in both Gen 1 and Gen 2 Apollo X interfaces, live plug‑in management in Console is made easier through a new Plug‑in Scenes feature, and UA have implemented their own take on the auto‑gain functionality that’s becoming widespread in studio interfaces with digitally controlled preamps.

In The ’Works

Sonarworks integration in the Apollo X requires both a SoundID Reference licence and something called the Apollo Monitor Correction Add‑on. The latter is currently free with the Gen 2 models on a time‑limited offer, while Gen 1 owners can purchase it for $79. SoundID itself comes in five flavours, from basic headphone‑only correction at one end of the scale to the full Multichannel implementation for immersive monitoring at the other. The stereo and Multichannel versions are available both with and without the calibrated Sonarworks measurement mic, but you can use a generic measurement mic if you prefer.

At present, calibration can be applied to the Apollos’ headphone outputs and to the main Monitor output, whether this is set up for stereo or surround monitoring, but the Alt monitor paths are not yet supported. Everything is handled from a pair of discreet boxes in the master section of the UAD Console window. Clicking on one of these brings up the Monitor Controller window, where you can apply the new Bass Management feature, launch SoundID, and enable or bypass correction for the chosen output, with the relevant EQ traces displayed in green. Bass Management designates an Apollo line output as a discrete LFE channel, with crossover filtering configured in UAD Console and implemented in the Apollo’s DSP. And if you buy and enable Apollo Monitor Correction, your Bass Management settings will be transferred into any SoundID measurement profile, with corrective EQ applied in the profile to the LFE output where needed, without requiring further complex setup.

In UAD Console, the SoundID profile can be found in the Monitor Controller pop‑up.

It should be noted that whether or not you buy SoundID Reference separately, you get a full...