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 When it superseded FireWire, the new standard seemed to promise everything you could possibly want for audio: high bandwidth, super‑low latency, support for hot‑plugging and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 licence, so you’re free to apply calibration through the Systemwide app or native plug‑in. On paper, though, integration into the audio interface solves the main logistical problems with these approaches: there’s no additional routing or layers of complexity, calibration is applied to all sound output from the computer, not just the DAW, and there’s no risk of accidentally bouncing mixes with corrective EQ baked into them.

Profile Pictures

Only one SoundID profile can be stored for any given headphone or monitor output (and, as always, in a system with multiple Apollos, only one main monitor output can be specified). To load or change a profile, you need to open the Monitor Controller pop‑up and click Open SoundID. This will launch Reference in a separate window, whereupon you can use the Measure utility to create a room profile or scroll through banks of headphone profiles. Once you’ve created or selected a profile and optionally applied a SoundID Target curve, you can hit the button that says Apply Profile To Apollo X.

This is all impressively slick and idiot‑proof, and absolutely delivers on the logistical advantages described above. Having speaker and headphone correction baked into the audio interface eliminates many potential sources of confusion, ensuring that absolutely everything you hear is corrected and at the same time ensuring that the correction stays firmly in its monitor‑path lane. And it can handle immersive setups up to 9.1.6. DSP load depends on the number of channels, but Apollo Monitor Correction never uses more than one full SHARC chip in total.

Are there any down sides? A few, but they are fairly inconsequential. For me, the Console GUI does not make it obvious enough whether SoundID calibration is active, especially on the headphone outputs. The Monitor box at least has a bypass button that appears when you hover the mouse over it, but the Headphones one is inscrutable until you click on it to open the Monitor Controller pop‑up. (Personally, I like to toggle headphone correction on and off pretty regularly, so I’d find a bypass button very useful.) And whereas SoundID itself allows settings to be changed instantly, it takes a couple of seconds to apply them to the Headphones and Monitor slots. If you want to swap to a different set of headphones, or check translation using one of SoundID’s target settings, there are extra mouse clicks and a small pause compared with doing this in the standalone or plug‑in version. But at least this is possible, which is very much not the case with many hardware calibration setups. All in all, this is a great implementation, especially when you consider how little you’re paying for something that you’ll use nearly all of the time.

When the Apollo Monitor Correction add‑on is installed, SoundID sports a new button allowing profiles to be transferred to the Apollo.

Elastic Bands

When running natively on a Mac or PC, SoundID is free to use all the processing resources it needs to perform correction, and a typical SoundID profile will be implemented using hundreds or even thousands of separate EQ bands. In a hardware context, by contrast, there will be a fixed quotient of DSP resources available, which in turn means that the hugely complex SoundID profile is approximated using a limited number of EQ bands. In some devices, this number can be as low as eight. Apollo Monitor Correction deploys 24 bands for headphones, main speakers and satellites, plus a further five bands for the LFE if used, which makes it one of the most faithful attempts to integrate SoundID into a hardware platform. I certainly couldn’t detect any noticeable differences between the same profile running natively and on the Apollo.

Another potential issue with DSP speaker or room correction is latency. The software version of SoundID gives the option to apply correction using either linear‑phase or minimum‑phase equalisation. Apollo Monitor Correction uses minimum‑phase equalisation, and this helps to keep latency extremely low: below 2ms at base sample rates and under 1ms at 88.2 or 96 kHz. (That is, of course, assuming that the calibration profile isn’t also applying delays in order to compensate for speakers being different distances from the listening position.) Being a Thunderbolt audio interface, the Apollo has good low‑latency performance, and is designed to encourage users to monitor live inputs through Console rather than their DAW in any case, so in the vast majority of cases it will be possible to leave Apollo Monitor Correction active at all times without latency becoming a problem.

I should point out, incidentally, that Apollo Monitor Correction is a walled garden, in that it’s not possible to use it other than by creating and applying SoundID profiles. There’s no way to use EQ settings created using other tools, even if you’re willing to set them up manually.

Gaining Ground

The other big selling point of the Gen 2 Apollo X interfaces, or at least those of them with Unison preamps built in, is something called Assistive Auto‑Gain. The idea of auto‑gain is a simple one: you tell the interface which inputs you’re going to use and instruct the musicians to play their instruments, whereupon the algorithm analyses the incoming signal level and sets the preamp gain appropriately. It’s most often found on entry‑level interfaces targeted at people who might not have extensive recording experience, and on models like the new Focusrite 4th Gen Scarletts and Audient’s EVO series, it’s pretty much a one‑button function. The Apollos occupy a slightly different sector of the market, and consequently, UA’s implementation of auto‑gain is rather more flexible.

That’s not to say you can’t use it as a one‑button function if you want to. Click the Auto‑Gain button on an input channel in Console, and a small pop‑up will appear, populated with some sensible default settings. Assuming you’re happy with these, you can just click Start, play your instrument and enjoy an appropriate level coming into your DAW. To perform auto‑gain across multiple inputs, you simply click more Auto‑Gain buttons, although the pop‑up has an annoying way of obscuring the one you want to get to.

The controls in the Auto‑Gain pop‑up are mostly self‑explanatory, and include the ability to vary the duration of the audition period — useful in cases where you are recording yourself and need time to move from computer to drum kit or piano. A Show More button reveals additional parameters, of which the most significant is Peak Target. By default, this is set to ‑8dBFS, which seems to me a bit on the high side, given the universal tendency of musicians to be much louder during takes than during soundchecks. It’s straightforward to reduce this at the point of use, in order to give yourself more headroom, but there doesn’t seem to be a way to set a different value as default.

Part Of The Unison

It’s one thing to implement auto‑gain on a conventional digitally controlled preamp that has only one gain control; quite another to do so on UA’s Unison modelling preamps, most of which have multiple parameters affecting signal level. Consequently, it’s not yet available for all of the emulated mic pres, nor any of the Unison guitar amps. At present, the list of Unison plug‑ins for which Auto‑Gain is supported comprises four Neve emulations, three APIs and the SSL 4000E Channel Strip.

Plug‑ins such as the Neve 1073 and API Preamp have, in addition to a main gain control, an optional input pad and an output fader or trim control. Auto‑Gain does not itself adjust the output trim controls, but does take their settings into account, so if for example you pull the output fader down in Neve 1073, Auto‑Gain will apply more gain on the way in. Where a preamp has a pad switch, Auto‑Gain will automatically engage this for very hot signals. However, there’s a small trap waiting here for the unwary, because if the pad is already engaged when you start the Auto‑Gain process, it will remain engaged even when you feed it a very quiet signal, leading to a rather suboptimal gain structure. I encountered a few other quirks when starting Auto‑Gain from an existing extreme setting, so it seems to be good practice to ‘zero’ any Unison preamps before beginning the process. But as long as you remember to do this, it’s very effective.

Moon Shots

The Apollo programme has been a hugely successful one for Universal Audio, and it’s hardly surprising that they haven’t made any radical changes to the basic form factor and I/O count of their interfaces — or moved away from the Thunderbolt platform that has served them so well. Even so, I think this refresh over‑delivers.

On the specifications front, I suspect that the previous generation was already well past the level where any flaws would be audible over typical studio monitoring systems, but the improvements place Gen 2 models right at the head of the field.

On the specifications front, I suspect that the previous generation was already well past the level where any flaws would be audible over typical studio monitoring systems, but the improvements place the Gen 2 models right at the head of the field, and I can certainly report that they sound great. I used the review system on a recording session with a very powerful drummer, and the built‑in headphone amps didn’t quite have enough power to deliver the levels he wanted, but I think the same would have been true of practically every audio interface headphone output. For everything I wanted to hear while tracking or mixing, they performed admirably. And it’s always reassuring to know that if you do hear any distortion, it definitely doesn’t originate with the converters or headphone amps!

The obvious and biggest Gen 2 highlight is the Sonarworks integration, and UA’s implementation is extremely impressive — probably the deepest we’ve yet seen. I’m not aware of any other interfaces that can load SoundID headphone profiles as well as speaker profiles, and the availability of up to 24 bands of EQ per channel means that Apollo Monitor Correction is more faithful to the original SoundID profile than most alternatives. Add that to the handy Assistive Auto‑Gain, the class‑leading audio performance and the new Plug‑in Scenes functionality, and you have a very meaty upgrade.

Information

See ‘Pricing’ box.

www.uaudio.com

See ‘Pricing’ box.

www.uaudio.com

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