PreSonus Quantum HD8

With their latest Quantum interfaces, PreSonus have swapped Thunderbolt for USB. Do they still maintain the same advantages?

When PreSonus first attached the name Quantum to a 1U audio interface, it was not short of unique selling points. Back in 2017, Quantums (or should that be Quanta?) connected to the host computer over Thunderbolt, and took full advantage of that protocol’s special powers. So much so, in fact, that even eight years later, the Thunderbolt Quantum interfaces are still unmatched for low‑latency performance, and nothing since has come close to the Quantum 4848 for huge I/O counts on a project‑studio budget. When the time came to refresh the Quantum range last year, however, PreSonus nevertheless gave up these advantages, switching to USB connectivity in pursuit of wider compatibility and lower cost.

There are obvious parallels here to what Focusrite have done with the Clarett range. In the first generation of Thunderbolt Clarett interfaces, the focus was on low‑latency performance; but when the Clarett+ refresh took place in 2021, Thunderbolt was dropped, and the current models are now all USB. Clarett+ became the ‘premium’ alternative to Focusrite’s bestselling Scarlett line, offering additional features and better specs rather than a fundamentally different platform. PreSonus’ move with the Quantum interfaces looks very similar, positioning them as upmarket alternatives to their Studio C range. So, what do the USB Quantums offer that’s special, and why should you buy one of these rather than its cheaper Studio C counterpart?

Four Front

There is a total of four models in the USB Quantum range (and the Thunderbolt Quantum 2626 is still a current product, too). The ES2 and ES4 occupy a wedge‑shaped, desktop form factor, whilst the HD2 and HD8 are 1U half‑ and full‑rack devices respectively. PreSonus sent all four models for review: I’ll focus mainly on the flagship HD8 and note any relevant differences where applicable. Build quality throughout the range is reassuringly robust, with stout metal shells and chunky faceplates to the fore. Everything is finished in a smart and businesslike black, though some of the legending on the rackmount models is quite small and hard to read at a distance.

All four models use a new mic preamp design dubbed 'Max‑HD', and I can’t discover any feature with the initials ES, so the thinking behind PreSonus’ naming conventions is a little obscure. The main functional differences are as follows. The ES models are USB powered, whilst the HD2 requires an external DC supply and the HD8 accepts an IEC mains cable. The ES variants have mini‑jack MIDI in and out, whilst the HD Quantums have a DB9 connector for a flying cable assembly that also features coaxial S/PDIF in and out. Both HD models can access up to 16 channels of ADAT Lightpipe digital I/O on two pairs of optical Toslink connectors; the HD8 also has word clock in and out, whilst the ES units offer no digital audio expansion. Worthy of note, the HD8 can also be used without a computer connection as a standalone ADAT expander.

The HD8 back panel includes an IEC power input, optical ports, a breakout port for MIDI and S/PDIF sockets, eight quarter‑inch line outputs, a pair of main outputs, and eight combi jack/XLR audio inputs.

On the analogue front, the ES2 and HD2 both have two mic/line inputs on combi XLR/jack sockets, while the ES4 has four and the HD8 eight. The first input on the ES2 and the first pair on the others also have dedicated high‑impedance jack sockets on the front panel, which override the rear‑panel combi sockets when a guitar or bass is plugged in. These are complemented on the HD models by the intriguing addition of a pair of front‑panel jack outputs specifically designed for re‑amping. The remaining analogue outputs are all on balanced jacks, of which the ES2 has two, the HD2 and ES4 four, and the HD8 no fewer than 10.

Universal Credit

It’s obvious from the moment you power up one of the new Quantums that PreSonus have gone all‑in on digital control. There is nary an analogue pot, button or switch to be found anywhere. Preamps, cue mixing, monitor control, metering and even headphone level are set digitally, using a single master rotary encoder. This delivers visual feedback using a ring of coloured LEDs, and has a push action to confirm parameter settings. It is accompanied by a small but detailed colour display, which does multiple duty as a meterbridge, numerical readout and so on.

The entire state of a Quantum interface, including all preamp settings, can be stored and recalled as a scene in the companion Universal Control software. This is available for both macOS and Windows, but note that versions of macOS prior to 10.12 are not supported.

All settings can be stored with the Universal Control software.

After a slow start, the vast majority of audio interface designers now understand that the principles of good user interface design apply to control panel software just as much as they do in DAWs and other applications. PreSonus' Universal Control is an excellent example, presenting a tidy, friendly and intuitive interface whilst offering a surprising degree of control and flexibility. The vast majority of your time will be spent in the mixer view, which for some reason isn’t the default, but is a pleasure to use once discovered. Nice touches abound, such as the Logic‑style graphical icons that can be used in addition to names on each channel, but it never looks cluttered or intimidating. (And, talking of Logic, Quantum preamp parameters can be adjusted directly from the Apple Logic mixer.)

Rather than present separate mixer panes for each output pair, PreSonus have chosen a single‑window model, with a channel for each physical input. The main mix output is hardwired to the main monitor output pair, but each channel can have up to 14 aux sends, allowing it to be distributed both to other physical outputs and to two stereo loopback buses. Adjacent to the main output fader you’ll also find a strip labelled Returns; here, you can select an output pair and hit Fader Flip, whereupon the channel fader caps will turn green and reposition themselves to reflect the level of the appropriate aux send. Digital and loopback channels can be hidden, as can sends to the ADAT channels. The Quantums’ headphone outputs aren’t independently addressable from your DAW, but can be switched to mirror either the main mixer output or any of the other output pairs.

As with most audio interfaces, there are enough monitor control features to be useful, but not enough that you won’t sometimes wish for a dedicated monitor controller. A Mute button can be repurposed as a Dim if you prefer, and there are some software‑switched options as to what the main encoder should control. It defaults to adjusting the level only at the main monitor outputs, but it’s possible to have it simultaneously adjust the level of outputs 1‑4, 1‑6, 1‑8, or of all outputs including the ADAT outs. This would allow basic level control over a surround speaker system, though any calibration would have to be carried out elsewhere. Alternatively, you can engage a speaker switching mode, in which outputs 3+4 are assigned to a second pair of monitors; there’s no option to apply a trim offset to compensate for level differences, though. The Quantums also lack other common ‘master section’ features such as talkback and mono fold‑down.

Sound Quality: To The Max

One of the most important differentiators for ‘premium’ interfaces is sound quality, at least as it is reflected in measurements and specifications. When even relatively affordable interfaces like the Focusrite Scarlett 4th Gen models offer specs that would have been considered state of the art a few years ago, it’s a challenge to stay ahead of the pack, but the new Quantums deliver some impressive numbers. Dynamic range on the line inputs and outputs is 118 and 123 dB (A‑weighted) respectively, but the most eye‑catching measurements concern PreSonus’ new Max‑HD preamp design. This has an A‑weighted Equivalent Input Noise of ‑130dBu at maximum gain, which is about as quiet as preamps get, and an absolutely colossal gain range. The digital gain control for each input spans 0 to 75 dB in 1dB steps, and on top of this, there’s also a switchable ‑20dB pad, so the difference between minimum and maximum input gain is effectively 95dB. I’m not aware of any standalone mic preamps that span such a huge range, never mind those built into audio interfaces.

The digital gain control for each input spans 0 to 75 dB in 1dB steps, and on top of this, there’s also a switchable ‑20dB pad, so the difference between minimum and maximum input gain is effectively 95dB.

Auto-Gain

The icing on this particularly well‑risen cake is that, like Universal Audio, Focusrite and Audient, PreSonus have also implemented auto‑gain. This is easy to activate from the front panel: press Auto, use the numeric buttons to select which preamps you want to include, and press Auto again. The LED ring around the main encoder will then turn red, whereupon you have about eight seconds to pick up your chosen instrument and make a suitable racket. As with some rival implementations, this makes it hard to use if you need to go and sit at a drum kit, for example. Adjacent odd/even input pairs can be linked in Universal Control so that gain is matched for stereo recording, but this can’t be done from the front panel.

The Quantums’ line‑level I/O is aligned such that 0dBFS corresponds to an analogue level of +18dBu. This is a reasonably common standard, though you may have an easier time working with professional outboard if your interface supports +24dBu line‑up levels. Modular aficionados will be pleased to learn that the line outputs are DC‑coupled, and hence capable of transmitting control voltages; the same is, however, not true of the inputs. The headphone outputs, meanwhile, are specified for +11dBu into 50Ω, which is a relatively conservative level. Their output impedance of 33Ω is also higher than the norm these days, when most manufacturers seek to present an impedance as close to zero as possible in order to drive low‑impedance headphones without loading them too much. Perhaps it was my imagination, but I found the headphone amps a little brighter than I was expecting with some cans.

Re-Amping

The most unusual feature of the Quantum HD models is the provision of dedicated re‑amping outputs. These are, as you’d expect, unbalanced, with a 100Ω output impedance, and are conveniently located on the front panel directly below the instrument inputs for channels 1+2. Slightly to my surprise, though, there is no way to mirror what’s coming in at those inputs on the re‑amp outputs. They don’t appear as destinations in the internal mixer, so you can’t create a real‑time, low‑latency send from, say, input 1 to re‑amp output 1.

The only way to address them is from your DAW, so if you want to simultaneously record the DI input and a re‑amped output, you’ll have to set up the appropriate routing in software and manage any timing offsets caused by latency after the fact. Even so, it’s a whole lot better than not having dedicated re‑amp outputs, as is the case with the vast majority of rival interfaces. These ones sounded good to me, and worked well.

Short Trips

Talking of latency, the Thunderbolt Quantums offered such blazingly fast performance that PreSonus didn’t feel it necessary to include an internal mixer. With round‑trip latencies of under 2ms achievable even at base sample rates, cue mixing could be handled perfectly well in your DAW. In fact, as long as you avoided using plug‑ins with look‑ahead, round‑trip delay times through the DAW could be lower than was possible using the ‘low‑latency’ mixers in some interfaces, including PreSonus’ own USB3 Studio 192.

I was pleasantly surprised to discover that Reaper reported input and output latencies of just 1.4 and 1.8 milliseconds respectively for a 32‑sample buffer.

Given that the new Quantums have abandoned Thunderbolt for USB, and that they do have an internal mixer, I was fully prepared to report a backward step on the latency front. Nearly all USB interfaces nowadays use Apple’s built‑in Core Audio driver; with a 32‑sample buffer, this usually delivers round‑trip figures of around 7ms at 44.1kHz, plus whatever is added by the internal mixer. That’s unproblematic in most circumstances, at least as long as your DAW session leaves enough CPU resources free to handle the processing overhead of running with the lowest buffer size, but it’s still significantly less good.

I was expecting the new Quantums to offer comparable performance, but I was pleasantly surprised to discover that Reaper reported input and output latencies of just 1.4 and 1.8 milliseconds respectively for a 32‑sample buffer. Re‑recording an audio click showed that although this reported 3.2ms round trip latency was not perfectly accurate, it was only out by about 14 samples, this presumably representing the delay through the mixer. A round‑trip latency of about 3.5ms is thus achievable on macOS even at base sample rates. This may not be quite as good as the Thunderbolt Quantums, but it equals or betters pretty much every other interface I’ve tested, including other Thunderbolt models. Full marks to PreSonus’ engineers for not being content with ‘good enough’ on this front.

In practice, then, I think the only retrograde step from the Thunderbolt Quantums concerns I/O count. Thanks to its dual ADAT ports and S/PDIF I/O, the HD8 offers a total of 26 physical inputs at base sample rates. That’s as good as all of its direct rivals, and more than enough for most purposes; moreover, I’m told that if you expand an HD8 using another HD8 over ADAT, the second unit can be remote controlled from within Universal Control. It’s a shame to see the Quantum 4848’s market niche stand empty, but I’m not going to view PreSonus harshly for this. Practically every manufacturer has abandoned Thunderbolt at this price point, and factors such as component costs and certification headaches are out of their control.

The second‑generation Quantums should be judged not against their Thunderbolt predecessors, but against rival products. And they stand up very well indeed.

Conclusion

Ultimately, the second‑generation Quantums should be judged not against their Thunderbolt predecessors, but against rival products. And they stand up very well indeed, with particular highlights being the Max‑HD preamp design, the unusually good low‑latency performance, the HD models’ dedicated re‑amping outputs — and their highly competitive pricing. You also get a full year’s worth of PreSonus’ Studio One Professional DAW thrown in for free. Rather than striking out on their own, PreSonus are now taking other interface manufacturers on at their own game, and making a very good fist of it.

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