Review: Presonus Quantum Thunderbolt Interface
Want to leave latency in your dust? Quantum will take you on a very quick roundtrip.
As I always state when reviewing Presonus gear, I’m a bonafide fan of the company’s products. Since 1995 the company has established itself as an innovative player in the semi-pro audio recording and production arena. To be honest, Presonus kicked off with some pretty chunky audio interfaces. Initial Presonus interfaces, inevitably named ‘Fire something-or-other’, had front panels milled from blocks of aluminium. They felt like you could have thrown them down a staircase and they’d bounce back to work like Lee Majors (’80s TV reference for all you youngsters).
First generation Presonus interfaces are difficult to come across these days. While they worked, and connected to a computer with a Firewire cable, they didn’t use the standard Firewire protocol. Instead, Presonus utilised Yamaha’s luckless mLan protocol (see sidebar). mLan was clever in that it could transport audio, MIDI data, and wordclock over a single Firewire cable, but in true Yamaha fashion the driver and patching software was archaic and clunky. Like the rest of the industry, Presonus moved on to the more reliable Firewire protocol, while updating its manufacturing processes to deal with a great numbers of devices. This is also when the company moved away from the chunky aluminium front panels in favour of the silver and blue plastic front panels.
Still, Firewire has its limitations. Firstly, there’s a limit to its bandwidth, and secondly, Firewire ports are becoming scarce. Sure you can use adaptors, but then you’re hobbling the potential speed of the Thunderbolt port to three Gigabits per second (FW400) and 6 Gb/s (FW800) — even USB 3 and 3.1 will outstrip Firewire. Thunderbolt 1 and Thunderbolt 2 speeds are rated at 10 and 20Gb/s respectively. That’s about 2.5 gigabytes per second; it’s fast. When it comes to audio interfaces not only does this mean more channels, it also results in much better latency results. This is precisely the point with Presonus’s latest interfaces.
The Presonus Quantum and Quantum 2 both take advantage of Thunderbolt 2 for data transport. They’re a vastly quicker machine than the previous USB 3.0 Studio 192. Both models are ‘stackable’ in that additional Quantum interfaces can be daisy-chained via Thunderbolt for up to 80 or 96 channels over four units, something Firewire promised but never really delivered. The Quantum 2 is the fledgeling of the family, with four mic/line inputs and four TRS outputs — additional I/O must be attained via ADAT-based expanders. The bigger brother Quantum offers eight mic/line inputs and eight line TRS outputs, again with expansion via ADAT optical. Dual SMUX is supported with both for 96k recording across all available inputs — 16 ADAT channels at 44.1/48k, and eight at 88.2/96k.
The Quantum units also represent Presonus’s first shift away from its signature design and blue/silver colour scheme — the Quantum units are black; how very rock. I’m all for black on black, it’s flattering I’m told, however, the new skin is no doubt to differentiate the Quantum Thunderbolt 2 services from Presonus’s Studio 192 and Studio 192 Mobile. To be frank, there’s no huge physical difference between the Studio and Quantum designs. The only real change appears to be the addition of five-pin MIDI ports on the Quantums, which makes you wonder why MIDI wasn’t included on the Studio 192 models. MIDI uses next-to-no bandwidth, and a single input and output is plenty nowadays with many users using virtual instruments. We can’t change history, so I’ll simply point out the MIDI ports as a damn good call.
NEED TO KNOW
BIGGER THAN 192
So apart from MIDI ports and a flashy black finish, are there any real advances with the Quantum interfaces, or are they simply revamped Studio 192 units with Thunderbolt 2 ports? Let’s look inside.
We’ll initially have a quick look around the ports and operational procedures with the flagship Quantum model I’ve been sent. The rear of the single rackmount unit presents six XLR/TRS combo inputs and eight TRS ¼-inch outputs. These are flanked by TRS ¼-inch main outputs followed by S/PDIF coaxial in and out and wordclock in and out. Next up are two sets of ADAT optical I/O for either 16 or eight additional sets of I/O — SMUX compatible as mentioned. Above these are two Thunderbolt 2 ports, so the same connector as a Mini DisplayPort. The first for connection to the computer, the second for chaining additional Quantum units or Thunderbolt devices. Beyond that, there’s the MIDI I/O and a power connection for the wall-wart power supply.
Out front are two additional combo connectors that can accept high impedance signals from guitars. As for the sound of the XMAX pres, as I mentioned in my review of the Studio 192, I have a set of these these Class-A units myself — I like them. They distort guitars quite well. All eight mic inputs have individual 48V power.
Closely mimicking the Studio 192, the Quantum includes control room features, with the idea that additional monitors connect via any pair of the eight TRS output jacks. The front panel has a large main output level control pot, and a single gain level control flanked by left/right buttons. The left/right buttons scroll through the eight preamp input gains, and while you’re set to control the gain of a particular preamp you can also hit the 48V button to send phantom power to the selected pre. A ninth ‘c’ setting adjusts gain for the built-in talkback mic. Unlike the Studio 192 the built-in talkback is your only option — you can’t use an external mic connected to one of the preamps. The preamp levels, and individual 48V power for each mic pre can be set from within your DAW using MIDI controller information, and you can snapshot your preamp levels between projects, just like the Studio 192. An inclusion unique to the Quantum is how the eight line outs and main outs are DC coupled. This allows triggering and control voltage (CV) signals to be sent out to analogue gear like synths and sequencers — a lovely touch — much like the MIDI inclusion.
DONE WITH DSP
As with most audio interfaces, Presonus supplies a free app for settings such as monitor paths, headphone routing and ancillary options such as how talkback systems operate. Presonus’s solution for the Quantum devices is Universal Control, which looks a lot prettier since I last ran a Presonus interface application. Universal Control primarily gives you software control over the preamps, setting headphone output sources, and S/PDIF behaviour, along with metering and a very nice spectrum analyser. Here’s where I noticed a major difference between the Studio 192 devices and the Quantums — there’s no onboard DSP, and no internal mixing.
I initially expected Presonus to have included its ‘Fat Channel’ signal processing — the same group of DSP tools the company has used throughout its StudioLive console and rack mixers, and the Studio 192 interfaces. This omission may steer potential buyers away from the Quantum, especially if they’re hoping to use the Quantum in live recording situations, it may not. It would depend greatly upon whether the host computer can supply enough processing via the DAW in use. It’s horses for courses, but without an internal mixer and mixer software you’ve got to use a DAW to alter bussing, inputs and outputs.
Notwithstanding, there’s a very good reason Presonus has given DSP the boot with the Quantum, and that is to keep the processing path between analogue input to analogue or digital output as sleek and as fast as possible. Being the Thunderbolt device that it is, the Quantum’s emphasis is on super low latency, and super low it is. At 96k and with a buffer setting of 32 in Logic Pro X the resulting roundtrip latency is a meagre one millisecond. With a quick playback and recording of a spike at these settings the latency came out at around 1.38ms. That’s extremely low, and virtually undetectable in a live monitoring situation. Bump things down to 44.1k and the roundtrip comes in at two milliseconds. Again, exemplary latency in live situations. If we want to get silly about this, at 192k we’re seeing roundtrip latency of 0.8 milliseconds. These speeds are up there with the best, from Apogee through to Universal Audio’s Thunderbolt interfaces.
A LOT FOR A LITTLE
Presonus hasn’t only provided impressive latency in the Quantum units, the company has also improved marginally on some audio specifications over last year’s Studio 192. The incumbent X-MAX mic preamps offer EIN of <131dBu over <128dBu, yet frequency response is 20Hz to 40kHz as opposed to the Studio 192’s 10Hz to 40kHz. Dynamic range of the instrument inputs is >106dB (A-weighted) compared with the Studio 192 at >110 dB, with the line inputs greatly improved at >118dB (A-weighted) compared with >114dB. Main monitoring and line outputs also see a marked improvement. Dynamic range is >118dB as opposed to the Studio 192 at >112dB and the total harmonic distortion is reduced from 0.005% to 0.0035%. ADC and DAC dynamic range is 120dB, above that of the Studio 192’s 118dB. The resulting audio quality is impressive, and goes to show there are always improvements in audio quality making their way into more affordable interfaces.
Speaking of audio quality, there’s nothing to dislike with the Presonus Quantum. In fact, there was little to dislike with the Studio 192 models. Presonus hasn’t rested on its laurels and has come up with an extremely competent interface. Going back even as little as five years would have seen you paying upwards of $5k for similar specifications.
So who’s going to find the Quantum the ideal interface solution? I’d imagine those looking for stellar quality I/O and needing an all-in-one solution. Super-low latency, MIDI, DAW programmable and saveable preamp gains, macOS and Windows compatibility. Throw in the ability to trigger CV-based analogue instruments, and this could be the ideal interface for the analogue synth brigade. Those needing internal mixing and direct monitoring may not find the Quantum to be their cup of tea, but with such low latency I can’t imagine this to be an issue. At a paltry $1500 you’re getting a lot of functionality: superb recording and monitoring conversion, with a control room system and talkback. It really deserves a place alongside far more expensive devices. The Studio 192 was great, but the Quantum is so much more.