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RME Digiface AES

USB Audio Interface By Hugh Robjohns
Published June 2023

RME Digiface AES

Originally developed for a German broadcaster, the Digiface is now available to everyone.

RME’s Digiface range of USB audio interfaces probably needs no introduction to regular readers of Sound On Sound, but in essence these units currently all provide straightforward digital format conversion to/from USB. For example, the company’s Digiface Dante, Ravenna and AVB models each provide 64 channels of audio‑over‑IP connectivity in different flavours — and both the Ravenna and Dante units also include another 64 MADI channels of I/O. For ADAT interfacing, the Digiface USB offers a quartet of Toslink connectors for 32 channels of I/O (am I alone in thinking Digiface ADAT would be a more descriptive name?).

The newest addition to this Digiface family is the Digiface AES — although it does rather more than you might expect from its name. When asked to review this new model I was expecting an uncomplicated 16‑ or 32‑channel AES3 to USB interface as a logical extension to the Digiface family. However, it turns out that the Digiface AES is really a fully‑featured 14‑input, 16‑output USB audio interface, and something much more closely resembling a Fireface product, really. In fact, comparing its capabilities and functionality I’d say the Digiface AES sits comfortably between the Babyface Pro FS and the UCX II.

As a quick overview, then, the Digiface AES features two mic/line analogue inputs and two balanced analogue line outputs, plus a stereo headphone output. On the digital side it possesses coaxial S/PDIF in and out, ADAT in and out (reconfigurable as optical S/PDIF), MIDI in/out and... oh yes, a stereo AES3 I/O as well.

Naturally, the unit enjoys RME’s excellent SteadyClock FS technology, and also includes two channels of sample‑rate conversion assignable to a selected stereo digital input, allowing a non‑synchronous digital source to be mixed with other clocked digital sources. It is also fully class compliant, can work in a standalone mode, is bus‑powerable, can be controlled from RME’s ARC, and comes with TotalMix FX and DIGICheck applications. The RME driver allows up to three supported interfaces to be used together (provided they are clock synchronous).

If the extensive overlap of facilities with existing products seems odd, it’s because this new Digiface AES was designed and built specifically as a custom product for a large German broadcaster whose requirements included easy connection to AES equipment, with bus‑powering, mic inputs and high‑quality monitoring. It wasn’t originally intended to be a ‘mass‑market’ product at all, but someone at RME saw the potential in it as a consumer interface and so it is now available, albeit at a price which reflects its slightly specialist origins (and possibly smaller‑scale production run).

Controls & Connectors

Looking at the hardware in more detail, the Digiface AES is built to RME’s familiar format, in a 1U high, half‑rack‑width chassis. The left side of the front panel features a pair of combi XLR mic/line inputs with the control section on the right comprising a compact colour display, value dial and four direct menu access buttons. There are no high‑impedance instrument inputs, but a single quarter‑inch headphone socket is located within the blue control section just right of centre. Both the main XLR and headphone outputs are DC‑coupled and can be used for scientific purposes or to create CV signals for synth modules. From an audio perspective, DC‑coupling also removes the LF phase shift introduced by coupling capacitors and some argue this is audibly beneficial.

While the Digiface AES was designed to be bus‑powered, it also features a bayonet‑locking power socket for standalone use or where a host computer struggles to supply enough juice. A double‑insulated, universal voltage, line‑lump power supply is included, accepting a figure‑8 (IEC C7) mains lead and providing a 12V/2A DC output.

Other rear‑panel facilities include a Kensington lock slot, a USB 2.0 B‑type socket for connection to a host computer, and a mini‑DIN connector providing MIDI in and out (a breakout cable terminating in a pair of full‑size 5‑pin DIN sockets is included). There is no word‑clock in/out provision.

The Digiface AES’s back panel features a USB‑B port, a socket for the breakout MIDI I/O, ADAT and S/PDIF I/O, and AES and analogue audio I/O on XLR sockets. A pair of combi XLR inputs and a headphone socket are found on the front panel.The Digiface AES’s back panel features a USB‑B port, a socket for the breakout MIDI I/O, ADAT and S/PDIF I/O, and AES and analogue audio I/O on XLR sockets. A pair of combi XLR inputs and a headphone socket are found on the front panel.

The digital audio I/O encompasses a pair of RCA phono sockets for coaxial S/PDIF in/out, with a pair of Toslink optical ports directly above configurable either for ADAT or optical S/PDIF connections. Two XLRs provide the AES3 I/O, and two more deliver the analogue line outputs.

All standard sample rates are supported between 44.1 and 192 kHz over the AES3 and both flavours of S/PDIF, while the ADAT interface can use S/MUX protocols to transfer four channels at double rates, and two at quad sample rates. AC3/DTS‑encoded surround material carried on an S/PDIF connection can be passed straight through to a home theatre decoder, if desired, although the unit’s sample rate must be set to 48kHz.

In terms of technology the digitally controlled mic/line preamps are the same transformerless design developed for the Babyface Pro FS, with AutoSet automatic gain adjustment, individually selectable 48V phantom power, a manual gain range of 75dB (in 1dB increments), a relay‑switched ‑10dB pad, and an EIN figure of ‑129dBu (A‑weighted, 150Ω, 20Hz‑20kHz). The mic input impedance is 2kΩ (rising to 5.3kΩ with the pad engaged), and the maximum mic input level is +18dBu (with the pad).

Line inputs present a 12kΩ impedance, enjoy the same gain range, and accept a maximum input level of +24dBu. When selected, phantom power is only present on the XLR terminals, not the inner TRS socket. Usefully, every physical input and output also features a fully‑featured three‑band parametric DSP EQ section.

The electronically balanced main outputs are switchable to any of RME’s three standard operating levels, aligning peak digital level (0dBFS) to either +19, +13, or +4 dBu (all from a 300Ω source). I was surprised that RME haven’t included a +24dBu output level option (which is now offered on other recent RME interfaces). However, the +19dBu option obviously meets the needs of German broadcasters so I presume a +24dBu mode wasn’t considered necessary in this custom product. There’s certainly more than enough output level to drive active monitor speakers, though, which is what most users would probably need them to do.

A point worth noting from the generously comprehensive 104‑page manual is that when driving an unbalanced destination the XLR pin 3 (cold) terminal should be left floating. Shorting pin 3 to ground — as most ready-made unbalanced adaptors do — apparently results in increased distortion.

The headphone output is switchable between high and low power modes equating to a maximum signal voltage of either +13 or +7 dBu, delivering 160mW per channel into 32Ω phones (with 0.1% THD and from a 5Ω output impedance). For comparison, the UCX II provides a beefier 210mW per channel, but I didn’t have any practical issues in the studio with headphone volume using AKG K702s or Sennheiser HD600s.

As usual, I ran my standard AES17 dynamic range test on the Digiface converters, as I find this to be a fair indicator of overall technical performance. My measured results are very similar to the published specs, with a figure of 119.8dB (A‑weighted) for the D‑A converter, which is an excellent result, and similar to other recent RME products.

For the A‑D stage the measured figure was 114dB (A‑weighted), which is similar to the Fireface UCX II but 5‑6 dB lower than more recent RME products (for example, the AIO‑Pro measured 119dB and the 12Mic 120.4dB. In terms of relative performance, the Digiface AES’s A‑D dynamic range lies roughly midway between that of the Audient ASP880 and the Ferrofish Pulse 16 — so certainly not bad by any stretch. RME tell me that the limiting factor in this dynamic range measurement is the mic preamp itself — the A‑D converter could manage 8dB more range — but apparently ultra‑wide dynamic range through the analogue inputs was not a customer requirement when designing the Digiface AES.

Talking of converters, the devices employed in the Digiface AES are ESS Sabre types (ES9842Pro A‑D and ES9080Q D‑A), both configured with minimum‑phase filter topology (like many other RME products). This delivers a much shorter latency than traditional linear‑phase designs, with only 0.07ms (3 samples) for the A‑D and 0.38ms (17 samples) for the D‑A, at a 44.1kHz sample rate. For comparison, most conventional converters (using linear‑phase filtering) introduce more like 0.75ms of filter latency at base sample rates.

Operating the Digiface AES is much the same as the Fireface models, with most things being configured through the front panel, while others are set using the TotalMix FX application on the host computer. Different I/O configurations and setups can be saved to six preset memories, allowing instant recall for different recording or playback requirements, and these can also be accessed in standalone mode. In other words, handy setups can be pre‑programmed for use away from the computer, and the (hardware‑based) TotalMix functions can be controlled remotely via MIDI, if required, which is a nice feature in standalone mode. As you would expect, the front‑panel data knob not only accesses key configuration parameters, but also serves as a volume control for both the main analogue balanced outputs and the headphone output, switching between them by pressing the knob.


Given the immense capabilities of the Digiface AES, I remain surprised the product isn’t marketed within the Fireface interface family. After all, it looks more like a Fireface than any of the current Digiface models, it has analogue I/O, and its facilities overlap the existing UCX II to a great extent, even sharing the same complement of digital I/O.

The very low A‑D converter latency and bus‑powering will undoubtedly be a big plus for many users.

That said, the Digiface AES has distinct features that set it apart from the UCX II, such as its two‑channel sample‑rate converter allowing two non‑synchronous digital sources to be mixed together, and its superior D‑A performance. The very low A‑D converter latency and bus‑powering will undoubtedly be a big plus for many users, too.

The UCX II’s strengths lie in having eight analogue inputs and outputs, with high‑impedance instrument facilities. It also has word‑clock in/out to help with external equipment synchronisation, a more powerful headphone amplifier, internal DSP allowing reverb and echo in TotalMix FX, DURec recording direct to a USB drive, and it also costs significantly less than the Digiface AES too.

So why would you choose the Digiface AES over the UCX II (or Babyface Pro FS)? That’s a tough question, just because they overlap in capability so much, but a choice would come down purely to specific application priorities and requirements. We’re very lucky to be offered such alternatives!


  • Bus‑powered.
  • Sample‑rate converter allows mixing of non‑synchronous digital sources.
  • Remarkably low analogue latencies.
  • Excellent D‑A performance.
  • Three‑band parametric DSP EQ on every channel.
  • Standalone operation.
  • TotalMix FX.
  • DC‑coupled outputs.


  • No high‑impedance instrument inputs.
  • Price.


A well‑featured compact interface with a unique selection of facilities to set it apart from other RME interfaces.


£1819 including VAT.

Synthax Audio +44 (0)1727 821870.

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