A-D & D-A Converters

Converters / Clocks

Published November 2024

Arturia’s ADAT expanders are a useful and affordable option for anyone who needs more I/O.

Not even misplaced ’90s nostalgia is likely to revive Alesis Digital Audio Tape as a recording format in 2024, but the ADAT Lightpipe digital audio transfer protocol remains ubiquitous. A single optical cable allows convenient one‑way transfer of up to eight mono channels of 24‑bit audio at base sample rates, or four at 88.2 and 96 kHz. It’s easy to use, cheap to implement and scaleable enough to suit most situations.

One of the original use cases for ADAT expansion was to interface digital recording systems with analogue mixing consoles. Many older A‑D and D‑A converters with ADAT ports thus operated purely at line level on the analogue side. But it now seems that the main application for ADAT connectivity is to add extra standalone mic preamps to a computer audio interface. Consequently, there are now very few ADAT expanders with only line‑level inputs, and almost none that provide only outputs. If you need such a thing, you could seek it out second‑hand, but the audio performance of a 20‑year‑old converter won’t match what’s possible even in budget gear today.

Back In Black

With the AudioFuse X8 In and X8 Out, Arturia have revived the line‑level ADAT expander. As the names imply, these two 1U, half‑rack units respectively offer eight channels of A‑D and D‑A conversion. Each of them boasts two optical ports, allowing the full channel count to be maintained at higher sample rates as long as the connected device plays ball, and a BNC word‑clock input with associated termination switch. Analogue signals enter the X8 In and depart the X8 Out on balanced quarter‑inch jacks. As these units are standalone converters rather than audio interfaces, bus powering is not an option, so both come with wall‑wart power supplies that have locking DC connectors. Both also come with optional widgets attached to the base that can be detached and used as rack ears.

One of the reasons why Arturia have decided the time is right to revisit the line‑level converter is that a new use case has emerged since the heyday of the Mackie 8‑Bus and Fostex VC‑8. Many people are now generating control voltage and gate signals from software to control modular synths. For this to work properly, a converter or interface needs two features. It has to be able to generate or accept a voltage swing of at least ±5V; and it has to be able to work with unchanging DC voltages as well as with conventional audio signals. Both the X8 In and X8 Out are calibrated such that a full‑scale digital signal corresponds to a +24dBu analogue input or output, which in turn equates to a peak voltage swing of more than ±17V, so there are no worries on the first score; and they are DC coupled, meaning that they are quite happy to engage with steady‑state non‑zero voltages.

These new additions to the AudioFuse line also fully exploit the power of modern converter technology. Whereas the original ADAT barely filled the theoretical dynamic range of a 16‑bit signal, the X8 In and X8 Out offer 119 and 120.5 dB respectively, with equally impressive THD+Noise figures.

Things are pretty much as you’d expect round the back of the X8 In: analogue audio comes in, digital audio comes out.

Rated X

The X8 Out is the simpler of the two devices. Apart from the power button at the top right of the front panel, it has only a single control: a Sync button to select the clock source from ADAT, ADAT S/MUX and word clock. The X8 In is somewhat more complex. The Sync button in this case determines whether the X8 In should be clock master or follow an incoming word clock (there’s no ADAT input, so that’s not an option). A second button labelled Clock sets the sample rate if the X8 In is acting as master; when it’s clocked externally, sample rate changes happen automatically, but the LED for the old sample rate flashes until you hit Clock to ‘accept’ it. I’m not sure why this is really needed, since there’s no obvious alternative course of action!

The X8 Out’s rear panel is pretty much identical to the X8 In, the only difference being that digital audio goes in and analogue audio comes out.

The left‑hand side of the front panel, meanwhile, sports a tiny LED for each input, and four buttons. In normal use, the LEDs offer basic signal metering, turning green in the presence of a signal above ‑60dBFS, orange when the input level hits ‑6dBFS and red when clipping occurs. The manual rather daringly recommends setting levels so that the loudest peaks register orange; on anything at all dynamic, I personally would want to be a bit more cautious, and would like the option to have the LEDs turn orange at ‑12dFBS.

The four buttons are used to engage what Arturia call ‘pads’. This is a confusing description for what is essentially the ability for each input to be switched between nominal +4dBu or ‑10dBV operating levels. With the ‘pad’ switched on, the inputs can accept peaks of up to +24dBu; disable the pad and you lose 12dB of that headroom. This is done by stepping left and right through the input list with the arrow buttons and double‑tapping the Pad button. Pad settings for adjacent pairs can also be tied together using the Link button, which seems a little unnecessary.

I have no doubt that there still are many people out there who would like to expand their computer I/O but don’t want or need additional preamps, and the X8s provide a cost‑effective, high‑quality way to do just that.

Conclusion

After a slow start, Arturia’s AudioFuse range has really come into its own in the last few years. They’ve developed superb mic preamps, and as befits a manufacturer of desirable synths, they’ve also thought about the needs of electronic musicians with products like the recent AudioFuse 16Rig. The X8 In and X8 Out are the first members of the range that aren’t themselves interfaces, but they certainly maintain the standard. I have no doubt that there still are many people out there who would like to expand their computer I/O but don’t want or need additional preamps, and the X8s provide a cost‑effective, high‑quality way to do just that.

Their arrival at my studio prompted me to finally make a change I’d been planning for a while. I ordered BNC cables and T‑adaptors in order to distribute word clock to all the audio hardware that supports it, including the X8 In and X8 Out. They were equally happy to work in this configuration as they were to clock over ADAT. Everything worked first time, sound quality was exemplary, and my setup had eight ins and outs that weren’t there before. If you’re looking for line‑level ADAT expansion and you don’t need the full 16‑in/16‑out configuration offered by something like the Ferrofish Pulse 16, the X8s may well be your only option — and they’re definitely a good option.

Summary

The X8s are simple but effective line‑level A‑D and D‑A converters with good specs and pricing that could be considered highly competitive — if they had any obvious competition!