This most hybrid of devices does far more than just put A‑D/D‑A conversion into a 500-series chassis. In fact, it could even make you reconsider how you use your studio...

Launched last year, Cranborne Audio's Camden 500 mic preamp was a wonderful debut product: boasting stellar technical performance and some novel processing options, it prompted our Technical Editor Hugh Robjohns to conclude (https://sosm.ag/cranborne-camden500) that "this is how I'd design and build a quality preamp." Announced at the same time as the Camden 500 were the 500R8 (reviewed here, and from hereon 'R8') and the 500ADAT, and these actually piqued my interest more, since both do something I've long wanted to see: they add A‑D/D‑A conversion to a 500-series chassis. As its name implies, the 500ADAT's digital interfacing is via ADAT, but the R8 adds stereo S/PDIF and multi–channel USB audio, as well as a low-jitter (Cranborne claim <0.5 picoseconds) master clock, to create an ambitious audio interface. But the digital side of things is only the start, as Cranborne have managed to pack much more into these devices, including a high-quality analogue summing mixer, monitor control facilities, and some novel analogue routing functions.

Possibilities

The R8 is a 4U-high, 19-inch rackmountable 28–in/30–out USB 2.0 audio interface with a built-in eight-slot 500-series chassis. Other than two TRS jack headphone sockets and the 500-series slots, all the analogue and digital connectors are on the rear. The first eight interface channels are assigned to the 500-series slots, whose XLR inputs and outputs are accompanied by a TRS insert point that sits between the module slot and the A‑D converter in the signal path. (Without a 500-series module, the XLRs can function as regular analogue line-level I/O, courtesy of a module bypass switch on the backplane). Two more interface channels access the stereo AES3-compatible coaxial S/PDIF I/O, and 16 are mapped to the optical ADAT streams — two pairs of Toslink connectors can carry 16 channels each way at 44.1/48 kHz, or eight channels via S/MUX at 88.2 or 96 kHz (192kHz support for four channels is planned in a firmware update in the near future). The remaining two USB inputs receive the analogue mixer's output, and the remaining USB outputs transmit two stereo DAW playback busses. The clock is accessed via the usual BNC connectors.

The idea of all that ADAT I/O is that you're able not only to hook eight 500-series modules up to your DAW, but also that you can connect a 500ADAT to an R8 to increase both the analogue I/O count and the system's capacity as a 500-series host. If you're happy with 44.1 or 48 kHz, it would be possible to add two 500ADATs, giving your DAW access to 24 channels of 500-series preamps, effects or processors with only a USB 2.0 cable and four ADAT 'lightpipe' optical cables. Alternatively, you could hook up any ADAT-equipped mic preamps or line-level converters to increase the analogue I/O count.

The possibilities don't end there, though. If you really wished — and had the financial means to make it happen — you could attach further 500ADATs (or other eight-slot 500-series chassis) to the system via the insert points on the first 'set', and start to construct something more akin to an analogue console, but one with the preamp, EQ and compressor stages of your choice on each channel.

The build quality seems very good. The powder-coated metal case is strong and remains rigid even before you screw in any 500-series modules. The back-panel connectors feel secure, and all of the switches and pots on the front feel suitably robust. That you can change the orientation of the rack ears for use as sturdy carry-handles is a nice touch, too, and will increases the R8's appeal as part of a location recording rig.

The 24V 5A power supply is an external 'line lump' switch–mode type, capable of accepting AC mains between 100 and 240 Volts. Each 500-series slot can draw 250mA, and there's a little headroom on top. I know some aren't fond of external PSUs but it's the right decision in this case. I mean 'case' quite literally, since there's no room inside this one to accommodate a PSU — that would have required a 5U or a deeper 4U chassis, and would have added weight to what, when fully loaded with transformer-balanced modules, is already rather a heavy device. The PSU's four-pin connector locks securely in the socket on the chassis; you can be confident that it won't get pulled out accidentally. This PSU features linear regulation on the DC inlet, and there's linear regulation on each 500-series slot of the chassis too, to prevent power noise and intermodulation distortion making its way onto the audio rails.

CAST Away!

Hopefully, that's whetted your appetite... but I've only really scratched the surface. Cranborne have also invented a new system for sending mic/line-level analogue audio signals over network cable. Called CAST (Cat5 Analogue Snake Transport; a backronym, I'll wager!), it conveys four channels (two sends, two receives) up to 100m over CAT5e, CAT6 or CAT7 cable, all of which are less bulky than traditional audio cables, not to mention less expensive, and are readily available.

To cater for this protocol, the R8 and the 500ADAT have five RJ45 connectors on the rear. The first four provide alternative inputs and outputs for channels 1-8, and the big idea is that Cranborne's forthcoming CAST 'expanders' will allow you to send a stereo monitor mix to an artist, and receive two channels back from them (for example, from a mic and DI, or a pair of mics). One of the two expanders already announced includes a headphone amp, but I believe a wider range of CAST expanders is likely to follow. I suppose you might think of it as a neat, low-hassle, and cost-effective alternative to networked digital audio such as Dante and AVB for smaller-scale installations, such as a small multi-room recording studio — and, being analogue, obviously there's absolutely no latency involved.

A fifth such connector is labelled 'CAST Link', and is reserved for two-way communication between the 500R8 and a single 500ADAT unit. It routes the 500ADAT mixer's stereo bus signal to the 500R8, where it is merged with the 500R8 mixer's summing bus at unity gain — thus creating a 16-channel summing mixer. (The mix bus, whether the standard eight-channel one or, augmented by a 500ADAT, a 16-channel one, is available to interface channels 9-10). It also routes the aux monitor signal — which can draw on that 16-channel mix and the DAW playback — from the 500R8 to the 500ADAT. So for an end user, this single cable connection should result in a more seamless way of combining the two devices than using ADAT alone. Not having a 500ADAT at my disposal, I wasn't able to test this properly, but it appears a very elegant solution.

That you can change the orientation of the rack ears for use as sturdy carry-handles is a nice touch, and will increase the R8's appeal as part of a location recording rig.

Mixing & Monitoring

The controls for the 500R8's analogue mixer occupy the space beneath the 500-series module slots. Each channel has a source selector — a chunky metal toggle switch which conveniently protrudes beyond the front panels of any modules you've installed. The available sources are the channel's CAST input, the 500-series slot, and the corresponding USB output from the DAW. Between each channel's controls is a smaller toggle switch, labelled Chain, which allows you to pass the signal from one module to the adjacent one — to create a channel strip, for example, without requiring any manual repatching.

Beneath the switches are two pots, one for the channel level and the other for pan. The latter is a continuous rotary pot, with a centre detent, which I prefer to the LCR switches found on many stand–alone summing mixers. There seems to me to be bags of headroom available on the mixer, which sounds lovely and clean — just as it should. And if you do want character, then you have the 500-series slots to play with.

Over on the right-hand side of the front panel, you'll find the monitoring controls. In the lower half of that panel are four knobs, the lower two of which determine what you hear on the main monitor outputs. The smaller knob on the left blends between the stereo out from the DAW and the analogue mix-bus signal, while the larger knob sets the monitor level. A small toggle switch determines which of the two USB DAW signals is heard, and the idea is that 'DAW 2' could be used to set up a click track or cue mix in your DAW. But there's another twist — a pair of analogue line-level inputs on TRS jacks intended for use with external DAWs/converters (but which could be used to monitor any line-level source). This is labelled DAW 2 and is summed with the USB DAW 2 signal in the monitor mix when DAW 2 is selected as the source. Another pair of knobs performs a similar function for the aux bus, the primary intended purpose of which is to deliver a cue mix to the performer.

A number of different physical outputs are associated with these four knobs. On the rear are two pairs of monitor outputs, one on XLRs, the other on TRS jacks. The stereo aux output is on another pair of TRS jacks. Also, the monitor and aux signals are delivered to the corresponding front-panel quarter-inch headphone jacks. The headphone amps provide more than enough 'welly' for my Sennheiser HD650s. Much more in fact — I doubt you'd have problems driving any headphones with them but, more importantly, they sound good. There are also dual quarter-inch jack outputs for the stereo mix-bus signal, and a talkback mic input, for which 48V phantom power is permanently on (which will be fine for moving-coil dynamics and capacitor mics... I'm not aware of anyone who likes to use a vintage ribbon for talkback!).

Returning to the front panel's right-hand section, the upper half sports more controls. At the top is a stereo LED peak meter, with 14 LEDs per channel. This is configured such that signal presence is indicated by the leftmost LEDs, with the rest showing increasing levels up to 0dBFS: LEDs are green until the final three, two of which light amber (at -3 and -1 dB) and the third red (at 0dB). Yes, I did say dBFS — while this is an analogue meter, it's calibrated to show the level that will hit 0dBFS on the converters and thus in your DAW. There are no indicators for the individual channels; you'd have to rely on the 500-series modules or your DAW if you want that facility, but I didn't miss it.

Immediately below the meter are various buttons. Currently, these are all single-action but, intriguingly, I gather that it would be possible via a firmware update for Cranborne to make these perform different functions for momentary or longer-held presses. We'll have to wait to see if anything happens there, but in the meantime we have: a speaker A/B selector (pushing switches, pushing again switches back); a mono button (dual mono, in both speakers, and again push once to switch, push again to switch back); mute and dim buttons (again, these toggle the status, and the dim button attenuates the monitor level by 15dB); and a talkback button, which routes the talkback signal to the aux bus and the CAST outputs. The talkback level is set by an adjacent knob (the talkback preamp gain is fixed at +30dB), and this button automatically engages dim, while ducking the rest of the aux bus by 9dB. The only other control on the front panel is the power button, which glows blue when the R8 is on. I'm pleased to see this on the front panel, as that makes it much more convenient to power down and reboot when installing/uninstalling 500-series modules than the rear-panel switch found on some other rack units.

USB Interface

The whole ensemble hooks up to your computer via USB 2.0 (no USB cable is included — to reduce waste, as most people will have suitable cables already). For Windows systems, you'll need to install Cranborne's ASIO driver (as used by Hugh for his technical performance tests — see box) but if you're on a Mac, as I was during the review period (2018 MacBook Pro running MacOS 10.14.1, connected via a Mokin USB-C hub), or iOS, it's recognised automatically as a Core Audio device, and configuration is via the OS's Audio & MIDI Settings app. (Speaking of which, the only I/O I've so far failed to mention are the rear-panel MIDI in and out, on the usual 5-pin DIN sockets.)

The USB interface will, as set out above, offer access to 28 inputs and 30 outputs in total. I say "will", because on this review unit the S/PDIF hardware had been fitted but was not yet accessible; a firmware update will implement this functionality soon (hopefully by the time you read this). Similarly, as mentioned earlier, 192kHz S/MUX support for ADAT will arrive soon.

Using the R8 as an interface with my Mac was a breeze. The channel layout is intuitive, with the first eight channels corresponding to the eight 500-series slots, for example, and the main stereo DAW output being suitably named by default.

The converters sounded really nice to my ears — very clean, with good stereo imaging. The latency performance was subjectively good too, and that impression was again backed up by the measurements in Hugh's 'Technical Performance' box. (I managed to achieve stable performance on my Mac with a 32-sample buffer at 48kHz.) Of course, for many users the latency question will largely be moot, since they can use the analogue mixing and monitoring facilities when tracking; it will be of more interest to those who play virtual instruments 'live'.

Getting Hands On

While my daydreams inevitably considered how I might build a 500-series console out of the R8 and a number of 500ADATs, in the real world I settled for experimenting with accessing a few different module setups from my DAW over the course of the week-long review period.

I created different recording chains comprising separate preamps, EQs, compressors and saturators; I tried filling the slots with 'mojo' processors (to borrow Cranborne's term) that I could use to process four stereo group busses with 'external plug-ins' in my DAW; and I created a four-stage stereo-bus chain, with an IGS stereo EQ, a Serpent bus compressor, a couple of Roger Mayer's new tape-emulation modules, and a pair of Cranborne's Camden 500 preamps —whose Mojo circuit sounds seductive on pretty much anything when set to 'Thump'!

I found the 500R8 really fun to use, which might strike you as a little odd for something as mundane as an audio interface. Largely but not exclusively, I think it's because it encouraged me to play more with my 500-series modules than I typically do, particularly while mixing. Whatever anyone says about the quality of plug-ins these days, I just find it so much more engaging using knob-per-function hardware like this, and it's a way of working that's just so easy to embrace when both the modules and the monitor controls are there at your fingertips — rather like on an analogue console. So yes, I think 'fun' is the right word!

It really is such a versatile system and, given that you can buy real mic preamps and other modules in this format for very little more than the price of some software models, it left me wondering why no-one's attempted it sooner. Still, I felt it my duty as a reviewer to search for niggles. Happily, I could find nothing that truly bothered me, but I should perhaps mention that the summing mixer controls feel a touch crowded; particularly when the unit was on my desktop rather than racked, I found myself knocking adjacent controls — but then I couldn't see a better way to arrange things in the available space. Also, I found myself wishing that there was a convenient way to process the analogue stereo mix bus with two 500-series channels before recording to the DAW — so you could mix through 14 channels of R8 and 500ADAT, into a stereo bus compressor on the remaining two, and record it in one pass. You can achieve that by patching the mixer outputs into two input channels, but I suspect most people would instead choose to hit the compressor in a second pass.

Verdict

The bottom line is that this melting-pot of an interface is a genuine triumph — and it's all the more impressive given what a mish-mash of compromises might have resulted from jamming so many different ideas together. Everything sounds good and feels as effortlessly integrated as I think is realistically achievable. Whether you're looking to build a high-quality tracking system, a hybrid-mixing coloration box, an analogue mastering chain, or something on a grander scale, there's definite potential to be explored. And Cranborne have managed to deliver excellent technical performance too — so they have a right to be very proud of this flagship product.

What's more, I think the 500R8 offers great value. Yes, you'll want to budget for mic preamps if you don't already have some, but that's true of many high-end interfaces — and you can offset some of that with savings in terms of the 500-series chassis and cabling. To put it another way, consider the price of a high-quality eight-slot 500-series chassis, an analogue summing mixer, and a monitor controller, and subtract the total from the price of the 500R8. That's a seriously impressive price for a multi–channel interface whose converters compete with the best!