AMS RMX16

The most classic of '80s reverberators has been reinvented — complete with retro controls — for the 500-series.

Advanced Music System's RMX16 is one of the all-time classic digital reverberation processors and, nearly four decades since its launch, the original hardware units are keenly sought after — today, a vintage RMX16 in good condition changes hands for around £2500$3000. It was essentially an upgraded version of the little-known but genuinely ground-breaking DMX15R, which was the very first microprocessor-controlled, full-bandwidth, digital reverberator, and was introduced in 1981.

We now take decent A-D/D-A conversion in audio products for granted, but these were some of the most complex and expensive parts of the early digital audio products, so while the (2U rackmounting) DMX15R contained all the digital processing gubbins, memory chips, controls, and displays needed to run AMS's nine innovative reverberation algorithms, it was given no analogue I/O of its own at all. Instead, it was delivered as an expansion unit that had to be connected into the back of AMS's DMX15‑80 digital delay line — it made use of the DMX15‑80's converters and the associated discrete-component analogue anti-alias and reconstruction filtering. In spite of this, the DMX15R quickly built a keen following and this prompted AMS to create, in 1982, a fully integrated, stand-alone model, with its own internal converters — the RMX16, whose controls, displays, operation and nine reverb programs were identical to those of its forebear. The only obvious difference to the casual eye was the addition of a pair of rotary controls on the left of the front panel to set the input and output levels

Those who want the sound but can't justify the cost of original hardware (or its ongoing maintenance) now have options in both plug-in and hardware forms. Back in late 2014, Universal Audio introduced a plug-in version, for their UAD platform, which provides an impressively accurate rendition for rather less than a fifth of the typical second-hand hardware cost (although a UAD DSP system of some form is obviously required to run it). The remarkable accuracy of the plug-in is due to AMS Neve's engineers — led by Mark Crabtree, the original designer — painstakingly porting the reverb algorithms directly, byte-for-byte, from the original code to run on the UAD platform's SHARC chips. The UA team also modelled the precise characteristics of the original converter circuitry, since these played a significant role in the RMX16's overall sound. (The A-D stage used a 12-bit converter, with two extra bits for gain-ranging to extend the dynamic range, and this data was then converted into a 16-bit word for the reverb processing algorithm). I reviewed this UAD plug-in in SOS January 2015 (https://sosm.ag/ua-rmx16) and I was so impressed with it that I've been using it regularly ever since.

It's worth noting that the UAD version includes a couple of extra features compared with the original hardware. First, it incorporates both a dry/wet mix control and a wet-solo monitor mode, which are very useful, allowing the plug-in to be used as an insert as well as in a conventional send/return loop. Secondly, while the original unit came with just nine effects algorithms, an additional nine variations were available to hardware users who had invested in the bespoke remote-control unit with attached barcode reader; the extra algorithms were accessed from a sheet of printed barcodes — very high-tech for the era! The UAD plug-in incorporates all 18 algorithms as standard.

Of course, superb-sounding though the UAD plug-in is, there's something rather appealing and rewarding, in a tactile sense, about using physical hardware — so I was overjoyed when I learned that AMS Neve had not only developed a 500-series module version of the RMX16, but that they were also sending me one of the very first units to try out before its launch at the 2020 Winter NAMM show.

500-series Module

This new 500-series module is an instantly recognisable and very attractively miniaturised and repackaged version of the original. It features a very similar numeric keypad and the same distinctively shaped turned-aluminium control knob, as well as the four-LED traffic-light level meter. Even the crisp 2.4-inch OLED screen is monochromatic red, simulating the alphanumeric LED displays of the original to show all of the program's parameters.

Although there isn't enough panel space for those characteristically chamfered 1980s control buttons, the new module does feature a set of smaller black buttons to access the same functions, and they have integral red status LEDs, too. The original's 'Pot' button is missing, but that's because the rotary control is now an encoder with a press-switch action, which is always available for parameter adjustment. Three extra buttons are provided in place of the original's two rotary controls to adjust the I/O levels. All in all, it's a very elegant and eye-catching reimagining of the original RMX16.

The original hardware was modelled as a plug-in, and the plug-in has effectively been rebuilt as a hardware unit. What a strange world we live in!

AMS Neve's new RMX16 module obviously contains much more modern circuitry than the 1980s original, which was crammed full with 14 large, vertical circuit cards plugged into a motherboard that occupied the entire floor area of the deep, 2U, rackmounting chassis. It's a rather sobering thought that all of the circuitry in this new 500-series equivalent is accommodated on a single PCB, measuring roughly 120 x 120 mm. Technology has come a very long way in 40 years! Nonetheless, this module occupies three 500-series slots — it's a mono-in, stereo-out device, but the front-panel controls requires this much space.

What 40 years ago filled a chunky rack unit now sits on a single PCB! The SHARC chip used to run the signal processing is the same as used in the UAD platform — for which there's a plug-in version of the RMX16 featuring the same reverb algorithms and converter modelling.

In place of the original's wheezing 22MHz processor and 12-bit, 40kHz A-Ds, we now have a 450MHz 32-bit SHARC DSP and 24-bit, 48kHz delta-sigma converters, both from Analog Devices. The choice of a SHARC DSP chip makes perfect sense, of course; having put in all that effort into porting the algorithm codes to run on the UAD platform, it was almost inevitable that AMS Neve would use the same core software and technology to produce a stand-alone hardware version — and that's why my references to the UAD plug-in are so relevant to this review.

As a direct consequence, the feature set of this 500-series RMX16 is essentially the same as that developed for the UAD plug-in. That means not only are all of the algorithms absolutely identical to the original, with the nine extra ('barcode') algorithms included alongside the standard nine, but the plug-in's wet/dry mix function is also included to accommodate modern workflows, and the particular sound characteristics of the original converters are modelled as well. So the original hardware was modelled as a plug-in, and the plug-in has effectively been rebuilt as a hardware unit. What a strange world we live in!

Although the fully enclosed module occupies three 500-series slots it has only two connector blades at the rear, and the middle slot's I/O is not used at all. As this is a mono-in/stereo-out reverb unit, the mono line input and left line output are accessed from the first occupied slot position, while the right line output is found on the third occupied slot — the second slot's I/O and the third slot's input are unused. The module draws 200mA of current in total, which is well within the VPR Alliance's standard allowance for three occupied modules.

Operation

As with the original, each reverb parameter (pre-delay, decay time, Lo- and Hi- decay filtering) is accessed via a dedicated button, and once selected the parameter value can be adjusted in any of three ways: by using the rotary encoder knob, by pressing the up/down nudge buttons, or by typing a numeric value using the keypad. For the last, the selected parameter button's LED flashes as a value is typed in, and it's only activated when the hash (#) button is pressed. The asterisk (*) button represents a minus sign for the filter parameters, but it has to be pressed after the numeral, not before!

Input and output levels are also adjusted after pressing their dedicated access buttons, as is the wet/dry mix. Again, any of the three methods described above will change the parameter values. The 'traffic light' LED meter is configured to light green at -2dBu, yellow at +4dBu, and red at +10dBu, but the maximum output from the module is +22dBu so there's plenty of headroom even if the first red light flicks on occasionally. The second red LED at the top indicates a 'processing overflow' — essentially, computational clipping within the reverb algorithm.

Above the rotary encoder a pair of buttons enables an effect's settings to be saved or recalled to/from any of 100 user memories, each of which can be uniquely named with up to eight characters. Hence the addition of the alphabet on the numeric keypad. Upon pressing the Save button, a name has to be entered using one of the three methods outlined above (the keypad is generally the easiest and quickest), and then a memory location identified. Recalling a preset is easiest with the encoder, although typing the memory number is quicker if known, and is activated by pressing the encoder knob or the hash button.

A USB type-C socket in the bottom left corner of the front panel is provided for future firmware updates (the review unit was running firmware v.1010). A short setup menu is accessed by pressing the Program and Down buttons together, with the firmware version displayed at the top, followed by the screen brightness setting and the delay period before the screensaver kicks in. Next is the screensaver mode which has three options: the screen can simply dim, or it can display a moving AMS logo, or it can both dim and show the bouncing AMS logo, which is the default. The final setup menu option is a full factory reset which wipes all saved presets and restores the factory defaults.

Sound Quality

Having previously reviewed the UAD plug-in version of the RMX16, whose algorithms are identical to those here, there seems little point me waxing lyrical about each individual program — you can read my thoughts on them and their applications by checking out that UAD plug-in review, which I linked to above. In essence, though, I've always loved the RMX16, whose introduction coincided with the start of my own professional career. It was a delightfully simple and straightforward reverb processor to set up and use and, whichever algorithm was selected for a specific task, it always sounded exactly right with the minimum of tweaking. The halls and rooms sound remarkably natural and believable, while the plate, nonlinear, and reverse programs are distinctive and musical. The Ambience program was always one of my favourites, though, and this new 500-series module accurately reproduces all of that reverberant loveliness — with buttons and knobs on!

Inevitably, the RMX16 is one of the most expensive 500-series modules currently available, even before you factor in the cost of the three slots it occupies. But I would argue that the cost is justified. It is beautifully engineered, instantly recognisable as a modern descendant of the RMX16, and it really does sound absolutely gorgeous. If you're already a 500-series user and prefer the hands-on approach, this is one extremely appealing reverb processor to add to the rack. Mrs R has had to hide my credit card