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Reverb Plug–in For UAD2 Platform
Published January 2015
By Hugh Robjohns

UA’s emulation of the AMS digital reverb shows exactly why the original is still regarded as a classic.

Advanced Music Systems’ RMX16 digital reverberation unit is most definitely one of the all–time classic audio processors. The manufacturers, more usually known as AMS back then (and AMS–Neve now), were set up in 1976 by former aerospace technicians Mark Crabtree and Stuart Nevison, who shared a passion for audio and expertise in digital electronics. This was at a time when digital audio processing was exciting and expensive cutting–edge technology.

The company really appeared on the industry’s radar when they launched their second product, the microprocessor–controlled DMX15–80 (15–bit) digital delay line, in 1978. This product appeared in several variations over many years, each with increasingly enhanced capabilities, but of relevance here is the unique add–on expander AMS introduced for the 15–80 in September 1981 called the DMX15R.

Digital delay units became extremely popular in the late ’70s and early ’80s, but digital reverb technology was very new and very expensive! Most commercial reverb systems at that time still used mechanical plates or springs, and only a few companies had developed high–quality professional digital reverberators. The DMX–15R was AMS’s first attempt, and it was an add–on 2U rackmount unit which bestowed the 15–80 with sophisticated programmable reverberation facilities.

UA RMX16Although immediately popular and immensely capable, the DMX15R expansion unit wasn’t particularly practical, and it was superseded just six months later, in March 1982, by the RMX16. In essence, AMS re–engineered the 15–80/15R combo into a self–contained stand–alone product: the world’s first integrated, microprocessor–controlled digital reverberation unit. Its front panel was the same as that of the 15R, except for the addition of a pair of knobs to set the input and output levels, and the first edition of its Operating Instructions was still titled ‘RMX16/DMX15R’ too, since the two units’ operation and programs were identical.

Famous Names

The leading lights in the digital reverb arena in 1982 included EMT’s 245 and 250, Eventide’s SP2016, Lexicon’s 224, Sony’s DRE–2000 and Ursa Major’s SST–282 Space Station — many of which are still in use and revered today! However, although the AMS RMX16 faced pretty stiff competition, it did very well indeed, largely because of its very musical character and superb usability, not to mention its compact size relative to many of its peers.With the addition of a separate board called the DMX 15R, AMS’s DMX 15-80S delay (centre) could produce digital reverb. The now-classic RMX16 (bottom) was in effect a single-box version of this combination, and was hugely successful. This fine-looking pair occupy rack spaces in Henson Studios.With the addition of a separate board called the DMX 15R, AMS’s DMX 15-80S delay (centre) could produce digital reverb. The now-classic RMX16 (bottom) was in effect a single-box version of this combination, and was hugely successful. This fine-looking pair occupy rack spaces in Henson Studios.Photo: Hannes Bieger

We take microprocessor control for granted today, but in the early ’80s it was still quite a new and unfamiliar technology. In the RMX16, it was employed to manage the internal reverb algorithms, load alternative algorithms, allow real–time display and adjustment of each algorithm parameter, and to store and recall 99 user parameter presets. The RMX16 could be controlled remotely, too, with an optional keypad unit (no Lexicon–style faders, sadly), and a revolutionary barcode–scanning ‘wand’ was available to import new reverb algorithm data from sheets of printed barcodes. In fact, AMS developed 18 separate reverberation programs in total, but only nine were stored in permanent ROM within the machine (locations 1–9). Three more could be loaded into dedicated battery–backup RAM (locations 10–12) within the rack unit, and another three in the Remote (locations 31–33), if required. (Third–party update kits are now available that install all of the programs in expanded hardware ROM.)

As you would expect, some of the nine factory algorithms simulated a range of conventional acoustic spaces such as rooms and concert Halls, while others emulated mechanical plates, and some provided delay/echo and chorus effects. However, the really popular algorithms that people still reminisce about today were the unnatural ones called Ambience, Non–lin and Reverse. These terms are quite familiar today, but were highly innovative in their day.

Internally, the original RMX16 hardware was crammed full, with 14 large circuit boards mounted vertically in sockets on a motherboard which covered the entire chassis floor area. Not surprisingly, the unit required forced–air cooling from a rear–panel fan. Technology–wise, its mono–in/stereo–out pseudo–16–bit audio converters delivered an 18kHz audio bandwidth and 90dB dynamic range — again, state–of–the–art in its day, and still very usable today — but the reverb algorithm number crunching worked with 28–bit words in the puny (by modern standards) 22MHz microprocessor.

Plug & Play

A pre–loved RMX16 will typically set you back between £1250 and £2500 today, depending on condition and accessories, such is the continuing demand for this well–engineered classic. However, Universal Audio have now released a plug–in version that makes its core algorithms available on the UAD platform; and although the plug–in’s $349 price tag is still substantial, it’s much less than you’d pay for the hardware! Apparently, all nine reverb algorithms are byte–for–byte identical to the original 1980s software, having been lovingly ported across by Mark Crabtree and a team of AMS–Neve and UAD engineers. Great care has also been taken in modelling the complex sonic characteristics of the original hardware’s analogue and converter circuitry, too, which played a big part in the overall sound.

At a reported 41.1 percent DSP load for a single stereo instance, the UAD RMX16 plug–in is on a par with complex emulations like the EL7 Fatso and Chandler Gav19T. Indeed, the RMX16 is one of the 10 most power–hungry plug–ins currently on the UAD2 platform, requiring more DSP effort than the Ocean Way Studio plug–in (38 percent) and way more than the Lexicon 224 (17 percent), EMT 250 (7.8 percent), and EMT 140 plate (15 percent). The inevitable consequence is that a UAD2 Quad card maxes out with eight RMX16s (at 44.1kHz), and proportionately half and twice the number on Duo and Octo cards, respectively.

You might well ask why it takes so much DSP power to emulate a relatively primitive digital device. Although the RMX16 reverb DSP code was sophisticated for the time, it’s not actually as complex as the code used in the Lexicon 224XL, where a chorusing process on the reverb tails is intrinsic to the unit’s lush character. However, the reverb algorithm processing was dependent on the hardware sample rate (which was, if memory serves, 40kHz), and so the UAD implementation may well involve DSP–hungry sample–rate conversions to accurately replicate the original algorithm’s parameters. The RMX16’s converters were actually gain–ranging 12–bit devices, too, and it seems reasonable to presume that the complexity of this analogue circuitry modelling accounts for much of the plug–in’s surprisingly high DSP demand.

Fortunately, I can’t recall any 1980s commercial recording studio ever using more than two RMX16s at a time! Reverberation is normally employed in an effects loop, receiving aux–bussed inputs from many channels and outputting the processed signal to an effects return channel — and this UAD plug–in is configured to work in the same way by defaulting to a fully ‘wet’ output. However, UA have added a wet/dry balance control so that the plug–in can be used as a channel insert; two push–buttons used for saving and recalling user presets on the hardware unit have been reallocated as ‘Wet Solo’ and ‘Wet/Dry Mix’ controls on the UAD plug–in, and preset save/recall duties are taken care of elsewhere in the GUI.

RMX Bandits

In use, the UAD RMX16 is identical to its hardware antecedent. Input and output levels are set using the rotary controls on the left–hand side, with a small bargraph meter, and all parameter adjustments are made by selecting the required function with the virtual push–buttons and then altering the numerical value in one of four ways. Three of these are identical to the hardware unit: a specific parameter value can be entered using the virtual keypad (followed by the # key to confirm the change); the Nudge up/down buttons can be used for small changes; or the rotary pot on the left–hand side can be employed. The new fourth option exclusive to the UAD plug–in is to click in any data display window and type in a value from the computer’s keyboard, followed by Enter.

The nine core algorithms are recalled by selecting the Program button, followed by a keypad number between 1–9 and the # key to confirm. Entering a higher-numbered memory location results in ‘E’ for error being displayed (the original hardware would usually crash!) The algorithm name associated with the selected program is also displayed above the nudge buttons. Not all of the configuration parameters are available for all nine programs, but the reverbs all offer pre–delay time, decay time, and high and low EQ. Some of the keys on the keypad serve no function, such as the asterisk and letters C–D, but the letters A–B are used to select the left or right channel when programming independent echo delays and feedback.

It’s been a while since I used an RMX16, but it was very much the go–to reverb unit during my formative years (with the later, and surprisingly similar, Klark Teknik DN780 as the first reserve). However, the unique character and quality of the RMX16 reverbs are still much in mind, not least because they are so obvious on virtually every pop album dating from the mid–’80s.

The Ambience program was and probably still is the most popular, with its fundamentally neutral but expansive–sounding reverb which blends very naturally with any existing room reverb on the track. It adds a beautiful space to any source and sounds warm and flattering, but without imposing any significant character of its own. Basically, it’s a very musical reverb that just works brilliantly in almost all situations and across a wide range of decay–time settings. As the unit’s first program it’s no surprise it became so popular, and often there’s simply no need to look any further!

One of the innovations pioneered in the RMX16 was the ability to scan in additional programs using a  handheld barcode reader.One of the innovations pioneered in the RMX16 was the ability to scan in additional programs using a handheld barcode reader.Another very useful feature of the Ambience program is that if the decay time is set to the maximum 9.9 value, the algorithm has almost infinite sustain, creating an ethereal choir effect. By dialling down the high–frequency filter, the sound mellows over time in a very natural way, too. Some RMX16s had a variation of this program called ‘Freeze’ (see box), which made it much easier to switch this mode on and off with or without new sound input.

Program 8, ‘NonLin2’, was another popular algorithm for small room effects, or for adding energy and scale to percussive sounds giving a kind of ‘Phil Collins’ quality. In essence, the early reflections don’t decay, which has the effect of extending the duration of short sounds, ending with a kind of gated quality as the short reverb tail dies quickly away. This was almost an industry–standard effect for ’80s drums and percussion! The ‘Reverse1’ algorithm (program 9) was another drum–centric effect, with the reverb character building and then stopping abruptly. Not surprisingly, the Room, Hall and Plate programs all do exactly what they say as well, and still sound extremely believable today, such was the quality and musicality of those original algorithms.

Character Actor

Does the UAD plug–in sound identical to the hardware? It’s hard to state categorically, given that two vintage RMX16s would be unlikely to sound identical to each other! But that’s not really the point: what matters is whether the plug–in delivers the same character of effect that made the original hardware so useful and popular, and I have to say an emphatic ‘yes’ to that one. The UAD RMX16 programs definitely have exactly the same sound characteristics, and the plug–in delivers the same kind of sound quality, which means you would choose and use it for the same purposes and achieve the same overall results. It’s about character and usability, at the end of the day, and the RMX16 plug–in has that in spades. The user interface is very simple and fast to adjust, just as the hardware original was, largely thanks to the very small number of parameters on offer. However, if manual tweaking is not your thing, there are — as with most UAD plug–ins — more ‘celebrity presets’ available than any sane user could possibly use in a lifetime of music–making.

I love the UAD RMX16, both for its familiar controllability, and for its superb sound character and versatility. It delivers the same sonic environments that I remember from the hardware, and although it might be a bit of a DSP–hog compared to other plug–in reverbs, I think it’s definitely worth it. In fact I’d suggest that one RMX16 in an effects loop is worth a dozen lesser reverbs inserted in individual channels. Highly recommended.


The EMT 250 and Lexicon 224 are contemporary alternatives to the RMX16, and emulations of both are available on the UAD2 platform, although neither has the same sound character, of course. The Eventide SP2016 and Ursa Major SST–282 Space Station are also available as plug–ins. There are also unofficial emulations of the Lexicon 224 and 480L from Native Instruments and Relab.

Standard Programs

The nine standard programs provided in the UAD plug–in are exactly the same as those of the RMX16 hardware unit:

  • Ambience: a very neutral reverb effect somewhere between a very clean, uncoloured plate and a small hall. Can be used to extend existing reverb very naturally. Setting the decay time to the maximum value (9.9) provides infinite decay, and new sound can be added to create a sustained choir effect, or a freeze effect with no new input.
  • Room A1: a typical small live-room sound, with coloration to simulate standing waves.
  • Hall C1: a classic hall sound with strong early reflections to give a defined size.
  • Plate A1: generic high–diffusion plate effect.
  • Hall B3: similar to hall C1 but with less pronounced early reflections.
  • Chorus 1: a five–voice effect, with each voice in a different spatial position and with random delays controlled by the pre–delay setting. The effect depth is determined with the Decay control.
  • Echo: dual–channel echo effect. Pre–delay sets the echo period, and Decay the amount of regeneration. Each channel is selected for control independently via the A and B buttons on the keypad. The two channels have different maximum delay settings.
  • NonLin 2: this provides a non–decaying reverb pattern for a short period (set by the Decay control), followed by a rapid decay. The effect helps to increase energy and loudness, particularly for percussive sources, and can also be used as a small room effect.
  • Reverse 1: a dual–mono effect with diffuse reflections on the left channel, and more discrete reflections on the right. The reverb effect builds gradually before stopping suddenly.

Additional Hardware Programs

The following additional programs were also available for the hardware RMX16, but had to be loaded into battery–backed memory via barcode sheets. They are all variations of the nine standard programs, but offered some useful benefits or alternate characters. Sadly, none of these are currently available for the UA plug–in, but they would be trivially simple to add at some future point if AMS–Neve and UAD decide to offer an upgrade option!

  • Delay: a single mono delay of up to 1.63 seconds (depending on hardware version) available on output 2 only, with output 1 producing a direct digital source feed. Delay time is set by the Pre–delay control, and feedback using the Decay control.
  • Freeze: a variation of the max–delay Ambience mode, making it easier to control. The Decay control has three settings: 0.0 is ‘clear effect’, 0.1 ‘freeze but accept new audio’, 0.2 ‘freeze with no new input’. These modes are easy to control via the nudge buttons.
  • Hall A1: an early version of the Hall C1/B3 programs, with a slightly coarser decay.
  • Image P1: similar to NonLin, but with reflections being panned between outputs. Sounds very similar to NonLin when summed to mono.
  • Plate B1: a variant of Plate A1.
  • Reverse 2: a stereo–output variant of Reverse 1.
  • Room A0: the original version of Room A1, shipped with early units. It has a coarser and brighter top end than Room A1.
  • Room B1: uses a different algorithm to Room A1/A0 and features a constant diffusion density with time. The Decay control affects impression of room size.
  • NonLin 1: a simpler, dual–mono version of NonLin 2, with the two mono outputs differing by providing only discrete or diffuse reflections.
Published January 2015