Building on Prism's high‑end converter range, the ADA‑128 caters for those working with high channel counts and multiple signal types.
For over 35 years, Prism Sound have been well known for offering some of the highest‑quality analogue‑to‑digital converters. One of their best‑known and longest‑serving products is the modular ADA‑8 (the current version is the ADA‑8XR), a configurable A‑D/D‑A converter system providing either eight channels in/out, or 16 channels in a single direction. It also serves as a system master clock, can handle different sample rates on different signal paths, and can be fitted with a variety of digital interface modules to suit different installations. Racks of ADA‑8XRs are a common sight in recording studios, mastering rooms and post‑production theatres throughout the world's high‑end facilities — I think it fair to say that this is a genuine 'industry standard'.
Popular though the ADA‑8XR remains, the advent of technologies with high channel counts, for example Dolby Atmos and Dante interfacing, have increased industry demand for converter systems with many more channels in a single, integrated package. Prism Sound have responded to this with the new Dream ADA‑128, reviewed here. Building on the concepts established in the ADA‑8XR, the new Dream's model numbering highlights its most significant feature: the ability to handle up to 128 analogue audio channels in and out simultaneously — thus accommodating the maximum channel count of the Dolby Atmos specification — and more (up to 384x384, depending on the cards) with digital audio. And all of this is contained within an elegant 2U rackmount box, and controlled either using a front‑panel touchscreen or remotely, through a standard browser over a network connection.
Overview
The Dream ADA‑128 is an all‑new design, but clearly builds on the company's considerable experience in advanced converter and digital routing technology. The very modest‑looking 2U chassis belies the enormous power within, as the unit can be configured and customised in myriad ways simply by installing different modules in its 20 rear‑panel slots. These modules come in two formats, called I/O and Host, and the ADA‑128 can accommodate up to 16 I/Os and four Hosts.
At the time of writing, there are currently three different options for the I/O modules, all designed to deliver or accept analogue or digital signals to/from external peripheral devices: an eight‑channel line‑level A‑D converter, an eight‑channel line‑level D‑A converter, and an 8x8 AES3 interface. But scheduled for imminent release is another eight‑channel A‑D module with both mic and line input capability. Every I/O module contains its own onboard DSP, which takes care of things like clocking, signal routing, programmable bi‑quad filters (eg. for 80Hz HPFs), M‑S processing and Verifile generation/checking. But Prism have hinted that there's additional processing capacity, which may be employed in future firmware updates to extend the system's overall functionality.
Host slots are intended to pipe multi‑channel signals from multiple I/O modules in and out of a DAW or other audio recording/playback system. Currently, there are two Host module options (both catering for 64 channels in and out) to interface with ProTools HDX or Dante. A 64x64‑channel MADI module is also expected soon, and alternative host formats will be developed as customer needs evolve, such as USB, Thunderbolt, Ravenna, AES67, and so on.
Central to the Dream ADA‑128's functionality is a system called ADRA (Advanced Digital Routing Architecture). This is controlled from a dedicated master routing DSP module installed in every ADA‑128, and this creates and manages all of the internal signal paths between the I/O and Host modules according to the user's requirements. Additionally, this routing system also supports direct routing between different I/O modules and for Host‑to‑Host bridging, if required. All routing setups are saved and loaded as 'configurations', with a number of typical configurations pre‑installed to assist in the initial setup. Obviously, personalised configurations can be created and stored by the user, too.
I don't know of any other single digital audio processor or router with such a versatile four‑clock capability.
One of the most impressive aspects of the Dream ADA‑128 is called QClock, and this provides four totally separate word‑clock 'domains', each capable of running independently at different sample rates from either internal or external clock sources (traditionally, converters, routers and everything connected to them had to be synchronised under the control of a single master clock, to ensure everything ran at the same sample rate and delivered samples at precisely the right time). Each I/O and Host module within the ADA‑128 can be assigned to and controlled by any one of these four clock domains, as required, affording exceptional flexibility and allowing a single ADA‑128 to route and process signals from, for example, four separate project studios or production systems, each running independently on their own local clock masters. Alternatively, subsets of digital equipment within, say, a complex transfer suite, can be interconnected in myriad ways while running under separate clocking regimes. Prism's ADA‑8XR could divide the signal paths to work with two separate clock systems, but I don't know of any other single digital audio processor or router with such a versatile four‑clock capability.
Another innovative feature of the Dream ADA‑128 — one that received little fanfare when introduced by Prism Sound a few years ago in their second‑generation DAW interfaces — is Verifile metadata [see box, later]. In essence, this ingenious technology modulates inaudibly the dither applied in each A‑D converter module, adding unique metadata to every audio sample. This metadata can subsequently be detected and analysed, either in a recorded audio file or in a real‑time digital audio stream, to confirm the absolute integrity of the recorded or transmitted signal, logging any data glitches that may have occurred during its passage from the A‑D. This feature is highly valued in professional archiving and mastering applications, but knowing that the stored file is uncorrupted also provides considerable peace of mind when recording in unrepeatable situations.
In practical terms, Verifile encoding is fully automatic and completely transparent to the user. All that's necessary to check a file is to open it using the Verifile Checker app, which generates a log file listing any audio data corruptions. To check an audio stream, all of the Dream ADA‑128's digital outputs can analyse the metadata in real time, indicating any detected errors on the unit's front panel or within the remote‑control app's metering display.
A screenshot of the remote‑control software, used with a multi‑card setup.
Prism Engineering
As you would expect, the ADA‑128 is beautifully constructed, with a large motherboard covering the entire base of the unit. Into this, using PCIe‑style slots, are plugged the Host and I/O modules. Three fans behind the front panel are available to force‑cool modules. When in use, these draw air in through inlet slots across the front panel and exhaust at the rear. But as well as being ultra quiet in operation, these fans are under the control of software that monitors internal temperature power regulators, I/O modules and so forth, and Prism say that in all rack configurations except the largest I/O counts (and even then only when used in hot ambient temperatures) the fans will never come on; it's perhaps not surprising, then that they're considering offering a fan‑free option. The unit is powered from a universal compact internal SMPS block at the right‑hand side, with the usual IEC mains inlet, fuse‑holder, and on/off switch at the rear.
The modular approach allows different daughter cards to be installed to suit the needs of a specific installation — these cater for a range of analogue and digital signal types, and can each operate at a different sample rate.
Alongside the power unit is a CPU control and clocking module that's fitted to all units. The rear panel of this module carries a USB‑B Host socket (for future use), two USB A sockets (also for future use), an RJ45 network socket (for networked remote browser control), and an HDMI socket (again, for future use — to attach an external display screen). To the left, but linked to the control board, is a sub‑assembly with XLRs for the DARS AES clock signals in and out, a pair of BNCs for word clock in and out, and a nine‑pin D‑sub for additional clocking sources (accessing a second word clock in and out, a third clock out, and a second DARS out); a bespoke break‑out cable for this port is available from Prism.
The analogue and AES I/O modules all use standard AES59 (Tascam) D‑sub connections conveying eight balanced analogue channels each (and in both directions for the AES cards). These modules are also colour‑coded to aid with installation and identification, so the Line In A‑D cards are red, Line Out D‑As are green, and AES3 interfaces are blue. The forthcoming mic/line A‑D module will be orange. The review unit was also fitted with a Pro Tools HDX Host card, which has a silver backplate and two DigiLink ports.
ADA‑128 In Use
Everything can be controlled, configured and monitored via the front‑panel touchscreen, and Prism Sound have made things reasonably simple to understand through a selection of Quick Start guides related to whichever Host modules may be installed. Since the system can also function as a straight analogue/AES converter, another quick guide is available for those more basic configurations too. Each of these guides takes the user through simple check lists to route channels, establish clocking domains, and generally get the system fully operational as easily as possible. A full and comprehensive PDF manual is also available with all the finer reference details when/if needed.
I found setting the unit up through the touchscreen perfectly logical and obvious, having no trouble routing signals between I/O modules in each direction and organising the appropriate clocking arrangements. An icon strip across the bottom of the display accesses eight main menu pages, while the majority of the screen defaults to showing coloured blocks for the I/O and Host modules, each with mini‑bargraphs (green for inputs, blue for outputs) to indicate passing signals. These menu pages cover Routing, Inspection (metering, filters, and various module‑specific parameters), core system Settings, Clock synchronisations, System status (CPU and module temperatures, power rail voltages, etc.), an Alarm page for critical system messages, and a Help page for context‑sensitive help messages.
When it comes to routing, the top half of the screen basically shows the 16 I/O modules, while the bottom half shows two of the four available Host modules, all clearly labelled to identify which is which. Signal routing is performed simply by tapping the required I/O module followed by an available Host or AES module (available destinations are highlighted on the screen), and then ticking an OK icon to confirm the desired routing. Eight contiguous channels are routed each time, and input sources can be assigned to multiple destinations, if required (assuming those destinations are on the same clock domain).
The Inspector page shows large bargraph metering for the selected module, along with module‑specific features like activating the Verifile system, selecting analogue converter alignments (eg. +18 or +24 dBu for 0dBFS, adjustable in 0.1dB increments), Mid‑Sides conversion, polarity inversion, 80Hz high‑pass filtering, Prism's Overkill limiter system, and so forth. On the AES modules there are also functions for selecting input impedance (75 or 110 Ω), output format (AES3, AES3id, S/PDIF), word length, noise‑shaping curves, and more.
A Settings menu page allows entire system configurations to be saved, recalled, renamed or deleted, while the Systems page accesses things like date/time settings, screen brightness, network connection parameters, firmware status, and so on. The Clock Domains menu page allows each of the four possible clock domains to be configured for reference source (internal, any of the external connections, or digital I/O module sources), clock rate, and video‑related pull‑ups/downs. This menu page also offers four separate sub‑menus to see at a glance the clocking arrangements of the four domains, or which clock domains are ascribed to all modules, or what the rear‑panel reference clock I/Os are receiving or dispatching.
Naturally, with such flexibility and capability within the ADA‑128 there's a fair degree of complexity and detail throughout the configuration menus, but the displays are all very clear and logical, with helpful colour coding, and context‑sensitive help if needed — I found navigation and setup pleasingly straightforward.
ADA‑128 Audio Performance
In terms of audio performance I ran my usual bench tests using an Audio Precision test set, as well as listening critically through my Crookwood mastering console. I'm pleased to report that the ADA‑128 scored very highly in the AES17 dynamic range test. This is something that I regard as a very useful comparison tool — of course, dynamic range isn't the be all and end all, and the AES17 test doesn't reflect every aspect of a converter's performance, but for a device to achieve a good score in this test requires critical attention to every aspect of a converter's design and construction, and as it is easily repeatable it makes comparing converters straightforward. I tested the Dream ADA‑128 by routing test signals between a pair of analogue I/O modules and an AES3 module, clocking internally for the A‑D test, and to the embedded AES3 clock for the D‑A test, both at 48kHz.
Among the rear‑panel I/O are some USB and HDMI sockets that are reserved for future use, and an RJ45 socket for networked remote browser control.
The Line Input module's A‑D conversion is based around an ESS Sabre ES9842 quad‑channel converter and achieved an AES17 performance of a very creditable 118.4dB (A‑weighted). I rate anything measuring 118dB or more as being of full professional mastering quality, and the ADA‑128 achieves that. It also performs slightly better than both the Titan and Lyra 2 interfaces I've measured from the same manufacturer. Within the (inherently not comprehensive!) list of converters that I've tested personally, the Dream ADA‑128 A‑D module currently sits in 14th place, and while this may not initially sound so impressive... it really is! The top scorer is currently the RME ADI‑2 Pro, which measured 124dBA, and it's interesting to note that there are now nine products in my list achieving 120dB or more in the AES17 dynamic range test. That's mightily impressive from a technological point of view, but I'm not convinced that such measured differences are genuinely audible. Either way, I have absolutely no qualms about the excellent sound quality achieved by the Dream's A‑D performance.
D‑A conversion typically scores higher in the AES17 dynamic range test than the A‑D in most dual‑converter products, and the Dream ADA‑128 is no different. The core D‑A converter employed in the Line Output module is the Cirrus CS43198, which, in this implementation, delivers an AES17 measurement of 124.5dBA, placing it an impressive fifth in my personally tested converter league table. Of currently available products, only the Benchmark DAC and Merging HAPI converters exceed the Dream's performance level — and not by much! Also, given that this is a modular system, if Prism Sound were ever to develop still better cards, they could be integrated into the system at a later date. It's largely pointless detailing any other technical specifications, since the ADA‑128 measured superbly well in all of them, agreeing with or exceeding the published specs in every case. Suffice to say this is a beautifully engineered product in every regard.
Conclusion
When fully loaded with Host and I/O modules, the Dream ADA‑128 is, inevitably, an expensive beast. But it is also unbelievably powerful and massively capable as a multi‑channel analogue converter, signal router, digital format converter, and general studio system hub. And with excess CPU power available on board each module, the system is likely to become even more capable through future firmware updates. So, while smaller facilities might not require the ability to handle 128 audio channels in each direction from the outset, the fact that the ADA‑128 is modular means a smaller and more focused system can be installed initially, and then expanded and upgraded very easily as, or if, requirements develop in time — and the one thing we all know for sure: the future always needs more channels! The Dream ADA‑128 is a serious investment, but one with a long operational return, excellent support, and future‑proof capabilities. I am very impressed, and it takes quite a lot to achieve that!
Prism Sound History
Prism Sound were created in 1987 by Ian Dennis and Graham Boswell, although these founders met originally in 1981 while working with the Neve team developing the world's very first digital recording console, the Neve DSP‑1. Set up initially as an R&D consultancy specialising in digital audio technology, in those early days they also worked on a marine RADAR system, designed public address installations for London Underground, and developed a huge communications matrix for the BBC to use at the 1992 Barcelona Olympics! By 1993 the company were mostly manufacturing mastering‑grade stereo 'Dream' converters (the AD‑1 and DA‑1), which quickly became industry standards for CD mastering.
Important to the huge success of these products was Prism's focus on maximising dynamic range and minimising low‑level distortion — these were both significant technical challenges in converter design at the time — through innovative engineering techniques and novel DSP technologies. Being able to test and evaluate the technical performance of digital interfaces and converters accurately is obviously paramount to improving their objective and subjective audio quality, but at the time suitable test equipment just wasn't available. So Prism Sound developed their own, starting with a handheld analyser called the DSA‑1 (which quickly became another widely adopted industry standard). As digital audio technology matured, Prism's AD‑1 was soon replaced by the improved AD‑124, and towards the end of the 1990s second‑generation converters (the AD‑2 and DA‑2) appeared, establishing performance benchmarks which are still applicable today.
By the turn of the millennium DAW systems were replacing traditional multitrack recorders, and Prism Sound addressed the need for multi‑channel conversion systems with the ADA‑8 modular converter. This provided eight channels of A‑D and eight channels of D‑A conversion (although it could also be configured for 16 channels of conversion in one or the other direction, if preferred). Concurrently, Prism Sound also developed the dScope III audio analyser that came to market in 2002 and remains a mainstay of audio R&D departments around the world.
As the professional audio industry glided through the new millennium, translating from the exclusivity of high‑end studios and mastering suites towards smaller, personal, DAW‑based project studios, Prism Sound developed new products to suit these emerging markets. The first of these was the eight‑channel Orpheus DAW interface in 2007, while the ADA‑8 was upgraded to support 192kHz sampling rates around the same time and renamed the ADA‑8XR. In 2013 Prism launched a new generation of DAW interfaces in the Lyra 1 and 2, Titan, and Atlas, models which all remain in production today. The newest addition to the family is the Dream ADA‑128 modular converter system, which builds substantially upon the core concepts of the ADA‑8XR.
Verifile
Verifile is a proprietary system developed by Prism Sound to embed metadata within the dither signal added to each and every digital audio sample created by a Verifile‑enabled A‑D converter. Prism Sound became aware in the late '90s that audio data corruptions were quite common in real‑world audio installations — due to dodgy connections, external interference, computer buffering, stored file corruptions, and so on. Such damage is often extremely difficult to hear, so Verifile was invented in 2014 to accurately log and quantify any problems.
Early versions of Verifile were trialled by numerous broadcast, recording, mastering and archival organisations around the world for several years before it was honed sufficiently for its commercial release. This was in 2018 in the company's Atlas, Titan and Lyra interfaces, with the Verifile encoding function being enabled or disabled by the user through the converter's setup configuration.
Technically, Verifile is a 'fragile steganographic' process — steganographic meaning the technique of hiding secret data within a non‑secret file or message. In essence, it encodes a rolling hash code into the dither of each and every sample dispatched from an A‑D converter, with the code being related to the amplitude value and timing of each specific sample. Consequently, a Verifile‑encoded digital signal or audio file can be checked either in real time (via a monitoring feed), or offline by examining the recorded file using Prism's Verfile Checker app (for Windows and macOS). Either way, the integrity of the audio stream or file can be analysed, detecting and locating even single‑bit errors.
Of critical importance in mastering and archiving is that Verifile's metadata encoding is completely transparent and inaudible to all users, and it is designed specifically not to alter the audible noise floor or to introduce any distortion artefacts. This in‑built transparency also means the Verifile metadata doesn't need to be decoded or stripped out before accessing and using the digital audio, so it doesn't interfere in any way with normal audio operations. However, unlike conventional 'audio watermarking' technologies, Verifile doesn't survive any kind of audio processing, since that would inevitably alter the least significant bits where the dither signal resides. So Verifile only works with original, pristine, live sources or files recorded directly from the A‑D converter via the transmission or recording signal path.
Verifile can be used across any number of audio channels and supports all standard sample rates, but currently only with 24‑bit word lengths. In theory, external metadata content could also be integrated within the Verifile information, such as unique source and copyright details, although such a feature has yet to be implemented.
Pros
- Up to 128 audio channels in each direction.
- Up to four separate clock domains.
- Modular I/O and Host configuration.
- Mastering‑grade analogue and digital performance.
- Easy and logical to configure via the panel or remotely.
- Network controllable.
Cons
- None other than the cost, and some module formats not yet being available.
Summary
A superbly versatile and flexible digital routing and converter system capable of handling up to 128 channels in and out, making it ideal for full Dolby Atmos installations or multi‑room studio facilities.
Information
Minimum configured system £6499. Option cards (line in, line out, mic/line, Dante, AES and Pro Tools HDX) from £1499 each. Prices exclude VAT.
Prism Sound +44 (0)1353 648888.
Minimum configured system $8129. Option cards (line in, line out, mic/line, Dante, AES and Pro Tools HDX) from $1879 each.
Prism Sound +44 1353 648888.
