In this Sound On Sound exclusive preview, we lift the lid on SEPIA by Karno: a radical new outboard format for the digital age.
From German consoles of the 1950s to classic API and Neve desks, modular systems have a long pedigree. In a professional environment the advantages are obvious. Modular systems are expandable. They’re adaptable to different use cases. They allow servicing and repair without any down time.
Modular systems can also become industry standards, allowing multiple manufacturers to offer compatible products. The classic example is API’s 500 series. Originally developed as a flexible way of specifying a mixing console, this took on a life of its own with the Lunchbox, a portable chassis that could host a small number of individual modules. Today, nearly all major console makers, and countless ‘boutique’ manufacturers, offer mic preamps, compressors, EQs and other processors in the 500‑series format.
However, the market for high‑end audio gear has changed since the 500 series was introduced. Recording studios are not the big spenders they once were, while live sound, broadcast and theatre have fully adopted digital audio. A 500‑series chassis might be perfect for the aspirational home studio or the recording engineer on the go, but it’s harder to integrate into a touring rig where audio‑over‑IP rules the roost, and was never designed to withstand life on the road.
Out Of The Box
In his previous role as Vice President of DPA Microphones, Adam Pierce had observed the frustrations of live and theatre engineers who felt boxed in by the move to digital consoles. Like their counterparts in recording studios, they were passionate about sound quality, and wanted access to high‑end outboard gear — but conventional outboard is hard to integrate into a digital environment. Several companies have adapted DSP plug‑ins to run on dedicated servers for live use, but many engineers considered software emulations a poor second best to the real thing. There was also a concern that these systems introduced potential instability, an obvious no‑no in any live show.
There have been huge advances in digitally controlled analogue technology since the 500‑series became popular. Could these be exploited to create a new modular format that would integrate equally well into studio, live sound and theatre workflows, with no compromise on audio quality?
Rather than creating more digital emulations, Adam began to wonder if there might be a way to package the original analogue circuits people really wanted to use, in a way that would meet the needs of engineers in all sectors. There have been huge advances in digitally controlled analogue technology since the 500 series became popular. Could these be exploited to create a new modular format that would integrate equally well into studio, live sound and theatre workflows, with no compromise on audio quality?
Extensive market research convinced Adam and his team at Karno that they could, and the result is a new modular system known as SEPIA. The first units will be on sale early in 2024, so a full SOS review will have to wait until then. But in the meantime, the system has been developed in consultation with some of the world’s most high‑profile engineers, and the previews we’ve seen have been impressive. Is SEPIA really, as Karno claim, “the final evolution of audio hardware”?
To answer that question, it would be helpful to know what SEPIA is...
Slot Machines
The range of Modules available at launch will include preamps, EQs and compressors — some of which will be very familiar to experienced audio engineers!At the most basic level, a SEPIA system comprises two hardware elements: Hosts and Modules. Initially, Karno themselves will exclusively manufacture SEPIA Host units, which can occupy any form factor including 19‑inch racks, stageboxes and desktop cases. Each Host unit will have slots into which SEPIA Modules can be fitted. Small enough to fit into the palm of the hand, these Modules will be manufactured by licensed partners. Modules from 12 manufacturers are already in active development, with another nine in advanced discussions, and the launch line‑up will feature preamps, compressors, EQs and other devices.
SEPIA Modules are designed to be remote‑controlled digitally, and most will have no physical controls. A SEPIA Host is thus much more than just a chassis supplying power and audio I/O. At the core of the Host is the Mainframe: a sophisticated array of digitally controlled analogue electronics that implements complex routing and switching, level translation and filtering. (The all‑important bridging signal flow between Host and Modules is the subject of a pending patent application.) The Host also contains an embedded computer, which handles configuration and communication with the outside world, and a newly developed power management system that can provide bespoke power rail voltages to individual Modules.
Deep Routes
A key feature of the Mainframe is the digitally controlled routing matrix, which allows the signal path within the Host to be configured. This may be simplified in smaller Hosts, but in the full implementation, each Module slot has a primary and a secondary audio input, and two audio outputs. The primary input can be at mic or line level, while the secondary input is a line‑level signal, so stereo‑in/stereo‑out is an option for individual Modules that operate at line level. Individual Modules within a Host can be given their own I/O paths or they can be chained, so that a mic input feeds a preamp followed by a compressor Module and an EQ Module.
The flexibility of the routing architecture goes much further than this, though. For example, if you have a Module that is a complete input channel with preamp, EQ and compressor, the manufacturer could make it possible to divide this functionality so that the mic preamp operates on the primary input, whilst the compressor is used to process a different signal on the secondary input. Alternatively, the secondary input could be used to feed in a separate side‑chain signal for a compressor Module. The split functionality can also be used to provide an insert point, so that other Modules can be patched into the signal path within a Module. It will even be possible to ‘mix and match’ elements of different Modules, such as input and output transformers. All of this configuration preserves a fully analogue signal path throughout the Host, so there’s no latency or A‑D/D‑A conversion involved in different routing setups, nor any interruption to signal flow if the computer side of things happens to glitch.
The electrical connection between Module and Host is made using 21 metal pins on the rear of the Module, which carry power, data and audio. On the right here is a double‑width Module shell such as may be needed for particularly complex circuits, or valve Modules.
As well as handling switching and routing, the Mainframe circuitry also includes ‘level translation’ elements such as clean gain stages and pads, allowing Module designs to be simplified or augmented. If a compressor Module needs a clean make‑up gain stage, there’s no need to build this circuitry into the Module itself, because it can be handled by the Mainframe. If a mic preamp has a transformer output stage that delivers a balanced output, this can be routed directly to the Host outputs, with the additional gain stages switched out of circuit using relays. By contrast, preamp Modules based on classic console circuits that produce an unbalanced output can be electronically balanced and, if necessary, boosted or attenuated using this Mainframe circuitry. If two Modules have a different understanding of what ‘line level’ means, this can be compensated for by precise gain adjustments when they’re patched together in series.
Each Module also has a measurement point where the signal can be tapped and metered. How this is used is up to the manufacturer. For example, a compressor Module might default to reporting input level with the option to switch to gain reduction or output level instead.
Screen Time
In addition to its analogue or digital audio processing circuitry, each Module also has its own data bus and built‑in storage. The latter holds the graphical resources that are used to generate user interfaces on whatever device is handling the control, along with preset data and much more. For example, if you happen to have used a particular Module on a well‑known artist’s signal, you can record that information to its built‑in storage for posterity. If you choose to participate, the SEPIA system can also store diagnostics and usage data. Karno anticipate that live sound rental companies will be among the early adopters, and these features will be helpful in allowing them to optimise their inventory over time.
The data bus is used for communication with the Host’s embedded computer, which runs custom software called the AEQUOREA Engine. Its primary function is to translate control input from a variety of sources into instructions that Modules can accept, and one of the core principles behind SEPIA is to enable parameter adjustment from as many types of device as possible. You’ll be able to hook up a computer using an Ethernet or USB cable, but WiFi and Bluetooth are also supported, enabling wireless control from a phone or tablet. Users of digital mixing consoles will be able to edit Module parameters directly from their touchscreens.
Modules will store two levels of user interface data. There will be a basic, generic list of parameters with information such as parameter names and ranges, such as you might see when editing plug‑ins from a typical HUI or MCU controller. However, most control devices will be able to exploit the higher level, which will present a full graphical user interface. For Modules that are based on existing designs, skeuomorphic graphics will broadly replicate the look and feel of the original rack or console version.
The Creator pane within Karno’s control software provides intuitive control over the internal routing.
On Mac, PC, phones and tablets, these lifelike interfaces will appear within Karno’s custom control software. The computer version will feature two main pages. Creator is where routing configurations are set up, using a friendly drag‑and‑drop interface that does away with the need for virtual patch cables or pin matrices. The Dashboard, which will be replicated on the phone and tablet app, gives you a real‑time overview over all the Modules in the system, presents parameters for editing and provides visual feedback such as meters. A variety of screen layouts will be available and it will be possible to enter numeric parameter values as well as clicking and dragging or assigning a MIDI controller.
The Karno software will run both standalone and as a DAW plug‑in, meaning that SEPIA setups can be saved and recalled with DAW projects. Parameters will also be automatable within your projects. At launch, the actual audio I/O will still be handled via your primary audio interface, so if you want to use SEPIA processing as inserts at mixdown, Hosts will need to be treated as external hardware devices using whatever mechanism your DAW offers for this. However, USB audio interfacing for Hosts is part of the product road map and is already in development.
The Dashboard lets you view and edit Module parameters in a variety of configurations.
Ins & Outs
Talking of I/O, the SEPIA architecture is designed to be both endlessly scaleable and entirely agnostic about how audio comes in and out. The first Host to market will be the L6, which will have six Module slots and eight primary audio I/O paths, with various different physical I/O options including Dante, MADI and analogue connectivity. Analogue purists could opt for an L6 with only analogue inputs and outputs, for a signal path with no conversion at all. By contrast, someone whose primary use case is analogue compression within a live sound context might choose to go in and out on Dante.
The duration of the Compact Disc format was supposedly dictated by the need to accommodate Beethoven’s Ninth Symphony on a single disc, and SEPIA Module dimensions have been specified with the goal of allowing a certain classic British mic preamp design with particularly meaty transformers to be encapsulated in a single Module. This nevertheless makes it an extremely compact system, with the L6 able to accommodate six Modules in a single 1U rack unit.
The SEPIA specifications also permit double‑width Modules, which will be of particular interest to one partner. When Karno surveyed live sound engineers to find out their ‘desert island’ Modules, many said that they would love to have a version of Thermionic Culture’s Culture Vulture that was adapted for touring use. Karno duly approached the Essex‑based valve specialists, who were quick to see the potential, and have been beavering away to adapt the circuit for the new format. The main challenge relates to heat dissipation; Karno and Thermionic Culture have come up with several working solutions and are currently figuring out which is the most effective.
On The Rails
Outwardly, the L6 is a very boring‑looking black box, slightly resembling a rack of RF receivers for radio mics. Internally, though, there is some very clever mechanical and electrical engineering at work. Existing modular analogue formats typically have fixed power rail voltages, and sometimes impose awkward limits on the amount of current each module can draw. 500‑series chassis, for example, have ±16V power rails, and the maximum current draw is officially 130mA per module. There’s nothing to stop manufacturers of individual chassis from beefing this up, and many do, but circuits that were originally designed for other consoles or standalone use may still need adaptation for use in 500‑series modules; and some classic audio processors, especially ones that use valves, have power and voltage requirements that can’t easily be met within the format.
SEPIA Hosts, by contrast, have a sophisticated three‑stage power supply that can deliver exactly what each Module needs to run. A switch‑mode power supply first generates 36V DC from the mains supply, then each rail has a tracking pre‑regulator feeding a linear power supply to Modules of maximum ±30V. The digitally controlled pre‑regulators allow these rail voltages to be dropped precisely to meet the demands of each circuit.
Inside the L6. The main circuit board is double‑sided, with the Mainframe circuitry largely underneath, but the power management features are visible here. The heatsink and fans have been removed in this shot.
Innovation is also apparent in the physical design of the system. The mechanism by which Modules are inserted and removed feels reassuringly solid, and makes it almost impossible to insert them incorrectly or incompletely; but it’s also an integral part of the SEPIA Host’s advanced thermal management system. Under each Module slot is something Karno are calling a ‘thermal bias spring’; as the Module is pushed into the slot, this forces its upper surface against a large aluminium plate with heatsinks attached. An array of small and near‑silent fans drives the dissipated heat away from these heatsinks through the rear of the unit. This gives the SEPIA platform a thermal design rating of 8W per Module slot. Hosts that have been prototyped for desktop use will be able to do away with the fans altogether and rely on passive cooling.
The Long Game
Each SEPIA Module will be the subject of a licensing agreement between Karno and the Module manufacturer. This allows Karno to enforce stringent quality control standards, which are absent in ‘open’ modular formats like the 500‑series or Eurorack, and ensures that manufacturers who devote time and money to developing SEPIA Modules aren’t undercut by cloners and copyists. Karno will also offer extensive assistance to guide Module designers through the development process, with the goal of ensuring that barriers to entry are minimal even for small manufacturers or those with no experience of digital control.
Karno also anticipate a lot of interest from small‑scale builders and enthusiasts, and plan to cater to this market with a Homebrew Module. This will effectively be a shell containing all the proprietary elements of the system, which users can populate with their own PCBs and components. Development kits and GUI design toolkits will be available, and once Homebrew designs have been tested and approved, their creators will be licensed to build them in limited numbers.
As well as the rackmount L6 (foreground) the SEPIA family will soon include Hosts in other formats.
Karno will be working with manufacturers to announce and market Modules, and you can expect SEPIA launches over the next few months to include both some obvious and some more surprising designs. Pricing for Hosts and Modules has yet to be finalised, but Karno expect that a SEPIA system will work out roughly the same as a 500‑series chassis containing equivalent modules. The 12 manufacturers already on board include several big names, and Karno are in talks with many others. Their own road map begins with the L6, which is targeted mainly at live sound rental companies, theatres and high‑end studios, but there are already plans for other Hosts aimed at project studios and even guitarists.
By the time you read this, large‑scale testing will have begun, with SEPIA units poised to join tours by Florence + The Machine, the 1975, Maroon 5, Avenged Sevenfold, Bloc Party and Daniel Caesar. I’m looking forward very much to getting my hands on one myself — and to hearing what all those live‑sound engineers can do when they finally have access to top‑quality analogue gear in a format they can use!