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Solid State Logic Sigma

DAW-controlled Analogue Summing Mixer By Bob Thomas
Published May 2014

Solid State Logic Sigma

An SSL analogue mixer with automation and both DAW and iOS integration — all packed in a 2U rack space. What's not to like?

Even at a distance approaching 30 years, the initials SSL still bring to my mind's eye an international network of major studios, all with the same acoustic designs, multitrack tape recorders and SSL consoles, in which (in theory at least) jet-setting producers and artists could work in essentially identical environments, wherever they happened to be. In the intervening years, big recording studios have largely vanished, and the disappearance of their core market didn't exactly leave SSL unscathed. Since the 2005 Peter Gabriel-led rescue, the company have built themselves a strengthening presence in today's DAW-centric, project-studio world, through a range of music production tools. That's not to say that SSL have abandoned the studio console market — a glance at their web site should quickly dispel any doubts you have about that — but even large-console users have a need to work with DAWs from time to time, and it is the company's focus on the needs and aspirations of today's DAW user that brings them into the project-studio environment.

The latest addition to the SSL Music Production Tools line-up is the Sigma Analogue Summing Engine, which, in essence, is a summing mixer. Housed in a 2U rackmount box with trademark SSL aesthetics, what makes the Sigma a little different from most such mixers is that it features DAW-driven digital remote control of an entirely analogue signal path. There's a school of thought that contends that mixing the output from a DAW via a high-quality analogue mix bus will often sound subjectively 'better' than staying entirely in the box. True though this may be, complex mixes on a non-automated console can be a bit of a three-ring circus, and it's the Sigma's delivery of automated gain levels in an analogue environment that makes it, to me, such an interesting product.


The SSL Sigma's front panel makes clear that the functionality on offer extends well beyond simply mixing its 16 stereo input channels (which can be individually switched to mono) down to stereo. The front panel is dominated by a large curvilinear panel carrying the LED ladder metering for the A and B legs (mono/stereo) of the 16 input channels, and a larger meter pair that shows the level of the output selected by the push-select rotary control knob. This knob also controls (and displays on an illuminated ring) the nominal level of the chosen output. The only other front-panel controls are a pair of user-programmable, dual-action switches, each of which can be set to switch any two of 14 available functions. Finally, a stereo iJack mini-jack allows you to connect your MP3 player via the Ext(ernal) input.

The vast majority of analogue signals are passed to and from the Sigma via D-sub connectors, with the main outputs being presented on pairs of XLR connectors. But the humble RJ45 connector is what enables the device to be controlled by computers, smartphones and the like.The vast majority of analogue signals are passed to and from the Sigma via D-sub connectors, with the main outputs being presented on pairs of XLR connectors. But the humble RJ45 connector is what enables the device to be controlled by computers, smartphones and the like.

On the rear panel, three pairs of balanced XLR outputs drive the Mix A, Mon(itor) and Alt(ernate) stereo outputs. All 32 channels' inputs and post-fade direct outputs, together with the Mix A and Mix B insert sends and returns, the mono line-level Talkback input, the stereo Ext input that parallels the front-panel iJack and the stereo headphone and Mix B outputs appear on 10 AES59 (Tascam)-format D-sub connectors. You'll also find a footswitch input jack that replicates the function of the front-panel User switches, the input for the Sigma's computer-style external power supply and a USB connector that's reserved for factory use.

The final rear-panel feature, the network cable connector socket, not only allows your DAW to communicate with the Sigma via MIDI but also gives you access to the unit's front-panel and setup functions via its onboard HTML5-compliant web page — without which the Sigma would be only marginally more useful than the proverbial chocolate fireguard.

Once you've got the browser page on screen, the true power of the Sigma becomes fully evident. There's an analogue mixer with 16 mono/stereo input channels summing into the A and B stereo mix buses, each of which has its own insert sends and returns. Mix B can be routed into Mix A, allowing for tasty tricks such as parallel compression. You also get a talkback system, a useful monitor controller with mono fold-down that can swap between two sets of loudspeakers, and a pretty comprehensive switching system that cycles you through the various monitor sources. In fact, you're well on your way towards having a DAW-controllable SSL Duality/AWS mix bus at your disposal.


If you're planning on summing a number of DAW tracks or stems via the Sigma, as most will, then you're going to need 32 channels of good-quality D-A converter outputs to feed it. As you might expect, SSL can help you out there with two of their Alpha-Link MX 4-16 interfaces plus a MadiExtreme PCI card, to give you a total of 32 analogue outputs to feed into your Sigma and eight analogue returns to your DAW. There are a good number of suitable alternative interfaces available and your choice of interface is going to depend a lot on what you already have, how you're already set up in your studio and, of course, on your budget. You could, conceivably, even use the Sigma toautomate fades on an older analogue desk without having to buy any interfaces.

The final bits of necessary audio hardware would be a patchbay or two. Unless you've got absolutely no intention of doing any audio processing in the analogue domain, you'll want a 32-way patchbay between your interface's outputs and the Sigma's inputs, and as many patchbays as it takes to route the Sigma's 32 direct outs, the analogue I/O of your processors and the insert I/O on the Sigma's Mix A and Mix B stereo outputs.


Installation was a veritable breeze. Once you've registered your unit, you download a ZIP file containing the installation guide, manual and a third-party ipMIDI driver from Installing ipMIDI and selecting the ipMIDI Port in an application removes the need for hardware interfaces for MIDI communication between applications running on different PCs and Macs. IpMIDI sends MIDI data over Multicast UDP (User Datagram Protocol), a common transport layer protocol for multicast addressing. All of this simply means that every application running on your network can receive MIDI data simultaneously — a pretty useful trick.

A tabbed HTML5 page allows computers and remote devices to control the Sigma. Pictured are two tabs: top is the channel control tab, and beneath that, the master. The other two take care of MIDI routing and configuration.A tabbed HTML5 page allows computers and remote devices to control the Sigma. Pictured are two tabs: top is the channel control tab, and beneath that, the master. The other two take care of MIDI routing and configuration.

Next you'll want to get the Sigma itself onto your network, and navigate to its built-in web page. There are extremely comprehensive instructions in the manual as to how to accomplish this painlessly if there are problems, and they're worth reading before you start, just so you know what you might have to deal with. In my case, plugging my DAW computer and the Sigma into a spare wireless router, thereby creating a separate network, put the two in contact and gave me wireless access to the Sigma web page from every other computer, tablet and smartphone in the house.

Fading Fast

The SSL Sigma communicates with your DAW in much the same way as a control surface, and uses the automation data generated by 16 assigned DAW faders to control the gain of the Sigma's 16 analogue mono/stereo channels. The automation data is sent over the network to the Sigma by the chosen protocol, which will be HUI, MCU or MIDI, depending on the DAW. Analogue gain changes for the Sigma channels are then derived from the DAW data using SSL's proprietary MDAC (Multiplying Digital to Analogue Converter), first used in the Duality and AWS consoles.

Obviously, different DAWs — with or without different controllers — require different setups. The only general rule is that you should ensure that you have a bank of 16 faders dedicated to the Sigma as the first 16 tracks in any session and, other than that, the manual contains specific setup examples for Pro Tools, Logic, Cubase/Nuendo and Ableton Live, and 'Other DAWs', with and without control surfaces. Should 16 mono/stereo automated channels not be enough, you can run two Sigmas in parallel to give you 32 channels, for a total of 64 inputs. The two units can sum their Mix A outputs by feeding the output of one unit into the Mix A Insert of the other and engaging the Mix A Sum function.

Just Browsing

Once you've got the network and DAW/control-surface setups sorted, the Sigma's internal HTML5 page gives you not only direct access to all the unit's front-panel control functions, but also to its other functional controls. The Master screen replicates the front-panel controls and, in addition, allows you to set the talkback and monitor dim levels, to activate the MIDI Learn and to select the footswitch function. MIDI Learn allows you to assign Continuous Controllers to all front-panel functions apart from the User buttons, which could prove extremely useful if you were using a control surface and you had the Sigma itself positioned out of reach.

The Channels screen is where you set individual channels to stereo or mono (at which point a pan control appears), routing to Mixes A and/or B,and solo or cut status. There are also three global functions, whereby you can obtain channel names from your DAW (if your setup supports that function), force global mono, stereo and Mix A and/or Mix B output routing and set Solo Safe for individual channels.

The first section of the Settings screen lets you define your brand of DAW, set your desired communication protocol, select MIDI ports and name your Sigma. A second area allows you to alter network settings, and the third and final part is where you set the meter scale (+18dB to +24dB), set Solo In Place or AFL modes, and set the function of the Solo switch. In Latch mode, pressing one switch after another will add channels to the solo buss; in Alt, pressing a second solo switch will cancel the first.

The last two tabs on the Sigma's web page enable you to save different Sigma setups on your computer as XML files and reload them at a later date. Should you access the web page on, for example, an iPad, these last two tabs are not shown.

As well as the universal HTML5 software, there are dedicated control apps for both iPad (pictured) and iPhone.As well as the universal HTML5 software, there are dedicated control apps for both iPad (pictured) and iPhone.

Overall, I have to say that I was mightily impressed with the Sigma's inbuilt HTML5-compliant web page. It was rock-solid, fast and responsive on every computer and handheld device that I tried it on, whether the connection was wired or wireless. Adding to your options in this area, at the recent 2014 Frankfurt Musik Messe SSL announced the forthcoming release of two free templates running on the very modestly priced Hexler Touch OSC (Open Sound Control) iOS app that allow full control of the Sigma (including fader levels) from an iPhone or iPad. This opens up the possibility not only of using the Sigma as a stand-alone mixer, but also the prospect of user-generated templates, since SSL intend to publish their OSC message specification.

In Use

Once up and running, the Sigma behaved impeccably, doing exactly what it says on the tin in operational terms. With or without a control surface driving the DAW faders, the response from the Sigma felt completely natural, and I never felt that technology was getting in the way of the music. The HTML5 page made changing settings on the fly a simple task and, in combination with the DAW-based automation and the Sigma itself, the whole delivered an easy to use, fast and great-sounding system.

The Sigma certainly lived up to SSL's reputation for sonic performance. Compared with the stereo output from my resident analogue mixer, the Sigma's main outputs delivered a wider soundfield, a higher level of detail and a deeper bass end. Admittedly this is a very subjective opinion, but I have a suspicion that the absence of almost anything other than gain control in the Sigma'ssignal paths definitely helps it to achieve its level of performance.

Mention SSL and the question of the legendary, thick, slightly overdriven, harmonically rich and somewhat compressed SSL 'sound' from the last quarter of the last century will eventually arise. Certainly, it's possible to drive the Sigma hard, but this is not a compact recreation of a 1980s or '90s SSL console, and it isn't ever going to sound quite like one. You can push the Sigma in this way, though personally I'd rather put a really great-sounding (and ideally valve) compressor in parallel with Mix A and drive that hard instead. However, there are no rights and wrongs in recording, and your mileage may vary.


As I said earlier, the SSL Sigma does exactly what it says on the tin. It will work flawlessly with your DAW and will deliver an exemplary audio performance. If you don't have multi-channel D-A and A-D conversion and a control surface already in your studio setup, you will want to invest in those in order to make the most of the Sigma's abilities. A few choice pieces of outboard effects processing and dynamics hardware would also be a good idea.

This could all start to get expensive but, personally, I'd have to say that if you're recording at a level where a Sigma would fit into your studio and your workflow, the expenditure should prove well worthwhile. I'm going to miss it when it has to go back.


Although there are plenty of analogue summing mixers on the market, the only one that I could find that got close to the Sigma was the Greiner Engineering Tools Sum.mation(£1980 including VAT), which features automation of its 16 mono channels via a DAW plug-in. The venerable AMS Neve 8816 gets close in terms of its monitor capabilities but, although its settings can be stored and recalled, a lack of dynamic automation puts it out of direct contention. A slightly leftfield alternative, if you were starting from scratch, could come in the shape of the Focusrite Control 2802 analogue console and DAW control surface which, in combination with a RedNet 2 interface, could work well in a smaller setup.

At-a-glance Specifications

  • Maximum I/O level: +18dBu, +22dBu or +24dBu.
  • Frequency response: 20Hz-40kHz, ±0.3dB.
  • THD+Noise: <0.025 percent (20Hz-20kHz).
  • Noise: channel input to output, less than -83dBu at +24dBu (20Hz-20kHz); channel input to Mix A, less than -75dBu at +24dBu (20Hz-20kHz) (Stereo, all channels routed.)
  • Depth: 32cm (12.75 inches).
  • Height: 8.9cm (3.5 inches).
  • Width: 43.5cm (17 inches).
  • Weight: 5kg (11lb).


  • High level of sonic performance.
  • Its technology doesn't get in the way of the mix.
  • DAW-driven level automation.
  • Excellent HTML5 web-based control interface.
  • Upcoming Touch OSC control of all functions via iPad.
  • Though expensive, it still represents good value.


  • None, other than the need for good-quality converters and peripherals to make the most of its performance potential.


The SSL Sigma is an innovative take on the analogue summing mixer that combines DAW-driven automation of digitally controlled analogue 'faders' with a very flexible monitor controller. Partnered with good-quality digital converters and analogue hardware outboard equipment, the Sigma is capable of producing really great-sounding mixes. Definitely one to audition.


£3359 including VAT.

Sound Technology +44 (0)1462 480000.