Solid State Logic Sigma Summing Engine

By Barry Rudolph

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Solid State Logic's Sigma Summing Engine is a remote-controllable 16 channel analog summing engine with a monitor controller section. It uses the same SuperAnalogue MDAC (Multiplying Digital to Analogue Converter) technology as SSL's Duality and AWS consoles.

Sigma accepts 16 stereo channels of line level audio from any DAW I/O unit(s) or a multi-track tape deck over four, Tascam standard AES59 25-pin D-sub connectors--four stereo pairs per DB25 cable. No other hardware is required for basic summing of 16 stereo pairs to a stereo mix bus plus monitoring.

Solid State Logic Sigma Summing Engine

Up Front

The thick, sculpted aluminum front panel of Sigma frames a large number of individual color-changing OLEDs mounted behind it showing input level metering for all 16 channels plus a larger, high-resolution stereo master meter. Each of the 16 channels can be configured as a stereo or mono source--but you cannot split a single stereo channel into two mono channels.

The green channel number LEDs light up to show channel(s) that are programmed to use the left side of a stereo source as mono. There are indicators for the individual channel assignments to either Mix Bus A (orange) or Mix Bus B (red). Any channel can connect to both Mix A and Mix B at the same time or none at all--for use of each channel's direct output only.

More green LEDs indicate: in/out stereo inserts for Mix A and B, stereo monitor sources such as Mix A, B, External monitoring input, connecting Mix B into Mix A via the B to A mode, and the headphones and their selected source.

Other features include: two user-programmable buttons, a 1/8-inch mini-jack for connecting a mobile player as a monitor source, 1/4-inch stereo headphone jack, and power on/off switch. Lastly, a blue knob rotary encoder selects (via its push function) front panel local control for: control room monitor, headphone, and both Mix Bus A and B master fader levels.

Solid State Logic Sigma Summing Engine

Rear Panel

Sigma's back panel has 16 stereo/mono inputs and 16 direct outputs using 8 D-subs. The 16 channel direct outputs are always active and sourced post-MDAC fader level.

Two more DB25s provide connections for Mix A and B bus insert send/returns, a line level stereo headphone output (studio headphone amp) two external monitoring stereo source inputs--CD player, 2-track analog tape, talkback microphone pre-amp, or DAW mix feeds.

Sigma's monitoring section has three pairs of analog line level L/R, XLRs outputs for Mix A, Main monitor, and Alternate monitor. The rear panel finishes with a 12-volt DC inlet jack for the included line lump power supply. There is a programmable footswitch jack, a RJ45 Ethernet socket, and an USB socket/switch for SSL diagnostics use.

Sigma Setup

Although you can use any analog I/O with Sigma, I wanted to run Pro Tools 11 using Solid State Logic's MADI system. I install Solid State Logic's MADIXtreme 64 PCIe interface card and its driver (ver 1.3) into my MacTel 8-core running OS 10.8.5 and Pro Tools® 11 HD and was good to go for up to 64 channels of simultaneous input/output audio at 44.1 or 48kHz or 32 channels for 88.2/96kHz all running Core Audio. (Host based--no Avid card or interfaces)

I used a 3-meter long twin glass multimode 50/125μ fiber optic cable (about $60) to connect to and from the MADIXtreme card to an SSL XLogic Alpha-Link MX 4-16 DAW I/O ($1,699 bundled with the MADIXtreme PCIe card) also fiber-looped to a second MX 4-16 ($1,449). The two MX 4-16s and MADIXtreme 64 card provide a total of 8 analog inputs and 32 analog outputs for a total cost of $3,148.

I installed ipMIDI software (ver 1.6)--a utility and shows up in Audio Midi setup app in the Mac. I also connected a NetGear GS105 5-port Gigabit switch between my WiFI router, Sigma, my SSL X-Patch and my computer. If you have other Ethernet-based control surfaces and computers, use an Ethernet switch capable of ihg data transfer rates for minimal controller latency.

You can also directly connect to your computer's Ethernet port (fixed IP) but you'd lose wireless operation and any connectivity to the Internet. After powering up and launching Safari, Sigma's browser GUI was available and ready for use at:

For including wireless control using my iPhone and iPad, I connected using DHCP (Dynamic Host Configuration Protocol) by utilizing the Mac's Bonjour feature. The Sigma User Guide walks you through many networking scenarios with instructions and recommendations for configurations using either a fixed IP address or a DHCP and controlling Sigma on WiFi connected devices.

 Control And Configuration 

For control, configuration, and relaying DAW fader automation data, the 2U Sigma is an IP-addressable device that connects directly to your computer or router with an Ethernet cable. All of Sigma's controls, setup, routing and configuration are done through the unit's embedded web page GUI that's accessible using any Flash-equipped browser on your DAW's computer or over WIFI using a tablet or smartphone. Any changes made in the browser GUI, manually on Sigma's front panel or on a WIFI connected device are synchronized across all screens.

Sigma uses standard controller protocol (HUI/MCU/MIDI) to receive fader automation from your DAW. Up to 16 fader channels of DAW automation are converted to analog gain changes using Sigma's MDACs. The well-written, extensive user guide has example setups and block diagrams to use Sigma with or without control surface(s) for Pro Tools, Logic, Ableton Live, and Cubase/Nuendo. MCU Control Surfaces, Avid® Artist Series (Eucon) and standard HUI/MIDI configurations are all supported.

Barry Rudolph

Browsing Sigma

Sigma's browser GUI has three main pages. The default Master page has buttons and drop down menus for meter source switching, master insert routing--including a insert sum function to connect a second Sigma, headphone source and level, footswitch setup and designating the function(s) of the two front panel push buttons. There is a MIDI Learn feature for generic MIDI controller programming for specific changes such as Mix Inserts in/out.

The Channels page mimics Sigma's front panel but with MDAC fader level indicated in dB and all channel names. It has buttons for global setup and solo modes plus 16 Mono buttons for changing any channel to mono. A pan pot will pop up for panning the new mono channel across the stereo bus(s). There are solo and cut buttons for each channel.

The Settings page has the DAW/Protocol and ipMIDI Port/Channel, IP address shown (fixed or DHCP), Meter scaling, solo modes (SIP/AFL, Latch/Alt) and software version and update button.

Configuration/setups done in the browser are named, modified and saved as .xml files (Extensible Markup Language) with the last setup reloaded at start up. When you save in the browser window, it always defaults to: "SigmaSettings.xml"--it does not track the given name of your last save--you'll have to retype it every time and replace the old one. I saved and named (by song or artist) setups for both mixing and tracking sessions.

After connecting 32 stereo analog sources from the Alpha-Link interfaces, I set the global operating levels for +24dBu via the browser. Mix A and Mix B buses have separate stereo inserts and (normally) sum together--with Mix B able to be routed pre/post Mix A. You could have all your vocal tracks on Mix A and all your instruments on Mix B for different stereo insert processing on each and then combine them--relative to their individual master fader settings.

My Sigma Method

Mixing and recording using Sigma requires organization and forethought to maximize its potential and the good use of its 'console center section' monitoring facilities. With so many routing and monitoring scenarios possible coupled with this unit's extensive I/O, I would recommend using a well-labeled, external patch bay. Sigma is an open architecture design with many ways to set up and utilize it.

Besides using it as a static summing amp and sending mix-leveled stems to Sigma for analog summing, there are two methods for sending fader-level automation data to Sigma's MDACs: HUI/MCU and MIDI Absolute (mutes are not supported).

HUI/MCU protocol in Pro Tools designates the first 16 faders in your mix must be audio tracks and uses ipMIDI ports 1 and 2 set in Pro Tools' Peripherals/MIDI Controllers page.

Sigma's MIDI Absolute mode designates ipMIDI Port 9 and channels 1 through 16 to control the Sigma's 16 MDACs. MIDI controller faders in Pro Tools use up no voices and can be located anywhere in the mixer and freely assigned (individually) to any Sigma channel.

I preferred MIDI Absolute and I got into the habit of naming the 16 MIDI faders by what they control and locating them near the track/buses they control. In addition, I also copied the stem bus names used in PT back in Sigma's browser window. HUI/MCU mode automatically sends the names from the first 16 faders to Sigma's screen but MIDI Absolute does not.

For mixing, I start by building stereo bus mixes (stems) of drums, bass, keyboards, percussion, backing vocals, vocals, and a couple of effects returns across channels 1 through 15 going to Sigma. I selected both Mix A and Mix B for all 15 channels. These are full-level stems and individual tracks that I tried to keep at unity inside of PT. For mute automation, I'd just mute stem outputs.

Move Mouse Over Any Image To Pause--iPad and Smart Phone Users Can Refresh-- 
-- Solid State Logic's SuperAnalogue CTRL Sigma Screen Shots Of The GUI Pages-- 

I like to record and playlist all mix passes into a new stereo audio track in Pro Tools, so I routed Sigma's Main Mix A output to the first two inputs of the first Alpha-Link MX 4-16. The mix's return used Sigma's last stereo output channel 16 and I deselected both Mix A and Mix B buttons--to prevent a feedback loop. Inputs 3 & 4 of the first MX 4-16 I reserve for last minute overdubs during the mix.

For monitoring, I connected channel 16's direct outputs to the L/R stereo External Input of Sigma via the rear panel DB25s. I selected Ext for the monitor source and controlled main monitor, alt monitor and headphone volumes with the rotary controller as needed.

Sigma's Mon L and Mon R XLR outputs connected directly to my powered monitors and the Alt L and R go to the amp that powers my Yamaha NS10m speakers. Back in Pro Tools, I solo isolated the mix track and locked it to Input monitoring while developing a mix. Deselecting input monitoring toggles the mix track for normal mix playback.

Is Sigma For You?

My Sigma review rig provided a tremendous amount of headroom to mix music and it took a while to get use to hearing so much detail, stereo width and space. There is virtually no bus noise floor and I was able to gain up or down any track or stem as well as gain up Sigma's mix bus without any noise.

Patching external compressors and/or equalizers between the AlphaLink's outputs and Sigma worked well without additional interfacing concerns. Because I used both Mix A and B buses all the time, I usually put the backing track on Mix A and the vocal production on Mix B. I also reserved channel 15 for routing all stereo effect returns generated in Pro Tools.

In Sum mode, Mix A and B inserts sums the insert return with the original main stereo mix bus signal and works excellently for separate processing of the track and vocals. This insertion point is also available for adding a second Sigma's stereo bus output for a total of 31 stereo pairs to mix (62 audio channels).

I performed my automation moves either on Pro Tool's screen with a mouse or by using my PreSonus FaderPort motor fader. I liked the monitoring facilities built into Sigma especially when going wireless from my iPad or iPhone. I can sit away from the "sweet spot" in front of my monitors or walk around the room and change volume or hit dim or cut the monitors as needed.

Sigma is a step up from typical in-the-box mixing and there is no comparison. I'm getting everything I love about mixing music on large and expensive analog consoles without any down side. I have the big and wide dynamic sound of analog summing combined with modern automation and the ease of mixing in the box! What could be better?

 Try This! 
Sigma's Mix Bus B can be injected into Mix A by engaging the "B To A" button in the web browser. I used this function to get some additional mix bus coloration by turning up Mix B's master fader above 0dB (it goes up to +10dB) and turning down Mix A's master fader.

This is an intense sound that does not sacrifice brightness and clarity for the sake of loudness.

Barry Rudolph
 Barry Rudolph 
Barry Rudolph is a recording engineer/mixer who has worked on over 30 gold and platinum award-winning records. He has recorded and/or mixed Lynyrd Skynyrd, Hall & Oates, Pat Benatar, Rod Stewart, The Corrs, and more.
Barry has his own futuristic music mixing facility called Tones 4 $ Studios and also teaches audio engineering at: Musician's Institute, Hollywood, CA..

He is a lifetime Grammy-voting member of NARAS, the 'New Toys' columnist for LA's Music Connection Magazine, and a contributing editor for Mix Magazine.

 Solid State Logic 
Web Site:

Product: Sigma Summing Engine

Price: $4,500

Pros: Awesome analog summed sound

Cons: Serious configuration/organization required.

Barry Rudolph is an L.A.-based recording engineer. Visit his Web site at: WWW.BARRYRUDOLPH.COM

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