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Greiner Engineering Tools Sum.mation

Analogue Mixer With DAW Plug-in Control By Matt Houghton
Published October 2014

If you use outboard gear with your DAW, this could be just what the doctor ordered.

Back in SOS May 2014, Bob Thomas weighed up the merits of Solid State Logic’s Sigma, a 16 stereo/mono–channel summing mixer, which features software remote control. You can find that review on the SOS web site at, and if you haven’t done so already, I’d recommend reading it as a point of comparison for the subject of this review, Greiner Engineering Tools’ Sum.mation. Greiner’s product beat the Sigma to market by a nose, but made its way more recently to the SOS offices.

The Sum.mation and Sigma are broadly similar in concept, but there are some important distinctions. First, the Sum.mation is always a 16–channel device: you can configure it to mix up to eight stereo or up to 16 mono signals. The Sigma’s 16 channels, on the other hand, can each be configured for mono or stereo use, giving you a possible 32 inputs in total — so when used in stereo it offers double the Sum.mation’s channel count. Second, the software side of things is less sophisticated in the Sum.mation. Finally, judged on the mono channel count alone, the Sum.mation is considerably more affordable.Greiner Engineering Tools Sum.mation

More Than Summing

It’s important to point out that, like the Sigma, the Sum.mation offers much more than summing alone. As well as the summing bus itself, there’s level automation for each of the 16 input channels (hence the ‘mation’ part of the name), courtesy of 16 THAT Corporation 2180A VCAs (voltage controlled amplifiers). Each VCA’s control voltage is determined by a D–A converter chip, which in turn is controlled by your DAW software.

Once attached to your computer via USB, you can set the Sum.mation up to receive control data via one of three MIDI ports. Choosing the first port means that the Sum.mation is controlled by its dedicated plug-in, which supports AU, VST, RTAS and AAX formats, in both 32- and 64-bit versions where the format allows, and both Apple OS X and Windows. You place the plug-in on an audio channel in your DAW, select port 1 and select the desired channel, and the plug-in’s fader will govern the level of the corresponding channel in the Sum.mation. The plug–in includes a MIDI learn feature, which makes it easy to hook up any MIDI control surface for real–time hands–on control. The remaining two MIDI ports cater for the HUI protocol, whereby the faders of your DAW’s first 16 channels (eight per port) are used to control the Sum.mation’s channel levels.

The plug–in allows for hassle-free remote control via almost any DAW software.The plug–in allows for hassle-free remote control via almost any DAW software.After the VCA gain stage, each channel’s signal is fed to the summing bus, but also to its own dedicated analogue output. That means that if you patch this thing into the inserts of a 16-channel console you’ll effectively have added channel level automation and recall to your desk. In a similar vein, you could patch it into a console with eight stereo subgroups to allow for automated stem mixing prior to summing.

Sum Difference

There’s plenty of debate in the various pro–audio forums about the relative merits of passive and active summing. Greiner felt that the user should be able to choose which they wished to use, and so there are actually two summing ‘engines’. One is a conventional active summing bus, whereas the other takes the form of a passive resistor network. Despite each having a dedicated output, you can’t use both engines simultaneously. The unit is set to active summing by default, and to switch to passive summing you need to move some internal jumpers. (I’d have loved to see an external switch for that).

One of the main benefits of passive summing is that the summing circuitry is about as ‘clean’ as is possible in the analogue domain. There’s inherently some loss in level, but the user is left with a choice about the nature of the makeup gain used — you could use a pair of very clean–sounding preamps, for example, or choose something with bags of tube or transformer character if you prefer. Despite the passive summing, each channel still flows through the VCA and may thus still be automatedThe rear panel caters for analogue I/O via DB25 D–sub connectors, and the USB port for remote control. The active stereo output is presented on balanced XLRs, while the unbalanced  TRS passive output and cascade input allow units to share a single mix bus.The rear panel caters for analogue I/O via DB25 D–sub connectors, and the USB port for remote control. The active stereo output is presented on balanced XLRs, while the unbalanced TRS passive output and cascade input allow units to share a single mix bus..


Outwardly, the hardware side of things couldn’t appear simpler. Each channel’s analogue signal is received via a balanced connection on DB25 D–sub connectors (there are two, each catering for eight channels), which conform to the ubiquitous Tascam wiring standard and are presented on the rear panel. Another pair of D–subs provides the balanced analogue line–level direct output for each channel. The main (active) stereo mix–bus signal is delivered to the outside world via a pair of balanced XLR connectors, while the passive output is unbalanced and presented on a single TRS jack socket. An IEC power inlet with integrated on–off rocker switch and a USB port for class–compliant connection (no drivers required) to a computer complete the I/O.

I had a single Sum.mation to test, but Greiner say two units may be connected so as to sum 32 inputs on a single stereo bus. To do this, you set one unit to passive summing and connect its passive output to the unbalanced TRS cascade input of a second unit. (The receiving unit may be set to active or passive.)

The simple, but attractively finished front panel is dominated by a series of numbers and associated switches, with a dual 10–segment LED meter for the mix bus indicating the level going into the bus, and thus how close the summed signal is to clipping. The numbers range from 1–16, each corresponding to one channel. A row of push buttons above the numbers is used to assign that channel’s signal to the left side of the stereo bus, and a row beneath to route the signal to the right. Each button has an associated bright–red LED which becomes lit when the switch is engaged, and when both are engaged — indicated by both LEDs being lit — the signal is routed to both the left and the right, placing it in the centre of the stereo field. In other words, what we have here in essence is an old–school analogue LCR pan mixer, with visual indication of the pan position via those LEDs.

Soft Centre

Hooking up the Sum.mation to my Windows (7, 64–bit) and OS X (9.2) systems was simplicity itself. It’s a class-compliant device, so you just plug in the USB cable, switch on and it is recognised by the OS. Once the plug–in is installed, you fire up your DAW and it should appear in the list just like any other plug–in. I tried it in Pro Tools 10 HD (which is 32–bit only), Cubase 7.5.2 64–bit and Reaper 4.591 64–bit, and in each case the plug–in showed up as expected. The only exception was that I’d installed the 64–bit AAX plug–in, which Pro Tools 10 couldn’t recognise. Checking the manual, this is expected behaviour: Pro Tools versions prior to 11 can’t use 64–bit AAX plug–ins; all you need to do is click to get past the warning screen, and the RTAS 32–bit version will appear and work as expected.

The plug–in interface is both simple and easy to understand: on the left-hand side you can set it up for external control, while on the right you select the channel (and on which unit, should you have more than one connected to the computer) you wish the plug–in instance to control. Play some material through the Sum.mation, waggle the virtual fader on the plug-in, and the level on the channel will rise and fall, just as you’d hope.

A row of THAT 2180A VCAs, each controlled by its own dedicated D–A, which allow for automated channel gain and recall.A row of THAT 2180A VCAs, each controlled by its own dedicated D–A, which allow for automated channel gain and recall.The HUI mode is similarly easy to configure and use, though I personally preferred using the plug-in. What you don’t have with either approach to software control is access to the LCR pan setting: that can only be switched manually, using the buttons on the hardware.

As I mentioned earlier, this whole approach to software control is slightly less sophisticated than that of SSL’s Sigma. The latter uses an HTML5 page that allows for control from any device, irrespective of operating system and irrespective of physical location: if you can connect to the router, whether via computer, tablet, smartphone or anything else that uses standard web-browser software, you can control it. The Sum.mation is less ambitious than this, but while it doesn’t support mobile/tablet operating systems, such as Android and iOS, directly and while it’s intended as a one–computer device (connecting, as it does, to a computer via USB), I don’t think this is a bad thing. SSL have certainly created a very versatile system, and I can see that its approach extends the potential appeal for large–scale production facilities. But Greiner seem deliberately to have focused on meeting the needs of the modern hybrid studio. Everything’s quick to set up, uncomplicated and does almost everything you could wish for in a single–studio setup — and if you really want to use your iPad? Well, if you can use an app to control your Mac or Windows DAW, then you can use it to control the Sum.mation via that DAW.

The Sound

I must admit to being something of a cynic when it comes to the reported sonic benefits of pure analogue summing. I just don’t see the point in coming out of your DAW via a D–A converter per channel, simply to sum signals back together, because 32– and 64–bit DAW software is more than capable of doing that job very cleanly indeed. (And even if it weren’t, in most projects you’d still be summing tracks down to stereo subgroups in order to run them through a 16–channel summing box — using precisely the same algorithms!). Sure, there may be microscopic differences, the sound having passed though converters to reach the summing mixer and, in active devices such as the Sum.mation, having passed through various ICs. That might introduce the tiniest bit of distortion, but it is vanishingly small.

The full circuitry of the Sum.mationThe full circuitry of the Sum.mationHaving said that, I do feel that analogue summing has potential advantages in some setups. First, when, as you inevitably do with analogue summing, you bring every channel’s signal out into the analogue domain, keeping them outside the box means you neatly side-step any risk of phase misalignment when returning signals to your DAW. (My, admittedly unscientific, tests suggest that DAWs’ automatic plug-in delay compensation systems aren’t always quite as ‘automatic’ or reliable as they should be, particularly when dealing with high latencies or ‘external’ plug-ins). Second, if you want to come out of the box to use outboard on your subgroups, it avoids some stages of A–D conversion. Third, it allows you to play with the analogue headroom, using your toys to ‘drive’ signals into the analogue summing bus, to achieve further pleasing distortions.

Sonically, the Sum.mation sounds very transparent, but if I ever felt that the sound was lacking in colour, then running the passive summing engine’s output into a pair of Neve 1073-style preamps compensated for that; as did running the mix into various bus compressors. The technical specs vary very slightly from the Sigma’s (see box), but I have no complaints here.

This means that the Sum.mation excels in this hybrid–studio role — the only thing that may be lacking here is a monitor or headphone output, or any sort of monitor control facilities, as you’d find on a full console. I could also see the system appealing to those who wished to add some degree of automation to an analogue console — patching one or more of these into the channel or bus insert points, for example, might be just enough to persuade someone that it’s worth bringing a console out of its metaphorical mothballs.

Hot Stuff!

Functionally and sonically, I don’t really have any major criticisms — only the minor point about the lack of pan-setting recall, which I’ve already discussed. But there was one thing about the Sum.mation which made lead me raise an eyebrow: the amount of heat being generated by the unit. On checking with Scott at Greiner, he assured me that they deliberately use the chassis as a heatsink, and that the electronics inside the box cope with the amount of heat generated without complaint. That’s all well and good, but I’d certainly suggest that you leave some sort of ventilation space around each unit when it’s placed inside your rack, just to stop it cooking adjacent units if nothing else!

Sum.ming Up

There are more dedicated summing mixers on the market today than I’d care to count, but the Sum.mation offers something very different and, for the right user, far more convenient. The standalone VCA level–automation device may not be a new concept — not only did various mixing consoles feature VCA automation, whether factory or retro–fitted, but Mackie, CAD and Behringer, amongst others, brought similar stand-alone products to market, in the form of the Ultramix, Megamix and Cybermix, respectively. Yet, the sonic performance of the Sum.mation is far superior to what went before. Also, those devices had no integration into the modern software DAW, which leaves SSL’s Sigma as the only direct competitor, and the Sigma and Sum.mation will have different pros and cons for different users.

Whether analogue summing is for you is another matter entirely, but if the answer is yes and the idea of level automation appeals, I’d urge you to evaluate the Sum.mation before deciding you need the slightly greater functionality of the SSL.

Facts & Figures

The technical specifications of the Sum.mation are perfectly respectable. The manual quotes a frequency response that’s within 0.25dB of ruler flat from 20Hz to 20kHz and tests confirmed this — I don’t have the facilities to test frequencies higher than that, but the Sigma boasts the same response all the way to 40kHz. The quoted dynamic range of 110dB A–weighted may be slightly lower than the Sigma’s >115dB figure, and well below the SPL MixDream’s 125dB — which is very impressive — but in practice this just isn’t an issue in this application; 110dB is plenty. The maximum input level exceeds +30dBu (higher than the Sigma), while the maximum output level is quoted as +27.5dBu, again higher then the Sigma. The total harmonic distortion (THD) of the signal path from channel input to stereo bus output is given as 0.027 percent — fractionally higher than the SSL’s 0.025, though I doubt even golden ears would detect this by listening! The input impedance is given as 48kΩ and the output impedance as 50Ω.


  • Very clean sound.
  • Switchable active/passive summing bus.
  • Simple to set up and use.
  • Adds basic level automation to any analogue mixer.
  • Seamless integration with your DAW.


  • Can’t assign/recall LCR panning remotely.
  • Runs a bit hot.


So much more than a summing mixer, and so much more convenient and clean–sounding than stand-alone VCA automation devices of yesteryear. It lacks a few of the bells and whistles of its main competitor, but it should still hold plenty of appeal for anyone running a hybrid analogue/digital studio.


£1980 including VAT.

KMR Audio 020 8445 2446


Greiner Engineering Tools +1 510 931 7682