Summ-thing for Everybody: DIYRE SB2 Passive Summing Mixer

Today, I'm going to tell you about an inexpensive way to get into analog summing, provided you already have some other necessary gear in your studio.  If you've looked into analog summing in the past, the word “inexpensive” probably isn't the first to come to mind, but by using passive components and outsourcing the assembly process to you, DIY Recording Equipment (DIYRE) has managed to produce a high quality summing mixer for the rest of us.  


What is Analog Summing Anyway?


Before we dive into an explanation of analog summing, it's helpful to understand what summing is.  Summing is the process by which all of the tracks and busses in a song are combined into one stereo track.  This may sound a lot like the definition of “mixing,” but summing is a different process than mixing.  Mixing is the work that a mixing engineer performs through level adjustments, panning, equalization, and so on in order to make a mix ready for release.  Summing is simply the work that your DAW or console does to turn the different tracks that you have prepared with EQ and other effects into one stereo track. 


For many people, the summing process occurs completely in-the-box and happens while bouncing down a final mix.  You can choose to bounce it down in real time or expedite the process, but in either case your DAW is crunching 1’s and 0’s to produce a stereo file.  This is digital summing. 


Analog summing is another way of producing a stereo track and would traditionally happen through the use of an analog mixing console bouncing down multiple tracks to a two-track tape machine.  A traditional mixing console has many different components that are not related to summing -- preamps, equalizers, and pan pots, etc.  These features are helpful for a recording studio to have nonetheless, because they enable recording and mixing. Because analog summing mixers don’t come equipped with these features which are found in large format consoles (preamps, EQ, etc.), they are sometimes jokingly referred to as “mixers that you can’t mix through.”  This is perhaps an important consideration when looking into summing mixers for your studio: they are designed strictly for hybrid mixing setups (sometimes called “out-of-the-box mixing”) where most of the mixing is done in the box, but stereo groups are sent to the summing mixer and bounced down to a stereo track.  If you want a full-featured analog console, look elsewhere. 


It might also be helpful to mention what analog summing does in terms of sound.  As I’ve said -- your DAW can already perform summing.  If digital summing gets the job done, why would anyone care about analog summing?  Proponents of analog summing often talk about certain sound qualities that can only be achieved in the analog domain.  Using analog summing, the mix opens up in a way that can’t be achieved digitally and the different tracks seem to have a bit more separation, depth, and what is often referred to as a “3D” quality.  While they can provide a nice touch to your tracks that you wouldn't be able to achieve otherwise, the effects of analog summing are all-in-all rather subtle.  Compared to digital summing, we are certainly not talking about a night and day difference, or even the 5 PM/7 PM difference that is sometimes likened to different microphone preamps.  In terms of workflow, you can route your groups through a summing mixer at the end of your mixing process, but it is probably more helpful to set it up at the beginning of a mixing session so that you can mix through it.  


Is Analog Summing Really Worth It?


There are some downsides to having a summing mixer, which we will cover before talking about the benefits.  In terms of workflow, using a summing mixer adds an extra step to the mixing process and can be a pain to work with if you want to go back and tweak your mix after recording the output of the mixer.  From both the hardware and software sides, it takes a few minutes to set up a summing mixer, and you will always have to record the output of the mixer in real time.  If you do not have a large number of hardware outputs on your audio interface and you want to use hardware effects in addition to the summing mixer, you may have to make compromises in the number of busses you can send to the summing mixer.  If you’re like me and you like to print out different versions of a mix, the time spent waiting for a mix to print in real time adds up when multiplied by dozens of mixes.  It may not seem like a huge deal to wait a few minutes for a mix to print, but it can become an annoyance if you are used to the speed of digital summing.


There is also a lot of equipment needed to use a summing mixer.  For instance, if you have a passive summing mixer (like the SB2), it won't be able to provide enough gain to bring your mix back up to an appropriate level.  You'll need a pair of mic preamps for that, and preferably ones with stepped controls.  This can represent a costly, and otherwise unneeded, upgrade for some studios.  There are more hardware considerations if you want to set up a passive summing mixer -- what if your converter or interface only has two physical outputs for your monitors?  You'll need at least 8 for many summing mixers, and the effects of analog summing are cumulative and more apparent with higher channel counts -- so 16 outputs and up may be ideal.  Again, an expensive upgrade may be in order.  What about all of the cabling needed to hook everything up?  You can see how there can be many obstacles to setting up even a simple passive summing mixer and the cost of all the extra equipment can quickly balloon far beyond the cost of the actual mixer.  Part of the reason I hopped on the analog summing train is that I already had a lot of the necessary gear lying around.  If you are happy working with an audio interface that doesn’t have the slew of analog outputs needed to operate a summing mixer, or do not see a good reason to buy a pair of stepped preamps, then maybe the cost of upgrading isn’t worth it. 

Signal Flow Chart for the SB2.

Signal Flow Chart for the SB2.

Considering all of the required hardware, combined with the fact that, with the advent of digital summing, analog summing is no longer necessary, it isn’t surprising that many choose to relegate the task job of summing to a DAW.  While critics would say that digital summing is cold, lifeless, and doesn't have the “3D” quality that analog summing does, they're missing something important.  Digital summing is super utilitarian, and accomplishes the task of summing with little to no fuss.  Plus, if you want to stay in the box, but bemoan the fact that your tracks aren't running through a vintage Neve console, there are even some plugins out there that claim to reproduce the effects of analog summing.  I have tried out Slate VCC in particular, and in my opinion it sounds quite good.


Of course, there will always be purists, and some people insist that analog summing sounds better no matter what, and that no plugin will ever be able reproduce its sound.  There are plenty of people on both sides of this debate, but in the interest of helping you to make an informed decision, I’ll tell you about my personal experience and thoughts on analog summing.  Since I started using the SB2 passive summing mixer, I have noticed more separation and clarity in my mixes. Being able to pair it with different mic preamps for different sounds offers versatility, and, although subtle, has a greater effect on the sound than I would have guessed.  There are even more tonal variations when I drive my preamps, and connecting them directly to an outboard bus compressor is often what I need to glue a mix together and give it a finished quality. I've noticed that using my CAPI VP-28s to bring my mixes back up to level does something to the low end that I don't think I could achieve digitally.  There is a certain weight that good analog gear imparts to audio that plugins don’t quite replicate, and for anyone who doesn't want to compromise on their mixdown chain, I'd have to recommend a summing mixer and some quality preamps to help you achieve this effect. Of course, it is up for debate how much of this sound can be attributed to the preamps and compressor, and how much is truly due to the SB2.


In the end, there are pros and cons to analog summing, and people ought to weigh them on an individual basis.  You can certainly make great mixes while staying 100% in the box, and there are many amazing mixing engineers such as Dave Pensado who mix entirely in the box.  It should come as no surprise that you’ll get way more mileage out of honing your mixing technique than from buying a summing mixer and that using a summing mixer will not fix a bad mix, or bad mixing technique.


Putting It All Together


So far we've talked about summing in pretty general terms while skirting around the subject of this post: the DIYRE SB2.  Although building your own summing mixer may sound like a daunting task, the SB2 is an incredibly simple design that would make an ideal first DIY project.  Because it is passive, you will not have to worry about building and testing a power supply.  Plus, unlike some passive summing mixers, there are no pan pots, further simplifying the build (panning with the SB2 is accomplished in the box).  Don’t, however, mistake the lack of features for a lack of quality.  Barebones as it is, the SB2 sounds great and opens up a realm of sonic possibility that may have previously been out of reach for many home and project mixing engineers. 


In terms of assembly, there is a case, PCB, and a few parts.  The build manual provided by DIYRE is comprehensive and easy to follow, and if you make a mistake their customer support is nothing short of fantastic.  The hardest part of the build is soldering the DB25 connectors in place because there are many points to solder and they are close together.  This is the only potential snag I see for beginners, but if you are attentive to detail and patient, it shouldn’t come a huge challenge (you may want to pick up a magnifying glass for your soldering station if you are feeling nervous).  


As with all DIY gear, the real magic of the SB2 is two-fold -- saving money (ok, maybe that part’s more boring than magic), and inspiring you to learn and grow as an audio engineer.  If you’ve never built a piece of recording gear, I promise it will help you grow your confidence and make you a better audio engineer. For those reasons alone, you should consider the SB2 summing mixer.