Undertone Audio: Pyra-Sum Summing Mixer

I still believe that analog mixing sounds better than in the box mixing, and I enjoy the workflow more as well. I’ve been mixing with a hybrid analog/digital setup and process for years now, and feel like I get faster, better mixes working that way. Fewer and fewer people still mix on large format analog consoles like Bob Clearmountain does these days (see our recent interview with Bob and Jesse Ray Ernster in Tape Op #151 for a discussion of both analog and in the box mixing methods), and many people mixing analog use some type of smaller footprint console or summing mixer. The summing mixer category was pioneered by Dangerous Music with their 2-BUS [#35] back in 1999. Since then, most audio console manufacturers (and many smaller audio companies) have introduced some style of summing mixer. I’ve been using the Roll Music Systems Folcrom RMS216 [#45] passive summing mixer, along with a 10-channel Spectra Sonics [#102] sidecar console, for the past decade or so, and really like the way it sounds. Granted, hardware is more expensive than software and plug-ins, but hardware comes with a perpetual license and never needs software updates. A lot of the gear in my mixing room is fairly affordable but gets great results, such as my Revive Audio modified ART Pro VLA compressor [#125] and affordable 500 Series modules like the API SV14 [#153] and dbx 530 [#119] EQs.

Most summing mixers are active, but like the RMS216, Undertone’s Pyra-Sum is passive. There are two big advantages to a passive summing mixer. One is that the make up gain stage is separate (you need to add a stereo mic preamp to the signal chain), so you can add (or not) whatever coloration you might want (or not want), based on what is used for make up gain and how hard it's pushed. The other big advantage is price; passive summing mixers are more affordable because the circuitry is less complex. They don’t even have power supplies! I’ve also used the AMS Neve 8816 summing mixer [Tape Op #55], which I loved the sound of, but it’s priced at over $3000, while the Pyra-Sum sells for $1600, and the RMS216 for $775.

Undertone Audio was founded by producer Eric Valentine [Tape Op# 45], and we interviewed him later about Undertone specifically [#133]. He’s an extremely thoughtful and knowledgeable engineer/producer with thousands of hours of mixing experience and well-known records to his credit. This is not a company run by a marketing committee trying to hit price points. Undertone initially started making consoles, but not many were manufactured – though the lucky few who own one, like Greg Wells [#123], swear by them. But times have changed, and Eric’s introduction in the Pyra-Sum manual sums this up (pun intended) nicely: “After working on the custom-built UTA large format consoles for ten years, I could no longer deny that the large format analogue console workflow could not compete with the speed and flexibility of a hybrid setup. As much as I adore the sound and power of the UTA custom consoles, I was ready to move on and embrace the world of hybrid mixing."

He goes on to discuss what he found missing in existing products: mainly the multi-bus architecture of large format consoles. I don’t use a multi-bus setup as extensively as Eric does, but what I really appreciate about the Pyra-Sum is its thoughtful and logical layout that groups instruments together allowing for mono or stereo inputs on crucial tracks such as kick, snare, bass, and lead vocal. Muting groups and instruments on the Pyra-Sum is easy and straightforward. However, if you wanted a version of the Pyra-Sum that does not have the drums, bass, guitar, vocal, etc. labeling, UTA also makes one with a simpler faceplate with the buses printed as letters and numbers instead. Most of what I do is pretty firmly in the pop music idiom, so I appreciate the more specific labeling.

The Pyra-Sum has four stereo buses: Drums, Music, Vocals, and the main stereo mix bus. Each bus has multiple inputs (both stereo and mono – depending on the instrument). UTA has a good video (vimeo.com/767165118) that shows the input structure for more details on this. There are 24 inputs to the bus groups. The Drum bus feeds into the Music bus, and the Music bus and the Vocal bus feed into the stereo Mix bus. There are also four stereo inputs that go directly into each of the four stereo buses, for a total of 32 inputs, which allows for parallel compression, among other uses.

I should mention that you'll need a fair amount of patchbay real estate to set up the Pyra-Sum in order to take full advantage of its flexibility in the ability to patch outboard gear in and out of it. Of course, if you have an easier setup or use the same gear on every mix, you could do a simpler, hard-wired setup between your D/A converters and the Pyra-Sum. But the idea here is that with the Pyra-Sum, a full patchbay, and some outboard EQs and compressors, one really can replicate a large format console with a much smaller footprint and improved recall ability. The manual also suggests adding some type of level automation system, such as the WesAudio ngLEVELER [Tape Op #152], which would add post-compression level automation – although I did not go down this path. I should also mention that in order to use the Pyra-Sum as designed, you'll need eight channels of matched mic pres (two for each stereo bus for make up gain).

As I tend to group and compress instruments from my DAW directly (i.e., 4 to 6 guitar tracks out of two converter outputs and into one stereo compressor), I initially tried to hook up the Pyra-Sum with just one pair of mic pres on the final stereo bus while trying to bypass the eight mic pre insert points with one straight wire DB-25 cable. It worked, but just barely, because each stereo bus has a 35 dB loss, so by the time the Drum bus feeds into the Music bus that feeds into the stereo bus, I needed 105 dB of make up gain, which isn't practical. So, to take advantage of Pyra-Sum’s flexibility, you'll need quite a bit of cabling and patchbay space, plus eight channels of high-quality mic pres. If you don’t already have all this on hand, expect to spend a bit of cash and realize the initial low cost of the Pyra-Sum will increase by the time it’s fully functional. The cool thing, however, is that you could mix up the mic pres if you wanted to. For instance, I tried one mix with Neve 1073s on the Drum bus, API 312s on the Music and Vocal bus, and UTA mic pre/EQs on the stereo bus.

I ended up patching into the Pyra-Sum with one of my Aphex 1788 8-channel mic pres. These are great-sounding pres with discrete circuitry, a Jensen transformer on each input as well as the ability to store your gain settings. As fun as it was to experiment with different pres on the buses, the 1788s sounded great, were consistent, and allowed me to get by with a bit less cabling and patchbay real estate. At the simplest level, you could hook up the Pyra-Sum so that it’s fed directly from your DAW, and the mic pres also directly connected. This would still allow for analog summing while eliminating the need for a patchbay, but would also make it very difficult to patch in any external outboard gear, which in my mind, is one of the main reasons to mix outside the box; fewer plug-ins. In the end, I dedicated 26 patchbay points to the Pyra-Sum and needed six 8-channel DB-25s to balanced TRS and XLR connectors to hook it all up. If you bought patchbays with DB-25 inputs, that could cut some cabling and connector costs. The suggested layout in the Pyra-Sum manual, with automation, compression, and EQ normalled on every input, requires 288 patch points!

After a fair amount of thought, even though I have the occasional guest engineer in my room, I set up my patchbay for the way that I mix, while still leaving options open for other scenarios. I opted to initially not put the direct-to-bus inputs on the patchbay, instead leaving them on a DB-25 to TRS snake that I could utilize if needed. I put all remaining 24 inputs on the patchbay, albeit in a way normalled for how I work and allowing for my UA Apollo’s 16 [Tape Op #113] outputs to be used in my specific workflow. So, output 1 was patched to input 1 (kick mono), output 2 to input 3 (snare mono), outputs 3 and 4 to inputs 5 and 6 (stereo drums), outputs 5 and 6 to inputs 13 and 14 (stereo guitars), output 7 to input 11 (mono bass) and output 8 to input 21 (lead vocal mono) with the next eight outputs going to other stereo pairs, and the last eight being the odd ones out I didn’t expect to use as much (including the other half of the mono inputs: kick, snare, bass, lead vocal). This made for some very confusing wiring, but it worked perfectly the first time I tested it all. This setup allows me to put the first ten outputs of my mix on faders with EQ on the Spectra Sonics sidecar without patch cables, or route around it if I don’t want the mixer in the signal path – and I can patch in outboard gear into any of the 24 inputs on the Pyra-Sum.

Bottom line – this is a serious piece of studio gear despite being a single rack space unit. It’s fairly affordable and will take nearly the same level of commitment in terms of cabling and patchbay space as buying a small console would. The manual details several patching examples, and I recommend reviewing it in advance of setting up a Pyra-Sum in your own studio space. Once I settled into mixing with the Pyra-Sum, I ended up swapping out the last two channels of the Aphex 1788s for a pair of UnderTone MPEQ-1 pre/EQs so that I had some EQ on my master bus, which was especially useful when printing to my Otari MX-5050 1/4-inch tape machine. It also felt appropriate to “close the loop" with the MPEQs on the master bus to get as close as possible to an Undertone console!

Once everything's patched in and working, there's still one more step before you can move your mixes out of the box, and that’s to calibrate the eight channels of mic pres for unity gain so that levels translate the way we expect them to out of the DAW. In other words, regardless of which of the three buses you route your outputs to gain should remain the same. I initially set this up using a test tone, moving sequentially through the four buses calibrating the mic pres and trim pots on the Pyra-Sum’s front panel to get it working – but the levels seemed a bit wacky across the eight channels of mic pres when trying to keep everything centered and at unity gain. I thought about it overnight and started over the next day. But this time, I worked backward, beginning first with the vocal and stereo bus (5-8) and then the instrumental bus (3-4), and then lastly, the drum bus (1-2). This time the levels were much more even, and everything settled into place perfectly as I routed various elements of my mix to the different inputs and buses. While not intuitive, working backward on the calibration should have been my obvious starting point.

I’ve been using the Pyra-Sum for several weeks now while mixing a 12-song album with a variety of different tracks, and I love it! It sounds great, and my workflow has become much faster and smoother. With the logically laid out face panel directly in front of me, I can quickly mute and solo tracks without having to cursor around in my DAW. Less time with the computer is more time spent on focused listening, and I’ve been able to get mixes up and printed much faster with the Pyra-Sum in my workflow. I always print stems when I mix so that I have some level of recall ability, and the muting options make that process go much faster and smoother as well. This is the most significant piece of gear I’ve added to my mixing space in years, and I enjoy the workflow much more than my previous setup. This is not a simple piece of gear, but I would highly recommend it to anybody wanting to commit to getting their mixes out of the box and into the analog domain.