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Fractio Solum deep dive

The year was 2019. Poodle skirts and bobby socks were in fashion. And Noise Engineering announced Fractio Solum, our voltage-controlled clock divider/multiplier. Well, there were a couple (read: a lot) of slowdowns along the way, but it’s finally here!

You may remember when we first introduced Fractio Solum. It’s versatile, strange, kinda cute from the right angle, and we’re pretty happy with how it’s turned out. We know we have a winner when we all want to play with a module more than we really have time to, and this one’s gotten a lot of patch time from all of us. Let’s talk about what Fractio Solum is, how to use it, and see what it can do in some patches.

Ratio rationale

So, what do those big numbers mean? At its core, FS is a clock divider and multiplier. You put a clock in. You get a clock out. Simple, right? But here’s where it gets interesting: you change how that clock comes out by turning the encoder and changing the ratio shown on the display. The ratio display works just like a fraction: the number on top represents the clock output. The number on the bottom represents the clock input. This makes seeing what your division is easy.

Now, that’s all well and good, but what clock ratios are actually available on FS?

The short answer is A LOT.

The more in-depth answer is that you can get everything from 1/16 to 16/1. To make it easy to move through these, we’ve grouped the ratios into three sets, selected by the switch in the middle of the displays. The “1” setting contains all the ratios that, as you may have guessed, have a one in the top or bottom of the fraction. Your normal divide by eight, multiply by four, divide by two can be found here, but so can more interesting things like 1/7, 9/1, 1/15, 10/1...

The “23” setting contains ratios involving powers of 2 and 3. You’ll find more standard things here: 1/16, 1/8, 3/1, that sort of thing. There are also a few oddballs like 8/3 in here, but if you need more ratios than the “1” mode gives you but don’t want to get too abstract, this is the mode you’ll want. We’ve found this to be the most “musical” mode, at least in the most traditional sense.

Lastly, there’s N/M mode. This mode has every single ratio from 1/10 to 10/1. If you like unusual timings, tuplets, and polyrhythms, this is the mode for you. I didn’t know 7/3 could be a fun time signature until I plugged FS in. This is the favorite mode around the NE house.

If you want to take a look at the complete list of all the ratios FS has available, check out the ratio tables in the manual here.

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Fractio Solum

Ins and Outs

We wanted to make the FS flexible and versatile, so we designed it with quite a bit of I/O. First, there’s your standard clock and reset inputs, labeled In and RST. Now, bear in mind that you don’t need to patch a reset signal here: all you have to do is patch in a clock and you’re off. I find the RST input very helpful when using FS for sequencing: I can dial in a wacky ratio, and then use the RST input to create a repeatable sequence based off my main clock. If you’re in 7/3 and using the /2 out, for instance, your output is gonna be pretty abstract compared to other rhythms that may be happening in your patch. The RST input helps tie everything together, though: trigger it at regular intervals and your 7/3 becomes a repeating rhythmic motif that’s much easier to fit into the rest of a patch.
Of course, there’s also a CV input: this lets you change the clock ratio of FS with an external CV source. This allows for some awesome stuff like automated time signature changes, rhythmic clock sequencing, burst generation… You name it.

On to the outputs: FS has four outputs. There’s the main out jack, labeled Out (clever, I know), which gives you the exact ratio shown on the display. Additionally, there are x2 and /2 outputs, which are respectively twice as fast and half as fast as the main Out jack. Lastly, there’s the BOC jack, which stands for Beginning Of Cycle (and also Boards of Canada. Because they are great). As the name suggests, it fires each time the FS completes a cycle, based on the slowest /2 output.


If you tap the encoder, all the outputs on FS get muted. It keeps track of the input clock while it’s muted, so when you tap it again to unmute it, it’ll be correctly in phase with the clock input. It’s a handy performance feature if you’re using FS as a rhythm generator for your voices, if you want to make a sequencer do interesting things, or if you just need things to be a little quieter for a second.

Fractio Solums? Fractio Soli? A flock of Solum?

Earlier, we made some pretty cool patches. However, we just used ONE FS. What if we have TWO? What will happen?? Polymetric patching, that’s what! Here, we have a melody and four-part percussion patch. Imitor Versio gives some delay and texture to the patch. Two Fractio Solum and a Vox Digitalis provide all the sequencing for the patch, and an external CV sequence modulates the FS ratios to keep things dynamic.

But don’t feel the need to stop there. Mult as many FS together as your heart desires for evolving landscapes of polymeters and polyrhythms.

A brief history of time (divider)

Fractio Solum as a concept came to us in 2017. We really liked the idea of being able to efficiently clock polyrhythms (who doesn’t?) in a compact interface. By 2018, we had a prototype and thought the firmware was in pretty good shape. We were close to release and thought it would be a March(ish) 2019 product. We showed it off at NAMM in January of 2019, where we discovered a bug in the firmware (NAMM has a way of making sure that everything that can go wrong does), so we held off on release while we tried to sort out the problem. Other modules took priority for a few months, but development finally resumed toward the end of 2019, at which point we realized that it was probably worth bringing the whole product to the new microcontroller line we’d moved to. Kris made a new prototype and Stephen set about rewriting the code for the STM line of chips. Markus braced for the next round of test, which, we won’t lie, was daunting from the beginning. If you have a bug in a 7/13 clock in the /2 out, how exactly do you tell? There was a lot of setting of expectations for test in this module, and a lot of decision calls to be made for behaviors.

We started 2020 with ambitions of releasing a LOT of modules. But that…didn’t happen. We got a final FS prototype and knew our hardware was gold but still had a bit of firmware to work out. We set a release date and continued to plug away at the firmware. We went through about a dozen firmware passes fine-tuning output behaviors and making sure it did everything we wanted it to. Two days before launch, Kris wrote a factory test plan (what the manufacturer uses to make sure units are built to spec before they ship them to customers) and kicked it to Markus to run through. We have a two pairs of eyes policy here because we catch a lot more mistakes that way and sure enough… Markus found a bug on the FS because the test plan Kris wrote revealed a firmware issue! Mad scrambling ensued, all hands once again on deck, but finally, FINALLY, we were able to sign off on firmware, and get the FS into the world. It was a definite journey and learning experience for all of us.

At this point you’re probably thinking, “Woah! When can I order my Fractio Solum??” At least, we hope you are. And we have good news: it’s available now! Go get it here. Add it to your rack. Clock the things. I’m not saying that the key to happiness and a long, fulfilling life is a clock divider, but I’m also not saying it’s not....

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