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Our Pals' Favorite Eurorack Modulation Sources

Malekko Voltage Block, Tiptop Buchla 266t, and Of Course—Maths

Ryan Gaston · 06/19/23

What makes a modular synthesizer so special? You can explain it in a lot of ways—for some people, it's all about having access to cutting edge sound generation. For some, it's about having means of processing sound that are rare in other hardware devices. For some, it's about being able to mix and match aspects of their favorite approaches to synthesis—creating a system that is uniquely their own.

But for us? One of the most significant, unique, and powerful aspects of modular synthesizers is centered around modulation itself. Sure, creative new means of sound generation are great: but modular synthesizers are also about creating new, novel ways of controlling and interacting with sound. You can incorporate sequencing, cyclical changes, randomness, and even performative controllers in any way that you can imagine: and as such, it's very possible to create an instrument that responds to your playing in a completely unique fashion. Your modulation sources are the brain of your modular system—telling sounds how they should change over time, and helping processes to unfold in whatever way you like.

We could rap on about why we think these open-ended approaches to modulation are so inspiring—and no doubt, we'll keep blabbing on about it in other articles for years to come. If you're completely new and looking for a good overview of how modulation works, or what role it plays in modular synthesizers, I'd strongly recommend checking out our Learning Synthesis series.

For now though, we're turning the mic over to some of our best synth friends—specifically, we're going to hear from our pals Omri Cohen, Stazma, and The Unperson to hear about their favorite modulation sources. Check out the video above for their personal takes on the Malekko Voltage Block, Tiptop Buchla 266t, and Make Noise Maths—and read on for a breakdown of how all of these rad modulation sources work.

Omri Cohen's Pick: Malekko Voltage Block

Omri's pick is the Malekko Voltage Block—a voltage storage module that can act as a macro controller, sequencer, voltage recorder, crude quantizer, and much more. The basic idea is this: Voltage Block has eight outputs, each of which has a slider dedicated to defining its voltage output level. Each of the outputs also has sixteen stages of memory—which you can think of like a sixteen stage sequence. So, when switching "stages" on the Voltage Block, you're not just changing a single output. Instead, you're selecting a group of eight voltages, which are simultaneously produced at each of the eight output jacks.

You enter data into each of the sixteen stages simply by using the sliders themselves. In fact, it's possible to send in a clock source to automatically step through all the stages; if you move a channel's slider around as the clock advances, the "sequence" will populate with the slider values you had entered, making it an expedient way of entering large amounts of manual modulation data.

Perhaps one of the most interesting aspects of Voltage Block is its ability to switch stages in a large number of ways. With no external clock or CV source connected, you can treat the sixteen buttons at the bottom of the module as a way of instantaneously accessing any of the sixteen stages. You can think of this like a sixteen-button keyboard, where each key retrieves eight voltages simultaneously. This is already a huge deal for macro control of your patches: random, instantaneous access to so many independently definable voltages is a big deal. Each stage could be used to define up to eight different aspects of how your patch sounds or behaves—so if you're clever, each stage could represent an entirely different type of sound, all of which you can switch between at the press of a button.

But there's more than just that. Voltage Block can also act as a sequencer. Simply plug a clock into the CLK/CV input and switch to CLK mode, and Voltage Block will instantly start stepping through its stages at a rate determined by the external clock and the dedicated DIVIDE knob (for controllable clock division). This leads to an almost Elektron parameter lock-like sequencing experience, giving you the ability to automatically switch between drastically different types of sounds. Interestingly, you can still use the buttons at the bottom of the module to interrupt the sequence, jumping to the selected stage at the next clock cycle—and if you hold down multiple stage buttons, it will sequence through them in order, allowing you to create performative sub-sequences.

Additionally, you can send an external CV into the CLK/CV input in order to address the sequence—using LFOs, random voltages, and more to "scrub" through the sequence. Add to that many other features like per-stage smoothing, multiple sequence orders, internal preset memory, and the ability to connect to Malekko's Varigate 8+ and other compatible modules, and you have one of the most interesting sequencers/performative controllers/macro controllers available.

Stazma's Pick: Tiptop Buchla 266t

Tiptop's Buchla 266t is a Eurorack re-imagining of Don Buchla's rare and peculiar 266 Source of Uncertainty. Built in the 1970s, the original 266 Source of Uncertainty is a vanishingly rare and quite strange module—designed for the exploration of stochastic control methods for electronic music. You might think "Source of Uncertainty" sounds an awful lot like a complicated name for a random voltage generator...and in a sense, you'd be right. But there's something quite special and beautiful about Don Buchla's 266, and Tiptop have endeavored to bring that charm and mystique to the realm of Eurorack modular synthesizers.

The 266t is an uncommonly dense module, organized into six individual sections. The first is a simple noise source, offering three flavors of noise at various levels of spectral brightness/darkness. The next section provides Fluctuating Random Voltages—two independent, continuously fluctuating random voltage generators with manual and voltage control of their probable rate of change. Smooth random voltages for days!

The next section is a quantized random voltage source, which features a pulse input and two outputs, each of which respects (in a slightly different way) the "quantization" knob. Both the 2^n and n+1 outputs produce stepped random voltages. Each of these "chooses" between a specific number of potential voltage values, as determined by the quantization knob's value (1–6) plugged into the specific output equation as the "n" value (2^n or n+1). Basically, it's a way to limit the number of potential states the outputs choose between.

The stored random voltages section also produces stepped random voltages when an incoming pulse is received. One output produces random voltages with more or less equal probability distribution across the entire output range; the other outputs allows you to manually or voltage-control the voltage distribution to focus toward any particular voltage range.

The next section is a complex, polyphonic sample & hold: it takes a pulse and CV input, and produces a CV output at each pulse, as well as alternating pulse and S&H-style CV outputs, great for allocating sequences duophonically or simply generating all manner of chaotic randomness. The final section on the module is an "integrator": a voltage-controllable slew limiter for smoothing out your stepped signals.

All in all, the 266t presents a powerful encapsulation of the features from the original 266, undoubtedly one of the best-thought-out and most peculiar random voltage generators of all time. If you're looking for random voltage generation with a high degree of control, attempting to add some life to your patches, or seeking out the brain for a generative modular system, it could be just the thing. (If you want to learn more about the Tiptop Buchla 266t, be sure to check out this article!)

The Unperson's Pick: Make Noise Maths

And of course, there's Maths: a module which needs no introduction. One of the most popular Eurorack modules of all time, Maths is a multi-purpose CV generator/processor that has found its way into thousands of Eurorack systems over the last 10+ years. But...what the heck makes it so ubiquitous?

Maths is a function generator and voltage processor based on a number of classic Serge and Buchla concepts—most notably the Serge Dual Universal Slope Generator, a module from late 1970s Serge systems which could accomplish an enormous number of tasks in a modular system. Like the DUSG, Maths contains two "slope generators," which may act as envelope generators, pseudo-LFOs, slew limiters, crude waveshapers, crude low pass gates, and more. Unlike DUSG, Maths features a quite extensive suite of voltage processing tools: a mixer with attenuverters, DC offset generation, inversion, analog OR functionality, rising/falling slope detection, and much more.

Maths is organized into four channels. Channels one and four are quite similar to one another, and channels two and three are quite similar to one another, so let's assess these as groups.

Channels one and four are the function generators themselves. These each have two inputs along the top of the module (a signal input and a trigger input), a unity gain output, and an output with a dedicated attenuverter for level control and inversion. Each of these channels also features a rise and fall control with individual and "Both" CV inputs, as well as a gate/trigger output (End of Rise and End of Cycle, respectively). Each also features a cycle button and gate input: press this, and the channel will begin to cycle at a rate determined by the rise and fall time controls, as well as the shape control (continuously variable from log through linear to exponential shaping). You can use the rise, fall, and shape controls to both alter the cycle duration and shape, great for all manner of LFO-like behaviors. Or, turn cycling off and use the trigger input: the channel becomes an AD envelope generator.

The signal input can be used to apply variable slew to incoming signals, with separate rising and falling slew times. This is great for everything from adding pitch glide to sequences, or for turning gates into AR envelopes.

The two center channels are simple attenuverters with voltage offsets normalled to their inputs. If you patch directly from their outputs, you can use these channels to generate manually variable voltage offsets—or, patch into their inputs to use as a simple attenuverter for external signals.

The outputs on Maths are a-plenty: each channel is normalled into the bottom SUM output, acting as a basic mixer (after the per-channel level controls). An inverted copy of the SUM is available at the INV output, and an analog OR output produces the highest voltage of all channels at any given moment. Patching from a channel's individual attenuverted output removes it from these final mixing processes, allowing fully independent operation.

When you combine these utilities into a single module, the possibilities are near limitless. Maths can be an excellent multi-segment envelope generator, a dual oscillator, a clock source, a clock divider, a waveshaper, an envelope follower, a rectifier, and voltage biasing utility, and much, much more. Combine this power with the pleasantly/carefully crafted knob scaling and fun graphic design elements and you have a recipe for a dang good time mangling some voltages.

Creating Your Own Modulation Station

Of course, there are plenty of other modulation sources out there. Be sure to check out our full selection of Eurorack modules—you might just find the modulation source that helps you bring the right kind of life into your music.