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This Month’s Module: DivKid’s Modulation Sources

Chris Meyer

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Want to create more interesting modular patches? Add more modulation sources such as the DivKid/Instruō øchd and DivKid/SSF RND STEP.

Ben “DivKid” Wilson is one of the better-known users in the Eurorack modular world. He’s created over a thousand YouTube videos on the subject, informed by his deep understanding of both modular synths and practical musical applications. When I got back into modular synths myself several years ago, Ben quickly became my go-to source for information on the latest toys.

Ben has been dabbling in designing his own modules. Instead of creating some complex mega-module, he has focused on creating small (all 4 hp in width) yet highly useful utility modules in collaboration with a variety of manufacturers. These include Mutes with Befaco to bring elements into and out of your patch, øchd with Instruō or smoothly varying modulations, and RND STEP with Steady State Fate for stepped modulation voltages. I’m going to focus on øchd and RND STEP in this article, as they are a good yin/yang pair of modulation sources.

Why More Modulation?

A normal synthesizer patch—driven just by note on/off events (gates) and normal envelope generators—will produce the same note every time, with little to no evolution while the note is being sustained. This can get boring after a while, no matter how nice the timbre.

Adding more modulation sources—control voltages that change in differing ways over time—can add more life to sustained notes and make each new note sound different. The first step is choosing modules that offer voltage control over the way they can change the sound. The second step is patching a variety of modulation sources to these voltage-control inputs. Slowly changing modulation voltages can create sequences and drones that evolve over time; fast modulation can add energy, articulation, or tension to individual notes.

DivKid/Instruō øchd

Ochd is Scots Gaelic for eight. This module contains eight analog ±5-volt triangle wave LFOs connected to a single Rate knob and control voltage input. The LFO outputs are arranged from fastest on top to the slowest on the bottom at roughly one-octave intervals, each with a bicolor LED showing its current state. 

The speed of the eight LFOs was tuned by ear to create a drifting sensation when used together, in contrast to being synchronized in lockstep. LFOs 2 through 4 run at slightly faster than half of the frequency of the LFO directly above. LFOs 5-8 run slightly slower than half of the speed of the one above.

The Rate knob can vary the speed from 160 Hz for LFO 1 to 25 minutes per cycle for LFO 8. External control voltage—routed through a front panel attenuverter—adds to the Rate knob’s position. It extends this range up slightly and down to 0 Hz. This means that large negative voltages—such as a gate signal, with øchd’s attenuverter turned full negative (counterclockwise)—can “stall” the LFO outputs at their current values. Patching an instant attack/slow decay envelope generator with the attenuverter at full CCW will cause the LFOs to stop at the start of each new envelope and then gradually allow them to ramp back up to normal speed. 

A great trick is to patch one of øchd’s LFO outputs back into its Rate CV input. Choosing a faster LFO for this feedback patch causes the slower outputs to pause and advance as the CV source goes negative and then positive, creating stair-stepped output waves (the left side of the image below). Patching a slower LFO back into its Rate CV causes the other LFOs to gradually slow down as the driving LFO goes negative. It then produces a high-speed spike as the driving LFO goes positive again (seen in the right side of the image above).

DivKid has created an introductory video demonstrating this plus a few other application ideas.

DivKid/Steady State Fate RND STEP

Compared to an LFO that creates continuously changing voltages, a sample & hold (S&H) freezes a voltage at its current value with each new trigger or gate it receives. RND STEP contains six sample & holds arranged as three pairs, with some interesting normalization (default patching) inside and between pairs.

Each S&H pair contains a trigger in, a voltage source in, a unipolar (positive only) voltage out, and a bipolar (positive and negative) voltage out. LEDs indicate the polarity and level of each output. Both outputs are normalized to their own internal pink noise sources to create two different random values for each trigger received. Patching an external signal into the voltage source input affects just the bipolar output. A trigger patched into the first section is normalized to trigger the other two sections as well. Patching a different cable into the trigger inputs for the lower sections overrides that connection.

The unipolar output behaves as if it is bipolar internally, with the negative voltages clipped off. This means roughly half the time, it outputs 0 volts. The internal sources for both outputs are also weighted toward lower values, as you can see in the chart below from the excellent manual. These decisions were made to create a more “musical” range of output values that spend more of their time in a similar range with a more subtle effect. Higher voltages then occasionally pop up as accents.

Despite this intention, some users have voiced a desire for a higher average output voltage when using the internal noise source. A set of six tiny trimmers on the circuit board allows you to set the range for each output. Please be gentle with them, as they have a limited range of rotation.

You can also patch any source CV as high as ±10 volts into the bipolar side’s input. For example, you can patch an LFO such as øchd to this input to create stepped values that follow a pattern; this is the yellow trace in the image shown earlier. RND STEP can also be clocked at high audio rates. This allows you to use RND STEP as a resampler for “down-sampling” audio signals patched to its sampling input.

Most analog sample & holds do not work well for controlling pitch. Their outputs tend to “droop” slowly back toward 0 the longer a sampled voltage is held. RND STEP performs exceptionally well in this regard, with a droop so slow that it will be imperceptible for most applications. It also captures a new voltage very quickly. Some other modules suffer from delays when trying to sample a new voltage at their inputs, potentially not capturing the intended voltage.

Below in an extensive video by DivKid that shows off several applications for the RND STEP.

Stay in Control

A common saying in the modular world is, “You can never have too many VCAs.” They allow you to vary the strength of both audio signals and modulation voltages in a patch. But to truly take advantage of those VCAs—as well as the rest of the modules you already have—you also need to have more modulation sources to drive them. These two modules provide eight smooth and six stepped CVs in just 8 hp, making it easy to add them to almost any system. They may not be flashy, but they could be just what you need to bring life to your patches.

Websites: Instruō øchd, instruomodular.com; Steady State Fate RND STEP, steadystatefate.com

Price: $199 each

Synth and Software would like to thank longtime modular user and former synth designer Chris Meyer for his contribution. Chris is the force behind Learning Modular, where he teaches others how to master modular synthesis.

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