Alphabet Soup #1: The DSG

The STS Serge Modular can be a daunting system at first blush, especially for those who come from an "East Coast" modular synth background. My first synthesizers were Moog analogs and my first Analog Modular Synth was an Arrick "Dotcom" system - so I started out with East Coast paradigms that I had to "unlearn" in order to use my Serge Modular to the fullest. For those of you coming from a similar background or those just discovering the Serge Modular for the first time, these "Alphabet Soup" pages are dedicated to you!

The Serge Modular is intuitive and fun to use - especially when you realize the main difference between a Serge Modular and most others has to do with the size of the building blocks, where a Moog or similar modular will have monolithic building blocks like ADSRs and Oscillators, the Serge can be more "low-level" in that you can build ADSRs and oscillators from Serge modules or, more properly, Function Blocks.
These Function Blocks usually come bearing arcane names that have been shortened to an "Alphabet Soup" conglomeration of acronyms. In this series of articles, I'll be talking about some of the ways to approach these Function Blocks to create much more useful, surprising, complex or just simply fun synthesis features.

The first function block we're going to look at is the "DSG", otherwise known as the Dual Universal Slope Generator. This mild-mannered module is in some ways the most powerful one in the entire Serge catalog because it can become so many different things depending on where you place the patch you'll soon see.

The DSG can seem deceptively simple at first. It's a pair of bi-directional slew generators, the kind of thing commonly used to create portamento for oscillators or for the "smoothing out" of a Control Voltage, creating a glide between voltages. In the Serge, the functionality can go a lot deeper depending on how we patch. Lets begin by looking at just the top half - the DSG is actually two identical modules, one placed above the other - hence the "Dual" in its name.

I'll be using the Block Diagram below to illustrate the patches in this article as they each only require half of a DSG:


Let's start our investigation by creating a simple attack-release envelope.

AR EG - Patch a Gate or Trigger signal into the "TRIG IN" jack. A attack-release (AR) voltage envelope is generated at the "OUTPUT" jack with its attack and release times controlled by the "RISE" and "FALL" pots respectively.

ASR EG - An attack-sustain-release envelope is implemented by routing a Gate signal into the "INPUT" jack. The resultant EG output will sustain as long as a Gate is present. Again, the attack and release times are controlled by the "RISE" and "FALL" pots respectively.

HINT: The above envelopes are linear envelopes. For an exponential response, stack a banana cable on the "OUTPUT" and patch it to the "VC IN" jack and adjust the "VC" pot positively to taste. The "RISE/BOTH/FALL" switch selects which part(s) of the envelope become exponential.

HINT: Complex envelope shapes can be created by mixing the outputs of more than one Slope Generator together into a single signal with a voltage mixer like an ACPR, MPRO or a PRC. For instance, if driven by the same gate, you could have one half a DSG doing the "AD" portion and the other half the "SR" portions of an ADSR envelope with unique control possibilities.

One interesting thing to note is that when an envelope finishes its cycle, the "GATE OUT" jack generates a new gate - which leads into the next use of a DSG - LFOs.


Low Frequency Oscillators are relatively easy to make. Lets start by patching the "GATE OUT" jack to the "TRIG IN" jack just below it. The DSG will start to oscillate all by itself with its frequency determined by the "RISE" and "FALL" knobs. Watch the LED for a visual reference of overall frequency as well as the rise and fall times.

SQUARE WAVE LFO - Stack another banana cord on the "GATE" jack and you'll get a square wave.

TRIANGLE/SAW WAVE LFO - Patch a cord into the "OUTPUT" jack and you'll have a triangle or saw wave. One nice feature of this waveform is you can control its shape by adjusting the "RISE" and "FALL" knobs. A short rise and slower fall gives a regular Saw waveform, a slow rise and quick fall gives a Reverse Saw and equal rise and fall times result in a Triangle. You can modulate the shape of this waveform by patching a CV into the "VC IN" jack and setting the modulation target with the "RISE/BOTH/FALL" switch. Lots of fun!

HINT: Complex composite LFO waveforms can be created by mixing the outputs of more than one Slope Generator together into a single signal with a voltage mixer like an ACPR, MPRO or a PRC.

HINT: To "soften up" a triangle or square waveform (or even a more complex composite LFO waveform), run it through an available 1/2 DSG patch-programmed as a Slew Generator (see "Directional CV Glide" below).

Audio Oscillator:

Let's speed things up a bit, shall we? Everything we learned about using the DSG to make LFOs is applicable here for audio oscillators as well - all we need to do to the above patch is to route a CV of choice into the "1V/OCT" input jack to drive the pitch of the oscillator. The TKB or various Sequencers are a great source of preset CVs.

The DSG doesn't track so hot in the higher registers (and won't track at all above a certain pitch) but is an excellent source of bass and mid-range tones with lots of character.

HINT: To "warm up" your oscillator, try running it through the top section of a Wave Multipliers function block with its switch set to "HI", you'll get a soft-clipped sound similar to a tube amp.

HINT: When mixing audio oscillators, sometimes it helps to invert one or more of the signals to help avoid "cancellation" issues, especially if you have a lot of feedback going on - unless that's the effect you're going for.

Trigger/Gate Delay:

Here's another deceptively simple patch that makes a great building block for more complex patches. Patch your Trigger or Gate signal into the "TRIG IN" jack and take your delayed signal from the "GATE OUT" jack. The amount of delay is set by the sum of the "RISE" and "FALL" knobs. You may need to invert the output depending on whether you need a rising edge or falling edge for your application.

Subharmonic Generator:

This patch works in a similar fashion to the Gate Delay patch above. What we're doing is setting the DSG to be re-triggered by the incoming signal like before but this time the source signal will be an audio signal and the DSG's output will be an audio rate square wave that will be a subharmonic of the original signal. Patch your signal into the "TRIG IN" jack and take the output from the "GATE OUT" jack. This patch will take some tweaking to "tune" to taste.

HINT: Square up the audio signal with a comparator first (or simply use a square/pulse wave oscillator) so the DSG's "TRIG IN" receives reliable triggers.

Envelope Follower:

Patch your audio signal into the black "INPUT" jack and set the "RISE" knob very fast (clockwise). Begin with the "FALL" knob set very fast but slowly bring it down (counter-clockwise" until the signal at the "OUTPUT" jack is following the peaks and valleys of the audio signal's volume envelope. This is another patch you will have to "tune" by ear - have fun!

Directional CV Glide:

Patch your CV into the "INPUT" jack and your slewed version will be available at the "OUTPUT" jack. The "RISE" and "FALL" knobs will set the slewing up or down of the original CV respectively. An obvious implementation of this is to patch a CV destined to control an oscillator's pitch through here to create "glide" or portamento - with the added trick that your portamento doesn't have to be bi-polar, you can have glide only on upward pitch changes, only on downward pitch changes or even have different amounts of glide on up and down pitch changes. Of course you're not limited to "pitch CVs" alone but can process any CVs this way.

HINT: The above patch has a linear response. An exponential response can be created by stacking a patch cable from the "OUTPUT" jack to the "RISE/BOTH/FALL" VC in jack and adjusting the curve to taste with the "VC" knob.

HINT: Patch an audio signal in place of the CV and set both "RISE" and "FALL" knobs relatively fast and the patch becomes a lo-fi Low Pass Filter. Patch a CV into the "RISE/BOTH/FALL" jack to make the filter voltage-controllable.

Lopsided Recursive Waveform Generator:

Start experimenting. Here's an idea to get you started. Patch a couple of Triangle/Saw LFOs using both halves of a DSG then patch the waveforms of each into the "RISE/BOTH/FALL" CV input jacks of the other. Adjust to taste. Tap the waveform out by stacking a patch cord on one of the outputs and route it somewhere that needs a lopsided, recursive waveform. This is only the beginning of the fun. There are no "carved in stone" rules so feel free to ignore everything I've said thus far. Improvise!

Where to from here?

Of course, the DSG is capable of much more - we have merely scratched the surface but hopefully you're beginning to see how the Serge Modular's unique "patch-programmable" philosopy gets us from "A" to "B". Keep in mind, all the above patches have only used half a DSG so you still have the other half of the module for another patch or to "complexify" your existing one!
By combining some of the functions shown above, or extrapolating new ones based on what we already know, we can make the DSG do things other, more rigidly defined modules can only dream of. If you're hungry for more, there is a much gentler intro as well as a few more "DSG Tips & Tricks" to be found in Rich Gold's excellent Serge Guidebook. For more info on other aspects of the Serge Modular, I invite you to visit all my dedicated Serge Modular Pages.

Quad Slope:

I'd be remiss if I didn't mention this in an article about the DSG - For a powerful double-dose of DSG goodness, I can highly recommend the Quad Slope M-odule which sports twin DSGs as well as a handy Scaling Buffer (for attenuation, inversion and voltage offset duties).
Paired with a Creature or a Gator, you'd have a surprisinly powerful yet compact system!

Serge Modular systems and panels (including the "Quad Slope") are currently manufactured by Sound Transform Systems in Hartland, Wisconsin. You can reach them at (262) 367-3030.

What you give is what you get.

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