{"id":3646,"date":"2020-08-22T16:11:00","date_gmt":"2020-08-22T21:11:00","guid":{"rendered":"https:\/\/pugix.com\/synth\/?p=3646"},"modified":"2025-01-07T11:18:25","modified_gmt":"2025-01-07T16:18:25","slug":"universal-slope-love","status":"publish","type":"post","link":"https:\/\/pugix.com\/synth\/universal-slope-love\/","title":{"rendered":"Universal Slope Love"},"content":{"rendered":"\n

Updated 01\/04\/2025<\/p>\n\n\n\n

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Original Serge DUSG Graphic<\/figcaption><\/figure>\n\n\n\n

My recent build of a Befaco Rampage prompted me to revisit several variations of the Serge Dual Universal Slope Generator that I have in Eurorack: Befaco Rampage, Random*Source DUSG, Steady State Fate Mini Slew, After Later Audio Tilt, Make Noise Function, and Joranalogue Contour 1. I learned a few things, too. But first let’s briefly look at the original Serge. I built a CGS Serge DUSG<\/a> board some years ago, in a banana jack format. It’s very much like the graphic above, with the addition of a Bipolar output.<\/p>\n\n\n\n

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USG<\/figcaption><\/figure>\n\n\n\n

There’s beauty in its simplicity. Patch from End to Trigger to make it cycle. Patch from Out to CV in for different curves. The Eurorack versions I’m looking at here all have added features to this basic design. And they are:<\/p>\n\n\n\n

Random*Source Serge DUSG<\/h3>\n\n\n\n

The R*S DUSG<\/a> is the closest in design to the original. It is also the largest, at 26hp width. I built mine<\/a> from a kit.<\/p>\n\n\n\n

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DUSG<\/figcaption><\/figure>\n\n\n\n

Befaco Rampage<\/h3>\n\n\n\n

The Rampage<\/a> implements the functionality with a completely different technical design. It’s 18hp wide. I built mine<\/a> from a full kit. The Rampage circuit is open source, with schematic supplied.<\/p>\n\n\n\n

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Rampage<\/figcaption><\/figure>\n\n\n\n

Steady State Fate Mini Slew<\/h3>\n\n\n\n

The Mini Slew<\/a> is a single unit; you need two for the equivalent of the DUSG, in 16hp total. I wrote a comparison<\/a> of Mini Slew with the Make Noise Function.<\/p>\n\n\n\n

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Mini Slew<\/figcaption><\/figure>\n\n\n\n

After Later Audio Tilt<\/h3>\n\n\n\n

Tilt<\/a> also comes as a single unit, so you need two for the Dual Slope functionality. But it’s only 6hp in width!<\/p>\n\n\n\n

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Tilt<\/figcaption><\/figure>\n\n\n\n

Make Noise Function<\/h3>\n\n\n\n
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Function<\/figcaption><\/figure>\n\n\n\n

Make Noise Function<\/a> has been in my kit for quite a while. Lately I decided to get another used one and found the perfect match to my existing Function, ca. 2012. It has the same revision PC board. I replaced the blue knobs with Davies clone black knobs, to which I’ve taken a fancy. The all black and silver scheme looks nice.<\/p>\n\n\n\n

Joranalogue Audio Design Contour 1<\/h3>\n\n\n\n
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Contour 1<\/figcaption><\/figure>\n\n\n\n

A relative newcomer to the universal slope space, the Contour 1<\/a> hits the ball out of the park. I bought a pair of them during a Spring sale. Same 8hp width as Mini Slew and Function and only slightly more expensive.<\/p>\n\n\n\n

NANO Modules ARC<\/h3>\n\n\n\n
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ARC<\/figcaption><\/figure>\n\n\n\n

After this post was originally written, I sold both Mini Slews and the Rampage, due to their quirks and because I kept enough USGs with the four remaining.<\/p>\n\n\n\n

When NANO Modules came out with their ARC<\/a>, I knew I would have to get it. I’ve done an investigation into ARC’s behavior and added it below.<\/p>\n\n\n\n

Feature Comparison<\/h2>\n\n\n\n

This is a simple list of features. We’ll get into functionality later.<\/p>\n\n\n\n

All have the following common features<\/strong>.<\/p>\n\n\n\n

    \n
  • Input for slewing<\/li>\n\n\n\n
  • Main output<\/li>\n\n\n\n
  • Output indicator<\/li>\n\n\n\n
  • Rise pot<\/li>\n\n\n\n
  • Fall pot<\/li>\n\n\n\n
  • Rise CV input<\/li>\n\n\n\n
  • Fall CV input<\/li>\n\n\n\n
  • Trigger input<\/li>\n\n\n\n
  • Shape control<\/li>\n\n\n\n
  • Cycle switch<\/li>\n<\/ul>\n\n\n\n

    R*S DUSG adds<\/strong>:<\/p>\n\n\n\n

      \n
    • One square wave output<\/li>\n\n\n\n
    • One bipolar output (inverted)<\/li>\n\n\n\n
    • End pulse output<\/li>\n\n\n\n
    • 1V\/Octave FM input<\/li>\n\n\n\n
    • Both CV input (summed to Rise and Fall CVs)<\/li>\n\n\n\n
    • Rise CV attenuverter<\/li>\n\n\n\n
    • Rise Exponential switch<\/li>\n\n\n\n
    • Fall CV attenuverter<\/li>\n\n\n\n
    • Fall Exponential switch<\/li>\n<\/ul>\n\n\n\n

      Rampage adds<\/strong>:<\/p>\n\n\n\n

        \n
      • Cycle gate input<\/li>\n\n\n\n
      • Trigger button<\/li>\n\n\n\n
      • Range switch<\/li>\n\n\n\n
      • Exponential FM input<\/li>\n\n\n\n
      • Rising gate output (10V)<\/li>\n\n\n\n
      • Falling gate output (10V)<\/li>\n\n\n\n
      • End pulse output (10V)<\/li>\n\n\n\n
      • A>B gate output (10V)<\/li>\n\n\n\n
      • Min output (trough)<\/li>\n\n\n\n
      • Max output (peak)<\/li>\n\n\n\n
      • Balance pot between A and B to comparator input<\/li>\n<\/ul>\n\n\n\n

        Mini Slew adds<\/strong>:<\/p>\n\n\n\n

          \n
        • Cycle gate input<\/li>\n\n\n\n
        • Variable level output (+\/- 9.5V)<\/li>\n\n\n\n
        • Variable level CV input, i.e. 4-quadrant multiplication<\/li>\n\n\n\n
        • Exponential FM input<\/li>\n\n\n\n
        • CV Sum<\/li>\n\n\n\n
        • Time Compensation<\/li>\n\n\n\n
        • Shape CV input<\/li>\n\n\n\n
        • End of Rise pulse output<\/li>\n\n\n\n
        • End of Cycle pulse output<\/li>\n<\/ul>\n\n\n\n

          Tilt adds:<\/strong><\/p>\n\n\n\n

            \n
          • Unipolar\/bipolar cycling switch<\/li>\n\n\n\n
          • Both CV input<\/li>\n\n\n\n
          • Variable level output (+\/- 9.5V)<\/li>\n\n\n\n
          • Bipolar output (+\/- 4.5V)<\/li>\n\n\n\n
          • Rising gate output (9V)<\/li>\n\n\n\n
          • Falling gate output (9V)<\/li>\n\n\n\n
          • Separate shape knobs for rise and fall<\/li>\n\n\n\n
          • Gated ASR with manual sustain level<\/li>\n<\/ul>\n\n\n\n

            Function adds:<\/strong><\/p>\n\n\n\n

              \n
            • End of Rise pulse output (11V)<\/li>\n\n\n\n
            • End of Cycle pulse output (11V)<\/li>\n\n\n\n
            • Exponential FM input<\/li>\n\n\n\n
            • Hang input<\/li>\n\n\n\n
            • Inverted output<\/li>\n<\/ul>\n\n\n\n

              Contour 1 adds:<\/strong><\/p>\n\n\n\n

                \n
              • Trigger button<\/li>\n\n\n\n
              • Full\/Audio range switch<\/li>\n\n\n\n
              • Shape controls (Bend) for both Rise and Fall<\/li>\n\n\n\n
              • CV inputs for both Rise and Fall Shapes<\/li>\n\n\n\n
              • Gate input<\/li>\n\n\n\n
              • Hold input<\/li>\n\n\n\n
              • Rising gate output (5V)<\/li>\n\n\n\n
              • Falling gate output (5V)<\/li>\n\n\n\n
              • Inverted output<\/li>\n<\/ul>\n\n\n\n

                ARC adds<\/strong>:<\/p>\n\n\n\n

                  \n
                • Loop toggle switch<\/li>\n\n\n\n
                • Loop gate input<\/li>\n\n\n\n
                • Trigger button – illuminates during Rise<\/li>\n\n\n\n
                • Range switch<\/li>\n\n\n\n
                • Sustain mode switch<\/li>\n\n\n\n
                • Exponential FM input<\/li>\n\n\n\n
                • Rising gate output (10V)<\/li>\n\n\n\n
                • Falling gate output (10V)<\/li>\n\n\n\n
                • Shape controls for both Rise and Fall<\/li>\n\n\n\n
                • Output gain\/polarizer pot<\/li>\n\n\n\n
                • Output offset pot<\/li>\n\n\n\n
                • ATT\/VER CV input<\/li>\n\n\n\n
                • Sum output<\/li>\n\n\n\n
                • X>Y gate output (10V)<\/li>\n\n\n\n
                • Min output (AND)<\/li>\n\n\n\n
                • Max output (OR)<\/li>\n<\/ul>\n\n\n\n

                  Generating Envelopes<\/h3>\n\n\n\n

                  Envelope peak voltage<\/h4>\n\n\n\n
                    \n
                  • R*S DUSG<\/strong> main output peaks at 5V<\/strong> when generating an envelope or cycling.<\/li>\n\n\n\n
                  • Mini Slew<\/strong> main output is about 8.5V<\/strong> and the variable output can go up to +\/- 9.5V<\/strong>.<\/li>\n\n\n\n
                  • Rampage<\/strong> outputs peak at 10V<\/strong>.<\/li>\n\n\n\n
                  • Tilt<\/strong> outputs up to +\/- 9.5V<\/strong> unipolar, or +\/- 4.5V<\/strong> bipolar.<\/li>\n\n\n\n
                  • Function<\/strong> main output peaks at about 8.5V<\/strong>.<\/li>\n\n\n\n
                  • Contour 1 <\/strong>output peaks at 10V<\/strong> (and has an inverted output)<\/li>\n\n\n\n
                  • ARC<\/strong> output peaks at +\/-10V<\/strong><\/li>\n<\/ul>\n\n\n\n

                    A common use for slope generators is to make an Attack-Decay envelope. Attack is started by a rising edge on the Trigger input. The output voltage rises to maximum at the rate set by the mix of Rise pot, Rise CV input, and FM input. The curve of the rise can be linear, logarithmic (log) or exponential (exp). Upon reaching the max voltage, the decay phase starts heading back to zero at a rate set by all the fall controls and with a linear, log, or exp shape. Of special interest is what happens if a new trigger is received before the cycle is completed. For all of these modules except for Contour 1<\/strong> and ARC<\/strong>, a new trigger (positive transition) arriving during Rise is ignored (contrary to what the Rampage manual states, that it will be a hard sync, i.e. a reset to zero). Contour 1 resets to zero when a new trigger is received at any time during a cycle<\/strong>.<\/p>\n\n\n\n

                    Contour 1<\/strong> offers a trigger button (and it’s big). Contour 1 also provide a Gate<\/strong> input, which enables a 10V peak Attack-Release (AR) envelope to be generated from any gate signal above a threshold, whereas the other USGs rely on using the input as a gate input for AR envelopes. The others rely on the height of the input to determine the peak output. Contour 1 can also be used this way.<\/p>\n\n\n\n

                    When a trigger is received during Fall<\/strong><\/p>\n\n\n\n

                    R*S DUSG<\/strong> just ignores<\/strong> triggers<\/strong> throughout the whole cycle. This makes it ideal for use as a pulse frequency divider. The End pulse will be a division of the number of trigger inputs that happen during the cycle.<\/p>\n\n\n\n

                    Mini Slew<\/strong>, touted also as a pulse divider, exhibits this behavior as well, but very oddly only if the trigger pulse height is around +5V<\/em>. It was very confusing when triggering Mini Slew from a Rampage 10V pulse output. With a 10V trigger Mini Slew will re-trigger<\/strong> during Fall! I view this as a design flaw, since the level of a trigger should never make a difference to anything.<\/p>\n\n\n\n

                    Rampage<\/strong> behaves as stated in the manual and re-triggers upon receiving a new trigger during Fall. Re-triggering means that the voltage begins rising again.<\/p>\n\n\n\n

                    Tilt<\/strong> also re-triggers when getting a trigger during Fall.<\/p>\n\n\n\n

                    Function<\/strong> also re-triggers when getting a trigger during Fall.<\/p>\n\n\n\n

                    Contour 1<\/strong> always resets to zero<\/em> when getting a trigger at any time during the cycle.<\/p>\n\n\n\n

                    ARC<\/strong> also re-triggers when getting a trigger during Fall.<\/p>\n\n\n\n

                    Envelope shapes<\/h4>\n\n\n\n

                    Each of these modules has a different idea about shape. The traditional curves for an envelope uses a logarithmic rise and an exponential fall, or a linear curve for both.<\/p>\n\n\n\n

                    R*S DUSG <\/strong>has one of the more flexible shape controls. Rise and Fall shapes can be set independently, making any combination of lin\/log\/exp Rise and lin\/log\/exp Fall possible. It’s accomplished by a reversible attenuator (attenuverter) plus an Expo switch. It works by feeding back some of the output into the Rise or Fall CV input. Thus, it mixes with whatever CVs are patched into the Rise, Fall, and Both CV inputs. And there are two positions of the Expo switch, which differ regarding the target voltage of the curves. In one position the target voltage is higher than +5V, resulting in reaching this max in a shorter period of time.<\/p>\n\n\n\n

                    Mini Slew<\/strong> has a Shape knob that goes from log through linear to exp. There’s also a Shape CV input which sums with the Shape knob setting. Given that changing the shape impacts rate, using this CV input might have unexpected results. With Mini Slew both Rise and Fall are the same shape, log, lin, or exponential.<\/p>\n\n\n\n

                    Rampage<\/strong> has yet another way of adjusting shape. A shape knob allows to choose between log attack and exp decay, or linear, or exp attack and log decay.<\/p>\n\n\n\n

                    Tilt<\/strong> features separate pots for rise and fall shapes, which facilitates the traditional log attack and exponential decay, if desired.<\/p>\n\n\n\n

                    Function<\/strong> has a single shape knob, like Mini Slew, with both Rise and Fall being affected in the same way. Function has no CV over shape.<\/p>\n\n\n\n

                    Contour 1 <\/strong>has the most control over shape (which it calls Bend). It features separate knobs for rise and fall shape, plus CV inputs to go with each of those. It’s easier to understand than how R*S DUSG does it.<\/p>\n\n\n\n

                    ARC<\/strong> features separate pots for rise and fall shapes, too.<\/p>\n\n\n\n

                    Here’s a nice instructional video about envelope shapes by someone else.<\/p>\n\n\n\n

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