Session 15: Mixuverter and Voltage Processing

Objective: Use the Mixuverter as a DC offset source, attenuverter, and CV mixer to scale, invert, and combine modulation signals for precise control over modulation depth and polarity.

What Is an Attenuverter?

In modular synthesis, voltage processing is the unsung essential. Raw modulation sources (LFOs, envelopes) often output signals that are too strong, the wrong polarity, or need to be combined. An attenuverter (attenuator + inverter) solves all three problems:

• Attenuate: Reduce a signal's strength. An LFO output of +/-5V becomes +/-2V, making the modulation more subtle
• Invert: Flip a signal's polarity. A rising envelope becomes a falling one. An LFO that sweeps the filter up now sweeps it down
• Offset: Add a fixed voltage to shift a signal's center point. A bipolar +/-5V LFO becomes a unipolar 0-10V signal

Without these tools, modulation is all-or-nothing. With them, you dial in exactly the right amount and direction of movement. Voltage processing is what separates a patch that sounds "sort of right" from one that sounds precisely musical.

Warm-Up (2 min)

Remove all cables. Set all knobs and sliders to noon/center. Play a MIDI note -- you should hear the normalled default tone. Patch S&H OUT -> VCF FM 3 IN, set FM 3 to ~30%, and tap the PUSH GATE button a few times -- recall the random filter steps from Session 14. Remove the cable.

Setup

From the normalled default:

• Mixer SAW at ~60%, all other Mixer sliders at 0%
• VCO A OCTAVE at 4
• VCF FREQ at ~50%, Q at ~15%
• Mixuverter ATTENUATOR at noon (center)
• Mixuverter x2 switch OFF
• Mixuverter POLARITY switch at UNI

Exercises

Exercise 1: Mixuverter as DC Offset Source (5 min)

This exercise requires one cable.

1. Patch Cable 1: MIXUVERTER OUTPUT -> VCF FM 3 IN. Set VCF FM 3 to ~50%
2. With POLARITY at UNI, slowly turn the ATTENUATOR from fully counterclockwise (~0%) to fully clockwise (~100%). You should hear the filter cutoff rise as you increase the voltage -- you are manually controlling the filter brightness with a knob that creates voltage from nothing
3. Switch POLARITY to -/+ (bipolar). Now the ATTENUATOR at center = 0V, clockwise = positive voltage (filter opens), counterclockwise = negative voltage (filter closes below the FREQ setting). Sweep the knob through its full range -- the filter goes from darker-than-FREQ through FREQ to brighter-than-FREQ
4. Enable the x2 switch. The voltage range doubles. With POLARITY at -/+ and x2 on, the Mixuverter outputs up to +/-10V. Sweep the ATTENUATOR -- the filter sweep range is now much wider. Disable x2

Exercise 2: Attenuverting an LFO Signal (7 min)

This exercise requires two cables.

1. Patch Cable 1: LFO X OUT -> MIXUVERTER MAIN INPUT. Patch Cable 2: MIXUVERTER OUTPUT -> VCF FM 3 IN. Set VCF FM 3 to ~60%, LFO RATE to ~30%
2. Set POLARITY to UNI, ATTENUATOR to ~100%. Play and hold a note -- you should hear a strong filter wobble, the full LFO signal reaching the filter
3. Lower ATTENUATOR to ~50% -- the wobble becomes more subtle. You have attenuated the LFO. Lower to ~25% -- barely perceptible movement. This is how you dial in the precise modulation depth you want
4. Switch POLARITY to -/+. Set ATTENUATOR to center (noon) -- the modulation disappears (0V output). Turn clockwise -- positive LFO wobble returns. Now turn counterclockwise past center -- the filter wobble returns but inverted: when the LFO rises, the filter closes; when the LFO falls, the filter opens. You have inverted the modulation

5. Return POLARITY to -/+, ATTENUATOR slightly clockwise of center for a moderate, non-inverted filter wobble

Exercise 3: Combining Two Modulation Sources (5 min)

Keep Cables 1-2 patched (LFO X -> Mixuverter -> VCF FM 3). Add one more cable:

1. Patch Cable 3: Envelope A ENV OUT -> MIXUVERTER SECONDARY INPUT. Set Envelope A to a percussive shape: Attack ~0%, Decay ~30%, Sustain ~0%
2. Play notes -- you should hear the LFO wobble on the filter PLUS a per-note brightness spike from the envelope. The Mixuverter sums both signals and sends the combined CV to the filter. The LFO provides rhythmic movement while the envelope provides per-note articulation
3. Use the ATTENUATOR to scale the LFO's contribution: turn it down to ~25% to emphasize the envelope, or up to ~75% to emphasize the LFO. The SECONDARY INPUT is not attenuated -- it passes through at full strength, so the ATTENUATOR only scales the LFO portion
4. Enable x2 -- the LFO contribution doubles in strength, making it dominant over the envelope. Disable x2 for a balanced mix
5. Remove all cables

Exploration (optional, hyperfocus days)

• Use the Mixuverter as a unipolar-to-bipolar converter: patch an envelope (0V to +5V) into MAIN INPUT, set POLARITY to -/+, ATTENUATOR at noon. The output swings from -2.5V to +2.5V -- now the envelope goes both up AND down from center, useful for creating pitch dips on note attack
• The patchbay section includes a dedicated BI>UNI converter normalled from LFO Z. Patch a bipolar LFO into BI>UNI IN and take the output -- it converts +/-5V to 0-5V. Compare this with the Mixuverter's approach
• Try combining S&H OUT (random) with an LFO via the Mixuverter for "structured randomness" -- the LFO provides a predictable base movement while the S&H adds unpredictable variation on top

Output Checklist

• Used the Mixuverter as a DC voltage source to manually sweep the filter
• Attenuated an LFO signal to control modulation depth precisely
• Inverted an LFO signal using bipolar (-/+) mode
• Combined an LFO and envelope through the Mixuverter's two inputs
• Session logged in Obsidian daily note

Key Takeaways

• The Mixuverter is a DC source with no input (normalled +5V), an attenuverter with one input (scale and invert), and a CV mixer with two inputs (sum and scale) -- three tools in one
• Voltage processing transforms raw modulation into precisely scaled and directed control, essential for musical patches where "too much" or "wrong direction" ruins the effect
• The x2 switch doubles the voltage range for stronger modulation or wider DC offset, and the POLARITY switch enables instant signal inversion

Next Session Preview

Session 16 moves into Advanced Patching with FM chains and cross-modulation -- using one oscillator to modulate another at audio rates, the Ring Mod as a modulation source, and building complex timbral chains that combine everything from Modules 1-5.