Uncertainty for Workshop System Computer

A tribute to the Buchla 266 Source of Uncertainty, sharing the card with a wavefolder (in the spirit of the 259 Complex Oscillator's timbre section) and a pulse alternator (in the spirit of the Model 140 Timing Pulse Generator), for the Music Thing Modular Workshop Computer.

Status: confirmed working on hardware.

What it does

Five things share this one card:

• Noise source — a source of hiss/static in three flavours: flat (even across the spectrum), low-biased (darker, bass-heavy), and high-biased (brighter, treble-heavy). Tap the switch down to cycle between them.
• FRV (Fluctuating Random Voltage) — a voltage that wanders continuously and unpredictably, sliding smoothly from one random value to the next rather than jumping. Speed is adjustable from a slow drift (one change every twenty seconds or so) up to a fast, buzzy wobble.
• QRV (Quantized Random Voltage) — a voltage that jumps to a fresh random value each time it receives a trigger, then holds perfectly still until the next one. The stepped, "sample and hold" counterpart to FRV's continuous drift.
• Wavefolder — takes an incoming audio signal and folds it back on itself once it gets loud enough, the way a real Buchla-style folder does. At low settings it's transparent; turn the drive up and the signal gets progressively more complex, bright, and eventually harsh.
• Pulse alternator — takes a pulse/clock/gate signal and echoes it out, alternating between two separate outputs each time a new pulse arrives. Useful for sharing one clock between two things, each getting half the rate.

Panel layout

                    ┌─────────────────────────┐
                    │   ●  MAIN                │
                    │  (fold drive / CV1 att.) │
              ○ 0   │   ○ X        ○ Y         │  ○ 1
   (noise: flat)    │  (FRV rate/  (QRV range/  │  (FRV level)
              ○ 2   │   FRV att.)   QRV att.)   │
 (noise: low-biased)│   [ (ON)-OFF-ON  Z ]     │  ○ 3
              ○ 4   │  up = attenuverters       │  (QRV level)
(noise: high-biased)│  down-tap = cycle noise   │  ○ 5
                    │                          │  (alternator hit)
                    │ AudioIn1  AudioOut1      │  fold in, fold out
                    │ (unused)  AudioOut2      │  noise out
                    │ CVIn1     CVOut1          │  fold drive mod, FRV out
                    │ CVIn2     CVOut2          │  FRV rate mod, QRV out
                    │ PulseIn1  PulseOut1      │  QRV trigger + alternator in, alternator out A
                    │ (unused)  PulseOut2      │  alternator out B
                    └─────────────────────────┘

Inputs and outputs

All the audio and CV jacks here work across roughly ±6V.

Controls

Main, X, and Y each do two jobs, depending on the switch:

What "attenuverter" means here: turn the knob to 12 o'clock and that control has no effect at all — it's silent/off. Turn it left (counter- clockwise) and the signal it's attenuverting comes out flipped upside down, growing stronger the further left you go. Turn it right (clockwise) and it comes out the normal way round, growing stronger the further right you go. It's a way of dialling in "how much, and which direction" with one knob. Because FRV and QRV are normally positive-only voltages, this is also what lets their attenuverters push them negative — turn one CCW of centre and that output starts swinging below 0V instead of only above it.

No jumps when you switch modes. Since each of Main/X/Y is doing two jobs, you'd normally expect a value to jump the moment you flip the switch and the knob's physical position suddenly means something different. That doesn't happen here — each knob remembers where it was left in both of its jobs. Flip to attenuverter mode, dial in an amount, flip back, and the knob's normal job picks up exactly where you left it; it won't start changing again until you turn the knob back to roughly where it was. Same going the other way. So you can freely flip back and forth to tweak an attenuverter setting without ever disturbing whatever the knob was doing a moment ago.

The Z switch:

• Down (tap): a quick press-and-release cycles the noise source through its three colours. It springs back up on its own.
• Middle: normal operation. Main/X/Y do their everyday jobs.
• Up: attenuverter mode. Main/X/Y switch to the jobs described above.

LEDs, top-to-bottom, left-to-right:

1. Lit when the noise source is set to flat.
2. Brightness follows FRV's current output — off at 0V, brightest the further it swings from there in either direction.
3. Lit when the noise source is set to low-biased.
4. Brightness follows QRV's current output the same way LED 2 follows FRV's.
5. Lit when the noise source is set to high-biased.
6. Lights up for the duration of every pulse arriving at Pulse In 1, regardless of which of the two alternator outputs it's currently being sent to.

Build and flash

From a configured Pico SDK environment:

cd releases/106_uncertainty
cmake -S . -B build -G "Unix Makefiles"
cmake --build build

This produces build/uncertainty.uf2 and build/uncertainty.elf. Flash by holding BOOTSEL while plugging in USB-C, then copying the .uf2 onto the RP2 drive that appears (or via picotool load, or SWD).

Credits

• Chris Johnson — wrote ComputerCard, the hardware library this whole card is built on (part of the Workshop Computer repo this card lives in), and Utility Pair, whose wavefolder this card's wavefolder is a direct port of, antialiasing technique and all.
• Eric Gao — the pot-pickup ("nothing jumps when you switch modes") logic is ported from his Alloy card, also in this repo.
• Parker et al., DAFx-16 — "Reducing the aliasing of nonlinear waveshaping using continuous-time convolution," the paper behind the antialiasing technique the wavefolder uses.
• Tom Whitwell / Music Thing Modular — the Workshop Computer platform this card runs on.
• Claude Code (Anthropic) — wrote the firmware from the author's brief.
• Don Buchla — the 266 Source of Uncertainty, the 259 Complex Oscillator, and the Model 140 Timing Pulse Generator, whose ideas this card is a tribute to rather than a copy of.

Licence

MIT, matching the ComputerCard framework itself.