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This was the name for the Buchla 265 and 266 modules that create random control voltages. Its name is often used for random source modules that follow or are inspired by the original Buchla template.

Source of Uncertainty modules are typically based on the Buchla 266, and usually have the following sections from the 266:

  • Three different colors of noise: pink, white, and blue.
  • Two ‘fluctuating random voltages’ – smoothly wandering outputs – with voltage controlled ‘rate of change’.
  • Two different ‘quantized random voltages’ – stepped outputs – that could either take on 1 of 7 different voltage levels (the ‘n+1’ output), or 1 of 64 different voltage levels (the ‘2n’ output). A new trigger selected a new value.
  • Two different ‘stored random voltages’ that shared their own trigger input. The first one was a set of completely random stepped voltages; the second one allowed you to choose the ‘probability distribution’ of whether the voltages tended to be low, high, or in the middle of the range.
  • An ‘integrator’ (slew) to smooth out changes in voltage.
  • sample & hold, with the extra feature that both the trigger in and voltage output could be alternated between two different jacks.

Several variations on this theme exist in the Eurorack format. The most faithful to the original Buchla is the Sputnik Modular West Coast Random Source. A close cousin is the Verbos Electronics Random Sampling, which replaces the integrator and S&H with an analog shift register. It also swaps the white noise with a ‘metallic’ output for simulating TR-808 cymbals.

The Frap Tools SAPÈL is a particularly nice evolution of the idea; its n+1 output has been quantized to octaves, and the 2n output to semitones. It offers a shared probability control to optionally affect any or all of the outputs. All of the functions also share a central clock, which may be internal, external, voltage controlled, or manually triggered. There are also random clock outputs. And, there are two of these sections in one module; their clocks can be cross-linked.

Videos of the Sputnik and Frap Tools modules are included in the Eurorack Expansion course. Also see page 256 of Patch & Tweak.

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