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lutra.md

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Lutra

Lutra is a re-imagining of Expert Sleepers' Otterley module.

Each output channel is a free running LFO with a subtly different clock speed. The spread of clock speeds is controlled by k2 (and optionally ain -- see configuration below)

Wave Shapes

The shape of the output wave can be changed by pressing b2 while the module is running. This choice is saved to the module and will be re-loaded every time Lutra starts. Available wave shapes are:

  • Sine Wave Sine
  • Square Wave Square
  • Triangle Wave Triangle
  • Saw Wave Saw
  • Ramp Wave Ramp
  • Stepped Random Wave Stepped Random
  • Smooth Random Wave Smooth Random (Linear)

When pressing b2 to select the wave shape, the selected shape will briefly appear in the upper left corner of the screen.

The stepped random wave will hold a randomly-chosen voltage for the duration of the cycle period, choosing a new voltage every period.

The smooth random wave moves linearly from the current voltage toward a randomly-chosen goal over the cycle period, choosing a new random goal voltage every period.

CV Input Configuration

By default CV signals applied to ain will adjust the spread of the output waves. If preferred, this can be changed to control the overall speed of the waves instead by creating/editing /config/Lutra.json on the module.

{
    "AIN_MODE": "spread"
}
  • AIN_MODE: sets the mode for ain. Must be one of spread or speed. If set to spread the spread of clock speeds of the outputs is controlled by ain. If set to speed the master clock speed is controlled by ain.

ain is expected to receive signals from zero to MAX_INPUT_VOLTAGE (default 12V -- see EuroPi configuration). Increasing the voltage will increase the speed or spread of the LFOs. Decreasing the speed/spread is not allowed, as EuroPi cannot accept negative voltages. Instead it is recommended to set k1 and k2 to set the minimum desired speed & spread with ain unpatched. Then send an attenuated signal into ain to increase the speed/spread as desired.

Knob Control

Turning k1 fully anticlockwise will set the clock speed to the slowest setting. Turning k1 fully clockwise will set the clock speed to the fastest setting.

Turning k2 fully anticlockwise will set the spread of the waves to zero; every output will have the same clock speed, (though depending on previous settings and random noise) they may be phase-shifted from each other.

Turning k2 clockwise will gradually increase the speed of cv2-6, with each output becoming slightly faster than the previous one. i.e. cv2 will be faster than cv1, cv3 will be faster than cv2, etc...

At the maximum clockwise position, the speeds of cv2-6 will be common harmonic intervals from cv1, as shown on the table below:

CV Output Ratio w/ `cv1 Max speed multiplier
cv1 1:1 x1
cv2 6:5 x1.2
cv3 5:4 x1.25
cv4 4:3 x1.3333...
cv5 3:2 x1.5
cv6 2:1 x2

Re-syncing

When b1 is pressed or din receives a high voltage all CV outputs are temporarily halted. Once b1 is released and the signal on din drops back to 0.0V the output signals will begin again, starting in their initial, synchronized state. This allows a very short gate (trigger) signal to reset all of the waves to re-synchronize them, or a longer gate can be used to hold the outputs at zero for as long as desired.