Pittsburgh Modular Microvolt 3900, Manual

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14. Modulation Sources
The Modulation sources section contains two independent modulation sources, a complex random gate and CV
generator, and an LFO with variable wave shapes. The CV output of the random source(126) and the ramp
output of the LFO(129) are mixed using the source balance trimmer(34) and output(131) is internally routed to
the modulation inputs of the voltage controlled oscillator.
Complex Random Generator
Inspired by the random source on the Buchla Music Easel, the complex random generator on the Microvolt 3900
is a digitally controlled random source generating both gate and CV signals. The random generator functions
similar to an analog, 6 stage shift register. When the clock signal triggers an update and the next register value is
loaded, there is a chance it will evolve. Think of it like a 6 step sequencer. The random generator cycles through
the 6 steps of the sequence and each time the sequencer jumps to the next step, there is a chance the value
stored in that step will be replaced with a new value. The result is a random source that feels both random and
evolutionary, with an ever evolving 6 step pattern cycle. The random complexity slider(33) sets both the chance a
CV value will change, the range the CV value can change, and also the density of the gates. Both the gate and
CV signals have a 0v to 5v range.
The complex random generator is triggered by the active clock source selected in the midi / arpeggiator section.
To adjust the chance a CV value will change with each step and the density of the random gates use the random
complexity slider(33). Moving the slider up will increase the chance a step will update.
LFO
The LFO is a utility low frequency oscillator with variable ramp and pulse wave outputs. Perfect for long sweeps
or audio rate frequency modulation. The LFO range button(36) switches between very slow modulation and audio
rate modulation. The LFO shapes trimmer(37) defines the wave shapes of the LFO. It defines the width of the
pulse wave and the ramp wave shifts from a ramp, to a triangle, to a saw wave.