PURE S&H is a classic modulation source that generates random voltages based on an incoming voltage (usually noise)

The GMSN! Pure Sample and Hold is often paired with Noise source to create randomly changing CV. This can then be patched into a VCO to create random sequences or, with more subtle use, to create "life-like" fluctuations, giving a more human feel to synthesised sounds.

The module has an internal clock, controlled by the Rate knob, an External Clock Input, Signal In and Signal Out jacks.

For more info on audio and control voltages, check out the Modular Synth Primer.