WAVE SHAPERS
Wave shapers are a class of module that take an incoming oscillator signal and modify it while leaving its initial form recognizable. These may take the form of wave folders, wave clippers, wave multipliers and even sometimes distortion units. The classic example is a Serge wave multiplier:
Wave shapers will have signal inputs and voltage controls over the various factors that can be modified. Folders and clippers will have a control for the amplitude level at which the signal is clipped or inverted, multipliers will have controls for the frequency modulation to apply to the incoming wave, and distortion can have settings like clip, starve, choke, etc.
LOW-PASS GATE
Low pass gates are the “west-coast” answer to both VCAs and to an extent, filters, both of which are sometimes missing from complex waveform synthesis. These are low pass filters with a cutoff frequency that goes below the range of human hearing as its control voltage approaches 0 volts, so that the input signal is functionally silenced. In a way this is the opposite of a VCA, which actively amplifies a signal based on a control voltage. The response of a LPG is usually a little slower and softer than that of a VCA, but the two can be modulated using the same input controls.
Many modern low-pass gates incorporate VCAs and filters into them, as in this example, the Pittsburgh Modular LPG. Here you see inputs for the signal being gated, as well as a control voltage input for the cutoff of the filter when used in filter mode, as well as a “ping” which is a gate/trigger input to flash the vactrol level and percussively modulate the frequency of the unit.