Most filters are based on an RC circuit – resistor plus capacitor – with their combination yielding the cutoff frequency of the filter. In most designs, the resistor or “R” is varied to change that frequency – either by a front panel knob, or a control voltage converted into either a variable resistance or a variable current. In a switched capacitor design, capacitors are switched in and out of the circuit at high speeds to create the average “C” required to produce the desired cutoff frequency. In some module designs, the frequency of the high speed clock used to switch the capacitors are in and out can be audible as its own pitch, creating aliasing-like artifacts. As a result, this style of filter is often associated with a grungy, aggressive, low-fi sound.
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