One simple electrical circuit that will serve as a lowpass filter consists of a
resistor in series with a load, and a capacitor in parallel with the load.
The capacitor exhibits reactance, and blocks lowfrequency signals, causing them to go through the load instead. At higher frequencies the reactance drops, and the capacitor effectively functions as a short circuit. The combination of resistance and capacitance gives you the time constant of the filter \tau = RC (represented by the Greek letter tau). The break frequency, also called the turnover frequency or cutoff frequency (in hertz), is determined by the time constant: fc = 1 / (2 * 3,141592 ) * R * C One way to understand this circuit is to focus on the time the capacitor takes to charge. It takes time to charge or discharge the capacitor through that resistor:
Another way to understand this circuit is with the idea of reactance at a particular frequency:
