When a capacitor is used in a filtering application, the purpose is to either block a DC voltage, or to allow an AC voltage to pass through. In other words, the capacitor will either resist or impede the DC voltage or enable the AC voltage to pass quickly through. The amount of resistance or impedance depends on the frequency of the signal being passed through the device. For low frequencies, a capacitor will act to block the signals that try to pass through and at high frequencies capacitors allow the signal to pass through easily. This trait of high resistance at low frequencies and low resistance at high frequencies allows the capacitor to be used to either block low frequency signals, or filter high frequency signals. The diagrams shown on this slide are an example of noise being filtered out of a waveform. The left plot has a large amount of high frequency noise on the waveform and the plot on the left shows the same waveform where a capacitor was used to filter out the noise.