Could anybody please explain how exactly high pass and low pass filters work?

Answer 1

Filters are composed of capacitors and inductors. These component "react" differently to different frequencies. If you modulated the voltage frequency to a series capacitor, it would start out looking like a very big resistance, which would become incrementally smaller as the frequency is increased. Inductors act in the exact opposite fashion.

A simple lowpass filter is compossed of a resistance and capacitor in series, with the output across the capacitor. Using a voltage divider:

Voutput = Vinput * (resistance of cap) / (resistance of cap + R)

A simple highpass filter is composed the same, with the output across the resistor.

This type of filter is a first order filter, because there is one inductor or capacitor. Adding more of these elements will cause rippling in the frequency response, and can cause the rolloff / decay to occur faster.

Putting two capacitors in series or parallel "looks" like one element, so for a second order filter you must use a cap and an inductor. For a third order, you must use two of one and one of the other "in between" them - for example have the input to a capacitor, where the other side is tied to the inductor and other capacitor; the inductor's other terminal is connected to ground, and the output is from the other capacitors second terminal.