Filter circuits are electronic circuits designed to allow certain frequencies of signals to pass while blocking others. They are commonly used in audio systems, radio communications, and signal processing to improve the quality of the output signal. Filters can be categorized into different types, such as low-pass, high-pass, band-pass, and band-stop, depending on the frequency range they affect. These circuits utilize components like resistors, capacitors, and inductors to achieve their filtering effects. For example, a low-pass filter allows signals below a certain frequency to pass through while attenuating higher frequencies. This functionality is essential in various applications, including noise reduction and signal conditioning.