Filter design is the process of creating systems that selectively allow certain frequencies of signals to pass while blocking others. This is crucial in various applications, such as audio processing, telecommunications, and electronics. By using mathematical techniques and tools, engineers can design filters that meet specific requirements, ensuring that the desired signals are clear and free from unwanted noise. There are different types of filters, including low-pass, high-pass, band-pass, and band-stop filters. Each type serves a unique purpose, depending on the frequency range that needs to be controlled. For instance, a low-pass filter allows low frequencies to pass through while attenuating higher frequencies, making it ideal for applications like audio equalization.