In signal processing, a system is used to manipulate signals in various ways. A system can be thought of as a process that takes an input signal and produces an output signal. A system can be described mathematically using an equation or a [[transfer function]] that relates the input signal to the output signal. Common types of systems used in signal processing include filters, amplifiers, mixers, and modulators. The design and analysis of these systems is an important part of modern communication systems, audio processing, video processing, and image processing applications.