Analog signals can be defined as continuous signals whose time-varying features (also known as their variables or their variable features) are representations of some other time-varying quantity. In other words, analog signals are analogous to some other time-varying signal. An example of an analog signal is an analog audio signal. Here, the instantaneous voltage associated with the analog signal continuously varies with the pressure associated with the sound waves. Analog signals are different from digital signals because digital signals feature a representation of a sequence of discrete values as the continuous quantity. Generally, the term ‘analog signal’ is used to refer to an electric signal. Other types of signals that can be considered as analog signals include human speech, pneumatic signals, and mechanical signals.