As signals, both analog and digital signals denote an electromagnetic or electrical current used for transmitting information between systems or networks. The two, however, differ fundamentally in their characteristics and applications. In addition, they feature different advantages and disadvantages.
Analog signals are time-varying and have a minimum and maximum value, typically ranging from +12 Volts to -12 Volts. However, an infinite number of values exist within this continuous range. Analog signals use a specific property of the medium to convey the information. For example, to represent the information in an electrical signal moving through a wire, one can vary its voltage, current, or frequency.
Analog signals measure changes in natural or physical phenomena such as colors, lights, sounds, temperature, pressure, and position. When represented in a voltage vs. time graph, an analog signal is a smooth, continuous sine wave without any discrete value changes.
Technological advances have led to the digitization of traditional audio and communication systems using analog signals. However, most systems interacting with real-world signals continue using analog interfaces for information capturing or transmission. Common analog signal applications include audio recording and reproduction, temperature and image sensors, and radio signals and control systems.
Among the main advantages of analog signals are easier processing, higher density, and the ability to represent more refined data. They are the best fit for transmitting audio and video. Furthermore, they more accurately represent changes in real-life signals. Analog signals use less bandwidth, or a range of frequencies within a band, compared to their digital counterparts. And communication systems using them display less sensitivity concerning electrical tolerance.
On the downside, in the case of long-distance data transmission, using analog signals may lead to undesirable signal disturbances. Analog cables are highly susceptible to external influences, and analog wire is expensive and lacks ease of portability. Analog signals also tend to have higher generation loss or progressive loss of quality when making copies of the source material. Generally, they are more prone to noise and distortion and are of lower quality than digital signals.
Digital signals, on the other hand, represent information as a sequence of discrete values. They can take on a single value from a fixed set of possible values at a specific moment. Digital signals carry the data in binary format (zero or one), and each bit represents two distinct amplitudes. In a voltage vs. time graph, digital signals form square waves, with small discrete steps.
The physical quantity representing the information in digital signals can come from variable electric current or voltage, an electromagnetic field phase or polarization, or the magnetization of a magnetic storage medium. Digital signals find a wide application in broadband and cellular communication systems, networking and data communications, and computing and digital electronics.
The key advantages of digital signals include the ability to convey information over long distances with better quality and higher accuracy, combined with a lower error probability rate. Digital signals are highly noise and distortion-immune, and the deployment of error detection and correction codes ensures their accuracy while minimizing errors. They are simple and relatively low-cost to mass reproduce and easy to store on all types of magnetic or optical media via semiconductor chips. In addition, digital signal processing offers higher security thanks to the ease in which digital data can be encrypted and compressed.
In terms of disadvantages, digital signals communication and processes require higher bandwidth and more complex hardware resources, which in turn mandate higher power dissipation than their analog counterparts. Furthermore, sampling, or the process of converting analog signals to digital ones, may result in the loss of information.