Anyone who works in electronics or signal processing should be familiar with the two main categories of devices: analog and digital. But what makes something analog? How does it differ from digital? For that matter, what makes something digital?
What is an Analog Signal?
At its base, an analog signal is a continuous signal in which one time-varying quantity (such as voltage, pressure, etc.) represents another time-based variable. In other words, one variable is an analog of the other. The result is that analog systems allow for a theoretically infinite number of values to be represented: it can achieve any value within the parameters governing the system.
For example, imagine a dimmer switch tied to a light bulb. In a perfect analog system, the dimmer will have an infinite number of positions between “off” and “full” – and a correspondingly infinite number of levels of output by the lightbulb. The output by the bulb is analogous to the time-dependent variable “position of the dimmer switch.”
Difference Between Analog and Digital Signal
Digital signals, by contrast, express variation in the system’s variable in response to a set of discrete values (more like a light with an “on/off” switch or a three-way bulb with multiple, discrete levels of output).
Examples of Analog Signals
In theory, we can use the term “analog signal” to describe any continuous signal that uses one time-variable quantity to represent another (such as mechanical systems like a dial thermometer). But for our purposes, we use it most commonly to describe electrical signals.
We use analog signals in a wide variety of applications, such as:
- • Audio recording and reproduction
- • Live sound/amplification devices
- • Older video signal transmission technologies (VGA, S-Video, etc.)
- • Radio signals
- • Television broadcast signals (until recently)
At one point in time, analog computers were even available. These early computing devices were used to calculate complex scientific and industrial problems prior to the development of sufficiently powerful digital computers. They used various physical phenomena (such as electrical or mechanical quantities) to model the problems to be solved.
In nearly all cases, digital versions have supplanted their analog counterparts. One recent example is the ubiquity of digital TV broadcast or HDMI video standards. In 2019, all new consumer TVs are digital, just as all consumer computers have been for many years. It is worth noting, however, that in audio recording, both analog and digital are currently in regular use, each with its own supporters.
Bottom Line: Analog vs Digital Signals
Analog signals represent one continuous variable as the result of another continuous time-based variable. They are capable of outputting continuous information with a theoretically infinite number of possible values.
We have seen analog signals in use in nearly every type of signal processing and consumer electronics application imaginable. In most cases, they have been replaced by digital versions, though analog processes are still common in the audio recording domain alongside digital recording equipment.
