Analog vs Digital – Part 2: Analog

In part 1, I defined the terms signal and gadget. In this post, I give a definition for an analog signal/gadget with an example.

signal: an analog signal is a signal that always has a value. They key term is always.

gadget: an analog gadget operates continuously on an analog signal.

By this definition, everything that occurs naturally is analog. This property of natural phenomena occurs because almost all physical laws are continuous—they define a relationship between signals that is true always. They don’t define a relationship between a sequence of values.

Analog Signals

Consider a runner’s distance from the starting line. Distance is an analog signal. A runner cannot start at the starting line and end at the finish line without being somewhere in-between during the race. Runners don’t simply disappear and re-appear elsewhere.

One can graph the runner’s distance from start to finish in a smooth manner—without lifting one’s pen off the paper:

Similarly, looking back at temperature measured at Chicago O’Hare airport, one can see that the temperature doesn’t make a step jump from 79 degrees in June to 84 degrees in July. It moves smoothly from one temperature to the other.

Analog Gadgets

Consider an analog watch. The analog watch gets wound up, and its little gears move smoothly. They don’t update the time ever second. They are constantly moving. The position of the hands on the watch don’t jump from point to point. They move smoothly from point to point.

Similarly, consider an analog recording: audio cassettes. A microphone picks up sound pressure and converts it to a current. The current is then passed to the tape recorder. The tape recorder generates a magnetic field proportional to the current (and therefore proportional to sound pressure), resulting in a recorded magnetic configuration on the tape.

Note that all this information transfer occurs continuously. The sound just flows to the microphone, producing an electrical current that flows to the magnetic medium which then impinges a magnetic field into the tape.