Just What is an Analog Signal
by Thomas Giannini, Esq.
The word conjures up images of your Dad's Marantz stereo receiver casting a warm orange glow on brown shag carpeting, or a guitar amp-head glowing from overheated vacuum tubes. All fond memories. Everyone talks about it, but what does the term analog actually mean?
Let's start with the word analogous. "A" can be analogous to "B" if "A" is similar to or corresponding to "B". For example, a pointer on a dial is used to measure some other quantity, so the pointer position on the dial is analogous to the quantity it measures.
The grooves and scratches cut into a vinyl record are analogous to the variations in sound pressure (music) that have been captured, converted and ultimately pressed into the record. How does this happen? Factor in current and voltage. A simple dynamic microphone operates when a sound wave, for example your voice, strikes a coil suspended in a magnetic field, creating an electrical current in the coil. You probably remember this from 6th grade science class. This electrical current, complete with its voltage drops and spikes, is routed through the signal chain (cable) to a coil in a loud speaker, where the resulting magnetic field and mechanical force vibrates and drives a speaker cone creating true analog sound!
In the above example, the voltage of the signal fluctuates constantly from the force of the sound wave. The voltage spikes and drops are therfore an "analog" of the sound pressure wave. Digital sound differs, yet the catalyst for a digital signal is an analog signal that is sampled and quantized into a single binary code, then stored onto a digital medium, e.g., hard disk or CD. So the digital sound is only an approximation of the audio signal it represents. This starts a whole world of debate regarding which sound is better, something we will explore in a later blog.
For now, it's time to dust off your parent's records and listen to some old school sound.