IANAMathematician, but I've tried to come up with a metaphor which I hope isn't too wrong:
1. You've start with a signal fluctuating going up and down, and it's on a strip of little LEDs labeled from -1 to +1.
2. You mount that strip to a motor, and spin it at a certain rate. After a while the afterimages make a blob-shape.
3. For each rotation rate, measure how much the shape appears off-center.
In this way you can figure out how much the underlying signal does (or doesn't) harmonize with a given rotation hertz.
replies(2):