CoachA signal is a physical quantity that varies in time to carry information: the air pressure at your eardrum, the voltage at a microphone’s terminals, the brightness of the light in an optical fiber. To study a signal, record it as a function of time and read the information off the curve.
Examples
Example 8.5 (Mains and concert pitch)
The mains voltage oscillates at : its period is . An orchestra’s concert A is a pressure signal at : one cycle lasts . Higher frequency, shorter cycle: and are inverses of each other.