Signal

A signal is the variation of a quantity over time and/or space, such as: 
– air pressure waves of sounds,
– colors of an image,
– depths of a surface,
– temperature of a body,
– current/voltage in a conductor or biological system,
– light,
– electromagnetic radio waves,
– commodity prices or volume and mass of an object

Signal Processing 
Manipulating a signal to change its characterictics or extract information Typical Problems:
– Eliminating “noise”
– Correcting distortion
– Extracting indirect quantity from measured signals

Signal Transformation
• The primary objective of signal transformation is to express a signal in terms of a combination of a set of simple elementary signals, known as the basis functions:
– In Fourier transform the basic elementary signals are a set of sinusoidal signals (sines and cosines)