ANALOG SIGNAL

• An analog or analogue signal is any continuous signal for which the time varying feature (variable) of the signal is a representation of some other time varying quantity, i.e., analogous to another time varying signal.
• The instantaneous voltage of the signal varies continuously with the pressure of the sound waves. 
• It differs from a digital signal.
• The term analog signal usually refers to electrical signals; however,mechanical, pneumatic, hydraulic, and other systems may also convey analog signals.
• An analog signal uses some property of the medium to convey the signal's information. 
• For example, an aneroid barometer uses rotary position as the signal to convey pressure information. In an electrical signal, the voltage,current, or frequency of the signal may be varied to represent the information.
• Any information may be conveyed by an analog signal; often such a signal is a measured response to changes in physical phenomena, such as sound, light, temperature, position, or pressure. 
• The physical variable is converted to an analog signal by a transducer. 
• In sound recording, fluctuations in air pressure (that is to say,sound) strike the diaphragm of a microphone which induces corresponding fluctuations in the current produced by a coil in an electromagnetic microphone, or the voltage produced by a condensor microphone.
• The voltage or the current is said to be an "analog" of the sound.