Analog Signal

An analog signal uses some attribute of the medium to convey the signal's information. For example, an aneroid barometer uses angular position as the signal to convey pressure information. Electrical signals may represent information by changing their voltage, current, frequency, or total charge. Information is converted from some other physical form ( such as sound, light, temperature, pressure, position) to an electrical signal by a transducer.

The signals take any value from a given range, and each unique signal value represents different information. Any change in the signal is meaningful, and each level of the signal represents a different level of the phenomenon that it represents. For example, suppose the signal is being used to represent temperature, with one volt representing one degree Celsius. In such a system 10 volts would represent 10 degrees, and 10.1 volts would represent 10.1 degrees.

Another method of conveying an analog signal is to use modulation. In this, some base carrier signal has one of its properties altered: amplitude modulation (AM) involves altering the amplitude of a sinusoidal voltage waveform by the source information, frequency modulation (FM) changes the frequency. Other techniques, such as changing the phase of the carrier signal are also used.<

In an analog sound recording, the variation in pressure of a sound striking a microphone creates a corresponding variation in the current passing through it or voltage across it. An increase in the volume of the sound causes the fluctuation of the current or voltage to increase proportionally while keeping the same waveform or shape.

Mechanical, pneumatic, hydraulic and other systems may also use analog signals. (wikipedia.org)