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. In an analogue 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. Other techniques, such as phase modulation or changing the phase of the carrier signal, are also used.
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. In such a system, 10 volts would represent 10 degrees, and 10.1 volts would represent 10.1 degrees.Īnother method of conveying an analogue signal is to use modulation. For example, suppose the signal is being used to represent temperature, with one volt representing one degree Celsius. Any change in the signal is meaningful, and each level of the signal represents a different level of the phenomenon that it represents. The signals take any value from a given range, and each unique signal value represents different information. Information is converted from some other physical form (such as sound, light, temperature, pressure, position) to an electrical signal by a transducer which converts one type of energy into another (e.g. Electrical signals may represent information by changing their voltage, current, frequency, or total charge. For example, an aneroid barometer uses the angular position of a needle as the signal to convey the information of changes in atmospheric pressure. An analogue signal uses some attribute of the medium to convey the signal's information.
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