1.3.1 Source And Source Encoding

The source is responsible for generating a representation of the information to be communicated. In real-world systems, this information typically originates as a physical phenomenon such as sound pressure variations, light intensity, or symbolic data generated by a computer.

In early communications systems, the source produced an analog electrical signal whose amplitude varied continuously with the source information. In contrast, most modern systems employ digital representations, in which the information is expressed as a sequence of discrete symbols or bits. This conversion is achieved through processes such as sampling, quantization, and analog-to-digital conversion.

The raw digital representation produced by the source often contains substantial redundancy. For example, successive samples of speech or video are highly correlated, and text data may contain predictable patterns. Source encoding (or compression) exploits this redundancy to reduce the number of bits required to represent the information, thereby reducing the required transmission bandwidth or transmission time. The objective of source encoding is efficiency: to represent the source information using the smallest possible number of bits while maintaining acceptable fidelity at the sink.