2.5 LOOKING AHEAD
Although this chapter has described the physical form of source signals, it has not yet addressed a crucial question: How much information does a source actually produce?
A speech waveform may occupy 3.1 kHz of bandwidth, but how many bits are required to represent it digitally? A sensor may produce a stream of samples, but how efficiently can those samples be encoded? Is there redundancy in the source that can be removed without losing essential information?
Chapter 3 addresses these questions through the theory and practice of source coding. We move from describing signals in physical terms to describing information in statistical terms. Concepts such as entropy, redundancy, and compression will allow us to quantify the information content of a source and determine the minimum rate at which it must be represented.
Where this chapter focuses on signal representation and bandwidth, the next chapter focuses on information efficiency. We will see that many sources contain substantial redundancy that can be removed—that is, the signal can be compressed—sometimes dramatically reducing the bit rate required for transmission.
The communication chain therefore advances from understanding the form of source signals to optimizing their representation.
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