Signals and Systems
Earlier chapters of this book have concentrated on the ways in which signals may be described and analysed, and, as a natural extension of the discussion, we now turn our attention to the ways in which signal properties are modified by various types of processing. Some of the major reasons for interest in signal processing were outlined in sections 1.3 and 1.4. There it was mentioned that by far the majority of signal processing devices are electrical or electronic, typical examples being the radio or radar receiver, telephone-exchange equipment, and the electronic computer. Fortunately it is not necessary to have any detailed understanding of electrical circuits or elements to appreciate the main concepts of signal processing. The approach adopted in this and following chapters is to consider a signal processing device simply as one which delivers to its output a modified version of a signal applied to its input. In other words, it is regarded as an ‘input-output’ device, whose detailed internal construction does not concern us. This is often referred to as the ‘black-box’ approach: it involves us in mathematical descriptions of the overall performance of the signal processor, but not of the detailed electrical circuits of which it is probably constructed.
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