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The Essential Guide to Digital Signal Processing by D. Lee Fugal, Richard G. Lyons

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2. Analog Signals

As we stated in the last chapter, the first step in understanding digital signal processing is to learn about analog signals. With that thought in mind, the goal of this chapter is to define and explain the nature of analog signals.

What Is an Analog Signal?

For our purposes an analog signal is defined as any representation of a physical quantity that

• typically varies in value over time,

• has a value at all instants in time, and

• contains information.

Those characteristics seem a little mysterious but they’re really not. You experience analog signals every day. The audio emanating from your cell phone speaker, the electrical video signal arriving from your television cable company, the height of the mercury column in an ...

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