Digital Signal Processing Reference
In-Depth Information
Chapter 1
What Is Digital Signal Processing?
A
signal
, technically yet generally speaking, is a a formal description of a
phenomenon evolving over time or space; by
signal processing
we denote
any manual or “mechanical” operation which modifies, analyzes or other-
wise manipulates the information contained in a signal. Consider the sim-
ple example of ambient temperature: once we have agreed upon a formal
model for this physical variable - Celsius degrees, for instance - we can
record the evolution of temperature over time in a variety of ways and the
resulting data set represents a temperature “signal”. Simple processing op-
erations can then be carried out even just by hand: for example, we can plot
thesignalongraphpaperasinFigure1.1,orwecancomputederivedpa-
rameters such as the average temperature in a month.
Conceptually, it is important to note that signal processing operates on
an abstract representation
of a physical quantity and not on the quantity it-
self. At the same time, the
type
of abstract representation we choose for the
physical phenomenon of interest determines the nature of a signal process-
ing unit. A temperature regulation device, for instance, is not a signal pro-
cessing system as a whole. The device does however contain a signal pro-
cessing core in the feedback control unit which converts the instantaneous
measure
of the temperature into an ON
OFF trigger for the heating element.
The physical nature of this unit depends on the temperature model: a sim-
ple design is that of a mechanical device based on the dilation of a metal
sensor; more likely, the temperature signal is a voltage generated by a ther-
mocouple and in this case the matched signal processing unit is an opera-
tional amplifier.
Finally, the adjective “digital” derives from
digitus,
the Latinword for fin-
ger: it concisely describes a world view where everything can be ultimately
represented as an integer number. Counting, first on one's fingers and then
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