What is Signal and Signal Perception?
1. What is Signal?
A signal is a virtual or physical quantity that varies with one or more independent variable(s). Graphically, in the Cartesian coordinate system, the independent variable is represented by the horizontal axis, or x-axis. And the dependent variable is represented by the vertical axis, or y-axis.
The independent variable would be time, space, or other independent variables like pressure and temperature. Furthermore, any quantity that provides context for a signal is an independent variable. For example, frequency can be considered for the X axis, where a frequency-dependent varying quantity is considered for the Y axis. These are some basic ways to form and perceive a signal. A signal is expressed as a mathematical function. For example-
Further,
on a seashore, a boy is observing a bird flying and recorded the flying speed
for 30 minutes. After plotting the recorded data, what we get is a signal as
follows:
If
we generate a signal, the signal could be continuous or discrete. The
continuous signal is plotted in continuous time, while the discrete signal is
plotted for discrete time. For example, in a poultry farm the yields of eggs
per day are plotted for the entire week as follows.
2. Signal Perception
We have started perceiving signals since we started to compare
dependent quantities against independent variables. In this way, our entire
human ecosystem is full of signals. For example, a random person standing
beside a busy highway road and counting the number of vehicles per unit time
(i.e., minute, hour) that are passing through. After documenting the counts
against time, what he will get is a signal. Similarly, any real-world natural
phenomena or processes to random social events can be computationally perceived
as signals. The construction scope of a signal is infinite, as there are
infinite variations in this observable universe where we live. However, the
more we are able to construct signals and then further process them, the more
we will be capable of impacting the context from which the signal is
constructed in the first place.
Signal and signal processing must be understood philosophically
first, and then come the mathematical tools that govern the processing of the
signal. The available resources (i.e., journal articles, books) majorly focus
on the tools of signal processing that quickly facilitate the processing of
signal. We must not overlook that signal processing came into being as a
powerful tool to understand and control the world from the philosophical
richness of pioneering scientists, thinkers, and philosophers. A signal
processing scientist and engineer must need to understand signal and signal
processing from a philosophical point of view to harness the full power,
capacities, and capabilities of available signal processing tools (i.e., FFT,
FIR, IIR).
How
can we philosophically think in signal processing? To think like a philosopher
in signal processing, one does not need to be a scientist or engineer nor need
academic qualification. Just look around you, where you live and breathe, and
at the world around you; notice the processes of the ambient ecosystem. How is
a tiny tree growing, how are small children becoming aged, how are rains nursing
the plantations and cooling the hot atmosphere, and how is the economy
changing? And, foremost, how are you changing in time? If you think, you will
find that the real world around you is constantly varying and then derive your
dependent and independent variables. If you start co-relationally comparing
dependent variables against independent variables, you will start getting tons
of signals.
However,
is it just thinking that generates benefits from signal processing to empower
our future? The answer is NO. If one seriously wants to be a signal processing
engineer, they must learn scientific and engineering concepts and tools of
signal processing like FFT, IDFT, convolution, filter banks, MATLAB, etc. The
modern engineering system’s raw materials existed on this earth even 1000 years
ago, but was it possible to construct sophisticated systems like cell phones,
airplanes, and the internet? The answer is NO, and we were not able to do it
because we did not perceive signals and systems in the past. For example, a 2
kg mass having a faint value, but when we taught the mass how to process the
signal and subsequently developed a computer (e.g., a laptop), then the 2 kg
mass now has a value of several hundred to thousands of dollars. The more
signals we will be perceiving, the more processing will be done, and we will
develop a stronger and more advanced civilization.
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