MAIN SIGNALSeptember 19, 2025

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.

Author: Main Uddin-Al-Hasan

Work Division: Signal Processing Philosophies (SPPhilo)

MAIN SIGNAL

Why Signal Processing?

MAIN SIGNALAugust 19, 2025

Our world is constantly changing. The change is often correlational; an object variation initiates the variation in another object. This relational variation needs to be mathematically realized and understood to be able to understand the variational process and control it. For example, the earth is rotating daily (diurnal motion) in time while we are observing sunrise and sunset. Now, to understand how the entire process works, we must relationally count sunrise and sunset in time. If we assign the value of 1 to sunrise and 0 to sunset, then over the course of one year, we will create a graph or signal.

Signal is all about realizing multivariate relational changes as a mathematical equation. The signal processing can also be termed “Variation Engineering” in all dimensionalities and forms. Now, a question could be raised: how important is signal processing in our lives? The truth is our very own body is constantly varying inside bones and veins, and it can be termed as bio signal processing. While our body is varying, our ambient is also varying. While the ambience is varying, the earth is also varying; while the earth is varying, the solar system is also varying; while the solar system is varying, the Milky Way galaxy is also changing. If we push the range further, the observable universe is also changing. Is there any blueprint that can relate all this variational pattern into a single equation or understanding? Even though a single blueprint of all variations is theoretically realizable, it is practically an impossible task. However, we are trying to make this impossibility into a possibility of some degree, whatever tedious task it is. The great feats in science and engineering, like CERN, are continuously working to solve this quest. And, verily, when we work toward a higher and ambitious goal, we get some understanding of technologies even after not being able to solve the fundamental quest. The great quest of understanding nature and all its variations is powered by “signal processing.”

Please watch the following videos [1] to have a short introduction on Signal Processing: