This is the personal site of Tom Roelandts. I’m trying to whet your appetite for science with this thing. My education and interests show through, of course, since I focus on stuff that I feel confident writing about. The site used to be solely about the photos, and I still think the thumbnails page is rather cute, but the emphasis has clearly shifted towards the articles lately.

What is a Spectrogram?

Spectrogram of square wave with harmonics 1, 3, 5, …, 19

A spectrogram is a graph that shows the evolution of the spectrum (the frequency contents) of a signal over time. Often, the frequency is on the vertical axis and time is on the horizontal axis. A spectrogram is computed by “chopping up” the signal into chunks and computing… read more

Submitted on 20 November 2013

Naive Square Wave

Naive square wave

After introducing finite-bandwidth square waves in previous articles, I’ll now describe what happens if you follow the naive approach, and just alternate sequences of 1’s and −1’s. As you might expect after reading the previous articles, there are several problems with this. The first problem is that the naive square wave is… read more

Submitted on 27 October 2013

Finite-Bandwidth Square Wave

Square wave with harmonics 1, 3, 5, …, 19

How would you produce a square wave on a digital system? At first sight, this seems completely trivial. You might think that you could just alternate a series of +1 values with a series of −1 values and be done with it. Well, it doesn’t work like that. An ideal square wave needs infinite bandwith, so creating one is… read more

Submitted on 2 October 2013

The Perfect Camera

Airy pattern

The perfect camera is diffraction limited. This article is written strictly from an optical point of view, so don’t expect a Nikon / Canon / Leica comparison here… Optically, a camera (or telescope or other optical instrument) can be described by its point spread function (PSF), which… read more

Submitted on 21 July 2013

Impulse Response

Unit sample function

The impulse response of a system is, perhaps not entirely unexpectedly, the response of a system to an impulse. This article introduces this all important concept, and shows how knowing only the impulse response of an LTI system can be used to… read more

Submitted on 6 July 2013

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