Signal Processing

This article is on a new method for detecting meteor reflections in radio signals for the BRAMS network. As shown below, these reflections are typically viewed as spectrograms. Hence, a straightforward way to approach the detection problem is to…

The famous “Wow!” signal is a radio signal that was received on 15 August 1977 as part of the SETI program. After all these years, it is still the most tantalizing candidate for being a true interstellar signal. Its name comes from the manually written word “Wow!” on…

How to create a simple band-pass or band-reject filter, given two cutoff frequencies? These filters can be created by combining low-pass and high-pass filters. To do that, you need…

How to create a simple high-pass filter, given a cutoff frequency and a transition bandwidth? A high-pass filter can be created by building a low-pass filter first, and then using spectral inversion to convert it into a high-pass one. Starting from the…

How to create a simple low-pass filter, given a cutoff frequency and a transition bandwidth? A low-pass filter is meant to allow low frequencies to pass, but to stop high frequencies. Theoretically, the ideal (i.e., perfect) low-pass filter is the sinc filter. The sinc function is defined as…

The Geiger counter (or Geiger-Müller counter) from The Clustering Illusion is actually quite interesting in itself. For starters, the script does not need an external audio file. Because the audio fragment is very short, I’ve just put it in a…

After deciding on the name, “Impulse Response”, for my consultancy company, the next step was to create a suitable logo for it. As I’ve explained before, impulse response is a basic concept from signal and image processing. For the logo, I wanted…

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…

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…

After introducing the finite-bandwidth square wave in a previous article, I’ll show in this one how such a square wave looks in a digital system, so in sampled form. The figure below shows one period of a square wave of 1 kHz, sampled at 44.1 kHz, a widely used…