about & FAQ

absorptions is a blog about my hobbies. So far it's mostly about signals and programming, but may pick up a random new field at any point. It's a place for me to direct my need to talk nerdy. Why? I like the smell of unsolved mysteries. Call them obsessions or special interests; I call them absorptions.

Here I've collected some questions often asked in the comments section etc.

• Contact info
• Who?
• Why?
• Could you release the source code for (x)?
• What are your rates for a sponsored article or guest post?
• How did you learn about signals? How could I learn, too?
• Do you do talks or workshops?
• How could I support this blog?
• What's your decoding software of choice?
• What kind of radio hardware you've used in this blog?
• What's the software you use to draw graphics and waveforms?
• Are you a hacker that breaks into computers?
• What are you working on right now?
• What's that weird language?
• How is your name pronounced?
• I have questions!

Contact info

• blog author: Oona Räisänen
• inquiries via david.bientechmedia@gmail.com
• please browse through this FAQ first
• @windytan@mastodon.social

Who?

Hi, I'm Oona, a computer geek from Finland. This is a blog about stuff I've found interesting along the years. In my working life I'm a software developer; I've mostly worked with real-time problems like Layer 1 networking and classical computer vision. You can follow me on Twitter for updates about new blog posts, although I don't tweet that much otherwise: @windyoona. There might be some fun stuff on my Youtube channel.

Why?

I write this blog because I want to share the joy of researching something interesting. And sound and waves are pretty interesting!

I'm the kind of person who enjoys absorbing information about something very specific and solving mysteries for no apparent reason. Or getting absorbed by them, if you will. Maybe it feels natural for people like us; maybe we see patterns in everything and are tempted to get to the bottom of them. Or maybe we never wanted to stop playing. Some would say there are lots of similarities with putting together puzzles. Perhaps you would like this Quora answer: Why do people like puzzles?

Sometimes I may do things the hard way, instead of the obvious way. Why? As a great composer once said, "only difficult solutions are worthwhile in art".

Could you release the source code for (x)?

No, to keep this hobby fun I prefer not to make software releases. It can be a lot of work to refactor and polish a hobby project into a presentable, portable, and legally license-compatible GitHub repository. It's also a big responsibility to publish and maintain software.

Instead of source code I prefer to share ideas, blog posts, diagrams, flow charts, algorithms; this is much more portable, and fun to create. Perhaps these could be used to formulate inputs for a chat bot to generate code?

However, I have published many of my command-line tools free on GitHub. These include:

• redsea, an RDS decoder that aims to be fast and light-weight while still supporting most if not all RDS features.
• deinvert, for descrambling a type of voice encryption known as voice inversion scrambling.
• darc2json, for receiving DARC carriers. At the moment it only supports a few types of data packets.
• squelch, a noise gate to facilitate RLE compression of PCM signals.
• stereodemux is an FM stereo demultiplexer. Thanks to testing by some active users it now works pretty well in real situations.

But what if I pay you?

Currently I don't sell software. I recommend looking into ChatGPT and other AI solutions!

How did you learn about signals? How could I learn, too?

You can learn a lot about sound by listening. Listen to how sounds in your everyday life resemble each other. What makes them sound alike or different? What's the difference between a 'high' pitch and 'low' pitch?

Pay attention to music. Can you make out which instruments are playing? If there are lyrics, try to hum to the second voice instead of the melody.

Listen to how sounds reverberate in rooms and other spaces. If you close your eyes and talk to yourself, can you tell something about the room just by how it resounds?

The way I learnt was by spending much of my free time experimenting with computers, playing musical instruments, and reading for many, many years; see my nerd story. This geeky stuff is what I've always enjoyed doing and I find it relaxing as well. It's like when some people like listening to heavy metal or playing a video game, and end up having a lot of knowledge on the subject as a byproduct.

Here are some sources about signal processing that might be suitable for beginners:

• Seeing Circles, Sines, and Signals – a compact primer on digital signal processing
• Let's learn about waveforms by Josh Comeau
• RTL-SDR Quick Start Guide – set up a cheap radio scanner based on the RTL-SDR

And a few more advanced ones:

• Tutorials on Digital Communications Engineering by Charan Langton
• The Scientist and Engineer's Guide to Digital Signal Processing by Steven W. Smith, Ph.D.
• Signal Analysis for Radio Monitoring, a book on Amazon (I haven't read it myself)

What are your rates for a sponsored article or guest post?

I don't do those at all, sorry.

Do you do talks or workshops?

There are some videos of past talks:

• SDR Analog Video Decoding Adventures (GRCon 2020)
• "My journey into FM-RDS" (30C3 2013)
• "Solving mysterious signals – a case study" (Reaktor Dev Day 2013)

How could I support this blog?

Maybe leave a nice comment, or better yet, get inspired to investigate some mystery yourself and blog about it :) It's a nice way to have a diary of past projects for yourself, too.

Which software you use to decode signals?

Some command-line tools I use (Linux and macOS):

• csdr does many kinds of basic low-level DSP tasks and can be used with Unix pipes on the command line. It can, for example, demodulate AM and FM, shift frequencies up and down, and convert integer data to floating point and back. It also works quite fast. It's not actively developed.
• SoX can do brick-wall sinc filtering and arbitrary resampling. It's sometimes easier to use than csdr because the frequency parameters are in Hertz. I also use it to change the number of channels, to write WAV file headers, to play sound into the speakers, and to convert between file types.
• For simple FSK stuff, minimodem might be the perfect choice.
• multimon-ng for many digital modes.

For visually browsing the live radio spectrum and listening to carriers by ear I use the GnuRadio-based gqrx (macOS/Linux) and SDR# (Windows). You can use TV-Sharp to decode analog picture signals. For all kinds of offline measurements and visual inspection I use baudline.

I also write my own tools, many of them in C++ using the liquid-dsp C library. Some of these are open source:

• redsea for RDS
• deinvert for inversion scrambling

What kind of radio hardware you've used in this blog?

In my projects I've used either

• a cheap USB DVB-T receiver stick, also known as RTL-SDR, or
• the more expensive Airspy R2.
• Some FM radio related projects were done using a modified "worldband receiver".

What's the software you use to draw graphics and waveforms?

• For waveforms I use my own program called oscille (explained in a blog post).
• Baudline renders beautiful spectrograms.
• For graphics design and compositing I use free software like Inkscape, Blender, GIMP, ImageMagick, and librsvg.

Are you a hacker that can break into computers?

I don't mind being called a hacker, but I can't break into computers. I used the word 'hacker' half-jokingly in a blog post because I reverse engineered a simple encryption that mentioned the word 'hacker' literally in its specification. I then decided to embrace the term for some time, because 'hacker' can also mean someone who does 'hacks', i.e. weird solutions to technical problems. People who build weird little electronic circuits can be called 'hardware hackers', and so on.

However, it unfortunately causes a common confusion with a more popular meaning: infosec people (security researchers) can also be called 'hackers', even though they do quite a different kind of thing, and are even professionals at that. Also, it often refers to computer criminals. I'm not an infosec professional, and I don't want to claim otherwise by using that term.

There's a Wikipedia article that discusses these definitions.

What are you working on right now?

I always have some posts as drafts, but there are no rigid plans or schedules. If the blog ever starts to feel like a chore I will take pauses of several months – even years – to pursue other interests.

For example, I make sleepy music (EP on Spotify). I also like city walks, bike rides, making 3D art, reading, and thinking about life.

What's that weird länguääge?

My native language is Finnish. Not many people speak it, so I've had to learn several more, English being one of them.

I'd like to use this opportunity to tell you how fun languages are. Knowing another language opens up whole new worlds and ways of thinking. Did you know, for example, that translating a sentence to another language isn't always even possible, and Google Translate won't tell you that?

It's actually never too late to start learning a language! In fact, you can start right now. Look up an online newspaper (or tech blog) in the language you wish to learn, and try to read an article with a dictionary in another tab. Make a note of every new word you encounter. You'll learn words quicker than you'd think! Later on, you can even do this with online radio stations (check out radio.garden) or YouTube videos.

How is your name pronounced?

If you're an English speaker, it's pronounced aw-nuh. I absolutely won't be offended if you adapt the sounds to your language. Or just call me Windy (as in weather, not roads).

I have questions!

Add a comment below and I'll try to answer!