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Articles from Oona Räisänen

Visit www.windytan.com, subscribe and follow @S

Plotting patterns in music with a fantasy record player

From www.windytan.com 1 month ago in Blogs

Back in April I bought a vinyl record that had a weird wavy pattern near the outer edge. I though I may have broken it somehow but couldn't even test this because I don't own a record player. *) But...

Capturing PAL video with an SDR (and a few dead-ends)

From www.windytan.com 1 year ago in Blogs

I play 1980s games, mostly Super Mario Bros., on the Nintendo NES console. It would be great to be able to capture live video from the console for recording or maybe even speedrun streaming. Now, how to make the 1985...

Beeps and melodies in two-way radio

From www.windytan.com 2 years ago in Blogs

Lately my listening activities have focused on two-way FM radio. I'm interested in automatic monitoring and visualization of multiple channels simultaneously, and classifying transmitters. There's a lot of in-band signaling to be decoded! This post shall demonstrate this diversity and...

Animated line drawings with OpenCV

From www.windytan.com 3 years ago in Blogs

OpenCV is a pretty versatile C++ computer vision library. Because I use it every day it has also become my go-to tool for creating simple animations at pixel level, for fun, and saving them as video files. This is not...

In pursuit of Otama's tone

From www.windytan.com 3 years ago in Blogs

It would be fun to use the Otamatone in a musical piece. But for someone used to keyboard instruments it's not so easy to play cleanly. It has a touch-sensitive (resistive) slider that spans roughly two octaves in just 14...

Descrambling split-band voice inversion with deinvert

From www.windytan.com 3 years ago in Blogs

Voice inversion is a primitive method of rendering speech unintelligible to prevent eavesdropping of radio or telephone calls. I wrote about some simple ways to reverse it in a previous post. I've since written a software tool, deinvert (on GitHub),...

Gramophone audio from photograph, revisited

From www.windytan.com 3 years ago in Blogs

"I am the atomic powered robot. Please give my best wishes to everybody!" Those are the words uttered by Tommy, a childhood toy robot of mine. I've taken a look at his peculiar sound mechanism a few times before (#1,...

Virtual music box

From www.windytan.com 4 years ago in Blogs

A little music project I was writing required a melody be played on a music box. However, the paper-programmable music box I had (pictured) could only play notes on the C major scale. I couldn't easily find a realistic-sounding synthesizer...

CTCSS fingerprinting: a method for transmitter identification

From www.windytan.com 4 years ago in Blogs

Identifying unknown radio transmitters by their signals is called radio fingerprinting. It is usually based on rise-time signatures, i.e. characteristic differences in how the transmitter frequency fluctuates at carrier power-up. Here, instead, I investigate the fingerprintability of another feature in...

Redsea 0.7, a lightweight RDS decoder

From www.windytan.com 4 years ago in Blogs

I've written about redsea, my RDS decoder project, many times before. It has changed a lot lately; it even has a version number, 0.7.6 as of this writing. What follows is a summary of its current state and possible future...

Barcode recovery using a priori constraints

From www.windytan.com 5 years ago in Blogs

Barcodes can be quite resilient to redaction. Not only is the pattern a strong visual signal, but also the encoded string that often has a rigidly defined structure. Here I present a method for recovering the data from a blurred,...

Pea whistle steganography

From www.windytan.com 5 years ago in Blogs

Would anyone notice if a referee's whistle transmitted a secret data burst? I do really follow the game. But every time the pea whistle sounds to start the jam I can't help but think of the possibility of embedding data...

The microphone bioamplifier

From www.windytan.com 5 years ago in Blogs

As the in-ear microphone in the previous post couldn't detect a signal that would suggest objective tinnitus, the next step would be to examine EMG signals from facial muscles. This is usually done using a special-purpose device called a bioamplifier,...

Case study: tinnitus with distortion

From www.windytan.com 6 years ago in Blogs

<!--"The generation of tinnitus is a topic of much scientific enquiry."[ref http://bmb.oxfordjournals.org/content/63/1/195.full]--> A periodically appearing low-frequency tinnitus is one of my least favorite signals. A doctor's visit only resulted in a WONTFIX and the audiogram on the right, which didn't...

Trackers and bank accounts

From www.windytan.com 6 years ago in Blogs

A Finnish online bank used to include a third-party tracking script in all of its pages. Ospi first wrote about it (in Finnish) in February 2015, and this caused a bit of a fuss. The bank responded to users' worries...

Receiving RDS with the RTL-SDR

From www.windytan.com 6 years ago in Blogs

I originally wrote redsea as a script to decode RDS from demultiplexed FM stereo sound. Later I've experimented with other ways to read the bits, and the latest addition is to support the RTL-SDR television receiver via the rtl_fm tool....

My chip collection

From www.windytan.com 6 years ago in Blogs

Old IC (integrated circuit) packages are fun and I collect them. This involves going to flea markets to look for cheap vintage electronics like telephones, answering machines, radios or toys, and then desoldering and salvaging all the ICs and other...

Visualizing hex dumps with Unicode emoji

From www.windytan.com 6 years ago in Blogs

Memorizing SSH public key fingerprints can be difficult; they're just long random numbers displayed in base 16. There are some terminal-friendly solutions, like OpenSSH's randomart. But because I use a Unicode terminal, I like to map the individual bytes into...

Mapping microwave relay links from video

From www.windytan.com 6 years ago in Blogs

Radio networks are often at least partially based on microwave relay links. They're those little mushroom-like appendices growing out of cell towers and building-mounted base stations. Technically, they're carefully directed dish antennas linking such towers together over a line-of-sight connection....

A determined 'hacker' decrypts RDS-TMC

From www.windytan.com 6 years ago in Blogs

As told in a previous post, I like to watch the RDS-TMC traffic messages every now and then, just for fun. Even though I've never had a car. Actually I haven't done it for years now, but thought I'd share...

Headerless train announcements

From www.windytan.com 7 years ago in Blogs

The Finnish state railway company just changed their automatic announcement voice, discarding old recordings from trains. It's a good time for some data dumpster diving for the old ones, don't you think? A 67-megabyte ISO 9660 image is produced that...

Broadcast messages on the DARC side

From www.windytan.com 7 years ago in Blogs

By now I've rambled quite a lot about RDS, the data subcarrier on the third harmonic of the 19 kHz FM stereo pilot tone. And we know the second harmonic carries the stereo information. But is there something beyond that?...

Time-coding audio files

From www.windytan.com 7 years ago in Blogs

One day you'll need to include real-time UTC timestamps in audio. It's useful when reconstructing events from long, unsupervised surveillance microphone recordings, or when constantly monitoring and logging radio channels. There's no standard method for doing this with WAV or...

Mystery signal from a helicopter

From www.windytan.com 7 years ago in Blogs

Last night, YouTube suggested a video for me. It was a raw clip from a news helicopter filming a police chase in Kansas City, Missouri. I quickly noticed a weird interference in the audio, especially the left channel, and thought...

Eavesdropping on a wireless keyboard

From www.windytan.com 7 years ago in Blogs

Some time ago, I needed to find a new wireless keyboard. With the level of digital paranoia that I have, my main priority was security. But is eavesdropping a justifiable concern? How insecure would it actually be to type your...

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