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),...

"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,...

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...

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...

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...

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,...

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...

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,...

<!--"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...

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...

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....

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...

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...

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....

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...

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...

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?...

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...

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...

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...

An Internet user is often warned by her browser that a web transaction is unencrypted and "could easily be read by a third party". So who's the third party? And how can anyone possibly listen in on traffic that's being...

A multinational burger chain has a restaurant nearby. One day I (exceptionally) went there and ordered a take-away burger that was not readily available. The clerk gave me a device that looked like a thick coaster, and told me I...

Many audio editor tools draw digitally sampled signals in ways that can be misleading or sometimes downright incorrect. I hope this post will be useful in explaining this recurring and confusing issue. In Audacity, let's set the project sample rate...

In the previous post I told about the 16 kbps data stream on FM broadcast frequencies, and my suspicion that it's being used by the bus and tram stop display system here in Helsinki. Now it's time to find out...

When PCM waveforms and similar function plots are displayed on screen, computational speed is often preferred over beauty and information content. For example, Audacity only draws the local maximum envelope amplitude and (what appears to be) RMS power when zoomed...