a blog about sound & signals by windytan [oona räisänen]
I always assumed that the recognisable 'whoosh' sound a plane or helicopter makes when passing overhead simply comes from the famous Doppler effect . But when you listen closely, this explanation doesn't make complete sense. (Audio clipped from freesound - here and here ) A classic example of the Doppler effect is the sound of a passing ambulance constantly descending in pitch. When a plane flies…
I can't remember how I first came across these near-ultrasonic 'beacons' ubiquitous in PA systems. I might have been scrolling through the audio spectrum while waiting for the underground train; or it might have been the screeching 'tinnitus-like' sensation I would often get near the loudspeakers at a local shopping centre. Whatever the case, I learned that they are called pilot tones. Many…
Steamboat Willie (1928) was one of the earliest cartoons with synchronized sound. That is, it had post-production sound effects; this was something new and exciting. Now that the cartoon has recently entered the public domain [bbc24] we can safely delve into its famous soundtrack. See, there's something interesting about how it sounds... If you listen closely to the soundtrack on Youtube it sounds…
This story, too, begins with noise. I was browsing the radio waves with a software radio, looking for mysteries to accompany my ginger tea. I had started to notice a wide-band spiky signal on a number of frequencies that only seemed to appear indoors. Some sort of interference from electronic devices, probably. Spoiler alert, it eventually led me to broadcast a webcam picture over the radio…
I've been experimenting with methods for visualising harmony, intonation (tuning), and overtones in music. Ordinary spectrograms aren't very well suited for that as the harmonic relations are not intuitively visible. Let's see what could be done about this. I'll try to sprinkle the text with Wikipedia links in order to immerse ( nerd snipe ?) the reader in the subject. Equal temperament cents…
I had a dream one night where a blackbird was talking in human language. When I woke up there was actually a blackbird singing outside the window. Its inflections were curiously speech-like. The dreaming mind only needed to imagine a bunch of additional harmonics to form phonemes and words. One was left wondering if speech could be transformed into a blackbird song by isolating one of the…
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 when I took a closer look at the pattern it seemed to somehow follow changes in the music. That doesn't look like damage at all. When I played the CD version it became clear: this was an artifact of…
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 speedrun attempts. Now, how to make the 1985 NES and the 2013 MacBook play together, preferably using hardware that I already have? This project diary documents my search for the answer. Here's a spoiler – it did work: Things that I tried…
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 also explain how my listening station works. Background: walkie-talkies are fun The frequency band I've recently…
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 one of its core functions but happens to be possible using its GUI drawing tools. Below we'll take a look at some video art I wrote for a music project. It goes a bit further than…
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 centimeters, which makes it very sensitive to finger placement. And in any case, I'd just like to have a programmable virtual instrument that sounds like the Otamatone. What…
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 Codeberg ), that does all this for us. It can also descramble a slightly more advanced scrambling method called split-band inversion. Let's see how that…
"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 miniature vinyl record sound mechanism a few times before ( #1 , #2 ), in an attempt to recover the analog audio signal using only a digital camera. Results were noisy at best. The blog posts resurfaced in a recent IRC discussion…
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 version either. They all seemed to be missing something. Maybe they were too perfectly tuned? I wasn't sure. Perhaps, if I digitized the sound myself, I could…
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 hand-held FM transceivers, known as CTCSS or Continuous Tone-Coded Squelch System. Motivation &…
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 developments. Input formats Redsea can decode several types of data streams. The command-line switches to activate these can be found in the readme. Its main use, perhaps, is to…
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 in the frequency fluctuation. I'm sure it's alternating between two distinct frequencies. Is it really that binary? How random is the fluctuation? Could it be synthesized to…
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, special-purpose electrodes, and contact gel, none of which I have at hand. A perfect opportunity for home-baking, that is! There's an Instructable…
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 shown here, which didn't really answer any questions. Also, the sound comes with some pecularities that warrant a deeper analysis. So it shall become one of my absorptions . The possible subtype (Vielsmeier et al. 2012) of tinnitus I have, related to a…
A Finnish online bank used to include a US-based third-party analytics and 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 by claiming that all information is collected anonymously: But is it true? As Ospi notes, a plethora of information is sent along the HTTP request for the…
redsea is a command-line RDS decoder. I originally wrote it 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. Redsea is on GitHub . It has minimal dependencies (perl core modules, C standard library, rtl-sdr command-line tools) and has…
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 interesting parts. Selected packages from my disorganized pile of chips follow. Most are POTS -related. Sony CXA1619BS A "one-chip-wonder", this is an…
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 characters in the Miscellaneous Symbols and Pictographs block. This Perl script does just that: @emoji = qw( 🌀 🌂 🌅…
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. I'm collecting a little map of nearby link stations, trying to find out how they're interconnected…
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 once belonged to an older-type onboard announcement device. It contains a file system of 58 directories with five-digit names, and one called "yleis"…