list of posts

2025

• Passing planes and other whoosh sounds

  You may recognise this common sound, but what causes it?

2024

• Ultrasonic investigations in shopping centres

  Some public address systems emit a continuous near-ultrasonic tone that gets modulated in interesting ways by the urban bustle.

• Smoother sailing: Studying audio imperfections in Steamboat Willie

  A deep dive into investigating and reducing the flutter distortion on the soundtrack of Steamboat Willie (1928).

2023

• Using HDMI EMI for high-speed data transfer

  HDMI is kind of loud in the radio. Could we use it for wireless video streaming?

2021

• Spiral spectrograms and intonation illustrations

  Wind a spectrogram on a spiral and see what appears!

• Speech to birdsong conversion

  How human speech could be converted to a birdsong by extracting one of the harmonics.

2020

• Plotting patterns in music with a fantasy record player

  Sometimes you can see patterns on the surface of vinyl records. What do they mean?

2019

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

  Trying to get live digital video from a 1980s gaming console.

• Beeps and melodies in two-way radio

  My PMR listening stations classifies and visualizes tones and beeps it hears.

2017

• Animated line drawings with OpenCV

  Creating simple animations at pixel level with a C++ computer vision library.

• In pursuit of Otama's tone

  Simulating the sound of the Otamatone for a music project.

• Descrambling split-band voice inversion with deinvert

  A tool to reverse a primitive kind of voice encryption.

• Gramophone audio from photograph, revisited

  Examining Tommy the robot's voice box once more.

• Virtual music box

  Findings and sound samples from a music box synthesizer project.

2016

• CTCSS fingerprinting: a method for transmitter identification

  Identifying FM walkie-talkies from demodulated baseband audio.

• Redsea 0.7, a lightweight RDS decoder

  Redsea the RDS decoder got fast enough to be run on a Raspberry Pi 1.

2015

• Pea whistle steganography

  Would anyone notice if a referee's whistle transmitted a secret data burst?

• The microphone bioamplifier

  Examining biological signals using a microphone preamplifier.

• Case study: tinnitus with distortion

  Speculation on the etiology of a specific type of tinnitus.

• Trackers leaking bank account data

  Under no circumstance is our customers' personal information transmitted to a third party.

• Receiving RDS with the RTL-SDR

  RTL-SDR support for my RDS decoder, redsea.

• My chip collection

  Selected specimens from my pile of salvaged ICs.

2014

• Visualizing hex dumps with Unicode emoji

  All 256 byte values mapped into human-friendly pictograms.

• Mapping microwave relay links from video

  Speculative article about a method for infering the directions of dish antennas.

• Headerless train announcements

  Reverse-engineering a proprietary ADPCM encoding.

• Time-coding audio files

  Ways to embed UTC time into audio recordings.

• Mystery signal from a helicopter

  Decoding helicopter telemetry first mistaken as interference.

• Misleading representations of discrete-time signals

  A weird artifact displayed by some audio tools, and ways around it.

2013

• Decoding radio-controlled bus stop displays

  Decoding the rest of the DARC layers plus the bus stop application.

• Broadcast messages on the DARC side

  Physical layer decoding of the DARC protocol.

• The burger pager

  Examining pager devices used in restaurants.

• LAN file transfer with netcat

  Silly hack for quick file transfer from the *nix command line.

• Squelch it out

  Silencing quiet passages of signals to lose entropy and save space.

• Reader challenge explained

  Explanations to the puzzles, but no actual solutions.

• The flyback sonar

  Could a CRT flyback transformer be used as a Doppler sonar?

• Reader challenge: Obfuscated messages

  Little puzzles for my beloved readers.

• Descrambling the voice inversion scrambler

  Simple methods to digitally reverse voice inversion.

• A determined 'hacker' decrypts RDS-TMC

  Cryptanalysis of the cipher used in RDS-TMC.

• Tomy Electronic PUCKMAN

  A toy I found at a flea market.

• How I discovered RDS

  My roundabout journey into FM-RDS and how I initially decoded it using only my radio's Line Out.

• Portable TV, Raspberry-Pified

  Mini-teardown of a mini-CRT, interfacing it with a Raspberry Pi, and destroying the Pi.

• Rendering PCM with simulated phosphor persistence

  A method for plotting nice-looking waveforms.

• Eavesdropping on a wireless keyboard

  Is it safe to use an old Logitech wireless keyboard?

• RDS display on a Raspberry Pi

  Porting the RDS decoder to the Raspberry Pi and attaching a little LCD.

• Voice over laser

  Modulating a laser beam with voice using everyday equipment.

• The laser-equipped Lego train

  Optical capture of gramophone audio from the Atomic Powered Robot.

• Case modding, the polish way

  Improving CD jewel cases using nail polish.

• The atomic powered robot

  Teardown of an old toy and examining its audio device.

• The GSM buzz

  What does the iconic sound mean?

• SSTV reception on Linux

  A C program for shortwave listeners.

• The infrared impulse

  Receiving an IR remote using a sound card.

2012

• The sound of the dial-up, pictured

  Explaining the various phases of the familiar dialup handshake process.

• Enchanting subcarriers on FM, part 2

  Modifying my radio by adding a digital RDS output connector.

• Enchanting subcarriers on FM

  Planning a direct RDS output from the radio's decoder chip, instead of the Line Out hack.

• Character recognition, the simple way

  A Perl hack for reading 1's and 0's out of a picture.

• Vintage bits on cassettes

  Save digital data on a compact cassette using an ordinary cassette deck.

• Summer fun: tinkering with a broken GPS

  Fixing a vintage GPS receiver and interfacing it with Linux.

• Google Earth on 64-bit Linux

  A tip to get it working.