signal processing

Technology Connections explains why the superheterodyne radio has its name and how mixing frequencies lets it tune stations well. It walks through the underlying wave phenomena and algebra and why the design solved a hard tuning problem.

3Blue1Brown's animated visual introduction to the Fourier Transform, showing how a signal breaks into frequency components.

Technology Connections explains why North American tail light rules, which allow red turn signals and flashing brake lights, make signals ambiguous. He argues for amber signals and cites studies showing a safety benefit.

Reducible's visual walkthrough of the Fast Fourier Transform, motivated by polynomial multiplication. It shows how the FFT's key ideas can be discovered by asking the right questions.

3Blue1Brown shows how the uncertainty principle arises from Fourier transforms. A wave packet cannot be narrow in both position and frequency, so the principle is a property of waves rather than of measurement.

Veritasium tells the story of the Fast Fourier Transform, from its use in detecting nuclear tests to Cold War politics, and how it could have changed the arms race. It includes a short, intuitive explanation of what the Fourier transform does.

Technology Connections explains why car turn signals appear to drift out of sync at stoplights and how thermal and other flasher designs work. It also covers how synchronization could be achieved.

MIT researchers show that sound can be recovered from silent video by analyzing tiny vibrations in objects such as a potato chip bag. It works even with consumer cameras by using rolling shutter.

CNLohr maps Wi-Fi signal strength at high resolution by moving an ESP8266 on a CNC mill, then visualizes the 3D data in WebGL. The result shows interference patterns in space.

A This Week in Startups episode in which Jason Calacanis interviews David Heinemeier Hansson of 37signals. They discuss bootstrapping, company philosophy and views on the tech industry.

The first lecture of Stanford's Natural Language Processing with Deep Learning course, taught by Chris Manning and Richard Socher. It introduces NLP and word vectors, including SVD, skip-gram, CBOW, negative sampling and word2vec.

An MTA video on communications-based train control, the system meant to replace the New York City subway's century-old signaling. It also shows the mechanical interlocks and signals in use today.

A 105-minute technical deep dive from Noise In Space evaluating whether Starlink satellites could work as synthetic aperture radar. It covers SAR signal-to-noise, amplifiers, antennas, duplexing, phased array beamforming and simulations of V2 Mini and V3 satellites.

Samuel Falvo II live-codes a text preprocessor and blog engine in Forth over about an hour. It shows Forth's dictionary being snapshotted and restored in place of mutation, and how a small Forth system gets real work done.

A short demonstration of radioteletype (RTTY), a digital communication mode used in amateur radio, showing what the signal sounds like.

Monty Montgomery of Xiph.org gives real-time demonstrations of sampling, quantization, bit depth and dither using real audio equipment, including both digital analysis tools and vintage analog bench gear. It shows that sampled audio is not stair-stepped and corrects common misconceptions about digital audio.

The first of four short videos from Bill Hammack (engineerguy) introducing and giving the history of a 100-year-old mechanical computer, Michelson's harmonic analyzer. The series goes on to explain Fourier synthesis, analysis and operation of the machine.

Mike Pound explains the discrete cosine transform and how it underpins JPEG compression. It is part two of Computerphile's JPEG series.

David Kriesel's 31C3 talk, in German, on the discovery that Xerox scanner-copiers silently replace digits and letters in scanned documents. He explains how the bug stayed unnoticed in the wild for years.

Huygens Optics explains the Fourier transform and shows how a lens performs one optically. A DLP projector is used as a Fourier filter to do simple pattern recognition on lithographic character patterns.

Tom Scott explains for Computerphile how Unicode and UTF-8 grew out of messy older character encodings to become the web's standard. It covers why the design works and how it handles worldwide text.

3Blue1Brown introduces Fourier series, from the heat equation to drawing arbitrary shapes with rotating circles. It builds a visual intuition for decomposing functions into sine waves.

David MacKay's 2007 Google Tech Talk presents Dasher, a text-entry system driven by continuous gestures and a language model, reaching about 35 words per minute with one finger and 25 hands-free. It explains the information-theory reasoning behind the design.

3Blue1Brown's discovery-oriented introduction to error correction codes, building up Hamming codes from the puzzle of locating a flipped bit. It explains the parity-check idea and why it is so efficient.

Tom Scott explains why confetti and snow wreck video quality, using interframe compression and bitrate. He demonstrates it live by changing the quality on screen.

Moxie Marlinspike speaks at Next Generation Threats 2014 about the challenges of encrypted communication and how Signal addresses them. He also draws on American action movies as narrative for secure communications.

A two-minute demonstration of the loudness war, showing how heavy dynamic range compression in CD mastering makes music louder while degrading sound quality. It uses audio examples so you can hear the distortion.

The first lecture of David MacKay's Cambridge course on information theory, pattern recognition and neural networks. It introduces the core ideas of his book Information Theory, Inference, and Learning Algorithms.

A short animation reconstructing a planet's looping orbit using Ptolemy's epicycles and deferents, with the epicycles tracing out the face of Homer Simpson. It shows how enough circles can reproduce nearly any shape.

Timur Doumler's CppCon 2015 talk on how C++ is used in the audio industry. It covers the patterns and tools audio developers rely on, including handling real-time constraints.

An episode of This Week in Startups in which Jason Calacanis interviews Ruby on Rails creator David Heinemeier Hansson. They discuss startups, bootstrapping and 37signals' approach to business.

A Justin Bieber song slowed down 800% with the PaulStretch program, turning a pop track into a long ambient drone.

Course outline for Stanford's online GNSS course, introducing how GPS works and the many uses of satellite navigation. The series pairs short lectures with backyard experiments using smartphones.

Onslaught's Bad Apple 64 is a Commodore 64 demo that streams over 2000 frames of the Bad Apple animation from a single disk side at 12fps, with each frame packed to around 70 bytes.

Tom Scott explains for Computerphile how floating point numbers work, why moving the binary point is fast, and why it handles money badly.

David Kriesel's FrOSCon talk on how Xerox scancopiers, due to JBIG2 compression, silently replaced digits in scanned documents. He walks through how he discovered the bug and why it is so dangerous.

3Blue1Brown uses Wordle as an excuse to teach information theory and entropy, building a solver that picks guesses by expected information and incorporating word frequencies.

Tom Scott explains why hold music sounds worse than it used to, tracing it to old telephone exchanges and the audio compression applied by modern switches. It is a short visit to the Milton Keynes Museum.

Dan Worrall explains when higher sample rates help in recording and mixing, and when they do not. He goes into oversampling versus higher sample rates, and aliasing in distortion plugins.

Edward Kmett's 2013 talk at Prezi in Budapest on succinct data structures, which store data in close to the information-theoretic minimum space while supporting fast queries. It ties together the research and walks through his Haskell succinct library.