Every time there’s a plane crash or other aviation safety incident, we often hear talk of the famous “black box”. Of course, anyone these days will tell you that they’re not black, but orange, for visibility’s sake. Plus, there’s often not one black box, but two! There’s a Flight Data Recorder (FDR), charged with recording aircraft telemetry, and a Cockpit Voice Recorder (CVR), designed to record what’s going on in the cabin.
It sounds straightforward enough, but the cockpit voice recorder has actually become the subject of some controversy in recent times. Let’s talk about the basics of these important safety devices, and why they’re the subject of some debate at the present time.
For a brief period in the 1940’s it might have been possible for a young enamored soul to hand his hopeful a romantic mix-spool of wire. This was right before the magnetic tape recorder and its derivatives came into full swing and dominated the industry thoroughly until the advent of the compact disk and under a hundred kilogram hard disk drives. [Techmoan] tells us all about it in this video.
The device works as one would expect, but it still sounds a little crazy. Take a ridiculously long spool of steel wire the size of a human hair(a 1 hour spool was 2.2km of wire), wind that through a recording head at high speed, magnetize the wire, and spool it onto a receiving spool.
If you’re really lucky the wire won’t dramatically break causing an irreversible tangle of wire. At that point you can reverse the process and hear the recorded sound. As [Techmoan] shows, the sound can best be described as… almost okay. Considering that its chief competition at the time was sound carved into expensive aluminum acetate plates, this wasn’t the worst.
The wire recorder lived on for a few more years in niche applications such as airplane black boxes. It finally died, but it does sound like a really fun couple-of-weekends project to try and build one. Make sure and take good pictures and send it in if any of you do.
[Nick]’s grandfather was quite the old school hacker. In the 1940s, he built his own wire recorder and microphone to capture everything from his children’s Chirstmas wishes to his favorite songs and programs from the radio. Only 20 or so spools have survived and were doomed to silence until [Nick] was able to find a vintage wire recorder, restore it, and feed digitized audio into Audacity.
Once he restored one of the two machines that he was able to get his hands on, [Nick] was in business. Since his grandfather also rolled his own spools, [Nick] had to build a playback spindle that would hold them. His uncle found an old mechanical counter to do the job, which [Nick] secured to the workbench. He fed the output from the wire recorder’s playback head into a guitar pre-amp, effectively digitizing the audio for recording in Audacity.
After playing all the spools, he adjusted the levels where necessary and cleaned up the recordings. His biggest challenge was feeding the wires back on to their original spools, which he managed with an electric drill and a rubber grommet. Be sure to check out the mp3 clips on [Nick]’s page. If you’re in the mood for old audio hacking stories, here’s one about building a tape recorder in 1949.
[Luke Wren] just wrote in to tell us about his new science blog called Wren’s Tech — it’s only a few days old, but he’s already got some pretty cool science experiments written up! Like how to estimate the muzzle velocity of a BB gun using just a voice recorder, and a curtain!
There are many different ways you could do this. One of the easiest is using a high-speed camera with a known grid or pattern as the background — like how Mythbusters does it. Unfortunately, high-speed cameras are usually out of reach for most hobbyists. [Luke] explains a rather cool system you can build with some electronics, whereby you have two thin wires a known distance apart — run current through both and use a circuit that can detect the interrupt as your projectile breaks the wires — or, you can use a voice recorder. Continue reading “Estimating BB Gun Muzzle Velocity With A Voice Recorder And A Curtain”→
[Ericdsc] is looking to capture the electrical impulses of his muscles by using an EMG. He went through several prototypes to find the right recipe for sensors to pick up the electrical signal through his skin. Above you can see the version that worked best. Each sensor is made starting with a piece of duct tape and laying out a patch of stripped wire on it. A 5cmx1xm piece of aluminum foil then covers this, and second smaller piece of foil covers the cable’s shielding (not pictured here). This will stick to your skin to hold the sensor in place after applying a dab of sugar syrup to help make a good electrical connection.
In this case, an audio recorder is taking the measurements. [Ericdsc] had been having trouble sleeping and wanted to find out if he’s restless in bed. The audio recorder can log hours of data from the sensors which he can later analyze on the computer. Of course, it wouldn’t be hard to build your own amplifier circuit and process the signals in real-time. Maybe you want to convert that mind-controlled Pong game over to use abdominal control. You’ll have a six-pack in no time.
A culture in which it’s fair to say the community which Hackaday serves is steeped in, is electronic music. Within these pages you’ll find plenty of synthesisers, chiptune players, and other projects devoted to synthetic sound. Not everyone here is a musician of obsessive listener, but if Hackaday had a soundtrack album we’re guessing it would be electronic. Along the way, many of us have picked up an appreciation for the history of electronic music, whether it’s EDM from the 1990s, 8-bit SID chiptunes, or further back to figures such as Wendy Carlos, Gershon Kingsley, or Delia Derbyshire. But for all that, the origin of electronic music is frustratingly difficult to pin down. Is it characterised by the instruments alone, or does it have something more specific in the music itself? Here follows the result of a few months’ idle self-enlightenment as we try to get tot he bottom of it all.
Will The Real Electronic Music Please Stand Up?
If you own a synthesiser, the Telharmonium is its daddy.
Anyone reading around the subject soon discovers that there are several different facets to synthesised music which are collectively brought together under the same banner and which at times are all claimed individually to be the purest form of the art. Further to that it rapidly becomes obvious when studying the origins of the technology, that purely electronic and electromechanical music are also two sides of the same coin. Is music electronic when it uses an electronic instrument, when electronics are used to modify the sound of an acoustic instrument, when it is sequenced electronically often in a manner unplayable by a human, or when it uses sampled sounds? Is an electric guitar making electronic music when played through an effects pedal?
The history of electronic music as far as it seems from here, starts around the turn of the twentieth century, and though the work of many different engineers and musicians could be cited at its source there are three inventions which stand out. Thaddeus Cahill’s tone-wheel-based Telharmonium US patent was granted in 1897, the same year as that for Edwin S. Votey’s Pianola player piano, while the Russian Lev Termen’s Theremin was invented in 1919. In those three inventions we find the progenital ancestors of all synthesisers, sequencers, and purely electronic instruments. If it appears we’ve made a glaring omission by not mentioning inventions such as the phonograph, it’s because they were invented not to make music but to record it. Continue reading “Where Did Electronic Music Start?”→
In our no-nonsense journey through the world of audio technology we’ve so far have looked at digital audio and the vinyl disk recording. What’s missing? Magnetic tape, the once-ubiquitous recording medium that first revolutionised the broadcast and recording industries in the mid-20th-century, and went on to be a mainstay of home audio before spawning the entire field of personal audio. Unless you’re an enthusiast or collector, it’s likely you won’t have a tape deck in your audio setup here in 2021 and you’ll probably be loading your 8-bit games from SD card rather than cassette, but surprisingly there are still plenty of audio cassettes released as novelties or ephemeral collectables.
The Device That Made The Sound Of The Latter Half Of The 20th Century
“Like a travelling razor blade”, a Blattnerphone steel-strip tape recorder at the BBC in 1937. Douglas Hallam, Jr., Public domain.
The first magnetic recordings were made directly on metal wires, but metal fatigues as it bends. By coating a flexible plastic tape in ferrous particles, the same simple technique of laying down an audio signal as variations in the magnetic field could be made smaller, lighter, and more robust. But the key to the format’s runaway success is the technical advancements that differentiate those 1950s machines from their wire recorder ancestors.
Whether it is a humble cassette recorder or a top-end studio multitrack, all tape recorders are very similar. There are two reels that hold the tape: the playback reel that houses the recording, and the take-up reel that stores the tape as it plays in the machine. The take-up reel is lightly driven to run faster than the tape speed, and the playback reel has a slight braking force to keep the tape under tension at all times. Continue reading “Know Audio: Mixtapes, Tape Loops, And Razor Blades”→
[Nick]’s grandfather was quite the old school hacker. In the 1940s, he built his own wire recorder and microphone to capture everything from his children’s Chirstmas wishes to his favorite songs and programs from the radio. Only 20 or so spools have survived and were doomed to silence until [Nick] was able to 
