We are used to seeing shots from TV news helicopters every day, they are part of the backdrop to life in the 21st century. But so often we hear them overlaid with studio commentary, so it’s interesting to hear that their raw audio contains telemetry. It caught the attention of [proto17], who took some audio pulled from a news helicopter video and subjected it to a thorough investigation to retrieve the data.
The write-up is at a very in-depth level, and while there’s an admission that some of the steps could have been performed more easily with ready-made tools, its point is to go through all steps at a low level. So the action largely takes place in GNU Radio, in which we see the process of identifying the signal and shifting it downwards in frequency before deducing its baud rate to retrieve its contents. The story’s not over though, because we then delve into some ASCII tricks to identify the packet frames, before finally retrieving the data itself. It still doesn’t tell you what the data contains, but it’s a fascinating process getting there nonetheless.
When building a new project, common wisdom suggests to avoid “reinventing the wheel”, or doing something simple from scratch that’s easily available already. However, if you can build a high-voltage wheel, so to speak, it might be fun just to see what happens. [Dan] decided to reinvent not the wheel, but the speaker, and instead of any conventional build he decided to make one with parts from a microwave and over 6,000 volts.
The circuit he constructed works essentially like a Tesla coil with a modulated audio signal as an input. The build uses the high voltage transformer from the microwave too, which steps the 240 V input up to around 6 kV. To modulate that kind of voltage, [Dan] sends the audio signal through a GU81M vacuum tube with the support of a fleet of high voltage capacitors. The antenna connected to the magnetron does tend to catch on fire somewhere in the middle of each song, so it’s not the safest device around even if the high voltage can be handled properly, but it does work better than expected as a speaker.
If you want a high-voltage speaker that (probably) won’t burn your house down, though, it might be best to stick to a typical Tesla coil. No promises though, since working with high voltages typically doesn’t come with safety guarantees.
We love the world of audiophiles here at Hackaday, mostly for the rich vein of outrageous claims over dubious audio products that it generates. We’ve made hay with audiophile silliness in the past, but what we really like above that is a high quality audio project done properly. It’s one thing to poke fun at directional oxygen free gold plated USB cables, but it’s another thing entirely to see a high quality audio project that’s backed up by sound design and theory to deliver the best possible listening. [Davide Ercolano]’s transmission line speakers are a good example, because he’s laid out in detail his design choices and methods in their creation.
Starting with the Thiele-Small parameters of his chosen driver, he simulated the enclosure using the Hornresp software. As a 3D-printed design he was able to give it paraboloid curves to the convoluted waveguide, making it a much closer approximation to an ideal waveguide than a more traditional rectangular design. In the base is a compartment for an amplifier module, with additional Bluetooth capability.
We’d be curious to know how well 3D printed plastic performs in this application when compared for example to something with more mass. However we like these speakers a lot; this is how a high quality audio project should be approached. We’ve delved into speakers more than once in the past, but if you’re looking for something really unusual then how about an electrostatic?
The Valve Index VR headset incorporates a number of innovations, one of which is the distinctive off-ear speakers instead of headphones or earbuds. [Emily Ridgway] of Valve shared the design and evolution of this unusual system in a deep dive into the elements of the Index headset. [Emily] explains exactly what they were trying to achieve, how they determined what was and wasn’t important to deliver good sound in a VR environment, and what they were able to accomplish.
First prototype, a proof-of-concept that validated the basic idea and benefits of off-ear audio delivery.
Early research showed that audio was extremely important to providing a person with a good sense of immersion in a VR environment, but delivering a VR-optimized audio experience involved quite a few interesting problems that were not solved with the usual solutions of headphones or earbuds. Headphones and earbuds are optimized to deliver music and entertainment sounds, and it turns out that these aren’t quite up to delivering on everything Valve determined was important in VR.
The human brain is extremely good at using subtle cues to determine whether sounds are “real” or not, and all kinds of details come into play. For example, one’s ear shape, head shape, and facial geometry all add a specific tonal signature to incoming sounds that the brain expects to encounter. It not only helps to localize sounds, but the brain uses their presence (or absence) in deciding how “real” sounds are. Using ear buds to deliver sound directly into ear canals bypasses much of this, and the brain more readily treats such sounds as “not real” or even seeming to come from within one’s head, even if the sound itself — such as footsteps behind one’s back — is physically simulated with a high degree of accuracy. This and other issues were the focus of multiple prototypes and plenty of testing. Interestingly, good audio for VR is not all about being as natural as possible. For example, low frequencies do not occur very often in nature, but good bass is critical to delivering a sense of scale and impact, and plucking emotional strings.
“Hummingbird” prototype using BMR drivers. Over twenty were made and lent to colleagues to test at home. No one wanted to give them back.
The first prototype demonstrated the value of testing a concept as early as possible, and it wasn’t anything fancy. Two small speakers mounted on a skateboard helmet validated the idea of off-ear audio delivery. It wasn’t perfect: the speakers were too heavy, too big, too sensitive to variation in placement, and had poor bass response. But the results were positive enough to warrant more work.
In the end, what ended up in the Index headset is a system that leans heavily on Balanced Mode Radiator (BMR) speaker design. Cambridge Audio has a short and sweet description of how BMR works; it can be thought of as a hybrid between a traditional pistonic speaker drivers and flat-panel speakers, and the final design was able to deliver on all the truly important parts of delivering immersive VR audio in a room-scale environment.
As anyone familiar with engineering and design knows, everything is a tradeoff, and that fact is probably most apparent in cutting-edge technologies. For example, when Valve did a deep dive into field of view (FOV) in head-mounted displays, we saw just how complex balancing different features and tradeoffs could be.
Although we all wish that our projects would turn out perfect with no hiccups, the lessons learned from a frustrating project can sometimes be more valuable than the project itself. [Thomas Sanladerer] found this to be the case while trying to build the five satellite speakers for a 5.1 surround sound system, and fortunately shared the entire process with us in all its messy glory.
[Thomas] wanted something a little more attractive than simple rectangular boxes, so he settled on a very nice curved design with few flat faces and no sharp corners, 3D printed in PLA. Inside each is an affordable broadband speaker driver and tweeter, with a crossover circuit to improve the sound quality and protect the drivers. The manufacturer of the drivers, Visatron, provides very nice speaker simulation software to select the appropriate drivers and design the crossover circuit. The front of each speaker consisted of a 3D printed frame, covered with material from a cut-up T-shirt. These covers attach to the main body using magnets and really look the part.
After printing, [Thomas] soaked all the parts in water to clean of the PVA support structures but discovered too late that the outer surfaces are not watertight and a lot of water had seeped into the parts. In an attempt to dry them he left them in the sun for a while which ended up warping some parts, so he had to reprint them anyway. The main bodies were printed in two parts and then glued together. This required a lot of sanding to smooth out the glue joints, and many cycles of paint and sanding to get rid of the layer lines. When assembling the different pieces, he found that many parts did not fit together, which he suspects was caused by incorrect calibration on the delta-bot printer he was using.
In the end, the build took almost two years, as [Thomas] needed breaks between all the frustration, and eventually only used one of the speakers. We’re glad he shared the messy parts of the project, which will hopefully spare someone else a bit of trouble in a project.
Listening to a high-quality audio setup is always a pleasure, and we’ve covered several projects from audiophiles, including affordable DML speakers, and 3D printed speaker drivers.
So often when we read of a modification on a classic piece of tube electronics we prepare to wince, as such work often results in senseless butchery of a well-preserved survivor. With [Frank Olson]’s work on a 1958 Ampex 601 tape recorder though we were pleasantly surprised, because while he makes a modification to allow its use as a stand-alone microphone preamplifier he also performs an extremely sympathetic upgrade to modern components and retains it in substantially the form it left the Ampex factory.
The video below the break is a satisfying wallow in pre-PCB-era construction for any of the generation who cut their teeth on tube, chassis, and tag strip electronics. We can almost smell the phenolic as he carefully removes time-expired capacitors and fits modern replacements complete with period features such as sheathing over their leads. The larger multiway can electrolytics are left in the chassis, with their modern miniaturised equivalents nestling underneath them out of sight. We all know that electronic components have become a lot smaller over the decades, but it’s still a bit of a shock to see just how tiny even a high voltage electrolytic has become.
The Ampex would have been a very high quality tape recorder when new, and while this one has a problem with its mechanism it’s that quality that makes it easier for him to do this work in 2020. There’s every chance that this one could be returned to service as a tape recorder if someone was of a mind to fix it, and meanwhile it will give Frank excellent service as a high quality pre-amp. This is how resto-mods should be done!
In the world of computer security, the good news is that a lot of vendors are finally taking security seriously now, with the result that direct attacks are harder to pull off. The bad news is that in a lot of cases, they’re still leaving the side-door wide open. Side-channel attacks come in all sorts of flavors, but they all have something in common: they leak information about the state of a system through an unexpected vector. From monitoring the sounds that the keyboard makes as you type to watching the minute vibrations of a potato chip bag in response to a nearby conversation, side-channel attacks take advantage of these leaks to exfiltrate information.
Side-channel exploits can be the bread and butter of black hat hackers, but understanding them can be useful to those of us who are more interested in protecting systems, or perhaps to inform our reverse engineering efforts. Samy Kamkar knows quite a bit more than a thing or two about side-channel attacks, so much so that he gave a great talk at the 2019 Hackaday Superconference on just that topic. He’ll be dropping by the Hack Chat to “extend and enhance” that talk, and to answer your questions about side-channel exploits, and discuss the reverse engineering potential they offer. Join us and learn more about this fascinating world, where the complexity of systems leads to unintended consequences that could come back to bite you, or perhaps even help you.
Click that speech bubble to the right, and you’ll be taken directly to the Hack Chat group on Hackaday.io. You don’t have to wait until Wednesday; join whenever you want and you can see what the community is talking about.
