Impeached Arizona governor Evan Mecham (shortened term 1987-1988) was probably very paranoid during his time in office, but nobody gave credence to his concern over the possibility of "reflected laser use" to surveil him. From Wikipedia (https://en.wikipedia.org/wiki/Evan_Mecham) ...
Throughout his administration, Mecham expressed concern about
possible eavesdropping on his private communications. A senior
member of Mecham's staff broke his leg after falling through a
false ceiling he had been crawling over, looking for covert
listening devices. A private investigator was hired to sweep
the governor's offices looking for bugs. The Governor was quoted
as saying, "Whenever I'm in my house or my office, I always have
a radio on. It keeps the lasers out." After this was reported,
a political cartoon by Pulitzer Prize winning cartoonist
Steve Benson appeared in the Arizona Republic depicting the
governor leaving his house outfitted for laser tag. When asked
about this by reporters, Attorney General Bob Corbin replied in
amusement, "We don't have any ray gun pointed at him."
The guy was a tool but the guy had a point about surveillance technology, and nobody took him seriously.
No one took him seriously because "I always have a radio on. It keeps the lasers out." is a textbook example of the kind of thing someone experiencing paranoid psychosis will say.
i.e. there are certainly listening devices that operate based on bouncing a laser off of a window[1] (or some other object), but his use of a quasi-magical protective measure (radios allegedly protecting against lasers) - in addition to the other behaviour mentioned - strongly implies that he was in need of psychiatric care, as opposed to being under surveillance.
FWIW, I've met multiple people with paranoid psychoses of one sort or another, and all of them have incorporated elements of real-world technology into their delusions.
Is he wrong? Adding noise from a radio or TV in the room may be an effective way to obfuscate attempts to use laser reflection surveillance on a window or other diaphragm. Both the device and the person speaking will cause the laser to jitter as the window vibrates.
> The group tested an eclectic selection of materials, including a bag of chips (excellent), a soda can (surprisingly mediocre), and a potted plant (average). They were even able to recreate music playing using footage of the vibrating ear buds. The best material of all was the thin foil wrapper on a Lindt chocolate bar Davis had been snacking on.
I hope it was the journalist who thought the soda can was surprisingly mediocre and not the researchers. The soda can is immensely stiff compared to the foil and much heavier so it will not move so much, meaning that there is simply less for the camera to see.
You can indirectly photograph any object via its reflectivenes if you have a movable trackable light source and a camera pointed at a wall the object is facing.
The sound is re-constructed from the shaking of the leaves. It's quite analogous to the way the sound is initially constructed from the vibration of a speaker membrane. The difference being that the medium of vibration which is used to propagate the "sound" is digital video rather than air.
You observe leaves shaking when there is wind (a correlation). To test for causality you need to make an intervention. You still the leaves - the wind keeps going. You block the wind - the leaves stop shaking. There clearly is an asymmetry here. The physical equations may be symmetric, but this doesn't justify calling a microphone "speaker".
>The physical equations may be symmetric, but this doesn't justify calling a microphone "speaker".
Actually a speaker is just a microphone with very small adaptations depending on the use (polarity, noise sensitivity, etc).
But this is not about the wind, but about sound. The wind you describe is external ("You still the leaves - the wind keeps going"). But you can just as well have a wind produced by the leafs themselves.
One could say these objects are both. They pick up sound, acting as microphones, and send it back out by vibrating, acting as speakers (amplifying it by a factor of less than one). The camera acts as the microphone for ‘hearing’ that sound.
I think you could hear that produced sound with a traditional microphone, but you would probably call it the echo of the original sound, and it might be hard to hear it over the original, typically much louder, sound.
It would be much more accurate to say these objects are neither speakers nor microphones. It is not a surprise that all objects vibrate in response to sound waves. What characterizes speakers or microphones is that they are transducers converting between acoustic signals and electrical signals. None of these objects are transducers so it's not accurate to call them speakers or microphones. It is reasonable to refer to the system of camera plus software plus observed object a kind of microphone but certainly not to refer to the observed objects as speakers or microphones.
An aeroplane flies through the air and a submarine travels through the ocean. I can throw a rock into the air or into the ocean, that doesn't make a rock an aeroplane or a submarine.
Silly question: isn't this phenomenon bound by the Nyquist limit, which means it would take at the very least 4k fps to reconstruct music (considering that a soprano can get no higher than 2 kHz)? That sounds like an impossibly high framerate.
4K fps? Impossibly high? Not at all. There are consumer compact cameras and even smartphone sensors that can hit 1K fps [1] -- and those are not even specialist high speed cameras.
Specialist cameras hit 4k fps at second gear, and can go as high as million fps (and even trillion fps [2])!
Besides, this is about reproducing music frequencies, whereas the most probable target for this technology is eavesdropping, not as a replacement for Neumann U87 -- and for that you need way less range.
They address that in the paper. They make use of the rolling shutter common in CMOS imaging chips to effectively increase the sampling rate to well above the frame rate.
They show in the last demo usage of this technique with rolling shutter. Considering image height for most cameras is now in thousands of pixels, this somewhat overcomes Nyquist limit problem
When I was growing up, we would often hear radio stations faintly in our vehicle after we had parked it and shut it off on our driveway - that's how I learned that radio waves go through everything all the time. It wasn't just one time or one vehicle, it happened in quite a few spots on our driveway.
Disclaimer: I work for a professional microphone manufacturer.
I wonder how long it'll be until this technique becomes feasible for recording professionally? Like, instead of capsules and diaphragms, we just have a laser that gets the cleanest, clearest possible signal it can, from the room around you ..
Do you guys have R&D working on moving the digitalization of audio into the mic? Like having a laser inside the mic read the ribbon and spit out a digital stream?
Higher-quality microphones tend to pick up more ambient sound because they're more sensitive and/or have a larger frequency response.
"Worse is better" sometimes applies to mics as well. For example, new podcasters are often advised to use cheap dynamic mics since it forces them to get close to the mic (improving their signal-to-noise ratio) and doesn't pick up audio over 15 kHz (which is not meaningful for voice recording).
I wonder if this could be applied to normal video and get results useful for any purposes. I realize it would be lower quality, but I feel like it might be possible to detect nearby gunshots on security camera footage that doesn't have audio. How cool would it be to see a murder trial enter audio recovered from footage of a house plant as evidence?
It's the same concept of detecting vibrations, but obviously this method is using a camera and processing a video, while the "laser microphone" [0] measures the difference in distance traveled by the laser beam.
It would be interesting to compare the two methods in various scenarios, i.e. through glass.
Obviously the laser method will work at night while the video method will not (probably depends how "dark" it is).
This is passive, laser microphones are active. I think another difference is laser microphones use motion parallel to the axis of the beam, whereas this is motion in the plane perpendicular to the line of sight.
I was wondering about using smartphone cameras as drum-head pickups, but the frame-rate problem put me off the idea. With the rolling-shutter trick it seems that it might be almost useful on bass drums, at least as a trigger rather than an audio source.
I used to be a sound engineer for live shows. I could imagine high speed cameras being used to replace instrument microphones in live performances one day, much like optical mice replaced the roller ball style.
By keeping a fixed object in view of the camera (e.g. a reflector on the stage), a camera could correct for its own vibrations and achieve perfect rejection of outside noise, unlike most microphones which have a cardioid pattern.
