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Multi-directional microphone

  [vote for,

Security systems often involve cameras, each generating a large bandwidth of signal which may be recorded for hours or days on a loop.

Audio, on the other hand, is seldom captured - why? Well, for one thing a microphone covering a large area will not pick up voices from some distance away, over any background noise. Highly directional microphones are available, but of course they only cover a narrow window.

So, why not have a roughly-spherical (or part-sphere, depending on needs) device, about the size of a football, consisting of a dense array of highly directional microphones, radiating outwards in all directions? The sound from each is recorded, collectively taking up (I would guess) not much more bandwidth than the output of a single camera. In the event of a crime taking place, the sound recorded from the various channels can be played back, until the right channel (right direction) is found. Or, if a camera is mounted nearby, the image would tell you which sound channels are likely to have captured voices.

Sound is, of course, not nearly as useful as video in bringing prosecutions, but it can still be a valuable adjunct to video. With a little audio processing, you would even be able to infer the direction from which sounds have come, even if they were produced outside the camera's field of view.

MaxwellBuchanan, Apr 14 2017

Not even vaguely related ... Pop-up_20Sprinkler_...d_20Laptop_20Camera
[normzone, Apr 14 2017]

One of my spatial audio tests https://youtu.be/ZNDjb3FRT5c
Not stereoscopic, not 3d visual, not video, don't bother looking in vr headsnorkels, just hold your phone up with your headphones on and move it (and you) around. [Ian Tindale, Apr 14 2017]

One of my prior spatial audio tests https://youtu.be/zmfLbjFuA5w
Still frame visuals in 3d hyperstereo (done incorrectly - stood too far apart, left and right eyes are not in phase), but the main test was spatial audio. [Ian Tindale, Apr 14 2017]

Related https://www.ribbonf...e-daredevil-camera/
Using an array of mems mics as a camera for sound [mitxela, Apr 14 2017]


       My first thought would be to use a regularly spaced lattice of omnidirectional mikes, with phase-matched / delay-matched recording channels, then do what's effectively beam forming in reverse to get the directionality.
Wrongfellow, Apr 14 2017

       Ok with me. how about "laser listening" where you beam a steerable laser at the moving person to record near person audio?   

       Laser listening is where a laser is pointed at a wall or window to measure vibrations, computers then translate this to sound. this might possibly work on softer materials.
beanangel, Apr 14 2017

       //regularly spaced lattice of omnidirectional mikes, with phase-matched / delay-matched recording channels// That might work too. Whatever it is needs to be something as cheap(ish) and simple(ish) as a security camera. Or have it combined with a security camera.
MaxwellBuchanan, Apr 14 2017

       A] a real-world example of this is called an ambisonic-b mic array. 3] I'm currently doing stuff involving recording ambisonic recording for vr.
Ian Tindale, Apr 14 2017

MaxwellBuchanan, Apr 14 2017

       mitxela: - A couple of years ago I was trying to build a modified binaural array (front-back, for each of left-right) out of mems mics I'd find, one by one, on the street. I'm always on the lookout for discarded iPhone headphones, which have quite good mems mics on a board in the mic piece.
Ian Tindale, Apr 14 2017

       They are quite cheap these days, only a few quid each, but a real hassle to solder to.   

       There's an interesting app note from Invensense where they built a studio-quality microphone by sticking 32 mems microphones onto a single circuit board and summing their output. Pretty cool stuff.
mitxela, Apr 14 2017

       At that stage it becomes a sound field mic array, which if treated as a phased array, could be matrixed into sounding like quite an impressive but virtual single point microphone.
Ian Tindale, Apr 14 2017

       One of the reasons sound isn't commonly recorded for security purposes could be wiretap laws.
notexactly, Apr 15 2017

       Hmm. That, I had not thought of. You mean that there's a law that prevents you from recording people's voices, even though you can video them?   

       And, golly gosh, Google tells me you're right. Does that apply in the UK as well, I wonder?
MaxwellBuchanan, Apr 15 2017


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