Re:The Gyroscopes in Your Phone Could Let Apps Eavesdrop on ...
by srean on Thursday August 14, 2014 @11:12PM
(#8180894)
That is what one would get with a single gyroscope. Now imagine several gyroscopes listening in, with their sampling frequency slightly/randomly out of phase, an array of receivers if you will. For this to work one needs to figure out the 'sync' of the gyroscopes but I dont see a fundamental problem with this approach.
Re:The Gyroscopes in Your Phone Could Let Apps Eavesdrop on ...
by Ajoo on Friday August 15, 2014 @11:46AM
(#8182684)
I don't know, requiring several phones within hearing range seems like it would severely limit the applicability of this technique.
If you think N phones provides at best N*(maximum sample rate of one phone) and that's assuming their phases a perfectly misaligned I'd think you'd still need quite a few to get something.
Plus the 100 Hz figure is optimistic. I dunno what kind of anti-aliasing these things have. If none you get an aliased signal and with a low order filter the practical maximum frequency detectable would be even less.
It shows. Sampling at 200Hz means your masimum detectable frequency is 100Hz, per the Nyquist theorem - that'll capture ~40% of the typical male frequency range (fundamental only - not enough for harmonics or formants) and little or nothing of the typical female frequency range. I question the claimed 65% success rate, and would like to know a lot more about the experimental conditions before I'd be inclined to accept it. I do enough synthesis to know what that sort of sample rate sounds like without having to test, and the short answer is 'awful'. I can see possibly getting numbers out of it when the phone is held up to one's head but only in perfectly controlled environments. For contrast POTS bandwidth is 300 to 3400 Hz.
Or if an app really needed to access the gyroscope at high frequencies, it could be forced to ask permission. “There’s no reason a video game needs to access it 200 times a second,” says Boneh.
I think it's quite plausible that people might be able to detect a lag greater than 5ms in the right game. That's around the envelope for involuntary variation by professional drummers.