Hacker News Reader

Comment by londons_explore | Hacker News Reader

Doesn't need to be live to reveal location.

2 loudspeakers playing pseudorandom white noise, inaudable from a few hundred yards away, would probably still leak any location in the city, as long as the stream isn't too aggressively compressed.

Correlating with a known signal over hundreds of thousands of audio samples has a massive snr gain...

View on HN

Sorry, is this like Liam Neeson - drop a handgrenade in one part of town then another and Liam (or rather is listening to Snowden microphones) can work out where he is?

Can that possibly work IRL?

I believe he is implying the NSA or other entity using the microphone input from cellphones (or maybe the microphones placed around many major cities on utility poles?) to do the locating. I think it would probably be theoretically possible, but I don't recall anything in the leaks about them ever researching that sort of capability.

They can just listen to the 50hz ground hum in the signal coming from his audio equipment and determine which relay stations are providing that power ..

?how?

50Hz is 50Hz everywhere.

It's never exactly 50 Hz, as the frequency is affected by load and generators can't compensate this perfectly. So record it in many locations, then correlate the signal extracted from audio/video against the database.

Main article: https://en.wikipedia.org/wiki/Electrical_network_frequency_a...

Not sure what you are getting at at all.

he's referring to

https://en.wikipedia.org/wiki/Cross-correlation

this could be sound from loudspeakers or broadcast audiorate electromagnetic waves getting picked up in the audio cables, or even a passive system of sensors throughout russia, i.e. using cross-correlation with background noise ...

one could also view this as a pseudorandom form of lock-in amplification, and even with a high noise floor the results do improve with number of samples, so patience is all they need.

Reply on news.ycombinator.com