I've seen an existance proof which indicates that this is possible.
Back when I was first getting involved with computers (circa 1972),
some digitizer tablets worked by speed-of-sound measurements.
The stylus tip contained a small spark gap which was energized
when the stylus pressed on the tablet. This created a spark,
and the spark a minuscule roll of thunder. Microphones situated
along the edges of the tablet recorded the arrival times of the sound,
and the location of the stylus calculated within a millimeter or two.
This was a peripheral for a DEC PDP-8E.
This was calculating a position over about 20 cm to a millimeter,
in real time, in 1972. Doing so to a resolution of a centimeter or
two, in 2001, ever several meters sounds feasible.
Peter Trei
> ----------
> From: Ray Dillinger[SMTP:[EMAIL PROTECTED]]
> Sent: Friday, January 12, 2001 4:37 PM
> To: John Young
> Cc: [EMAIL PROTECTED]
> Subject: Re: NONSTOP Crypto Query
>
>
>
> On Fri, 12 Jan 2001, John Young wrote:
>
> >Wright also describes the use of supersensitive microphones
> >to pick up the daily setting of rotors on cryptomachines of the
> >time, in particular the Hagelins made by CryptoAG.
>
> Hmmm. That sounds like a trick that could be brought up to
> date. If you get two sensitive microphones in a room, you
> should be able to do interferometry to get the exact locations
> on a keyboard of keystrokes from the sound of someone typing.
> I guess three would be better, but with some reasonable
> assumptions about keys being coplanar or on a surface of known
> curvature, two would do it. Interesting possibilities.
>
> Bear
>
> [A quick contemplation of the wavelength of the sounds in question
> would put an end to that speculation I suspect. --Perry]
>
