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From:	Mike Goldberg <michael.goldberg@*******.COM>
Subject:	White Noise Generators....
Date:	Thu, 27 Feb 1997 09:30:06 MST

Message no. 1 I just came up with an interesting idea following up my understanding
of frequencies and thinking about white noise generators and
Ultrasound sighting systems?

While I may indeed bring this onto shadowtk, this is probably at this
stage more appropriate for shadowrn. So can someone out there send me
what is the address of that list? (and while you are at it, the
address of where I need to subscribe to it as well?)

Mike

From:	Jeffrey Mach <mach@****.CALTECH.EDU>
Subject:	Re: White Noise Generators....
Date:	Fri, 28 Feb 1997 17:35:11 -0800

Message no. 2 On Thu, 27 Feb 1997, Mike Goldberg wrote:

> I just came up with an interesting idea following up my understanding
> of frequencies and thinking about white noise generators and
> Ultrasound sighting systems?

An ultrasound scrambler perhaps? Whether you want my two yen or not, I'll
toss a few ideas out just to get more bandwidth flowing through plotd.

From what I understand, simple white noise generators foul with
microphones by sending out loud random frequencies which can mask the
underlying sounds to a microphone which is trying to record all the
frequencies it hears. Human beings (or sophisticated computer algorithms)
can try to sort through the sonic "clutter" (much easier the closer you
are to the other person speaking relative to the generator) and pull out
the data (namely what the person is saying) that you are looking for.
Anybody into acoustic neurobiology want to chime in?

The more advanced (aka higher rating) white noise generators, I would
assume, also employ noise cancellation. By sending the right frequencies
at the right time, you can basically send a wave from one speaker that
will exactly cancel the wave generated by another as long as the listener
is a certain distance or more away. The closer you are, the less
effective this method is (basically, the closer the "anti-voice" is to the
voice, the closer the listener has to be to hear anything). Imagine two
pistons some distance apart, one pushing down into a pool of water, the
other pushing up from below. Close by, you feel a big disturbance and can
clearly tell that something is going on, because the time that it takes
the closer wave to get to you is much smaller than the time it takes for
the farther wave to get to you. Farther out (or, as the distance between
the listener and the pistons becomes large relative to the distance
between the pistons) the waves arrive at about the same time and they
cancel out. Hence the white noise generator designed as an earing in
_NeoAnarchist's Guide to Real Life_ (I think I got the title right).
However, I think that design might give the wearer a titanic headache, so
I would suggest a pendant or lapel pin for the fashion conscious. Note
that this design, by its nature must be able to listen for the sounds it
is supposed to cancel, so you couldn't very well hide it under your jacket
or something like that.

Since the majority of human speech is within a very narrow bandwidth, and
all of it, by necessity audible, I don't think your average white noise
generator would be designed to handle high powered ultra-sonic output.
That would be basically what you would want in order to fool ultrasound
sensors. Unfortunately, just like electronic jammers for radar, while you
would be rendered into an unrecognizable huge blob by this tactic, making
it hard to pinpoint and target you, if someone was looking around with
ultrasound sensors, there would be no doubt in the world you were there.
(i.e. a EA-6b Prowler turns on its jammer to avoid a radar-guided missile,
suddenly causing it to have the radar return of the Rock of Gibraltar;
while this may confuse or even blind the missile, everyone in radar range
knows that someone is out there just not exactly where).

Conversely, I don't think that the cancellation technique I mentioned
earlier would be practical. First, you would have to deal with possible
multiple _moving_ sources of sound at various--hopefully long--distances.
To make sure to cancel the returning wave, the thing would have to figure
out the exact pattern of your echo (major computational difficulty) to
some target (that you must know is there in the first place) that may be
moving (more computational difficulty to handle doppler shifting, etc)
then you have to send the signal back to them. Adding sources (aka other
people hunting you with ultrasound) makes the problem grow geometrically
if not exponentially since you also have to consider what their signal
would look like to the other listeners. On top of that, if you happen to
be in-doors, multiply the complexity of the problem by several times since
you don't want to look like a hole and have to take into account
reflections off of walls, furniture, plants etc. So unless you want to
look like a walking advertisement for >insert favorite sound system
manufacturer here (NHT!)< I think that we can leave this concept to the
round file.

So, I guess I would say that a pocket-sized ultrasonic jammer is quite
feasible (like a flash-pack but more expensive and you can leave it on
longer). Frankly, I don't know why it isn't in the source books yet since
they usually are good about sticking the countermeasures in with the
measures. Probably similar game effects, and hey, you can use it to mess
with paracritters with Sonar abilities.

> While I may indeed bring this onto shadowtk, this is probably at this
> stage more appropriate for shadowrn. So can someone out there send me
> what is the address of that list? (and while you are at it, the
> address of where I need to subscribe to it as well?)

The same listserver that handles shadowtk also handles shadowrn. If you
have web access, check out:
http://www.cybernothing.org/jdfalk/shadowrun/faq.html

Same subscription message like shadowtk:

TO: majordomo@********.itribe.net
SUB: <leave blank>
1st line: subscribe shadowrn

(this is quoted from the FAQ, but I'll leave it to Mark I. to correct me.
It may be running listserv by now and so that would be
listserv@********.itribe.net and not majordomo. If you get nothing, try
the other.)

--My two yen

Jeff

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