🚀 go-pugleaf

riepe@ifwm11.ifw.uni-hannover.de (Michael Riepe) writes:

>In article <24875@castle.ed.ac.uk>, cam@castle.ed.ac.uk (Chris Malcolm) writes:
>|> In article <dfAW02=71de601@JUTS.ccc.amdahl.com> drp40@cd.amdahl.com writes:
>|> 
>|> >I'd like to be able to use two-way radios for skydiving.  Problem
>|> >is, 120mph of wind hitting up against a microphone would probably
>|> >mask out any voices.  Anyone have any ideas of how to get around
>|> >this?
>|> 
>|> 	1) A throat mike under clothing.
>|> 
>|> 	2) Use combined ear speaker/mike, inside substantial ear muff.
>|> 	The voice gets to the ear via head transmission.

>3) Use 2 mikes connected to a differential amplifier.

I don't get it; don't you want to sum the signals from the two mikes?
Assuming they both pick up the same voice signals, but that the
noise from each is uncorrelated, this would improve the SNR by sqrt(2).

This reminded me of the solution to the problem of allowing pilots
to understand voice communications on their headsets in the presence
of lots of noise from the aircraft.  Legend has it that this was
discovered by chance when someone made a wiring error, but the idea
is that one ear's speaker is wired up backwards, so that that ear
gets an inverted signal.  The noise, which comes throught the air
is correlated, between the two ears, while the signal is anti-correlated.
It is an empirical psychological finding that this improves the
"perceptual SNR"; this is thought to be related to the mechanisms of
sound localization.

Maybe this idea could be combined with the two mike idea:  one mike
per ear.  The listener's brain might do some of the work of
separating correlated voice signals from the uncorrelated
noises from the two mikes, as well as the uncorrelated wind noise
generated at each ear.

Unfortunately, this would require twice as many radios, or some
kind of modulator/demodulator to send both signals using one radio...

-- 

	Jeff Mulligan (jbm@eos.arc.nasa.gov)
	NASA/Ames Research Ctr., Mail Stop 262-2, Moffett Field CA, 94035
	(415) 604-3745