Posted by
Jim Brown-10 on
Aug 10, 2009; 6:10am
URL: http://elecraft.85.s1.nabble.com/K3-Filter-Ring-with-Noise-tp3410069p3415606.html
On Sun, 9 Aug 2009 15:21:21 -0700, Ron D'Eau Claire wrote:
>I'm not expert on human hearing, but I suspect we can discriminate tones
>(and hear tones in noise) much better than we can discriminate subtle
>changes in amplitude
YES! And there are also several ways in which humans can hear VERY small
differences in arrival times of the same acoustic signal coming from two
directions. One of those ways is selective fading, which is primarily the
cancellation between two signals arriving via different paths that are
slightly different in length. The repetition rate of fading is inversely
proportional to wavelength, so is quite long on 160M (slow QSB) and quite
short on 2M (picket-fencing).
Another way is when the same electrical signal is fed in phase and in
polarity to two loudspeakers that are at different points in space. If you
use broadband noise as the test signal and walk a straight line parallel
to a pair of speakers about ten feet apart (that is, with one ear facing
them) about six-ten feet in front of them, you will hear coherent addition
at the point where you are precisely on centerline, and a strange sort of
"phasy" distortion that Lou Burroughs called "acoustic phase
cancellation" and modern sound engineers call "comb filtering."
If with the same setup you FACE the loudspeakers and "crab walk" side to
side between them, you will hear the image be dead center in front of you
on centerline, and quickly shift to the closest loudspeaker as you move
only a few inches off centerline. A difference in travel time on the order
of a few tens of microseconds can be clearly heard as an image shift.
73,
Jim K9YC
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