It is commonly known that the human brain is a good processor for
picking signals out of the noise. I found the following excerpt
(slightly edited) on psychoacoustics at http://www.ka7oei.com/qrss1.html
==start==
" ...the "trained ear" can fairly easily resolve a bandwidth of less
than 30 Hz - assuming the presence of random noise in the background.
This means that if you have a single CW signal amongst 2.4 KHz of white
noise - or even other CW signals that are at roughly the same strength
but at a different pitch, then your brain/ear is perfectly capable of
picking it out, being able to "ignore" the 2.4 KHz of noise and the
other "dissimilar" signals: Under these conditions, narrower filters
won't always improve the "copy" for a skilled operator*/./* Put this
same CW signal in amongst other similar signals - some of which are much
stronger and very close to the same frequency- and even the trained ear
is hard-pressed to make out the "buried" signal."
===end===
But long ago I discovered I can sometimes aid my ability to pick out
weak CW signals if I use a filter with a wider bandwidth and tune across
the signal as I'm trying to receive it. Apparently I'm aiding the
ability of my brain to distinguish the weak signal from random noise by
providing a predictive quality to the tone of the signal. I have to
tailor the tuning rate to the speed of the CW, of course. If I tune too
fast I run past the filter sidewall before decoding enough, and if I
tune too slow the predictive effect isn't there. As KA7OEI says, it
doesn't work when the noise isn't random or when other signals are there
to confuse my brain, or if rapid QSB distorts the characters, but under
some conditions it actually helps for picking out a report or a callsign.
I assume others have noticed this but I haven't seen much written about
it so I thought I'd pass it on. I would think that the effect could
even be implemented somehow in DSP software.
Or am I just imagining I can tell a difference ... ?
Dave AB7E
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