Bob:
As you correctly note, a CW signal is not a pure sinusoid. The
Fourier spectrum of an individual dot or dash is a distribution of
frequencies with a peak at the "dead carrier" frequency. There is an
inverse relationship between the width of a pulse in the time domain
and the width of its Fourier spectrum. This is no surprise. A dash is
a closer approximation of a "dead carrier" than a dot, and
consequently has more of its energy concentrated closer to the peak
of the spectrum.
At higher speeds, the dots and dashes would have broader spectra than
at lower speeds. (That is why EME operators achieve extreme noise
reduction by using audio filters on the order of 10 Hz and
transmitting at 2-3 WPM.) Thus, I expect that the higher the code
speed, the more likely that the distinction in the specta of dots and
dashes would be discernable to human sensibilities.
In cognitive processing of sensory data, the brain functions a
differencing engine. Each brain has a capability of distinguishing
audible spectra, but some are more sensitive to particular nuances of
difference than others. Apparently, your hearing is more sensitive
than normal to the nuances of difference between dots and dashes. As
you have guessed, you are not hearing "slightly different
frequencies." You are experiencing the dot and dash spectra as two
distinctly different Gestalts. In other words, you are hearing two
slightly different frequency distributions as two distinct whole events.
Your experience seems somewhat akin to the small group of women (it
never happens in men) who have four sets of rods and cones in their
retinas. These women do not actually see a color invisible to the
rest of us. What they do see is the subtle distinction in shades of
color that the rest of us are incapable of noticing.
73,
Steve
AA4AK
At 10:11 AM 9/20/2006, Robert Carroll wrote:
As long as we are discussing hearing cw I'd like to ask a question that has
been bothering me for many years. I am very sensitive to chirp, and that is
not what I am referring to. When I listen to a good cw signal in the range
of about 20-35 wpm I heard the dots and dashes as at slightly different
frequencies. This may simply be some sort of psychological quirk unique to
me. I am not even sure "slightly different frequencies" or tones is correct
way to describe it. Realizing that I am not listening to a sinusoidal tone
but sequences of short and long symbols and that long strings of dots will
have wider sidebands than long strings of dashes, I wonder if this is
relevant in any way. Most likely it is some sort of personal quirk. But I
wonder if anyone on this reflector by any chance notices anything similar or
has an explanation?
Bob W2WG
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