Many years ago I read an article in the Journal of the Franklin
Inst (I think) about some research that was done on the ability
to recognize tones below 0 dB S/N ratio. It seems that the brain
can select a single tone in noise or even in the presence of
other tones and the equivalent audio bandwidth can be as narrow
as 50 Hz.
Any good CW operator knows this, of course. Operating conditions
play a large part in which receiver filters will be most
effective at any given time.
George
W2VJN
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