an old friend wrote:
oridinary humans HMM is it realy proven that ordinary human can do it
by ear Cecil or merely proven that enough to man the telagraphs of the
day could do so?

Please note that I didn't say ordinary human beings could read
telegraph code. All I said was that ordinary human beings could
distinguish between the sound of a dot and the sound of a dash.

I think that's a pretty safe assumption with "ordinary" in the
sense of an average human possessing average hearing abilities.
I would bet that a dog could even be trained to distinguish a
dot from a dash.
--
73, Cecil http://www.qsl.net/w5dxp