Brian - you seem to have totally missed my point. My point was NOT that
"nothing exists" near 10khz - my point IS that in designing a receiver
for maximum fidelity one must consider that between the audio "source"
and the received signal - there are a lot of factors to consider - one
such is that there IS a roll-off as one approaches 10khz.

I never suggested that there was "nothing there" - only that if one were
to try to "reconstruct" the audio as it existed from the original source
-- processing needs to be taken into consideration - including the NRSC
- and any roll-off approaching the "brick wall".

How do you know that the 10khz signal in your last picture wasn't
originally 20db higher than shown here - before being "processed"?

(at this point Jeff adds):

Jeffie hands you another bucket of pearls to cast before the swine.

Oh, give 'em time - they'll learn - you didn't "pop-out" spouting this
stuff either... well- come to think of it --- never mind.

One more time - without knowing exactly what was going into the
transmission chain - your pictures are annecdotal at best. While they
show conformance with NRSC-1 - they on NO WAY tell us anything about
what indignities the audio suffered on it's way through the chain. You
are assuming that something that "looks flat" is. Let me remind you -
if it's flat after being pre-compensated 75us (10db at 10Khz)- SOMETHING
ate some of it!!!!!

To answer your last question (bandwidth to fully recover modulation)

Go look at John Byrns recent post where he shows the curve comparison
between two IFTs. Note that even in this very broad filter - there is
STILL some loss at Fc +/- 5khz. (You're the one that said "FULLY" - i.e.
total - no loss). Even these won't do that. And in fact - no circuit is
that ideal - too many trade offs - so one settles for practical.

To accomplish "usual" standards of fidelity - Johns numbers show that
these particular IFTs would have a "passband" of 40khz. Can you
determine why that is?

The problem (in this case using IFTs - implying a hetrodyne system) - is
that with a 40Khz passband (+/- 3db points - ooops gave away the answer
to the above question)- unwanted "stuff" pours through on unwanted
hetrodynes as well. But that's another issue.

best regards...
--
randy guttery

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