Actually, the preemphasis on FM nowadays with all the high end
processing can be done away with...to try to process (compress, limit,
clip) the 0-15 kHz spectrum and especially the high end, means you will
overshoot and overmodulate the xmtr unless you clip/limit the hell out
of it..but when you clip, you cause even more problems....
MOST engineers today agree that the PRE AND DE emphasis curves could be
done away with entirely...because the field has changed a lot since
Armstrong's days and the FCC's early development of the FM rules.
With today's processing and EQing, you really donot need PRE
emphasis...and if you donot need it, why have DE-emph in the rcvr???

The RIAA curve for records was done because of the material used & the
freq response in early days...technology has left that behind and that's
a moot point today...CD's donot have such a requirement...and I always
record my cassettes with Dolby C ON and then play them back with Dolby C
OFF so the high end sounds cleaner and brighter

If the rcvr makes had wanted to, they COULD have had flat response to
10-15 kHz in an analog rcvr and put a filter switch on it (like my Sony
XRA-33 AM STEREO car rcvr has)...but they didn't want to listen to car
buyers bitching about the noise and whine while listening to AM adj
channel...so they made the rcvrs narrow....same reason why 50% of the
time your radio FM stereo light is ON, you are actually listening in
blended mono!!!

Chris
WB5ITT
Houston

WBRW wrote:


Because there has to be a level playing field. Why do you think the
RIAA curve for phonograph records was established? Because there was
too much variance and too much confusion, and it was inhibiting the
goal of providing the consumer with increased fidelity and
convenience.

This also applies to AM radio. Whether it be today's 10 kHz or the 5
kHz that IBOC proponents want, consumers will never get to experience
analog AM radio at its full fidelity unless there is a level playing
field and a universal standard which manufacturers can design their
receivers to meet.


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