🚀 go-pugleaf

>>  Would someone (Bill?)  mind giving an explanation of deemphasis, how it is
>>done, the reason for doing it, what is done the the signal, etc.?  Thanks.
>   Your explanation left out the reason why pre- and de-emphasis is necessary

>   The Bass signals are often too strong and would overload recording media, 
>so the signal strength is reduced (SNR is not a major consideration in this 
>frequency range).  During playback, the Bass frequencies are boosted to 
>restore their balance with the Midrange and Treble.

Not quite; while this is the correct explanation for RECORDING pre-emphasis,
remember that the original question was in the context of FM broadcast signals.
In FM, preemphasis is necessary to maintain a reasonably consistent SNR across
the frequency range of the original modulating signal; due to some of the
mathematical complexities of the FM process, the SNR will be lower for the
high-frequency components of the original signal IF the deviation is the same
across the frequency range in question.  Boosting the high end prior to 
modulation compensates for this by causing greater deviation for the high-end
signals, relative to the bass end.  Of course, it has to be UN-done at the
receiving end (to restore the proper tonal balance), and so the need for
DEemphasis at the receiver.  This process would NOT be necessary if phase
modulation is used, but PM has other problems which make it less suitable for
broadcast (music) applications.

(Further understanding of why the SNR varies with orig. freq. as mentioned
above requires some understanding of the spectrum resulting from the FM
process; consult a good communications text for details.)


Bob Myers  KC0EW   Hewlett-Packard Co.      |Opinions expressed here are not
                   User Interface Tech. Div.|those of my employer or any other
myers@fc.hp.com    Fort Collins, Colorado   |sentient life-form on this planet.