[BC] Is overprocessing illegal?

[Jerry Mathis]

On 12/24/06, Kevin Tekel <amstereoexp at yahoo.com> wrote:
>
> I found this in the FCC rules....
>
>
> Sec. 73.1570  Modulation levels: AM, FM, TV and Class A TV aural.
>
> (c) If a limiting or compression amplifier is employed to maintain
> modulation levels, precaution must be taken so as not to substantially
> alter the dynamic characteristics of programs.


This was one of those Rules written with good intentions, with which the
road to Hell is abundantly paved. The problem: Define "substantially alter".
You'll find as many definitions as there are people doing the defining. I
personally would tend to trust definitions offered by people the likes of
Bob Orban and Frank Foti. I would most distrust most PD's and ALL
programming consultants.


What I was trying to find is some definition of the allowed audio
> bandwidth for monaural FM stations... the rules constantly refer to "50 to
> 15,000 Hz" but the only definite regulation regarding FM audio bandwidth
> seems to be that "an FM broadcast station shall not use 19 kHz +/-20 Hz,
> except as the stereophonic pilot frequency".  So is it correct that a mono
> FM station only needs a 19 kHz notch filter in its audio to avoid
> triggering the MPX pilot decoder in receivers, and not the traditional 15
> kHz brickwall filter?



No. Practically all modern audio equipment will pass frequencies well beyond
19 kHz. And in today's overprocessed, clipped, squashed, smashed, and
deliberately distorted audio, there's likely to be lots of that, probably
not intended to be heard, but the byproduct of the aforementioned
overprocessing, clipping, squashing, smashing, and distorting audio. We
would call them "artifacts" or "grunge", but if they pass into the
composite signal, they would play hell with the stereo reception of said
audio. The FM stereo system now in use was not designed to pass audio above
about 15 kHz. So just filter it all out and be done with it.

JM