[Scan-DC] [OT] De-Ess and FM

[Sheldon Daitch]

Shawnerz wrote:

> All,
> I've got another off topic question.
> You may remember that I'm overseas.  There are
> broadcast stations that, well, lets just say that they
> don't meet FCC rules.

    And why should they meet FCC rules?  They aren't under
    FCC jurisdiction.  OK, that is the smart butt answer.
    FCC rules require pre-emphasis to meet a 75 microsecond
    curve, where most non-US FM broadcasters meet a 50
    mincrosecond pre-emphasis curve.

See:

    http://cnyack.homestead.com/files/modulation/pre_emp.htm

One thought on two-way pre-emphasis is at:

 http://www.repeater-builder.com/rbtip/prereason.html

Bob Orban talks a bit about pre-emphasis here:

 http://www.masterdigital.com/24bit/radioprocess.htm

Another interesting pre-emphasis site has this:

http://www.oldradio.com/archives/hardware/fm.htm



>
> Here's my question: in FM, what causes "S's" to be
> slurred at the receiver?
> Is it lack of dynamic range in the transmit path?
> Lack of pre-emphasis?
>
> Another question along the same vein, remember when
> MSP's main radio operation was on low band VHF? (I
> know they still use it for talk around).  The audio
> always sounded "muddy."  I assumed that the reason for
> that was their transmit audio was not pre-emphisized.
> Does anyone know if this was the reason?

We are now discussing two way systems, correct?   I'd
submit that "muddy" audio was a function of the audio
systems used in interconnecting radios for talk around
operation, rather than pre/de-emphasis in the radio system
itself, but I am only guessing.

73
Sheldon

>
>
> Thanks in advance,
> -Shawn
>
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