[BC] AM Stereo On A Mono Radio-FM Loudness

[Darryl Parker]

...and, Lyle, the TFT 844A and 884 FM Modulation Monitors have a similar peak weighting circuit, called "Peak Modulation Duration Differentiator", that Joe Wu came up with back in the warring days with Eric.

Your assessment is quite correct.

Darryl

-----Original Message-----
From: broadcast-bounces at radiolists.net
[mailto:broadcast-bounces at radiolists.net]On Behalf Of RADIO DOCTOR
Sent: Wednesday, October 03, 2007 9:13 AM
To: Broadcasters' Mailing List
Subject: Re: [BC] AM Stereo On A Mono Radio-FM Loudness


On Wed, 3 Oct 2007, Tom wrote:

> Stereo, unlike FM Stereo, doesn't hurt mono coverage.  (FM doesn't 
> either, except in terms of loudness - for every subcarrier added, the 
> mono signal must be reduced to accommodate it, which is NOT the case 
> in AM Stereo).

True.  However, many people are still under the impression that one has 
to reduce the FM main channel by more than is necessary.  Using a peak 
weighted modulation monitor can permit more loudness than metering that 
responds too quickly, as most exciters and modulation monitors do.  It's 
good to have the near instantaneous capability to know what's really 
going on, but the FCC says a peak is 1 millisecond long and you can 
ignore any that are shorter than that.

Eric Small's fine paper discussing this in detail is at: 
http://www.modsci.com/images/whitePapers/radioProducts/fmmm2/LOSTSCA.pdf 
He's talking about SCA, and the advantage of peak weighting is 
especially noticeable there, but it helps no matter what's all on your 
composite signal.  The more different frequencies there are making up 
the total, the more narrow and ignorable peaks occur.

Stations who try to be legal by carefully controling peak modulation, 
but don't have peak weighted monitors such as The Wizard or ModMinder 
are cheating themselves, usually by several dB.


...Lyle, FMeXtra evangelist, in Los Angeles, CA     Cell: 213-880-4690
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           Go digital on FM with FMeXtra!  http://fmextra.com
Lyle Henry, CPBE  THE RADIO DOCTOR  K9DKW/K7OO  Silver Lake/Los Angeles
  SCA Consultant, Contract Engr: Brazil, China, Mexico, Taiwan, SE Asia
                         323-660-4690 Office/Home
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