[Boatanchors] TURBO RANGER FS

[Mike Langner]

Hello from a now retired career broadcast engineer who has spent waaaaay too
much time trying to please programming folks with audio processing -- you
know, louder, clearer, jump-out-of-the-dial, beat the competitors audio.

Phase linear bandwidth limiting is, in fact, very real.

Envision this.

When we clip audio, we create square (perhaps more accurately, squared-off)
waves.  Square waves have the greatest possible average/RMS power in the
wave of any waveform short of pure DC.  Square waves are essentially
switched DC!

But -- if the audio circuitry following the clipping and the generation of
the square waves isn't "phase linear" -- and indeed, frequency-response
linear as well all the way down to DC -- the steep vertical beginning and
endings of each pulse/square wave will become bent, as will the flat top.
Worse, for folks trying to be loud, overshoot and possible ringing will
create peaks that extend above the flat tops of the square waves.  Since
modulation percentage is figured on the peak value of positive and the
negative going modulation, and should never exceed 100% negative, two things
are extremely important!  Do not distort the square waves which phase
anomalies, among other flaws, will do, and always try to have the
positive-going peaks stronger than the negative-going peaks. And any of
those little peaks that stick up above the flat top of the square wave will
reduce the average/RMS power in the audio signal relative to the peak value
of the wave.

By the way, originally, AM broadcast rules did not limit positive-going
modulation percentage -- just negative-going ones.  As a result, many
broadcast engineers (myself included) used unbalanced push-pull amplifiers,
negative-cycle loading, asymmetric clippers, and the like, resulting, in
some cases, positive-going modulation peaks reaching 200% while holding
negative-going modulation peaks to 100%.  Some years ago the FCC decided
this was going to have to stop, and mandated positive peaks not to exceed
125% modulation.  Took the fun right out of it!

Anyway, that the romance many of us felt for broadcast and shortwave AM when
we were kids seems a harmless, if expensive, corner of our Amateur radio
service and hobby!

Note: average and RMS are similar, but not exactly the same.  Either term
works for this discussion.

So dust of those old Volumax, Audimax, CRL processors, Optimods, and the
like, and let the hi-fi roll on!

73 all !

Mike/
K5MGR
__________________


-----Original Message-----
From: Boat Anchor Owners and Collectors List
[mailto:BOATANCHORS at LISTSERV.TEMPE.GOV]On Behalf Of Bry Carling
Sent: Thursday, March 13, 2008 6:10 AM
To: BOATANCHORS at LISTSERV.TEMPE.GOV
Subject: Re: [Boatanchors] TURBO RANGER FS


de Nigel Holmes <Holmes.Nigel at ABC.NET.AU>
> phase linear bandwidth limiting

Now THERE Is a five dollar term if ever I heard one!

How do you do bandwidth limiting that isn't "phase linear?
What does it sound like?

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