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PROGRAM PEAK CONTROL
Control of program peaks by the DAVID IV is accomplished in
two sections: 1) a broadband final limiter, and for FM broad-
casting: 2) ‘adaptive pre-emphasis,’ which is essentially inde-
pendent limiting for high frequencies that are subject to pre-
emphasis.
The broadband peak limiter acts on program audio that is de-
livered to any of the unit’s outputs, whether it’s a flat, 20kHz
signal for digital broadcasting or other full-power-bandwidth
application, or for FM transmission. But FM transmission re-
quires additional processing to restrict energy in the pre-
emphasized portion of the spectrum. This is provided inde-
pendently by the adaptive pre-emphasis stage that follows the
broadband limiter, and is active only for FM transmission.
Broadband limiting and adaptive pre-emphasis will be dis-
cussed separately.
BROADBAND LIMITING
PIPP* Limiting
PIPP* is an acronym for
Polarity-Independent Peak Processing
,
an Inovonics-proprietary (patented) technique used in the more
recent analog and digital processing products from our firm.
This is a function that can be turned on or off by the user, and
when disabled the DAVID IV peak controller behaves much like
any contemporary “lookahead” limiter.
In the PIPP* mode, the program audio waveform is split into
positive-going and negative-going components. Each half of the
waveform is then independently limited to a peak value that
corresponds to 100% carrier modulation in the respective direc-
tions, and the components then recombined. The purpose of
this somewhat roundabout exercise is to optimize carrier mod-
ulation regardless of waveform asymmetry.
The initial response to this elementary explanation is generally
one of astonishment that such a degree of “distortion” would
deliberately be introduced, much less tolerated. Please allow us
to debunk this knee-jerk reaction.
The only truly undistorted audio waveform is a pure tone; that
is, a sine wave. A sine wave is inherently a symmetrical wave-
form and the positive and negative halves are mirror-images of
one another. The PIPP* limiter would divide, limit and recom-
bine these halves to create a spitting image of the original: an
amplitude-limited symmetrical sine wave with no added distor-
tion components.
An asymmetrical program waveform, notably speech, vocals or
a solo musical instrument, will demonstrate a ‘peaky’ nature in
either the positive or negative direction. This is due to the ad-
dition of natural overtones (harmonics) that assign the source
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