Optimod-AM 9400 V1.2 Operating Manual - Orban

OPTIMOD-AM DIGITAL INTRODUCTION 1-17
creases loudness and brightness, and will produce dense positive peaks up to 125%
if this is desired. However, such asymmetrical processing by its very nature produces
both odd and even-order harmonic and IM distortion. While even-order harmonic
distortion may sound pleasingly bright, IM distortion of any order sounds nasty.
There is really nothing lost by not modulating asymmetrically: Listening tests easily
demonstrate that modulating symmetrically, if time dispersion has been applied to
the audio, produces a considerably louder and cleaner sound than does asymmetrical
modulation that retains the natural asymmetry of its program material.
Some of the newer transmitters of the pulse-width modulation type have circuitry
for holding the carrier shift constant with modulation. Since artificial asymmetry can
introduce short-term DC components (corresponding to dynamic upward carrier
shift), such carrier shift cancellation circuitry can become confused, resulting in further
distortion.
Transmission Presets and Transmitter Equalization
OPTIMOD-AM's transmitter equalizer can cure linear problems caused by the transmitter
or antenna system. However, the transmitter equalizer cannot cure nonlinear
problems, particularly those caused by inadequate power supplies, modulation
transformers, or reactors. If any of these components saturate or otherwise fail to
perform under heavy power demands, no amount of small-signal equalization will
solve their problems.
OPTIMOD-AM was designed with the assumption that one audio processor would
be devoted to no more than two transmitters, usually called main and standby (or
alternate). Each transmitter might be called upon to change power at night or to
drive a different antenna array. Only one transmitter is assumed to be on the air at a
given time.
To drive two transmitters, OPTIMOD-AM provides two analog outputs (called
ANALOG OUTPUT 1 and ANALOG OUTPUT 2) and two corresponding AES3 digital
outputs (DIGITAL OUTPUT 1 and DIGITAL OUTPUT 2).
OPTIMOD-AM provides four transmission presets for its transmitter equalizer controls
and certain other controls. Only one preset can be active at a given time; all
four outputs receive the same transmitter equalization. This is consistent with the
principle that only one transmitter will be on the air at any time.
You can access these presets in SETUP > TX PRESET. These presets can be modified in
SETUP > MODIFY > TX PRESET. Unlike settings in the factory processing presets, transmission
preset control settings automatically save and update when you change
them.
Transmitter equalizer controls in a given transmission preset include:
LF Gain for the LF tilt equalizer for L+R (mono) [L+R LF GN]
LF Breakpoint Frequency for the LF tilt equalizer for L+R [L+R LF FR]