Orban OPTIMOD-FM 8700, Operating Manual

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OPTIMOD-FM DIGITAL OPERATION
3-87
About the Multiplex Power Controller’s Time Constants
Although the BS412 specification calls for a 60-second integration time, the integra-
tion time of the Optimod’s MPX power controller is about 10 seconds. The problem
with making the integration time longer is that the BS412 standard states that the
integrated MPX power in any
arbitrary 60-second time period cannot exceed the av-
erage power of the sinewave that produced
±
19 kHz carrier deviation. In other
words, whenever you start measuring , you must not exceed the total integrated
power limit over the following 60 seconds.
This makes it impractical to "bank" power over the full 60-second window. For ex-
ample, at first glance one might think that a classical music station could exploit a
period of quiet music to allow a crescendo to get louder than it would using the
8700i's relatively fast integration time. However, what happens if someone starts an
arbitrary 60-second measurement period not at the beginning of the quiet passage
but at the beginning of the crescendo?
Because an automatic MPX power controller does not know what is coming after
the crescendo, it must reduce the level of the crescendo so that it complies with the
MPX power requirement over an integration time that is shorter than 60 seconds.
Otherwise, it might have to dramatically reduce the level of following (as yet un-
known) program material in order to ensure that the MPX power limit is not ex-
ceeded over the 60-second measurement period in question. This kind of gain
pumping would be far worse than the pumping produced by using a relatively short
integration time.
MPX Pwr Ctrlr Gate: To minimize audible side effects of the MPX power controller’s
gain reduction, its release time is dual-speed and changes as a function of the audio
level: if the audio level is below a preset threshold, the slower time constant acti-
vates. There are five preset values for the gating, which set the level below which
gating occurs, as well as the release times above and below the threshold. Higher-
numbered presets provide slower release times both above and below the gating
threshold.
Unlike the
MPX P
OWER
T
HRESHOLD
control (a System control), the
MPX P
WR
C
TRLR
G
ATE
control is part of the active processing preset.

Preset 0: No gating: Works like Orban’s older, non-gated MPX power controller.

Preset 1: Only the quieter passages are gated and the gated release is faster than
it is in the other presets. Created to maximize loudness within the BS.412 limit
while providing more on-air dynamics and preventing unnecessary gain pump-
ups.

Preset 2: A compromise between Preset 2 and 3. Works well with more dynamic,
more open-sounding presets.

Preset 3: Recommended for most CHR-style presets. Quieter parts of the music
are effectively frozen to achieve less audible BS412 control. It is still possible to
stay at the BS.412 limit most of the time.