Orban OPTIMOD 6300, Руководство по эксплуатации

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OPTIMOD 6300 DIGITAL OPERATION
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ness of the 6300's output. When subjective loudness would otherwise exceed a pre-
set threshold, the Loudness Controller enhances the normal gain control produced
by the processing with further gain reduction, preventing loudness from exceeding
the threshold. The user can adjust this threshold from the Full modify screen of any
2-band preset. The edited preset can then be saved as a user preset.
The Loudness Controller may reduce the dramatic effect of certain sounds in enter-
tainment programming, like gunshots, explosions, or screeching tires. Operators may
therefore want to turn the Loudness Controller on during commercial breaks and
off during normal programming. Most Sound-for-picture 2-band presets have the
Loudness Controller on. The easiest way to turn the Loudness Controller off is to re-
call the 2B GEN PUR NO LC preset. If you have created a custom preset, you can save
two variations—one with the loudness controller on and one with it off—and recall
these by remote control via the 6300’s GPI inputs.
The 5-band structure does not have extra loudness control because its multiband
processing will automatically re-equalize and condition program material to control
loudness variations.
Low-IM Look-Ahead Limiter: The 6300’s peak limiter prevents overshoots by ex-
amining a few milliseconds of the unprocessed sound before it is limited. This way
the limiter can anticipate peaks that are coming up.
It is important to minimize audible peak-limiter-induced distortion when
one is driving a low bitrate codec because one does not want to waste
precious bits encoding the distortion. Look-ahead limiting can achieve
this goal; hard clipping cannot.
One can model any peak limiter as a multiplier that multiplies its input
signal by a gain control signal. This is a form of amplitude modulation.
Amplitude modulation produces sidebands around the “carrier” signal.
In a peak limiter, each Fourier component of the input signal is a sepa-
rate “carrier” and the peak limiting process produces modulation side-
bands around each Fourier component.
Considered this way, a hard clipper has a wideband gain control signal
and thus introduces sidebands that are far removed in frequency from
their associated Fourier “carriers.” Hence, the “carriers” have little ability
to mask the resulting sidebands psychoacoustically. Conversely, a look-
ahead limiter’s gain control signal has a much lower bandwidth and pro-
duces modulation sidebands that are less likely to be audible.
Simple wideband look-ahead limiting can still produce audible inter-
modulation distortion between heavy bass and midrange material. The
look-ahead limiter in your Optimod uses sophisticated techniques to re-
duce such IM distortion without compromising loudness capability.
2-band Purist Processing
The 6300’s 2-band algorithm can be set to be phase-linear. We believe that this is the
ideal processing for classical music and jazz programming because it does not dy-
namically re-equalize high frequencies; the subtle HF limiter only acts to reduce high
frequency energy when it would otherwise cause overload because of the TV pre-