Itu-R 412 Compliance; Two-Band Purist Processing - Orban Optimod-FM 8300 Operating Manual

OPTIMOD-FM DIGITAL
While the processing never clips the pilot tone, the extra spectrum generated by the
processing can fall into the 19 kHz region, compromising the ability of receivers to
recover the pilot tone cleanly. Therefore, the 8300's composite processor has a 19
kHz notch filter to protect the pilot tone. This filter does not compromise stereo
separation in any way.
We still prefer to use the 8300's main clipping system to do the vast majority of the
work because of its sophisticated distortion-controlling mechanisms. This means that
the 8300 does not rely on composite processing to get loud. Consequently, people
using its left/right-domain AES3 digital output can enjoy the loudness benefits of
the 8300's processing — the 8300 gets very loud without composite clipping.

ITU-R 412 Compliance

ITU-R 412 requires the "average multiplex power" to be limited to a standard value.
The 8300 contains a patented, defeatable feedback multiplex power limiter that
constantly monitors the multiplex power according to ITU-R 412 standards. The
power controller automatically reduces the average modulation to ensure compli-
ance. It allows you to set the "texture" of the processing freely, using any preset. If a
given processing setting would otherwise exceed the multiplex power limit, the
power controller automatically reduces the drive to the peak limiting system by in-
creasing the amount of multiband compression. This action retains the processing
texture but reduces distortion while controlling multiplex power.
The 8300 gives you control over the multiplex power threshold. This allows you to
compensate for overshoots in the signal path upstream from the 8300, preventing
excessive reduction of the multiplex power.
The ITU412 control is found in the Modify / Stereo Encoder screen.
Power control is applied to all outputs, not just the composite output.
Patents are pending on this system.

Two-Band Purist Processing

In addition to five-band processing, suitable for pop music and talk formats, the
8300 offers a very high-quality two-band algorithm. This is phase-linear and features
the same AGC as the five-band processor, followed by a two-band processor. Sophis-
ticated multiband high frequency limiting and distortion-controlled clipping com-
plete the chain.
We believe that this is the ideal processing for classical music 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 FM pre-
emphasis curve. We have heard four-band, allegedly "purist" processing that caused
dynamic HF lift. This created a strident, unnatural sound in strings and brass. In con-
trast, the 8300's two-band phase-linear structure keeps the musical spectrum coher-
ent and natural.
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OPERATION