Itu-R 412 Compliance; Two-Band Purist Processing - Orban OPTIMOD-FM 5500 Operation Manual

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OPERATION

ITU-R 412 Compliance

Two-Band Purist Processing

15, 16, or 17 kHz lowpass filtering, and the requisite preemphasis and deempha-
sis filters to allow the 5500 to accept, flat, preemphasized, or flat+J17 preem-
phasized audio.

Left/Right Overshoot Limiter. This is intended to remove overshoots in stu-
dio/transmitter links caused by lossy digital audio compression (like MP2) or by
unflat frequency response and group delay distortion. This is a very fast limiter
using look-ahead and anti-aliased clipper technology. We recommend using no
more than 3 dB of gain reduction.

DSP-derived Core Stereo Encoder (stereo generator)

Composite Limiter/Clipper.
ITU-R 412 requires the "average multiplex power" to be limited to a standard value.
The 5500 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 5500 gives you control over the multiplex power threshold. This allows you to
compensate for overshoots in the signal path upstream from the 5500, preventing
excessive reduction of the multiplex power.
The ITU412 control is found in the M
Power control is applied to all outputs, not just the composite output.
In addition to five-band processing, suitable for pop music and talk formats, the
5500 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 5500's two-band phase-linear structure keeps the musical spectrum coher-
ent and natural.
> S E
ODIFY TEREO NCODER
ORBAN MODEL 5500
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