Orban OPTIMOD-FM 8600, Operating Manual

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3-14
OPERATION ORBAN MODEL 8600
Two-Band Purist Processing
In addition to five-band processing, suitable for pop music and talk formats, the
8600 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 with
look-ahead limiting. Sophisticated multiband high frequency limiting and distortion-
cancelled clipping complete 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
preemphasis 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 contrast, the 8600’s two-band phase-linear structure keeps the musical spectrum
coherent and natural.
The look-ahead limiter prevents speech from being audibly clipped and prevents
similar audible problems on instruments with rapidly declining overtone structures
like grand piano, classical guitar, and harp.
Digital Radio Processing
Only the phase rotator, highpass filter, AGC, and Multipath Mitigator are common
between the FM analog and digital radio processing chains. The processing chain
splits into two paths after the AGC. Each path contains a structurally identical but
independently adjustable equalizer and multiband compressor. Each preset has an
FM

HD C
ONTROL
C
OUPLING
control that determines if audio controls affecting the
HD equalizer and HD multiband compressor/limiter will follow their counterparts in
the FM analog processing chain or if the HD and FM controls can be adjusted inde-
pendently. (See
FM

HD Control Coupling on page 3-78.)
The peak limiter in the digital radio processing chain is a mastering-quality look-
ahead limiter. This limiter minimizes IM distortion in addition to minimizing harmon-
ic distortion. The resulting peak limiting is almost always undetectable when used
with reasonable amounts of gain reduction (i.e., frequently recurring gain reduction
of 3-4 dB).
Certain unusual program material may cause infrequent instances of gain reduction
as high as 12 dB with the above settings. This occurs on isolated transients and is no
cause for concern unless it is frequent.
Except for the fact that its input has been de-emphasized, the HD look-ahead limiter
receives the same processing as the FM peak limiting section if the
FM

HD C
ONTROL
C
OUPLING
is set to
FM

HD.
Earlier processing has often been adjusted to help com-
pensate for the inevitable high frequency loss caused by preemphasis limiting in the
FM peak limiter. Therefore, the HD output can be excessively bright without further
adjustment.
In
FM

HD
mode, you can use the 8600’s parametric high frequency shelving filter to
supply a high frequency rolloff that tames excessive brightness in the HD output.