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3-28
OPERATION
Unlike the presets in Orban's FM processors, no OPTIMOD-PC preset uses
phase rotation. Therefore, if you use OPTIMOD-PC to process the main
digital channel in HD Radio, some care must be applied in cross fading to
avoid momentary audible comb filtering because of the different phase
responses of the analog and digital channels. In practice, this means that
the cross-fade should be quite fast—perhaps 50 milliseconds.
Broadcasters using Orban's Optimod-FM 8300, 8400, or 8500 will ordinar-
ily use these processors' HD FM digital outputs to feed the digital channel
in an IBOC transmission. This eliminates any potential comb filtering be-
cause both analog and digital outputs have identical amounts of phase
rotation.
Of course, if OPTIMOD-PC is used to process a secondary channel in HD
Radio, there is no need to worry about smoothness of crossfades. This is
an excellent application for this product.
CLASSICAL: As their names imply, the CLASSICAL 5-BAND and CLASSICAL 2-BAND
presets are optimized for classical music, gracefully handling recordings with very
wide dynamic range and sudden shifts in dynamics. The Five-Band version uses heavy
inter-band coupling to prevent large amounts of automatic re-equalization, which
could otherwise cause unnatural stridency and brightness in strings and horns and
which could pump up very low frequency rumble in live recording venues.
The Five-Band preset defeats the AGC, using only the five-band compressor for gain
reduction. It also defeats phase rotation to ensure the most transparent Five-Band
sound available.
Even more transparent, "purist" classical processing is available from the
CLASSICAL 2-BAND preset, which is phase-linear and which preserves the spectral
balance of the original material as much as possible. However, if you need a bit
more automatic re-equalization than the CLASSICAL 2-BAND preset provides, use
the CLASSICAL 5-BAND preset.
CLASSICAL-5B+AGC uses the AGC set for 2:1 compression ratio. Because of the
AGC, it affects more of the total dynamic range of the recording than does the
CLASSICAL-5 BAND preset. However, the AGC provides extremely smooth and un-
obtrusive compression because of the gentle ratio and window gating. This preset
uses the Five-Band compressor very lightly with a fast release time as a peak limiter.
The AGC does almost all of the compression.
There is also a corresponding two-band preset called CLASSICAL-2B+AGC.
CLASSICAL-2B SFTKN (Classical using 2-Band Soft-Knee Compression) defeats the
AGC and exploits Optimod-PC's soft-knee 2-band compression. Quiet material is
gently compressed with a very low compression ratio. The compression ratio in-
creases as the source material gets louder (see Figure 3-5 on page 3-54). Very quiet
material is typically amplified by 10 dB. This level-dependent compression ratio pro-
vides very smooth, subtle compression.
ORBAN MODEL 1101
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