Orban OPTIMOD-FM 8600, Operating Manual

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OPERATION ORBAN MODEL 8600
shoot and without the need for distortion-producing overshoot compensation
schemes.
A defeatable 30 Hz 18 dB/octave highpass filter and a defeatable phase rotator
complete the input-conditioning block. These have both been features in Orban FM
processors for many years. Most users will defeat the 30 Hz filter and leave the
phase rotator in-circuit, although the choice is always yours.
Stereo Enhancement: The 8600 provides two different stereo enhancement algo-
rithms. The first is based on Orban’s patented analog 222 Stereo Enhancer, which in-
creases the energy in the stereo difference signal (L–R) whenever a transient is de-
tected in the stereo sum signal (L+R). By operating only on transients, the 222 in-
creases width, brightness, and punch without unnaturally increasing reverb (which is
usually predominantly in the L–R channel).
Gating circuitry detects “mono” material with slight channel or phase imbalances
and suppresses enhancement so this built-in imbalance is not exaggerated. It also
allows you to set a “width limit” to prevent over-enhancement of material with sig-
nificant stereo content, and will always limit the ratio of L–R / L+R to unity or less.
The second stereo enhancement algorithm is based on the well-known “Max” tech-
nique. This passes the L–R signal through a delay line and adds this decorrelated sig-
nal to the unenhanced L–R signal. Gating circuitry similar to that used in the “222-
style” algorithm prevents over-enhancement and undesired enhancement on slight-
ly unbalanced mono material.
“Multipath Mitigator” Left/Right Phase Skew Correction
The phase skew corrector maximizes the quality of a mono mixdown or blend that
might occur in a receiver. At higher frequencies (where audible comb filtering of the
mono sum is most likely to occur), the corrector removes phase differences between
the left and right channels, converting the HF signal into “intensity stereo” while
preserving phase differences at lower frequencies where these differences are im-
portant for psychoacoustic “envelopment.” The
P
HASE
C
ORRECTOR
C
ROSSOVER
con-
trol in the EQ tab of the active Processing Preset sets the crossover frequency above
which phase correction occurs.
By removing phase shifts between the left and right channels, the process minimizes
the amount of energy in the stereo subchannel, which consequently minimizes mul-
tipath distortion without compromising stereo separation. It can allow more stereo
enhancement to occur for a given amount of multipath distortion. The process also
minimizes the amount of peak overshoot during SSB/VSB operation of the stereo
encoder, thus minimizing the amount of composite limiting needed to constrain
peak modulation to 100%.
This process can not only correct problems due to phase skew between the left and
right channels of an analog recording due to head gap misalignment, it can also cor-
rect comb filtering caused by spaced microphones feeding the left and right chan-
nels, which can occur on drum kits and other sources that have been multi-miced.
Because the process can subtly alter the stereo spatial effect, it may be inappropriate
of “audiophile” formats, although its advantages in reducing multipath distortion