Optimod-AM 9400 V1.2 Operating Manual - Orban

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OPERATION ORBAN MODEL 9400
Stereo Enhancer Controls
The 9400 provides two different stereo enhancement algorithms. The first is based
on Orban’s patented analog 222 Stereo Enhancer, which increases the energy in the
stereo difference signal (L–R) whenever a transient is detected in the stereo sum signal
(L+R). By operating only on transients, the 222 increases width, brightness, and
punch without unnaturally increasing reverb (which is usually predominantly in the
L–R channel).
The second stereo enhancement algorithm is based on the well-known “Max” technique.
This passes the L–R signal through a delay line and adds this decorrelated signal
to the unenhanced L–R signal. Gating circuitry similar to that used in the “222-
style” algorithm prevents over-enhancement and undesired enhancement on
slightly unbalanced mono material.
It is unwise to use stereo enhancement with low bitrate codecs. At low bit rates,
these codecs use various parametric techniques for encoding the spatial attributes of
the sound field. Stereo enhancement can unnecessarily stress this encoding process.
Both modes have gating that operates under two conditions.
The two stereo channels are close to identical in magnitude and phase.
In this case, the enhancer assumes that the program material is actually
mono and thus suppresses enhancement to prevent the enhancement
from exaggerating the undesired channel imbalance.
The ratio of L–R / L+R of the enhanced signal tries to exceed the threshold set by
the L-R / L+R RATIO LIMIT control.
In this case, the enhancer prevents further enhancement in order to prevent
excess L–R energy, which might increase distortion in AM stereo
transmission.
The stereo enhancer has the following controls:
Amount sets the maximum spatial enhancement.
Enhancer In / Out bypasses the stereo enhancer. OUT is equivalent to setting the
Stereo Enhancer Controls
Basic / Intermediate Name Advanced Name Range
Amount Amount 0.0 ... 10.0
Enhancer In / Out Out / In
Ratio Limit Ratio Lim 70 … 100%
Diffusion Diffusion Off, 0.3 ... 10.0
Style Style 222 / Delay
Depth Depth 0 … 10
Table 3-4: Stereo Enhancer Controls