Optimod-Surround 8685 V1.0 Operating Manual - Orban

OPTIMOD SURROUND PROCESSOR OPERATION 3-47
look-ahead limiter distortion control. The range (with reference to the look-ahead
limiter threshold) is –6 dB to +6 dB (and OFF). As you raise the threshold of the clipper,
you will get more bass but also more distortion and pumping. Be careful when
setting this control; do not adjust it casually. Listen to program material with heavy
bass combined with spectrally sparse midrange material (like a singer) and listen for
IM distortion induced by the bass’ pushing the midrange into the look-ahead limiter.
Although the low-IM technology in the 8685’s look-ahead limiter substantially reduces
this distortion, overdriving the limiter hard enough can still cause problems.
Because the sound-for-picture presets typically produce little or no look-ahead limiting
with reasonable values of DIALNORM, the bass clipper is not needed and is turned
off to prevent its adding unnecessary distortion.
In the Five-Band structure, band 1 drives the clipper. In the Two-Band
structure, the Bass band drives the clipper.
For 2.0 processing, note that the SPEECH BASS CLIP THRESHOLD control overrides the
BASS CLIP THRESHOLD control when OPTIMOD-PC automatically detects speech (see
Speech/Music Detector on page 3-6). For surround processing, the center channel
(which usually carries dialog) has an independent CENTER BASS CLIP THRESHOLD control.
Bass Clip Shape allows you to change the knee of the input/output gain curve of
the bass clipper. It allows you to control the shape of the “knee”—the transition between
no clipping and flat topping. “0” provides the hardest knee, where the transition
between linear operation and flat topping occurs abruptly as the clipper’s in-
Figure 3-1: Bass Clipper Input/Output Transfer Curves as Bass Clip Shape Control is
Varied from 0.0 (Hard) to 10.0 (Soft)