Orban OPTIMOD 6300, Руководство по эксплуатации

Страница: 157 / 255

OPTIMOD 6300 DIGITAL OPERATION
3-39
the look-ahead limiter, causing audible intermodulation distortion between the bass
and higher frequency program material.
Some 6300 users feel that the bass clipper unnecessarily reduces bass punch at its
factory settings. To accommodate these users, the threshold of the bass clipper is
user-adjustable. The range (with reference to the look-ahead limiter threshold) is
–10 to +10dB (and
O
FF
). 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 in-
duced by the bass’ pushing the midrange into the look-ahead limiter. Although the
low-IM technology in the 6300’s look-ahead limiter substantially reduces this distor-
tion, overdriving the limiter hard enough can still cause problems.
In the 5-band structure, band 1 drives the clipper. In the 2-band structure, the Bass
band drives the clipper.
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 be-
tween no clipping and flat topping. “0” provides the hardest knee, where the tran-
sition between linear operation and flat topping occurs abruptly as the clipper’s in-
put level is changed. “10” is the softest knee, where the transition starts 6 dB below
B
ASS
C
LIP
T
HRESH
setting and occurs gradually. The factory default setting is “7.6.”
Final Limit Drive controls (AGC and MB) adjust the level of the audio driving the
low-IM look-ahead limiters that OPTIMOD-PC uses to control fast peaks, thereby ad-
justing the peak-to-average ratio of the processed audio. The
F
INAL
L
IMIT
D
RIVE
con-
trols primarily determine the loudness/distortion trade-off.
Turning up the F
INAL
L
IMIT
D
RIVE
control drives the look-ahead limiter harder, reduc-
ing the peak-to-average ratio, and increasing loudness. When the amount of limit-
ing is increased, the audible intermodulation distortion caused by limiting increases,
even though special algorithms minimize the increase compared to less sophisticated
designs. Lower settings reduce loudness, of course, but result in a cleaner sound.
When you use OPTIMOD-PC in a preemphasized mode (step 7 on page 2-23 and step
8 on page 2-23), this inserts a frequency-dependent high frequency boost before the
look-ahead limiter. This boost can be as large as 20 dB at 20 kHz. When using pre-
emphasis, you must turn down the
F
INAL
L
IMIT
D
RIVE
control to prevent the look-
ahead limiter from causing audible gain pumping.
Distortion Control Adjustments
Name Range
AGC Final Limit Drive –20.0 … +12.0 dB
Bass Clip Shape 0.0 … 10.0
Bass Clip Threshold –10.0 … +10.00 dB, OFF
Multiband Final Limit Drive –20.0 … +12.0 dB
Speech Bass Clip Threshold –10.0 … +10.00 dB, OFF
Table 3-7: Distortion Control Adjustments