Orban Optimod-PC 1101, Operating Manual

Page: 107 / 258

OPTIMOD-PC INSTALLATION
2-51
and/or to reposition OPTIMOD-PC’s input and output cables to reduce RF pickup
on their shields.
•
The AES3 inputs and output are transformer-coupled and have good resistance
to RFI. If you have RFI problems and are using analog connections on either the
input or output, using digital connections will probably eliminate the RFI.
Poor peak level control
•
OPTIMOD-PC audio processing ordinarily controls its output peak levels to an
accuracy of ±2% when operated with 48 or 96 kHz output sample rate. As ex-
plained in the note on page 1-31, output sample rate conversion will slightly
compromise this control because the peak control occurs with reference to indi-
vidual sample values at 192 kHz. The converted samples no longer have the same
peak values as the 192 kHz samples, and some values can be slightly higher.
However, the overshoot of the converted signal will not exceed 0.5 dB (over-
shoot is typically much less) and is therefore not a significant problem.
Using the analog output will cause similar amounts of overshoot because the
samples in the transmitter or encoder are not synchronous with the peak-
controlled samples in OPTIMOD-PC. (This is commonly termed the “0 dB+ issue.)
•
Further, analog connections can cause analog-domain overshoot if the connec-
tion is not phase linear and has a low-frequency cutoff of greater than 0.15Hz (at
–3dB).
Loudness is unexpectedly low at output set to receive P
ROCESSOR
M
IXER
P
OST
L
IMIT
•
D
IALNORM
processing has been activated accidentally by setting the
D
IALNORM
O
UTPUT
control in the I/O Mixer to a setting other than N
ONE
. (See step 6 on page
2-26.)
Audible distortion
•
Make sure that the problem can be observed on more than one sound system
and at several locations.
•
Verify that the source material at OPTIMOD-PC's audio inputs is clean. Heavy
processing can exaggerate even slightly distorted material, pushing it over the
edge into unacceptability.
•
The subjective adjustments available to the user have enough range to cause au-
dible distortion at their extreme settings. Advancing the
F
INAL
L
IMIT
control too
far will inevitably cause distortion. (Distortion is very probable if gain reduction
in the final limiter frequently exceeds 8 dB.) Setting the
L
ESS
-M
ORE
control be-
yond “9” will cause audible distortion of some program material.
•
If you are using analog inputs, you must correctly match the headroom of the
unit's analog-to-digital (A/D) converter to the peak audio levels expected in your
system. If your peak program level exceeds the peak level you have specified,
OPTIMOD-PC's A/D converter will clip and distort. See step 1 on page 2-35.