5-4
TROUBLESHOOTING ORBAN MODEL 8685
• Particularly if you are using the Two-Band structure, try using the 8685’s HF En-
hancer. See Dialog is muffled above.
Too much bass when the loudness controller is producing large amounts of GR
• The loudness controller is producing too little gain reduction in the below-200
Hz band. Set the L
OUDNESS BASS COUPLE control closer to 0 dB. See Loudness
Control on page 3-14.
RFI, hum, clicks, or buzzes
• For good RFI resistance, always use balanced analog outputs and be sure that the
cables connected to the digital inputs and outputs are well shielded.
The 8685 has been designed with very substantial RFI suppression on its
analog and digital input and output ports, and on the AC line input. It
will usually operate adjacent to high-powered transmitters without diffi-
culty. In the most unusual circumstances, it may be necessary to reposi-
tion the unit to reduce RF interference, and/or to reposition its input and
output cables to reduce RF pickup on their shields.
The AES3id inputs and output are transformer-coupled and have very
good resistance to RFI.
Unexpected gain pumping when processing 5.1 material
• Make sure that the Lb and Rb channels are not accidentally receiving a signal.
The feed to the Lb and Rb channels must be turned off. See step 15 on page 2-
35.
Poor peak modulation control
• The 8685 typically controls peak modulation to an accuracy of ±2% when oper-
ated with 48 kHz output sample rate. As explained in Section 1, output sample
rate conversion will slightly compromise this control because the peak control
occurs with reference to individual sample values at 48 kHz. The converted sam-
ples no longer have the same peak values as the 48 kHz samples; some values can
be slightly higher. However, the overshoot of the converted signal almost never
exceeds 0.5dB and is therefore not a significant problem.
• Using the analog output will cause similar amounts of overshoot because the
peaks in the reconstructed analog waveform are not necessarily synchronous
with the peak-controlled samples in the 8685. Moreover, analog connections can
cause analog-domain overshoot if the connection is not phase-linear and does
not have a –3dB low-frequency cutoff below 0.15Hz.
Audible distortion
• Make sure that the problem can be observed on more than one monitoring sys-
tem.
• Verify that the source material at the 8685's audio inputs is clean. Heavy process-
ing can exaggerate even slightly distorted material, pushing it over the edge into
unacceptability.
• The subjective adjustments available to the user have the potential to cause dis-
tortion when too much fast gain reduction occurs in the multiband compressors
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