Gain Pumping When High Frequency Energy Is Present; Shrill, Harsh Sound; Dull Sound - Orban OPTIMOD 6300 Operating Manual

OPTIMOD 6300 DIGITAL
The 6300's AES3 input is capable of receiving words of up to 24 bits. A 24-bit word
has a dynamic range of approximately 144 dB. The 6300's digital input will thus
never limit the unit's noise performance even with very high amounts of compres-
sion.
If an analog studio-to-transmitter link (STL) is used to pass unprocessed audio to the
6300, the STL's noise level can severely limit the overall noise performance of the
system because compression in the 6300 can exaggerate the STL noise. For example,
the overload-to-noise ratio of a typical analog microwave STL may only be 70-75 dB.
In this case, it is wise to use an Orban Studio AGC to perform the AGC function prior
to the STL transmitter and to control the STL's peak modulation. This will optimize
the signal-to-noise ratio of the entire transmission system. An uncompressed digital
STL will perform much better than any analog STL. (See Studio-Transmitter Link,
starting on page 1-12.)

Gain pumping when high frequency energy is present

This will occur with most OPTIMOD-PC factory presets when the 6300's preemphasis
is set to 50 µs or 75µs. [See step (10.C) on page 2-25.] The gain pumping happens be-
cause the preemphasis creates a large high frequency boost before the look-ahead
limiter, so the look-ahead limiter must produce large amounts of gain reduction to
control peak levels.
To correct this problem, turn down the F
pumping is no longer audible. It may also be helpful to adjust band 5 so that it pro-
duces some high frequency limiting. Then save your work as a User Preset.

Shrill, Harsh Sound

This problem can be caused by excessive HF boost in the HF Equalizer and HF Enhan-
cer. It could also be caused by an excessively high setting of the band 4 or band 5
compression threshold control (if you are using the 5-band Structure), or by exces-
sively high settings of the B
Advanced Modify).
In applications where you are protecting a pre-emphasized link, you must set the
6300's output to F
emphasis, which will cause very shrill sound (and very poor peak modulation con-
trol). Note, however, that it is always preferable to defeat the preemphasis filter in
the link and to set the 6300's output to P

Dull Sound

If you are using the 2-band structure, dull-sounding source material will sound dull
on the air. The 5-band Structure will automatically re-equalize such dull-sounding
program material to make its spectral balance more consistent with other program
material.
In applications where you are protecting a pre-emphasized link, if the 6300's output
is set to F in S
LAT
supplied somewhere else in the system. This will cause very dull sound.
and B
4 M
AND IX
in the S
S
LAT YSTEM ETUP
S > O
YSTEM ETUP UTPUT
L D control (page 3-39) until the
INAL IMIT RIVE
controls (located in Full and
5 M
AND IX
screen to prevent double pre-
> O
UTPUT
. This will optimize peak control.
-E
RE MPH
, there will be no preemphasis unless it is
TROUBLESHOOTING
5-3