Orban OPTIMOD-FM 8700, Operating Manual

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OPTIMOD-FM DIGITAL OPERATION
3-3
2B HF meters display the gain reductions in dB of the independent left and right
channel high frequency limiters in the 8700i’s Two-Band structure. These meters ap-
pear only when the 8700i is in Two-Band mode.
Out meters display the 8700i’s instantaneous peak output level.
Comp meter displays the stereo encoder’s output level before the C
OMP
1 or C
OMP
2
attenuators, using a linear percent scale over a 0% to 125% modulation range.
Multiplex Power / BS.1770 gain reduction uses a two-color display to indicate the ac-
tion of the ITU Multiplex Power controller and the BS.1770 safety limiter in the ana-
log radio processing chain. It shows how much the Multiplex Power Controller and
BS.1770 Safety Limiter have reduced the clipper drive, reducing the average power
in the processed audio. The BS.1770 gain reduction is shown in cyan and the multi-
plex power gain reduction is shown in dark blue.
This meter, labeled L
OUDNESS
, is displayed on the 8700i’s screen. It always
appears when the Two-Band Structure is active. If the Five-Band Structure
is active, it only appears if the Multiplex Power Controller or BS.1770 me-
ter is turned on.
Multiplex Power Level meter indicates the amount of multiplex power produced by
the 8700i. The meter complies with the ITU-R BS.412 standard and is calibrated and
with reference to the 8700i’s 100% peak modulation level.
HD (HD Digital Radio) G/R meters show the gain reductions in the left and right HD
look-ahead limiters.
These meters only appear when the
M
ETER
S
EL
Switch (on the HD
D
IGITAL
R
ADIO
page of the 8700i’s I
NPUT
/O
UTPUT
menu) is set to
HD GR
.
Introduction to Processing
Some Audio Processing Concepts
Reducing the peak-to-average ratio of the audio increases loudness. If peaks are re-
duced, the average level can be increased within the permitted modulation limits.
The effectiveness with which this can be accomplished without introducing objec-
tionable side effects (such as pumping or intermodulation distortion) is the single
best measure of audio processing effectiveness.
Compression reduces the difference in level between the soft and loud sounds to
make more efficient use of permitted peak level limits, resulting in a subjective in-
crease in the loudness of soft sounds. It cannot make loud sounds seem louder.
Compression reduces dynamic range relatively slowly in a manner similar to riding
the gain: Limiting and clipping, on the other hand, reduce the short-term peak-to-
average ratio of the audio.
Limiting increases audio density. Increasing density can make loud sounds seem
louder, but can also result in an unattractive busier, flatter, or denser sound. It is im-