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14
COMPOSITE
PROCESSING
In the fully-counterclockwise (
OUT
) position, an
output “safety” clipper catches only those very fast
peaks and overshoots which sneak by the earlier
protection circuitry. As the
COMPOSITE
PROCESSING
control is rotated clockwise, the level
applied to the safety clipper is increased by the dB
value indicated on the front panel. Composite clipping
will increase apparent loudness, but at the expense of
generating some spurious harmonic products. The
following tabulation is approximate.
COMPOSITE
PROCESSING
PEAK VALUE OF
CLIPPING PRODUCTS
OUT
>60dB below 100%
1dB
50dB below 100%
2dB
45dB below 100%
3dB
40dB below 100%
Composite clipping is performed
prior
to 19kHz stereo
pilot insertion. This averts clipping or other pilot
amplitude modulation. Nevertheless, crosstalk of the
program audio into RDS or SCA subcarriers is
exacerbated by composite clipping and its inevitable
intermodulation and harmonic generation.
Use this
feature sparingly!
COMPOSITE
OUTPUT / PILOT / SUB
The
PILOT INJ.
and
SUB INJ.
controls set the injection
levels of the 19kHz stereo pilot and an externally-
applied SCA or RDS subcarrier. The
OUTPUT LEVEL
control varies the overall composite output level of the
DAVID-II
delivered to the exciter or STL.
OUTPUT
LEVEL
is a “master” adjustment and does not affect
the relationships (level ratios) between the stereo
program, pilot and RDS/SCA subcarrier.
AUDIO PROCESSING
In the
IN
position, this switch routes the input audio
program signal through the AGC and compressor/
limiter processing circuitry. When
AUDIO
PROCESSING
is switched
OUT
, program audio
completely bypasses
the processing section. The green
LED indicates normal operation, the red LED shows
that processing has been manually defeated.
The
OUT
position defeats program audio pre-emphasis
as well. However, “Bass-Enhance” equalization (if
enabled), low-pass filtering (and its overshoot
correction), and composite processing
do remain active
in the program signal path. It is important to leave
the
AUDIO PROCESSING
switch in the
IN
position
