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APPENDIX L:
Specifications
Frequency Response ( System in PROOF mode)
Follows
standard
75us
preemphasis
curve + 0.75dB,
50-15,000
Hz.
50us
preemphasis available on special order. Deemphasis jumper on line amplifier card
permits
flat output + 0.75dB 50-15,000Hz for use with external preemphasis. All
preemphasis networks include a fourth- order lowpass filter and fourth- order phase
corrector
prior
to
the
high- frequency
limiter
and
clipper
to
prevent
these
elements
from
processing
out- of- band
program
material
and
to
minimize
overshoot,
thus
minimizing
the
amount
of
high- frequency
limiting
and
clipping.
Input Conditioning
Highpass Filter: Third- order
Chebychev
,
Nith
30Hz
cutoff
2nd
0.5dB
passband
ripple.
Down 0.5dB at
30Hz;
10.5dB at 20Hz;
31.5dB at
10Hz. Protects against
infrasonic destabilization of certain exciters'
AFC's, as well as infrasonic gain
modulation in the compressor.
Phase Scrambler: Allpass network makes peaks more symmetrical to best utilize
the symmetrical peak overload characteristics of the FM medium.
Noise
-75dB below 100% modulation, 50-15,000 Hz maximum; - 81dB typical.
Total System Distortion ( PROOF Mode; deemphasized; 100% Modulation)
Less
than
0.25%
THD,
50-15,000Hz ( 0.02%
typical);
less
than
0.2%
SMPTE
Intermodulation Distortion ( 60/7000Hz; 4:1).
NOTE
"THD"
is
defined
as
the
root- sum- square ( R.S.S.)
sum
of
all
harmonics, 50-30,000Hz. Noise ( which is unavoidably included in the
reading on a typical THD analyzer) is specifically excluded from this
specification.
IM
distortion must be measured with the COMPRESSOR PROOF/OP
switch
in
PROOF
and
the
LIMITER
PROOF/OP
switch
in
OP
to
avoid an artifact of the Hilbert- Transform Clippers when in PROOF
mode
which
would
otherwise
cause
falsely- high
IM
readings.
This
same
effect
also causes
the increase
in
measured THD between 4
and
5kHz
in
PROOF
mode.
See ( 5.b)
of
Appendix
B (Circuit
Description) for an explanation.
"Master" Band Compressor Characteristics
Attack Time: approximately lms
Release Time: program- controlled --
varies
according
to
program
dynamics
and
amount of gain reduction ( see text). Process can be scaled fast or slow by means
of
continuously
variable
RELEASE
TIME
control.
Employs
delayed
release
for
distortion reduction.
L-1
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