Composite Output Level; Built-In Calibrated Line-Up Tones - Orban OPTIMOD-FM 5500 Operation Manual

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INTRODUCTION

Composite Output Level

Built-in Calibrated Line-up Tones

put, the maximum digital word at the input corresponds to the 0 dB point on the
5500's input meter.
The Orban 5500 Audio Processor controls instantaneous, absolute peak levels to a
tolerance of approximately 0.1 dB. Composite modulation is indicated in percent-
age modulation, absolute instantaneous peak indicating. 100% is calibrated to the
highest composite peak modulation level that the processing will produce, including
the pilot tone, under any program, processing, or setup condition (except when the
processing is switched to BYPASS, is being operated in stand-alone stereo encoder
mode without overshoot limiting, or when the final clipper is defeated in Setup).
100% ordinarily corresponds to 75 kHz-carrier deviation.
Note that if the 5500's subcarrier inputs are used, the meter will not indicate the
subcarriers' effect on composite modulation because the subcarriers are mixed into
the composite signal in the analog domain, after it is metered. Therefore, you must
mentally add the subcarriers to the meter indication, or refer to an external, cali-
brated modulation monitor.
To facilitate matching the output level of the 5500 to the transmission system that it
is driving, the 5500 contains an adjustable test tone oscillator that produces sine
waves at 5500's (analog or digital) left, right and composite outputs. The frequency
and modulation level of the line-up tones can be adjusted from the front panel (as
described in Section 3).
The stereo encoder is calibrated so that 100% left or right modulation will provide
100% modulation of the stereo composite signal, including pilot tone but excluding
any SCA subcarriers.
The pilot tone stereo system has an interleaving property, which means that the ste-
reo composite modulation is approximately equal to the higher of the left or right
channels. Because the pilot tone is phase-synchronous with the stereo subcarrier, the
composite modulation will actually increase about 2.7% when the modulation is
changed from pure single-channel to L+R modulation while the peak audio level is
held constant.
When the 5500's left/right analog output is switched to F
inserted between output of the 5500's audio processing and its line output. Thus, as
the frequency of the Test Tone is changed, the level at the 5500's line output will fol-
low the selected de-emphasis curve. In most cases, the pre-emphasis filter in the
driven equipment will undo the effect of the 5500's internal de-emphasis, so the
5500's output level should be adjusted such that the tone produces 100% modula-
tion of the transmission link as measured after the link's pre-emphasis filter. At
100Hz, switching the de-emphasis out or in will have negligible effect on the level
appearing at the 5500's left and right audio outputs.
You can adjust the frequency and modulation level of the built-in line-up tone. You
can use the front panel, the PC Control software, or the opto-isolated remote con-
trol interface ports to activate the Test Tone.
ORBAN MODEL 5500
, a de-emphasis filter is
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