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INTRODUCTION ORBAN Model 8400
Note that if the 8400’s subcarrier inputs are used, the meter will not indicate the subcarri-
ers’ 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, calibrated modulation monitor.
Built-in Calibrated Line-up Tones
To facilitate matching the output level of the 8400 to the transmission system that it is
driving, the 8400 contains an adjustable test tone oscillator that produces sine waves at
8400’s (analog or digital) left, right and composite outputs. The frequency and modula-
tion level of the line-up tones can be adjusted from the front panel (as described in Sec-
tion 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 stereo
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 8400’s left/right analog output is switched to
Flat, a de-emphasis filter is in-
serted between output of the 8400’s audio processing and its line output. Thus, as the fre-
quency of the Test Tone is changed, the level at the 8400’s line output will follow the
selected de-emphasis curve. In most cases the pre-emphasis filter in the driven equipment
will undo the effect of the 8400’s internal de-emphasis, so the 8400’s output level should
be adjusted such that the tone produces 100% modulation 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 8400’s left and right audio out-
puts.
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 control interface
ports to activate the Test Tone.
Built-in Calibrated Bypass Test Mode
A Bypass Test Mode is available to transparently pass line-up tones generated earlier in
the system. It will also pass program material, with no gain reduction or protection
against overmodulation. It can transparently pass any line-up tone applied to its input up
to about 130% output modulation, at which point clipping may occur.
Monitoring on Loudspeakers and Headphones
In live operations, highly processed audio often causes a problem with the DJ or pre-
senter’s headphones. The delay through the 8400 can be as much as 39 milliseconds
(when
Soft bass clipping is selected). This delay is likely to be audible as a distinct echo,
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