Test Modes; Calibrated Bypass Test Mode; Calibrated Line-Up Tones; Setting Output/Modulation Levels - Orban OPTIMOD 6300 Operating Manual

OPTIMOD 6300 DIGITAL
to working in decibel units, Jones and Torick chose to map loudness on a
LED ladder display encompassing –20 to +5 dB in 0.5 dB increments, with
the understanding that the perceived loudness doubles every 10 dB at
loudness levels typically heard by broadcast audiences.
The J & T meter is monophonic. Psychoacoustic studies indicate that
when multiple acoustic sources are present in a room, loudness is most
accurately expressed by summing the power in the sources. For example,
driving two loudspeakers with identical program produces 3 dB higher
loudness than a single speaker produces. Therefore, to extend the J & T
algorithm to multichannel reproduction, we implement one eight-filter
filterbank for each channel and compute RMS sums of the outputs of
corresponding filters in each channel before these sums are applied to
the eight nonlinear lowpass filters. As in the monophonic J & T algo-
rithm, the sum of these lowpass filters drives a second nonlinear filter,
which drives the display.

Test Modes

Calibrated Bypass Test Mode

A BYPASS Test Mode is available to transparently pass line-up tones generated ear-
lier in the system. It will also pass program material, applying no gain reduction or
protection against overmodulation. It can transparently pass any line-up tone ap-
plied to its input up to about 130% output modulation, at which point clipping may
occur.
BYPASS is not appropriate for normal on-air use because switching to and from it
will usually cause clicks or other program disruptions and because it does not protect
against inadvertent output clipping. To defeat the dynamics processing on-air
(which might be desired when switching from a local to a network program, for ex-
ample), use the P
T
factory preset.
HROUGH

Calibrated Line-up Tones

To facilitate matching the output level of the 6300 to the transmission system that it
is driving, the 6300 contains a test tone oscillator that produces sine waves at 6300's
outputs. You can adjust the frequency and modulation level of the built-in line-up
tone via the front panel or PC Remote software, and you can specify which outputs
emit the tone. You can use the front panel, the PC Remote software, or the opto-
isolated remote control interface ports to activate the Test Tone.

Setting Output/Modulation Levels

In a perfect world, one could set the peak level at OPTIMOD 6300's output to 0
dBFS. However, there are at several potential problems that may make it desirable
to set the modulation level slightly lower.
First is asynchronous re-sampling, which we have discussed at length earlier in this
chapter. (See page 1-16, for example.) If any digital processing that causes its output
samples to be asynchronous to its input samples is used after OPTIMOD 6300's out-
-T factory preset or a user preset derived from the P
ASS HROUGH
1-25
INTRODUCTION
-
ASS