Orban OPTIMOD 6200, Operating Manual

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OPTIMOD INTRODUCTION
1-13
OPTIMOD-DAB’s bandwidth can be adjusted from 4kHz to 20kHz to provide correctly
anti-aliased audio for any of these systems. Provided that any anti-aliasing filters follow-
ing OPTIMOD-DAB’s output are phase-linear and that they have integer-sample time
delays, these will pass the band-limited OPTIMOD-DAB output without introducing
overshoot because they remove no further spectrum and do not cause their output sam-
ples to become asynchronous with the peak-controlled samples at the 6200’s output.
OPTIMOD-DAB always operates at 48kHz sample rate internally. Its output is equipped
with a sample rate converter that can output at 32kHz, 44.1kHz, or 48kHz. These rates
can be synchronized to the
AES/EBU SYNC INPUT
.
We expect that transmitters that transmit sample rates below 32kHz will provide internal
sample rate conversion, and that most will probably accept audio at 48kHz sample rate
regardless of the final sample rate of the transmission. Any sample rate conversion may
cause the transmitted sample to become asynchronous to the peak-controlled samples
emerging from the 6200 and may therefore introduce overshoot. Fortunately, as the au-
dio bandwidth becomes lower this becomes less of the problem because the 48kHz sam-
ple rate within the 6200 oversamples the audio and therefore becomes less likely to let
peaks “slip between the samples.”
Subframe Delay
OPTIMOD-DAB provides an adjustable time delay of up to 96 milliseconds. This allows
the installer to force the total delay through the processing to equal one frame. The defi-
nition of “frame” depends on the system in which the 6200 is installed.
The selections are
off
(approximately 14ms delay), 24 milliseconds, 30 fps,
29.97 fps (NTSC color video), 25 fps (most PAL video), 24 fps (film), and
96 milliseconds.
Program-Associated Data (PAD)
OPTIMOD-DAB provides two serial ports. One is designed for use with a PC-based re-
mote control. The other is designed to interface to a DAB transmitter to provide Pro-
gram-Associated Data (particularly the Dynamic Range Control signal).
Version 2.0 (and lower) of the 6200 firmware does not yet support PAD be-
cause Orban is still working with transmitter vendors and customers to de-
fine exactly what is required and desired.
Setting Modulation Levels
In a perfect world, one could set the peak modulation level at the 6200’s output to 0dBfs.
However, there are at least two potential problems that may make it desirable to set the
modulation level slightly lower.