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1-22
INTRODUCTION
Genlocking OPTIMOD-PC Cards to a Reference Sample
Frequency
Studio-Transmitter Link in Digital Broadcasting
dropouts in the stream. Therefore, it is desirable to use an encoder (such as
OPTICODEC-PC) that can automatically reconnect to the server in the unlikely event
that the connection is dropped.
Many facilities have a reference sample frequency to which all digital equipment is
locked. While OPTIMOD-PC's word clock input is not supported in 1101 v1.0 soft-
ware (it will be supported in a future free software upgrade), either AES3 input can
accept a reference sample frequency via an AES3 or AES11 signal. OPTIMOD-PC's
output sample frequency can then be locked to this reference [see step (4.B) on
page 2-22.]
This reference can be the sample frequency of one of the active audio inputs. On
the other hand, if you have an AES3 stream available exclusively as a sample fre-
quency reference, you can then connect this stream to the input that you specify as
the "reference" and mute the reference input in the Orban I/O Mixer application.
(See Figure 1-4: OPTIMOD-PC Signal Flow and I/O on page 1-13, and Figure 1-5: Typi-
cal I/O mixer on page 1-16.)
Because of hardware limitations in the sample rate converters, input frames are not
necessarily phase-aligned to output frames according to the strictest interpretation
of the AES-11 standard. However, the sample frequency of the output will be identi-
cal to the sample frequency of the input. In addition, these limitations prevent the
passing of AES3 user bits from digital input to digital output.
Using OPTIMOD-PC's internal crystal reference, you can also set the output sample
frequency to be independent of the input sample frequency. In this case, you can
freely set the output to 32, 44.1, 48, 88.2, or 96 kHz.
If the input reference sample frequency deviates from the preset output
sample frequency by more than ±4%, the output sample frequency will
lock automatically to OPTIMOD-PC's internal crystal reference instead of
the input reference.
In all cases, OPTIMOD-PC's internal processing operates at 48 kHz, locked
to OPTIMOD-PC's internal crystal reference. The output sample rate con-
verter, which is always in-line, determines the output sample rate.
The following information is mainly relevant to digital radio broadcasters who have
their transmitters and studios at different locations. It assumes that you are using
OPTIMOD-PC as a replacement for a stand-alone audio processor. In this context,
you use OPTIMOD-PC's external analog or digital inputs and outputs and do not
route the audio through the host computer.
ORBAN MODEL 1101
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