Orban OPTIMOD-PC 1100, Руководство по эксплуатации

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INTRODUCTION ORBAN MODEL 1100
word length, following standard AES3 or SPDIF protocols. Because both digital in-
puts have sample rate converters, both inputs can be mixed (even if asynchronous
with each other) and neither need be synchronous with the output.
If the netcasting servers are located remotely, then there is a particular advantage
to transporting the compressed stream instead of the raw PCM. If the data rate of
the compressed stream is less than 128kbps, it can be transported on an ISDN line. If
the rate is greater, or if more than one stream is being transported, a fractional T1
line is often suitable. In general, IP connection via the Internet is insufficiently reli-
able for “broadcast contribution quality” connections, introducing a risk of gaps and
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.
Genlocking OPTIMOD-PC Cards to a Reference Sample
Frequency
Many facilities have a reference sample frequency to which all digital equipment is
locked. While OPTIMOD-PC does not have a word clock input, either AES3 input can
accept a reference sample frequency via an AES3 signal. OPTIMOD-PC’s output sam-
ple frequency can then be locked to this reference [see step (4.B) on page 2-23.]
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
automatically lock 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.