Alesis BRC Reference Manual page 72

input.
6. Press the DIGITAL I/O button again;
The display will show the following:
AI-1 Clock:
4 8K
7. Use the UP/DOWN buttons to select the AI-1's clock source (48K
or 44.1K). This determines the output sample rate of the AI-1.
Important: When recording audio from AES/EBU or S/PDIF, the
ADAT(s) derive their clock source from the incoming digital
audio via the optical digital bus, and are therefore perfectly in sync
with the incoming source. However, it is important to note that
the BRC also requires a 48 KHz clock in order to be synchronized
to the incoming digital signal. Since the BRC has nothing to do
with the ADAT's optical digital bus, you will need to route clock
information from the AI-1 to the BRC by connecting the AI-1's 48
KHz output to feed the BRC's 48 KHz input (see section 2.2B).
Note: The BRC's 48KHz, SMPTE, and MIDI outputs will not be usable
if the AI-1 provides no timing reference for the BRC. If the BRC is
synchronizing to the 48KHz clock, SMPTE, or video sync, then all
of the BRC's outputs will be usable. However, it is up to you to
insure that the AES/EBU or S/PDIF digital audio signal is
synchronous to the clock source that is connected to the BRC by
providing it with clock information.
Note: When the DIGITAL I/O button is turned on and the digital
input has been set to either AES/EBU or S/PDIF, the EXT SYNC
button will automatically turn on and disable the pitch controls
(the Pitch display will read " – – – "). The EXT SYNC's clock source
will be set to 48 KHz. It is possible, however, to disable the EXT
SYNC button by pressing it without turning off the DIGITAL I/O
button. This is not recommended, since the BRC would no longer
be in perfect sync with the digital source's clock rate, which could
result in clicks in the audio.
For more information about sample rate conversion and interfacing
the AI-1 with other digital audio equipment, please refer to the AI-1's
owners manual.
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