M-AUDIO Delta RBUS - Manual (Page 15)

In situations where the Delta R-BUS is synching to an external R-BUS device,
such as a clock from a Roland digital multitrack or digital mixer that has
R-BUS I/O, the Delta R-BUS Audio Card should similarly be configured to
get its master clock from the external R-BUS wordclock data stream, labeled
“R-BUS In.” The reason for this is the same – an R-BUS data stream coming
from an external source is rarely going to be in sync with the Delta R-BUS
Audio Card (or other digital audio devices in the system), even if the sample
rates are set the same. If the master clock were set to use the internal crystal
(or any selection other than the proper R-BUS clock source), then the
incoming R-BUS audio would have "pops," "crackles," and other undesirable
audio artifacts present in it. Instead, setting the master clock to "R-BUS In"
will synchronize the Delta R-BUS Audio Card to the R-BUS input data and its
digital audio will be transferred properly. The special case to consider, again,
is the external unit sending the R-BUS digital audio to the Delta R-BUS card
may be "locked" to the word clock emitted from the Delta R-BUS card. In
these cases, the Delta R-BUS and the external R-BUS device are in-sync, and
the R-BUS data would therefore be in-sync with the Delta R-BUS system
when the Delta R-BUS card is set to “Internal Xtal.”
When using more than one Delta R-BUS card, the second and subsequent
Delta R-BUS cards may be synchronized to the first Delta R-BUS card by
selecting “R-BUS PCI” as the master clock. The Delta R-BUS has
connections on the PCI card that allow you to connect and synchronize
the R-BUS clock on multiple Delta R-BUS cards using the supplied
internal sync cable. This is necessary to prevent the "pops," "crackles,"
and other undesirable audio artifacts that occur in unsynchronized
digital audio. This is covered further in the “Hardware Settings” section
of this manual.
Finally, the S/PDIF In and R-BUS In (as well as R-BUS PCI) options may
be used to operate the Delta R-BUS at non-standard sample rates. When
one of these options is selected, the Delta R-BUS’s sample rate will
automatically match that of the incoming S/PDIF or R-BUS data stream.
NOTE: When either the S/PDIF or R-BUS In is selected as
the master clock source, the Delta R-BUS mixer’s frequency
response will be affected by whatever sample rates you
inject at the S/PDIF or R-BUS In. This is because (1) the
digital mixer operates at the same sample rate as the rest of
the board, and (2) sample rate and frequency response are
directly correlated.
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