M-AUDIO Delta RBUS - Manual (Page 14)

Delta R-BUS’s outputs may accept audio from software sources (these output
devices are visible in your audio software applications) or from hardware
sources such as the analog and digital inputs (R-BUS or S/PDIF), or the
monitor mixer. This capability makes the Delta R-BUS quite flexible for WAV
or AIFF output, monitoring, or directly connecting inputs to outputs for
system test purposes or input monitoring.
Synchronization
For proper operation, the entire Delta R-BUS system is always
synchronized to a single master clock. The master clock is chosen via the
Delta Control Panel software, and this clock may be derived from the Delta
R-BUS’s internal crystal oscillators, S/PDIF In, or R-BUS In (either internal
or external). Much of the time, the master clock is taken from the internal
crystal oscillators. However, the S/PDIF and R-BUS options are used in
situations where the Delta R-BUS must be synchronized to external digital
audio or sample rates derived from an external device. The Delta R-BUS
may be synchronized to other R-BUS capable devices using “R-BUS In” as
your choice for master clock. Multiple Delta R-Bus cards may be
sychronized by choosing “Delta R-BUS” as the master clock, and by
making the proper connections and additional hardware settings.
Using the initial default setting, the master clock is derived from the
internal crystal oscillators. Operation in this mode is similar to that of a
generic sound card – for instance, when a WAV or AIFF file is played
through the Delta drivers, the software application playing the WAV or
AIFF file is responsible for setting the sample rate in the sound card
hardware. The Delta R-BUS supports these sample rates by using either
of its internal crystal oscillators and dividing the rate of that oscillator by
some value to derive the proper sample rate.
In situations where S/PDIF In is being used, the Delta R-BUS Audio Card
must be configured to get its master clock from the S/PDIF In data stream.
The reason for this is simple – a S/PDIF data stream coming from an
external source is rarely going to be in sync with the Delta R-BUS card (or
other digital audio devices in the system for that matter), even if the sample
rates are set the same. If the master clock were set to use the internal crystal,
then the incoming S/PDIF audio would have "pops," "crackles," and other
undesirable audio artifacts present in it. Instead, setting the master clock to
"S/PDIF In" will synchronize the Delta R-BUS card to the S/PDIF input
data and its digital audio will be transferred properly.
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