M-Audio Delta 1010 Manual page 13

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 file is played through the Delta drivers, the
software application playing the WAV file is responsible for setting the sample
rate in the sound card hardware. The Delta 1010 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 1010 should usually be
configured to get its master clock from the S/PDIF In data stream. The reason
for this is simple – an S/PDIF data stream coming from an external source is
rarely going to be in sync with the Delta 1010 (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 1010
to the S/PDIF input data and its digital audio will be transferred properly. There
is one special case to consider, however. The external unit sending the S/PDIF
digital audio to the Delta 1010 may be "locked" to the word clock emitted from
the Delta 1010, or both the external unit and the Delta 1010 are locked to the
same external word clock. In these cases, the Delta 1010 and the external
S/PDIF device are in-sync, and the S/PDIF data would therefore be in-sync with
the Delta 1010 system.
We've discussed internal crystals and S/PDIF In as master clock sources. The
third option is Word Clock. Word Clock is the desirable choice when you want
to synchronize the Delta 1010 with the word clock of something else in your
system. That "something else" may be a another unit that has a word clock
output, or it may be a dedicated house word clock generator.
Finally, the Word Clock and S/PDIF In options may be used to operate the Delta
1010 at non-standard sample rates. When one of these two options is selected,
the Delta 1010's sample rate will automatically match that of the incoming word
clock or S/PDIF data stream.
NOTE: When either the S/PDIF In or Word Clock is selected as the
master clock source, the Delta 1010 mixer's frequency response
will be affected by whatever sample rates you inject at the S/PDIF
In or Word Clock 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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