Making Sync Connections; Synchronization Connections - MOTU 828 User Manual

MAKING SYNC CONNECTIONS

If you connect devices digitally to the MOTU 828,
or if you need to synchronize the MOTU 828 with
an outside time reference such as SMPTE time
code, you must pay careful attention to the
synchronization connections and clock source
issues discussed in the next few sections.
Do you need to synchronize the MOTU 828?
If you will be using only the MOTU 828's analog
inputs and outputs (and none of its digital I/O),
and you have no plans to synchronize your MOTU
828 system to SMPTE time code, you don't need to
make any sync connections. You can skip this
section and proceed to chapter 4, "Installing the
MOTU 828 Macintosh Software" (page 29). After
you install the MOTU 828 software, you'll open the
MOTU 828 Control Panel and set the Clock Source
setting to Internal as shown below in Figure 3-5.
For details, see chapter 5, "MOTU 828 Control
Panel" (page 33).
Figure 3-5: You can run the MOTU 828 under its own internal clock
when it has no digital audio connections and you are not synchroniz-
ing the MOTU 828 system to an external time reference such as
SMPTE time code.
Situations that require synchronization
There are three general cases in which you will
need to synchronize the MOTU 828 with other
devices:
Synchronizing the MOTU 828 with other digital
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audio devices so that their digital audio clocks are
phase-locked (as shown in Figure 3-6)
Slaving the MOTU 828 system to SMPTE time
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code, such as from a video deck or an analog multi-
track tape recorder
Both of the above
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I N S T A L L I N G T H E M O T U 8 2 8 H A R D W A R E
Synchronization is critical for clean digital I/O
Synchronization is critical in any audio system, but
it is especially important when you are transferring
audio between digital audio devices. Your success
in using the MOTU 828's digital I/O features
depends almost entirely on proper synchroni-
zation. The following sections guide you through
several recommended scenarios.
Be sure to choose a digital audio clock master
When you transfer digital audio between two
devices, their audio clocks must be in phase with
one another — or phase-locked. Otherwise, you'll
hear clicks, pops, and distortion in the audio — or
perhaps no audio at all.
Not phase-locked
Device A
Device B
Figure 3-6: When transferring audio, two devices must have phase-
locked audio clocks to prevent clicks, pops or other artifacts.
There are two ways to achieve phase lock: slave one
device to the other, or slave both devices to a third
master clock. If you have three or more digital
audio devices, you need to slave them all to a single
master audio clock.
Master
Slave Slave
Figure 3-7: To keep the MOTU 828 phased-locked with other digital
audio devices connected to it, choose a clock master.
Also remember that audio phase lock can be
achieved independently of time code (location).
For example, one device can be the time code
master while another is the audio clock master. But
only one device can be the audio clock master. If
you set things up with this rule in mind, you'll have
trouble-free audio transfers with the MOTU 828.
Phase-locked
Master
Slave
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