Making Sync Connections - MOTU 828mkII User Manual

MAKING SYNC CONNECTIONS

If you connect devices digitally to the 828mkII, or
if you need to synchronize the 828mkII with an
outside time reference such as SMPTE time code,
you must pay careful attention to the synchroni-
zation connections and clock source issues
discussed in the next few sections.
Do you need to synchronize the 828mkII?
If you will be using only the 828mkII's analog
inputs and outputs (and none of its digital I/O),
and you have no plans to synchronize your
828mkII 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 828mkII Macintosh Software" (page 35). After
you install the 828mkII software, you'll open the
MOTU FireWire Audio Console and set the Clock
Source setting to Internal as shown below. For
details, see chapter 5, "MOTU FireWire Audio
Console (Mac OS X)" (page 41) or chapter 6,
"MOTU FireWire Control Panel (Mac OS 9)"
(page 47).
Figure 3-7: You can run the 828mkII under its own internal clock
when it has no digital audio connections and you are not synchroniz-
ing the 828mkII system to an external time reference such as SMPTE.
Situations that require synchronization
There are three general cases in which you will
need to resolve the 828mkII with other devices:
Synchronizing the 828mkII with other digital
■
audio devices so that their digital audio clocks are
phase-locked (as shown in Figure 3-8)
Slaving the 828mkII system to SMPTE time code
■
from a video deck, analog multi-track, etc.
Both of the above
■
22
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 828mkII's digital I/O features depends
almost entirely on proper synchronization. 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 3-8: 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 3-9: To keep the 828mkII 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 828mkII.
I N S T A L L I N G T H E 8 2 8 M K I I H A R D W A R E
Phase-locked
Master
Slave