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9.2 Clock Modes - Synchronization
In the digital world, all devices are either the 'Master' (clock source) or a 'Slave' synchronized
to the master. Whenever several devices are linked within a system, there must always be a
single master clock. The DIGI9652's intelligent clock control is very user-friendly, being
able to switch between clock modes automatically. Selecting 'AutoSync' will activate this mode.
In AutoSync mode, the DIGI9652 constantly scans all digital inputs for a valid signal. If
this signal corresponds with the current playback sample rate, the card switches from the
internal quartz (Sync Ref displays 'Internal') to a clock generated from the input signal (Sync
Ref displays 'S/PDIF' or 'ADATx'). This allows on-the-fly recording, even during playback,
without having to synchronize the card to the input signal first. It also allows immediate
playback at any sample rate without having to reconfigure the card.
AutoSync guarantees that normal record and record-while-play will always work correctly. In
certain cases however, e.g. when the inputs and outputs of a DAT machine are connected
directly to the DIGI9652, AutoSync causes feedback in the digital carrier, so
synchronization breaks down. To remedy this, switch the DIGI9652 clock mode over to
'Master'.
Remember that a digital system can only have one master! If the DIGI9652's clock mode is
set to 'Master', all other devices must be set to 'Slave'.
All the ADAT optical inputs in the
DIGI9652
as well as the
S/PDIF
input
simultaneously. Because there is
no input selector however, the
DIGI9652 has to be told which
of the signals is the sync reference
(a digital device can only be
clocked from a single source). This
is why the card has been equipped
with
automatic
clock
selection, which adopts the first
available input with a valid digital
signal as the clock reference input.
The input currently used as sync
reference is shown in the 'Sync Ref'
status
field,
together
current sample frequency.
Via 'Pref Sync Ref' (preferred
synchronization
reference)
preferred input can be defined. As
long as the card sees a valid signal there, this input will be designated as the sync source,
otherwise the other inputs will be scanned in turn. If none of the inputs are receiving a valid
signal, the card automatically switches clock mode to 'Master'.
To cope with some situations which may arise in studio practice, setting 'Pref Sync Ref' is
essential. One example: An ADAT recorder is connected to the ADAT1 input (ADAT1
immediately becomes the sync source) and a CD player is connected to the S/PDIF input. Try
recording a few samples from the CD and you will be disappointed. Few CD players can be
synchronized. The samples will inevitably be corrupted, because the signal from the CD player
is read with the (wrong) clock from the ADAT i.e. out of sync. In this case, 'Pref Sync Ref'
should be temporarily set to S/PDIF.
will
work
source
with
the
a
DIGI9652 User's Guide © RME
10
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