RME Audio Fireface 802, User Manual

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User's Guide Fireface 802 © RME 33
14.2 Clock Modes - Synchronization
In the digital world, all devices must be either Master (clock source) or Slave (clock receiver).
Whenever several devices are linked within a system, there must always be a single master
clock.
A digital system can only have one master! If the Fireface’s clock mode is set to 'Master', all
other devices must be set to ‘Slave’.
The Fireface 802 utilizes a very user-friendly, intelligent clock control, called
AutoSync
. In
AutoSync mode, the system constantly scans the digital input for a valid signal. If any valid sig-
nal is found, the Fireface switches from the internal quartz (
Clock Mode
– Current Internal) to a
clock extracted from the input signal (
Clock Mode
– Current ADAT, AES or Word). The differ-
ence to a usual slave mode is that whenever the clock reference fails, the system will automati-
cally use its internal clock and operate in clock mode Master.
AutoSync guarantees that 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 Fireface 802, AutoSync may cause feedback in the digital carrier, so synchronization breaks
down. To solve this problem switch the Fireface clock mode to Master (Clock Source – Inter-
nal).
The Fireface's ADAT optical and AES inputs operate simultaneously. Because there is no input
selector however, the unit has to be told which one of the signals is the sync reference (a digital
device can only be clocked from a
single
source). By selecting a Clock Source a preferred input
is defined. As long as the unit sees a valid signal there, this input will be designated as the sync
source.
In some situations changing the clock mode can not
be avoided. Example: An ADAT recorder is
connected to the ADAT input (ADAT immediately
becomes the AutoSync source) and a CD player is
connected to the AES 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 clock from the ADAT.
In this case the Clock Source should be temporarily
set to
AES
.
RME’s exclusive
SyncCheck
technology (first implemented in the Hammerfall) enables an easy
to use check and display of the current clock status.
SyncCheck
indicates whether there is a
valid signal (Lock, No Lock) for each input (Word Clock, ADAT, AES), or if there is a valid
and
synchronous signal (Sync). In the field
Clock Mode
the clock reference is shown. See chapter
38.1.
In practice, SyncCheck provides the user with an easy way of checking whether all digital de-
vices connected to the system are properly configured. With SyncCheck, finally anyone can
master this common source of error, previously one of the most complex issues in the digital
studio world.