User Manual

User's Guide Fireface 802 © RME
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8.8 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 Auto-
Sync mode, the system constantly scans the digital input for a valid signal. If any valid signal 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 difference to a
usual slave mode is that whenever the clock reference fails, the system will automatically 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) offers 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 syn-
chronous signal (Sync). The field Clock Mode shows the clock reference. See chapter 37.1.
Under WDM the Fireface will (has to) set
the sample rate. Therefore the error shown
to the right can occur. A stable signal with a
sample rate of 32 kHz is detected at the
ADAT input (Sync), but Windows audio had
been set to 44100 Hz before. The red
colour of the text label signals the error
condition, and prompts the user to set
32000 Hz manually as sample rate. Under
ASIO the audio software sets the sample
rate, so that such an error can not happen.
If the input sample rate is different then
there will be no Sync indication.
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.