Intel Fireface 800 - Manual (Page 39)

User's Guide Fireface 800 © RME
39
19.2 Clock Modes - Synchronization
In the digital world, all devices must be either ‘Master’ (clock source) or ‘Slave’ synchronized to
a master. Whenever several devices are linked within a system, there must always be a single
master clock. The Fireface'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 system constantly scans all digital inputs for a valid signal. If any valid
signal is found, the Fireface switches from the internal quartz (System Clock – Mode displays
'Master') to a clock extracted from the input signal (System Clock - Mode displays 'Slave'). 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 'Master' mode.
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 800, AutoSync may cause feedback in the digital carrier, so synchronization breaks
down. To remedy this, switch the Fireface’s clock mode over to 'Master'.
Remember that 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's ADAT optical and SPDIF inputs operate simultaneously. Because there is no
input selector however, the Fireface 800 has to be told which of the signals is the sync refer-
ence (a digital device can only be clocked from a single source). Via Pref. Sync Ref (preferred
synchronization reference) a preferred input can be defined. As long as the card sees a valid
signal there, this input will be designated as the sync source.
To cope with some situations which may arise in studio practice, defining a preferred sync ref-
erence is essential. One example: An ADAT recorder is connected to the ADAT input (ADAT
immediately becomes the AutoSync source) and a CD player is connected to the SPDIF 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 SPDIF.
If several digital devices are to be used simultaneously in a system, they not only have to oper-
ate with the same sample frequency but also be synchronous with each other. This is why digi-
tal systems always need a single device defined as ‘master’, which sends the same clock signal
to all the other (‘slave’) devices.
RME’s exclusive SyncCheck technology enables an easy to use check and display of the cur-
rent clock status. SyncCheck indicates whether there is a valid signal (Lock, No Lock) for each
input (Word Clock, ADAT1, ADAT2, SPDIF), or if there is a valid and synchronous signal
(Sync). The AutoSync Ref display shows the input and frequency of the current sync source
(see chapter 35.1).
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.