User`s guide

User's Guide Fireface 800 © RME
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15.2 Clock Modes - Synchronization
In the digital world, all devices must be either Master (clock source) or Slave (clock receiver).
Whenever several devices are linked 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 'Internal', all
other devices must be set to ‘Slave’.
The Fireface 800 utilizes a very user-friendly, intelligent clock control, called AutoSync. In
AutoSync mode, the system constantly scans all digital inputs for a valid signal. If any valid sig-
nal is found, the Fireface switches from the internal quartz (Clock Mode Master) to a clock ex-
tracted from the input signal (Clock Mode Slave/AutoSync). 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. Remedy: switch the Fireface clock mode over to Clock Mode Master.
The Fireface 800’s ADAT and SPDIF inputs operate simultaneously. Because there is no input
selector, 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). The Clock Source selection is used to define a pre-
ferred input for the automatic clock system, which stays active as long as a valid signal is found.
To cope with some situations which may arise in studio practice, defining a sync reference 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, the Clock Source should be set tem-
porarily to SPDIF.
RME’s exclusive SyncCheck technology (first implemented in the Hammerfall) enables an easy
to use check and display of the current clock status. Input Status indicates whether there is a
valid signal (Lock, No Lock) for each input (Word Clock, ADAT, SPDIF and LTC), or if there is a
valid and synchronous signal (Sync). In the field Clock Mode the clock reference is shown. See
chapter 30.1.
With SyncCheck, finally anyone can master this common source of error, previously one of the
most complex issues in the digital studio world.
15.3 Bandwidth Limit
This option allows to reduce the amount of bandwidth used on the FireWire bus. A typical ex-
ample is the use of the Fireface with a laptop. Only in rare cases both ADAT ports are needed,
in many cases even both stay unused. The option Analog+SPDIF will reduce the amount of
constantly (!) transferred data from around 5 MByte (10 in both directions) to only 2 MByte (4 in
both directions). The FireWire connection will be more stable, reliable and robust, leaving addi-
tional bandwidth for other devices. At the same time the CPU and system load is reduced, as
less channels have to be processed and to be transferred. More details are found in chapter
30.4.
Available Settings
All channels (default) activates all 28 input and output channels
Analog + SPDIF + ADAT1 disables channels 21–28 (ADAT2)
Analog + SPDIF activates all 10 analog channels plus SPDIF
Analog 1-8 activates only the first eight analog channels