User Manual
38
User's Guide Fireface UC © RME
Output Format
Word
The word clock output signal usually equals the current sample rate. Selecting Single Speed
causes the output signal to always stay within the range of 32 kHz to 48 kHz. So at 96 kHz and
192 kHz sample rate, the output word clock is 48 kHz.
Optical
The optical TOSLINK output can operate as ADAT or SPDIF output. The Channel Status is
fixed to Consumer state.
Note
: The optical input detects the incoming format automatically.
SPDIF coax.
The coaxial SPDIF output can have the Channel Status Consumer or Professional. For further
details please refer to chapter 27.2.
19.2 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. The Fireface UC 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
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 etc). 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 UC, AutoSync may cause feedback in the digital carrier, so synchronization breaks
down. To remedy this, switch the Fireface’s clock mode over to Master (Clock Source – Inter-
nal).
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 UC's ADAT and SPDIF inputs operate simultaneously. Because there is no input
selector, the Fireface UC 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 preferred input for the automatic clock system. This input will stay 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.