Clock Modes - Synchronization - RME Audio Fireface UCX User Manual

9.8 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 UCX 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, SPDIF 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 UCX, 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 – Internal).
The Fireface's ADAT optical and SPDIF input 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, it will be used 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 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 cor-
rupted, 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 SPDIF.
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, SPDIF), or if there is a valid and
synchronous signal (Sync). In the field Clock Mode the clock reference is shown. See chapter
32.1.
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 color
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.
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User's Guide Fireface UCX © RME