Word Clock; Word Clock Input And Output - RME Audio Fireface UCX User Manual

24. Word Clock

24.1 Word Clock Input and Output

SteadyClock guarantees an excellent performance in all clock modes. Based on the highly effi-
cient jitter suppression, the Fireface refreshes and cleans up any clock signal, and provides it
as reference clock at the BNC output (see section 32.8).
Input
The Fireface's word clock input is active when Pref. Sync Ref in the Settings dialog has been
switched to Word Clock, the clock mode AutoSync has been activated, and a valid word clock
signal is present. The signal at the BNC input can be Single, Double or Quad Speed, the Fire-
face UCX automatically adapts to it. As soon as a valid signal is detected, the WC LED is lit,
and the Settings dialog shows either Lock or Sync (see chapter 32.1).
Thanks to RME's Signal Adaptation Circuit, the word clock input still works correctly even with
heavily mis-shaped, dc-prone, too small or overshoot-prone signals. Thanks to automatic signal
centering, 300 mV (0.3V) input level is sufficient in principle. An additional hysteresis reduces
sensitivity to 1.0 V, so that over- and undershoots and high frequency disturbances don't cause
a wrong trigger.
The Fireface UCX word clock input can be high impedance (not terminated) or internally termi-
nated (75 Ohms). The state is comfortably selected within the Settings dialog. To terminate the
input check the option Termination under Options / Word In.
Output
The word clock output of the Fireface is constantly active,
providing the current sample frequency as word clock signal.
As a result, in Master mode the provided word clock is defined
by the currently used software. In Slave mode the provided
frequency is identical to the one present at the currently
chosen clock input. When the current clock signal fails, the
Fireface UCX switches to Master mode and adjusts itself to
the next, best matching frequency (44.1 kHz, 48 kHz etc.).
Selecting Single Speed in the Settings dialog (Output Format
Word) 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.
The received word clock signal can be distributed to other devices by using the word clock out-
put. With this the usual T-adapter can be avoided, and the Fireface UCX operates as Signal
Refresher. This kind of operation is highly recommended, because
•
input and output are phase-locked and in phase (0°) to each other
•
SteadyClock removes nearly all jitter from the input signal
•
the exceptional input (1 Vpp sensitivity instead of the usual 2.5 Vpp, dc cut, Signal Adapta-
tion Circuit) plus SteadyClock guarantee a secure function even with highly critical word
clock signals
Thanks to a low impedance, but short circuit proof output, the Fireface delivers 4 Vpp to 75
Ohms. For wrong termination with 2 x 75 Ohms (37.5 Ohms), there are still 3.3 Vpp at the out-
put.
User's Guide Fireface UCX © RME
43