User's Guide HDSP AES-32 - RME

23. Word Clock
23.1 Word Clock Input and Output
SteadyClock guarantees an excellent performance in all clock modes. Based on the highly efficient
jitter suppression, the HDSP AES-32 refreshes and cleans up any clock signal, and provides
it as reference clock at the BNC output (see chapter 30.6).
Input
The HDSP AES-32's transformer isolated 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 HDSP AES-32 automatically adapts to it. As soon as a valid signal is
detected, the Settings dialog shows either Lock or Sync (see chapter 30.2).
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 are 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 word clock input is shipped as high impedance type (not terminated). An internal jumper
besides the BNC socket allows to activate proper termination (75 Ohm).
Output
The word clock output of the HDSP AES-32 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 or the DDS dialog. 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 HDSP AES-32 switches to Master mode and adjusts itself to the next, best matching frequency
(44.1 kHz, 48 kHz etc.).
Selecting the options Double Wire or Quad Wire in the Settings dialog the output frequency is
changed to always be the same as the sample rate on the AES outputs. At 192 kHz operation
with activated Double Wire operation the AES-32 will generate a word clock signal of 96 kHz.
The received word clock signal can be distributed to other devices by using the word clock output.
With this the usual T-adapter can be avoided, and the HDSP AES-32 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 Adaptation
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 HDSP AES-32 delivers 4 Vpp to
75 Ohms. For wrong termination with 2 x 75 Ohms (37.5 Ohms), there are still 3.3 Vpp fed into
the network.
User's Guide HDSP AES-32 © RME 41