14
User's Guide ADI-4 DD © RME
8.3 Word Clock Input and Output
Input
The ADI-4 DD's word clock input is active when SYNC WC is chosen. The signal at the BNC
input can be single or double speed, the ADI-4 DD automatically adapts to it. As soon as a valid
signal is detected, the WC LED is constantly lit, otherwise it is flashing slowly.
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 ADI-4 DD's word clock input is shipped
as high impedance type (not terminated). A
push switch allows to activate internal
termination (75 Ohms). The switch is found
on the back beside the word clock input
socket. Use a small pencil or similar and
carefully push the blue switch so that it snaps
into its lock position. The yellow LED will be
lit when termination is active. Another push
will release it again and de-activate the
termination.
Output
The word clock output is constantly active and basically delivers the sample rate of the left part
as word clock signal. Thanks to SteadyClock, the output word clock is independent from the
quality of the received clock and almost jitter-free (< 1 ns). The unit can even be used as clock
refresher and regenerator. In case the current word clock source fails, the last valid sample rate
will be held automatically.
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 ADI-4 DD operates as
Signal Re-
fresher
. 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 also with most critical word
clock signals.
The word clock output usually operates in Single Speed mode, as do all ADAT ports.
In S/MUX or Double Speed mode, the word clock output will therefore be no higher than 48
kHz. In case a Double Speed word clock is needed (88.2 or 96 kHz), press the key DS MODE
until the LED WCK is lit.
Thanks to a low impedance, but short circuit proof output, the ADI-4 DD 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.
