RME Audio DMC-842, User Manual

Page: 36 / 56

36
User’s Guide DMC-842
© RME
16. Word Clock
16.1 Word Clock Input and Output
SteadyClock guarantees an excellent performance in all clock modes. Its highly efficient jitter
suppression refreshes and cleans up any clock signal, and provides it as reference clock at the
BNC output (see section 18.10).
Input
The DMC-842's word clock input is active when WCK is chosen in the clock section. The signal
at the BNC input can be Single, Double or Quad Speed, the DMC-842 automatically adapts to
it. As soon as a valid signal is detected, the WCK LED is constantly lit, otherwise it is flashing.
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). A push switch allows
to activate internal termination (75 Ohms). The switch is found on the back beside the BNC
socket. Use a small pencil or similar and carefully push the blue switch so that it snaps into its
lock position and the yellow LED lights up. Another push will release it again and de-activate the
termination.
Output
The DMC-842's word clock output is constantly active, providing the current sample frequency
as word clock signal. In master mode, the word clock will be fixed to 44.1 kHz or 48 kHz (DS x
2, QS x 4). In any other case the sample rate is identical to the one present at the currently
chosen clock input. When the current word clock source fails, the last valid sample rate will be
held automatically.
Selecting the option
Si in the Setup menu Co causes the word clock output 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 word clock signal received by the DMC-842 can be distributed to other devices by using the
word clock output. With this the usual T-adapter can be avoided, and the DMC-842 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 also with most critical word
clock signals.
Thanks to a low impedance, but short circuit proof output, the DMC-842 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.