User’s Guide Hammerfall DSP MADI
© RME
11
8.3 Word Clock I/O
HDSP MADI includes SteadyClock, guaranteeing 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 19).
Input
The transformer-isolated word clock input is loacated on the Expansion Board. It is activated
via
Pref. Sync Ref
/
Wordclock
. As soon as a valid word clock signal is detected, the green
'Lock' LED beside the input jack lights up, and in the Settings dialog the field
AutoSync Ref
shows
Word
. Below the detected frequency of the word clock is shown.
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 between the BNC jacks. Use a
small pencil or similar and carefully push the blue switch so that it snaps into its lock position.
When termination is active the yellow TERM LED will be lit. Another push will release it again
and de-activate the termination.
Due to the HDSP MADI's outstanding clock control a synchronization of the output signal to the
input signal is not only possible at identical sample rates, but also at half, quarter, double and
quad sample rates.
Example 1: A playback or recording at 44.1 kHz can be synchronized via an external signal of
44.1 kHz, 88.2 kHz or 176.4 kHz.
Example 2: A playback or recording at 192 kHz can be synchronized via an external signal of
48 kHz, 96 kHz or 192 kHz.
The input accepts all those frequencies fully automatically.
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.
Output
The word clock output of the HDSP MADI is always active. It provides the current sample
frequency of the HDSP MADI as word clock signal. As long as the HDSP MADI operates in
'Master' mode (field 'Clock Mode'), the word clock will be fixed to the current sample rate. In
'AutoSync' mode the sample rate is identical to the one present at the currently chosen input
(Pref. Sync Ref). Without a valid input signal, the card will change between the inputs
automatically. As long as no valid input signal is found, the card will stay in Master mode. This
way, the card will always generate a valid output signal.
The word clock signal received by the HDSP MADI can be distributed to other devices by using
the word clock output. With this the usual T-adapter can be avoided, and the HDSP MADI
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 also with most critical
word clock signals.
