Intel Fireface 800 manual Word Clock Input and Output

30. Word Clock

30.1 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 37.9).

Input

The Fireface's transformer isolated word clock input is active when Pref. Sync Ref in the Set- tings 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 Fireface 800 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 37.1).

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 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 Fireface's word clock input is shipped as high imped- ance type (not terminated). A push switch allows to acti- vate 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 of the Fireface is constantly active, providing the current sample fre- quency 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 pre- sent at the currently chosen clock input. When the current clock signal fails, the Fireface 800 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 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 800 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.

60 User's Guide Fireface 800 © RME