Clock Modes - Synchronization - RME Audio Digiface AES User Manual

8.7 Clock Modes - Synchronization

In the digital world, all devices must be either Master (clock source) or Slave (clock receiver).
Whenever several devices are linked within a system, there must always be a single master clock.
! A digital system can only have one master! If the Digiface's clock mode is set to 'Master', all
other devices must be set to 'Slave'.
The Digiface AES utilizes a very user-friendly, intelligent clock control, called AutoSync. In Auto-
Sync mode, the system constantly scans the digital input for a valid signal. If any valid signal is
found, the Digiface switches from the internal quartz (Clock Source – Current Internal) to a clock
extracted from the input signal (Clock Source – Current AES, SPDIF, ADAT). The difference to a
usual slave mode is that whenever the clock reference fails, the system will automatically use its
internal clock and operate in clock mode Master.
AutoSync guarantees that record and record-while-play will always work correctly. In certain
cases however, AutoSync may cause feedback in the digital carrier, so synchronization breaks
down. To remedy this, switch the Digiface clock mode to 'Internal'.
RME's exclusive SyncCheck technology enables an easy to use check and display of the current
clock status. SyncCheck indicates whether there is a valid signal (Lock, No Lock) for each input
(AES, SPDIF coaxial, ADAT/SPDIF optical), or if there is a valid and synchronous signal (Sync).
See chapter 38.1.
Via Clock Source a preferred input can be defined. As long as the Digiface sees a valid signal
there, this input will be designated as the sync source, otherwise the other inputs will be scanned
in turn. If none of the inputs are receiving a valid signal, the Digiface automatically switches clock
mode to 'Internal'.
Under WDM the Digiface will (has to) set the
sample rate. Therefore the error shown to the
right can occur. An AES, SPDIF or ADAT
signal with a sample rate of 48 kHz is used as
sync source, but Windows audio had been set
to 44100 Hz before.
The red color of the text label signals the error condition, and prompts the user to set 48000 Hz
manually as sample rate.
Under ASIO the audio software sets the sample rate, so that such an error will usually not happen
– but it can too. In slave mode the external sample rate has priority. Feeding 44.1 kHz will prevent
the ASIO software to set 48 kHz – obviously, as the only way to do so would be to enter a different
clock mode (Master/Internal).
In practice, SyncCheck provides the user with an easy way of checking whether all digital devices
connected to the system are properly configured. With SyncCheck, finally anyone can master this
common source of error, previously one of the most complex issues in the digital studio world.
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User's Guide Digiface AES © RME