Clock Modes - Synchronization - RME Audio Project Hammerfall DIGI9652 User Manual

9.2 Clock Modes - Synchronization

In the digital world, all devices are either the 'Master' (clock source) or a 'Slave' synchronized
to the master. Whenever several devices are linked within a system, there must always be a
single master clock. The Hammerfall's intelligent clock control is very user-friendly. Selecting
'AutoSync' will activate this mode.
In AutoSync mode, the Hammerfall constantly scans all digital inputs for a valid signal. If this
signal corresponds with the current playback sample rate, the card switches from the internal
quartz (Sync Ref displays 'Internal') to a clock generated from the input signal (Sync Ref
displays 'SPDIF' or 'ADATx'). This allows on-the-fly recording, even during playback, without
having to synchronize the card to the input signal first. It also allows immediate playback at any
sample rate without having to reconfigure the card.
AutoSync guarantees that normal record and record-while-play will always work correctly. In
certain cases however, e.g. when the inputs and outputs of a DAT machine are connected
directly to the Hammerfall, AutoSync causes feedback in the digital carrier, so synchronization
breaks down. To remedy this, switch the card's clock mode over to 'Master'.
Remember that a digital system can only have one master! If the Hammerfall's clock mode
is set to 'Master', all other devices must be set to 'Slave'.
All the ADAT optical inputs in the
DIGI9652 as well as the SPDIF
input will work
Because there is no input selector
however, the DIGI9652 has to
be told which of the signals is the
sync reference (a digital device can
only be clocked from a single
source). This is why the card has
been equipped with automatic clock
source selection, which adopts the
first available input with a valid digital
signal as the clock reference input.
The input currently used as sync
reference is shown in the 'Sync Ref'
status field, together with the current
sample frequency.
Via 'Pref Sync Ref'
synchronization reference)
preferred input can be defined. As
long as the card 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 card
automatically switches clock mode to 'Master'.
To cope with some situations which may arise in studio practice, setting 'Pref Sync Ref' is
essential. One example: An ADAT recorder is connected to the ADAT1 input (ADAT1
immediately becomes the sync source) and a CD player is connected to the S/PDIF input. Try
recording a few samples from the CD and you will be disappointed. Few CD players can be
synchronized. The samples will inevitably be corrupted, because the signal from the CD player
is read with the (wrong) clock from the ADAT i.e. out of sync. In this case, 'Pref Sync Ref'
should be temporarily set to SPDIF.
simultaneously.
(preferred
a
User's Guide DIGI9652 © RME
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