User’s Guide HDSP System Digiface
© RME
13
If several digital devices are to be used simultaneously in a system, they not only have to
operate with the same sample frequency but also be synchronous with each other. This is why
digital systems always need a single device defined as ‘master’, which sends the same clock
signal to all the other (‘slave’) devices. RME’s exclusive
SyncCheck
technology (first
implemented in the Hammerfall) enables an easy to use check and display of the current clock
status. The ‘SyncCheck’ field indicates whether no signal (‘No Lock’), a valid signal (‘Lock’) or a
valid
and
synchronous signal (‘Sync’) is present at each of the three ADAT optical inputs. The
‘AutoSync Ref’ display shows the current sync source’s input and frequency.
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.
An example to illustrate this: The ADAT1 and ADAT2 inputs are receiving signals from a digital
mixing desk that has been set to clock mode 'Internal' or 'Master'. An ADAT recorder is
connected to the ADAT3 input. The Hammerfall DSP is set to AutoSync mode. As expected,
SyncCheck shows that the ADAT1 and ADAT2 inputs are in sync (as they are driven by the
same clock from the mixing desk), but shows ‘Lock’ instead of 'Sync' for the ADAT3 input.
Because the ADAT
recorder is not
receiving any signals
from HDSP or from
the mixer, it will
generate its own
clock at a rate which
is (almost) the same
as the sample
frequency of the
mixing desk - but not
identical. Remedy:
To drive the ADAT
recorder from its
digital input, set it to
slave mode (DIG),
and connect the input
to the HDSP’s ADAT3 output. The Hammerfall DSP is already in sync with the mixing desk, so
it will send an identical (synchronous) signal to ADAT3 out. The ADAT recorder will lock onto
this, its output will also be in sync. The signal from the ADAT recorder is now fully in sync with
the signals from the mixing desk.
Thanks to the its AutoSync technique and a lightning fast PLL, the HDSP is not only capable of
handling standard frequencies, but also any sample rate between 25 and 105 kHz. The input
selected in 'Pref Sync Ref' serves as synchronization source. If word clock is selected as input,
this will serve as the synchronization source, allowing any sample frequency between 25 kHz
and 56 kHz in varispeed operation.
The current sample frequency at the SPDIF input (displayed in the ‘SPDIF In’ field) is useful for
troubleshooting and checking the configuration of all connected digital devices. If an input
without a valid signal (or a faulty one) is selected, ‘No Lock’ will appear. In varispeed mode, or
if the sample frequency is way out of tune, ‘Lock’ is displayed. The Sync state of the SPDIF
signal is shown by a blinking (locked) or constantly lit (Sync) input LED on the front of the
Digiface.
At 88.2 or 96 kHz: If one of the ADAT inputs has been selected in ‘Pref Sync Ref’, the sample
frequency shown in the ‘SPDIF In’ field differs from the one shown in ‘AutoSync Ref’. The card
automatically switches to its Sample Split mode here, because ADAT optical inputs and outputs
are only specified up to 48 kHz. Data from/to a single input/output is spread over two channels,
the internal frequency stays at 44.1 or 48 kHz. In such cases, the ADAT sample frequency is
only half the SPDIF frequency.
