RME Audio Hammerfall HDSPe MADI FX, Руководство пользователя

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User's Guide HDSPe MADI FX © RME 79
30.2 Lock and SyncCheck
Digital signals consist of a carrier and the data. If a digital signal is applied to an input, the re-
ceiver has to synchronize to the carrier clock in order to read the data correctly. To achieve this,
the receiver uses a PLL (Phase Locked Loop). As soon as the receiver meets the exact fre-
quency of the incoming signal, it is locked. This
Lock
state remains even with small changes of
the frequency, because the PLL tracks the receiver's frequency.
If a MADI signal is applied to the HDSPe MADI FX, the unit indicates LOCK, i. e. a valid input
signal. This information is presented in the HDSPe MADI FX Settings dialog. In the status dis-
play
SyncCheck,
the state of all clocks is decoded and shown as simple text (No Lock, Lock,
Sync).
Unfortunately, LOCK does not necessarily mean that the received signal is correct with respect
to the clock which processes the read out of the embedded data. Example: The HDSPe MADI
FX is set to 44.1 kHz internally (clock mode Master), and a mixing desk with MADI output is
connected to the card's MADI input. The status display will show LOCK immediately, but usually
the mixing desk's sample rate is generated internally (it is Master too), and thus slightly higher
or lower than the HDSPe MADI FX internal sample rate. Result: When reading out the data,
there will frequently be read errors that cause clicks and drop outs.
Also when using multiple clock signals, a simple LOCK is not sufficient. The above described
problem can be solved elegantly by setting the HDSPe MADI FX from Master to AutoSync (its
internal clock will then be the clock delivered by the mixing desk). But in case the card is
clocked to word clock, this signal can also be un-synchronous, and there will again be a slight
difference in the sample rate, and therefore clicks and drop outs.
In order to display those problems, the HDSPe MADI FX includes
SyncCheck
. It checks all
clocks used for
synchronicity
. If they are not synchronous to each other, the status display will
show LOCK. If they are synchronous to each other (i.e. absolutely identical), the status display
will change to SYNC. In the example above it would have been obvious immediately that the
entry LOCK is shown in
SyncCheck
instead of SYNC, right after connecting the mixing desk.
With external synchronisation via word clock, both entries Word Clock and MADI must display
SYNC.
In practice, SyncCheck allows for a quick overview of the correct configuration of all digital de-
vices. So one of the most difficult and error-prone topics of the digital studio world finally be-
comes easy to handle.