User’s Guide Hammerfall DSP MADI
© RME
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11.2 Cables and Termination
Word clock signals are usually distributed in the form of a network, split with BNC T-adapters
and terminated with resistors. We recommend using off-the-shelf BNC cables to connect all
devices, as this type of cable is used for most computer networks. You will find all the
necessary components (T-adapters, terminators, cables) in most electronics and/or computer
stores.
To avoid voltage loss and reflections, both the cable itself and the terminating resistor should
have an impedance of 75 Ohm. If the voltage is too low, synchronization will fail. High
frequency reflection effects can cause both jitter and sync failure.
Ideally all outputs of word clock delivering devices are designed with very low impedance, but
all word clock inputs with high impedance, in order to not weaken the signal on the chain. But
there are also negative examples, when the 75 Ohms are built into the device and cannot be
switched off. In this case the network load is often 2 x 75 Ohms, and the user is forced to buy a
special word clock distributor. Note that such a device is generally recommended for larger
studios. Also, 75 Ohm cable is almost impossible to find these days. 50 Ohm cable is standard
- this will also work as long as the termination resistors are 75 Ohm.
The HDSP MADI’s word clock input can be high-impedance or terminated internally, ensuring
maximum flexibility. If termination is necessary (e.g. because HDSP MADI is the last device in
the chain), activate the switch TERM between the BNC jacks on the Expansion Board so that
the yellow TERM LED lights up.
In case the HDSP MADI resides within a chain of devices receiving word clock, plug a T-
adapter into the BNC input jack, and the cable supplying the word clock signal to one end of the
adapter, but connect the free end to the next device in the chain via a further BNC cable. The
last device in the chain should be terminated using another T-adapter and a terminator plug as
described in the previous paragraph. Some devices (like the HDSP MADI) have switchable 75
Ohm resistors, which saves both T-adapter and terminator.
Due to the outstanding SteadyClock technology of the HDSP MADI, we recommend not to
pass the input signal via T-adapter, but to use the HDSP MADI's word clock output instead.
Thanks to SteadyClock, the input signal will both be freed from jitter and - in case of loss or
drop out – be held at the last valid frequency.
11.3 General Operation
The green ‘Lock’ LED at the Expansion Board will light up as soon as a word clock signal is
detected. Selecting ‘Word Clock’ in the ‘Clock Mode’ field will switch clock control over to the
word clock signal. As soon as there is a valid signal at the BNC jack, 'AutoSync Ref' will display
'Word'. This message has the same meaning as the green ‘Lock’ LED, but appears on the
monitor, i.e. the user can check immediately whether a valid word clock signal is present and is
currently being used.
12. Using more than one Hammerfall DSP
The current drivers support up to three Hammerfall DSP MADI. All cards must be in sync, i.e.
have to receive valid sync information (either via word clock or by using AutoSync and feeding
synchronized signals).
