OPERATION
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PreSonus 2007
3.2.3 Master/Slave and Multiple Digital Devices
Whether you are using the ADAT output of the DigiMax D8 to generate word clock or you are using the BNC
word clock output of another device as your word clock generator, it is necessary to denote one device as the
“master” word clock device to which all other digital devices are synced or “slaved”. The DigiMax D8
should perform equally well as a master or a slave in most cases, although syncing it to a lesser quality clock
source may affect performance. Not all word clock generators are created equal. The general approach is to
determine which device has the best clock from which to reference and to designate that device as the word
clock master. This is done with careful listening and A/B testing.
Once you’ve determined which device is to be your Master clock, you will need to sync the remaining digital
devices either through series or parallel distribution or some combination thereof. Of course, if your digital
device chain only consists of one master and one slave, syncing the two is as simple as connecting a 75
Ω
BNC word clock cable from the output of your master device to the input of the device you are slaving. When
working with multiple slaved devices, the job gets a bit more complicated. Series distribution requires that
your digital devices have both a BNC word clock input and a BNC word clock output. Parallel distribution
uses a BNC “T-connector” attached to the BNC word clock input of each slaved device. This allows the word
clock signal to be sent to that device and then sent on to another. A BNC word clock output on the slaved
devices is not used or required for parallel word clock distribution. If the last device in the chain does not
have a word clock terminate switch, it will require a BNC terminator plug to be attached to the other side of
the “T-connector”. This helps to stabilize the word clock sync as well as to keep the word clock signal clean.
Both word clock terminator plugs and BNC T-connectors can be purchased at most recording supply
retailers. For a complete description of parallel word clock distribution as it relates directly to the DigiMax
D8, see section 3.3.2: “Using multiple DigiMax D8s with the FireStudio LightPipe”.
A third option for syncing your digital devices is to purchase a high quality dedicated word clock generator;
and many engineers believe that using dedicated word clock generators, rather than utilizing series or parallel
word clock distribution, enhances the performance of their digital audio devices. A dedicated word clock
generator and distribution amplifier exists for one purpose and one purpose only: to be a Master clock. Word
clock generators usually have one BNC word clock input and multiple BNC word clock outputs (sometimes
TDIF, S/PDIF, or ADAT outputs as well to make them compatible with as many types of digital devices as
possible). Without a dedicated word clock generator, it is necessary to split the word clock signal generated
by the Master device by daisy chaining the slaved devices as described above. Because of this, many engineers
feel that the resulting digital audio signals will be of a higher quality when a dedicated word clock generator
is used; because all the digital devices are receiving the same digital pulse from the same source at exactly
the same time.
Whichever approach one uses, it is always advisable to use good quality BNC cables that are not excessively
longer than necessary for the job at hand and, as with any audio cabling, it is always good to keep word clock
cables separate from AC cable lines or other possible sources of interference.
3.2.4 Setting Up Your DAW Software
If you are planning on using your DigiMax D8 as the master clock for your digital device system, you will
need to refer to the instructions on external synchronization provided by the manufacturer of both your audio
interface and your DAW recording application. Setting external sync usually must be done in both the audio
interface’s control panel software application (if it has one)
and your recording application. As a general
rule of thumb, this will be necessary when you are using any device other than your audio interface as the
master clock for your system.
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