13
Operation Guide
Oper
a
tion
Guide
Sync Card and Cables - Word Clock and Digital Synchronization
The Sync Card provides ports to synchronize the MDR24/96’s sample clock and
time/transport position to other equipment. The functions of the jacks and switch,
from top to bottom are:
• SMPTE Input / Output – This 1/4" TRS jack serves as an input when
slaved to incoming SMPTE time code, and as an output when generating
SMPTE time code to synchronize other devices with the MDR24/96.
•
Termination Switch – This pushbutton switch selects the termination
impedance of the Word Clock / Video Input jack. When the switch is out,
the impedance is 3.3k
Ω
(bridging); when in, the impedance is 75
Ω
(terminated).
• Word Clock / Video Input – This BNC jack receives either word clock,
composite video, or video blackburst as determined by the MDR24/96
Sample Clock setting. Use this input when the MDR24/96 is operating as a
word clock slave.
• Word Clock Output – This BNC jack transmits word clock to other devices
in the system when the MDR24/96 is configured as the clock master.
Whenever digital audio connections are made between devices, the sample clock
of every device must run at exactly the same rate. This is usually accomplished by
selecting one device as the “master” clock source and distributing its word clock
signal to all the “slave” devices in the system. The master is configured to run
from its internal clock, and the slaves from external word clock. Some digital
interfaces are self-clocking (such as the AES input on many DAT machines) and
do not require a separate work clock connection. Others simply cannot be
configured as slaves. The master/slave designation must be made correctly for
each device to avoid the clicks and pops associated with asynchronous clocks.
Whenever time code (positional) synchronization is used, all the devices in a
system, both analog and digital, must be synchronized to a common timing (speed)
reference. This is often achieved by distributing video from a master video sync
generator (sometimes called “house sync”) to all the slave devices in the system
when word clock cannot otherwise be used. The MDR24/96, like many other
digital devices, can synchronize its sample clock to a video signal. However, video
does not provide enough timing precision to properly synchronize devices whose
digital audio paths are interconnected; word clock must be used instead.
Generally it doesn’t matter which device in a system serves as the word clock
master, except when synchronizing to time code or video. For example, if your
MDR24/96 Inputs and Outputs are connected to the Tape Inputs and Outputs of a
Mackie Digital 8•Bus console using TDIF, either the MDR24/96 or D8B can be the
word clock master. However, if you later synchronize the MDR24/96 to time code
from a VTR, you must lock the VTR and MDR24/96 to a master video sync source
and lock the D8B (which can’t sync to video) to word clock from the MDR24/96.
In this case the MDR24/96 becomes both a video slave and a word clock master.
For more detailed information on setups involving video and time code
synchronization, see the HDR24/96 Technical Reference manual, available to
download at www.mackie.com.
SYNC
NOT
WARNING
SMPTE Input/
Output
Termination
Switch
Word Clock/
Video Input
Word Clock
Output
Note:
Note:
Note:
Note:
Note: For audio-for-video applications, the MDR24/96 can lock its word clock to
a video signal. In this configuration, there must be only one word clock depen-
dent device (The MDR24/96) locked to the video source. The MDR24/96 then
becomes the word clock master for the other digital devices in the system (for
example, a digital mixing console). Do not attempt to lock multiple digital de-
vices to the video signal, or you’ll get clicks.
