MDR 24/96

SMPTE Input/ Output

Termination

Switch

Word Clock/

Video Input

Word Clock

Output

SYNC

Sync Card & 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 3.3kΩ (bridging); when in, the impedance is 75Ω (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 correctly made 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 Technical Reference manual.

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 dependent 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 devices to the video signal, or you’ll get clicks.

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MDR 24/96