Sound Devices 744T - Manual (Page 25)

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Word Clock
A stable word clock source is essential for high quality digital audio. The 744T uses a rock-stable
time code crystal to generate its internal word clock frequencies. The 744T can clock external devices
from its word clock and accept and lock to external clock sources for recording.
The 744T disregards external clock, both AES and word clock, during playback.
Clock Master
When sending digital audio to several devices, one unit is designated as the word clock master and
the others as slaves. Generally, the device with the analog-to-digital converter is designated as the
word clock master.
The 744T can function as an A/D converter and can be used as the master word clock source. Slaved
digital devices derive their word clock timing from either their digital audio inputs, S/PDIF or AES/
EBU, or through their word clock input connection. As a word clock master the 744T generates word
clock whether or not audio is sent. If devices use separate word clock sources unpredictable behavior
will result.
Clock Slave
When connecting digital audio sources to the 744T inputs, the recorder will derive its clock signal
from the AES (S/PDIF) stream. It will slave to the external device. If, for example, you are using a
wireless receiver with a digital output, it may not have an external word clock input, and will be the
word clock master.
If digital audio is connected to the 744T from more than one digital device, you must word clock
theses sources together, otherwise variations between the sources will render their signals unusable.
If the 744T is slaved to external word clock, be certain that the source is stable. Loss of the word clock
signal during recording can cause the 744T to revert back to its internally set sampling frequency.
If this occurs, the portion of the file recorded after the loss of word clock may not play back at the
proper speed. For reliability, we recommend you set the 744T to the same sample frequency as the
word clock source. Loss of the word clock signal in this case will most likely cause a glitch in the file,
but the file may still be usable.
Multi-Unit Linking Via C. Link
The proprietary C. Link (control link) connection enables multiple 744T, 722, 702T, and 702 record-
ers to be connected for recordings requiring high track counts. C. Link also enables connection to the
CL-1 Remote Control and Keyboard Interface.
When linked, the 7-Series recorders have a master/slave relationship. The master recorder and the
slave unit will share sample accurate start and stop record times. Multiple units can be daisy-chained
together to record nearly unlimited tracks. The C. Link protocol links carries the following data:
• word clock
• time code information (744T, 702T only)
• RS-232 machine transport data