Sound Devices 788T - Manual (Page 71)

Synchronization and Timecode
Synchronization
A stable sample clock source is essential for high quality digital audio. Setups involving multiple
digital recording/playback devices often require that all devices are locked to a common clock refer-
ence to ensure they are synchronous, i.e. run at the same speed and in phase with one another.
The 788T can act as either a clock master, where it is the provider of word clock, or as clock slave,
where it locks its internal word clock to a received external master reference clock. Incorrect word
clock settings can result in poor audio quality, sample clock timing errors, and time code drift.
The 788T uses a rock-stable word clock and PLL circuitry to generate its internal clock frequency.
The 788T only uses its own word clock during playback, ignoring AES clock and video sync during
playback.
Clock Master
The 788T provides a master clock reference via its WORD OUT BNC connector or from any of its bal-
anced digital AES3 outputs. The difference between Word Out and AES is defi ned below.
Word Out
Word clock is purely a signal for sync purposes and contains no audio information. It is a square
wave signal with a frequency equal to the 788T’s internal sample rate. The 788T word clock output is
always active. Connect the 788T’s WORD OUT to the slave device’s WORD INPUT.
AES Digital Outputs
AES digital outputs provide both PCM audio data and word clock within the same stream. A com-
patible slave device can derive its reference clock from this stream at the same time as receiving the
digital audio. This is ideal for recording the digital outputs of the 788T to a slave device with AES/
AES3id inputs. No additional Word Clock connection is required.
Clock Slave
The 788T can accept external clock sources as its word clock reference. The 788T accepts word clock,
AES clock, and various video sync formats for clock. Audio devices often output word clock or AES
digital audio. Cameras and video decks often provide video sync (video black) which can be used
for word clock.
When the 788T is slaved to an external clock source, be certain that the signal is stable. Loss of sync
signal during recording can cause the 788T to revert back to its internal set sampling frequency caus-
ing audio glitches and/or sync issues later in post.
The 788T’s sync reference is selected in the Rec: Sync Reference Setup Menu. The options for sync
sources are:
• Internal
• Word Clock
• Video Sync
• Digital Inputs 1-2
• Digital Inputs 3-4 • Digital Inputs 5-6
• Digital Inputs 7-8
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Sync
hronization and T
imecode
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788T/788T-SSD User Guide and Technical Information
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