Chapter 6: Additional Synchronization Information 59
Examples of Auto-Switch LTC/VITC
The SYNC HD will switch to LTC for posi-
tional reference during hi-speed searching and
cueing, for example, or whenever the tape speed is
too high to read VITC.
The SYNC HD will switch to VITC if LTC
stops or is unavailable. This will include, for ex-
ample, if a tape is paused or parked.
If both LTC and VITC are available, the
SYNC HD chooses which one to use based on the
speed of playback. The switch-over point is ap-
proximately 75% of full 1x playback speed. Above
75% playback speed, LTC is favored; below 75%
speed, VITC is favored.
If a dropout occurs, the SYNC HD waits until the
Freewheel duration has expired before attempting
to switch over to the opposite source. If neither
source is available, the SYNC HD will stop read-
ing timecode.
Digital Clock Signal Types
A reference clock signal is part of any digital re-
cording system. It is required because whenever
digital audio information is mixed together or
passed between devices, the playback samples
must be aligned with the recording samples. In
some cases (such as with AES/EBU or S/PDIF
digital interfaces), the clock signal is embedded in
the data stream itself. In other cases, such as SDIF,
the clock signal is carried as an entirely separate
signal from the digital audio sample data.
SYNC HD is able to resolve to AES/EBU and
Word Clock.
AES/EBU
Some professional digital audio products use
AES/EBU “null clock” (which is an AES/EBU
data stream that contains only clock information
only and no audio information) as a system clock
reference source. These systems rely upon a single
AES/EBU master clock source that is distributed
throughout a digital audio facility, in much the
same way that house synchronization is distributed
throughout a video facility. If you are connecting a
SYNC HD to such a system, you will want to use
the SYNC HD AES/EBU input as the clock refer-
ence connection, so that all system components are
referenced to the same time base. (Note that
AES/EBU does not support 176.4 kHz and
192 kHz sample rates.)
In some cases (such as using the SYNC HD as a
standalone clock resolver or timecode generator
without a digital audio workstation), you may wish
to use an audio DAT machine (or other similar de-
vice) as a source of AES/EBU null clock, and re-
solve your system to this reference source. In this
case, the audio sample data in the AES/EBU data
stream is stripped off, and only the clock informa-
tion is used.
Word Clock
Many professional digital audio products—includ-
ing open-reel multitrack tape recorders, digital
mixing consoles, and the Tascam DA-88 modular
digital multitrack—have Word Clock (1x sample
rate) connectors.
Word Clock allows the DA-88 (and other Word
Clock-compatible devices) to send or receive ex-
ternal clock information which controls the sample
rate, which in turn (where applicable) controls the
play and record speed.
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