Specifications

Pro Tools Reference Guide540
of these references; for example, a black burst
generator provides only a clock reference. Some
peripherals, such as the Digidesign SYNC I/O,
can provide both.
Synchronizing Pro Tools
Pro Tools TDM systems require a clock refer-
ence, in addition to time code, to maintain cor-
rect synchronization once it has been achieved.
In addition, transfers (recording) between digi-
tal devices must be performed to a resolved clock
source.
You can resolve Pro Tools to an external clock
reference without locking it to a positional ref-
erence. For example, you can use any HD-series
audio interface to resolve the Pro Tools sample
clock to an incoming digital signal (S/PDIF, or
Word Clock, for example) without synchroniz-
ing Pro Tools to external time code.
In the following example, Pro Tools uses time
code for positional information, and a clock ref-
erence to maintain synchronization. Pro Tools
is slaved, using the SYNC I/O or USD, to a video
tape recorder, with Pro Tools and the VTR refer-
enced to the same house video reference source
(house sync).
Example: Pro Tools slaved, through a SYNC I/O or
USD, to a video tape recorder
In this example, house sync is provided to the
SYNC I/O, which provides the master Loop Sync
signal to the Pro Tools|HD system through an
HD-series audio interface. The SYNC I/O (or
USD) can also output 256x Slave Clock as re-
quired on Pro Tools|24 MIX and Pro Tools|24
systems. House sync is also provided to the VTR.
1 When you start the video tape, time code (LTC
or VITC) is read from the tape and routed to the
SYNC I/O or USD. The SYNC I/O (or USD) reads
the time code position and continuously for-
wards the positional reference information down
the SYNC I/O serial connection to the Pro Tools
card.
2 Pro Tools takes the first time code address it re-
ceives, and calculates the sample location in the
session that corresponds to the address. Though
you can work with Pro Tools using any standard
time code format, it calculates internally in sam-
ple numbers.
3 Assuming that the time code address corre-
sponds to a sample number that is within the
Pro Tools session, Pro Tools converts the time
code address to a sample number within the ses-
sion, and begins playing from that point. The
point from which playback starts is the trigger
point. The clock reference is used by Pro Tools
and the VTR to keep them running at the same
speed.
4 At this point, if the video tape is stopped, re-
wound, and started again, the process repeats,
based upon a newly calculated trigger point.
About Positional References
Time code is positional information in an ana-
log signal or a digital streaming signal that can
be recorded on magnetic video or audio tape.
Time code can be used as a positional reference,
to synchronize the playback and recording of
your Pro Tools system with another machine’s
time code signal, such as an analog multitrack
tape machine or a video tape recorder (VTR).