Avid Technology Pro Tools SYNC HD, Manual

Page: 67 / 166

Chapter 6: Additional Synchronization Information 61
This explains how the SYNC HD can use a Bi-
Phase/Tach signal to deduce the direction, and
how it also uses the signal as a clock reference—as
long as the SYNC HD is told the starting frame of
the first clock signal.
Pilot Tone
SYNC HD can resolve to an external Pilot Tone
signal for synchronizing to (or transferring audio
from) certain types of open-reel audio tape record-
ers.
In general, Pilot Tone is a sine wave reference sig-
nal running at the “line frequency” or “mains fre-
quency,” meaning the same frequency transmitted
by the AC line voltage from the local power utility.
Pilot Tone is used on location film shoots to estab-
lish a common synchronization reference between
a film or video camera with a portable 1/4-inch an-
alog ATR (such as those made by Nagra or Stella-
vox). On location, Pilot Tone is derived by clock
referencing the camera to the local AC line fre-
quency (which is 60 Hz or 50 Hz depending on the
country of origin), and this same frequency is then
used to clock-reference the ATR. The result is that
both the camera and the ATR will run at the same
speed.
You can think of Pilot Tone as a kind of inexpen-
sive and readily available “house sync” for loca-
tion production. Increasingly, it’s being replaced
by timecode, since new-generation film cameras as
well as many portable DAT recorders are time-
code-capable.
Please note that Pilot Tone contains no positional
information; it is simply a clock reference. Most
1/4-inch machines have a center track for timecode
or pilot.