DigiDesign SYNC HD, Manual

Page: 79 / 103

Appendix A: Additional Synchronization Information 73
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
The SYNC HD can resolve to an external Pilot
Tone signal for synchronizing to (or transferring
audio from) certain types of open-reel audio
tape recorders.
In general, Pilot Tone is a sine wave reference
signal running at the “line frequency” or “mains
frequency,” meaning the same frequency trans-
mitted by the AC line voltage from the local
power utility.
Pilot Tone is used on location film shoots to es-
tablish a common synchronization reference be-
tween a film or video camera with a portable
1/4-inch analog ATR (such as those made by Na-
gra or Stellavox). On location, Pilot Tone is de-
rived by clock referencing the camera to the lo-
cal AC line frequency (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 inex-
pensive and readily available “house sync” for
location production. Increasingly, it’s being re-
placed by time code, since new-generation film
cameras as well as many portable DAT recorders
are time code-capable.
Please note that Pilot Tone contains no posi-
tional information; it is simply a clock reference.
Most 1/4-inch machines have a center track for
time code or pilot.