Specifications

Appendix A: Additional Synchronization Information 71
This explains how SYNC I/O 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 SYNC I/O is told the starting frame of
the first clock signal.
Pilot Tone
SYNC I/O can resolve to an external Pilot Tone
signal for synchronizing to (or transferring au-
dio 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
between 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 refer-
ence. Most 1/4-inch machines have a center
track for time code or pilot.