Specifications

SYNC HD Guide74
Using just Word Clock, it is possible to create a
“chain” of digital devices in your studio by pick-
ing one source as the Word Clock master, and
configuring other sources as Word Clock slaves.
Bi-Phase/Tach
Bi-Phase and Tach are used with mag ma-
chine,16, 35, and 70 mm projectors, flatbed ed-
iting systems and other types of motor-driven
film equipment. Bi-Phase (sometimes called
Quadrature Sync) and Tach information are
similar, though they do differ.
Bi-Phase A Bi-Phase signal consists of two
square waves, which are generated directly by a
device’s transport mechanism, and which are
90° out-of-phase with one another. As a Bi-
Phase-generating device plays it outputs a
steady stream of square waves that the SYNC pe-
ripheral can use as its clock reference, at nearly
any speed including still/paused.
The SYNC peripheral uses the phase relation-
ship between the two square waves to determine
the device’s direction (forward or reverse).
However, this is relevant only when the SYNC
peripheral is using the Bi-Phase signal as a posi-
tional reference.
Tach A Tach signal is a variation of Bi-Phase.
With Tach’s two signals, one is used only as the
direction indicator, while the other is used as
the velocity, or rate indicator. The SYNC periph-
eral uses this rate signal when resolving to Tach
as a clock reference.
There are several different standards for the
number of pulses-per-frame for Bi-Phase or
Tach devices. You can set the SYNC peripheral
to match the PPF rate of the external device’s Bi-
Phase/Tach encoder from Pro Tools, or using
the SYNC Setup software utility’s Pulse Per
Frame setting (Windows only).
Strictly speaking, Bi-Phase/Tach signals are
clock reference signals, and do not contain posi-
tional information of their own. However, they
do contain enough information for the SYNC pe-
ripheral to calculate positional information.
Bi-Phase/Tach signals use two square waves to
generate pulses that can function as a clock ref-
erence. The two square waves are 90° out-of-
phase, in a pattern that resembles this:
With a Bi-Phase signal, the SYNC peripheral can
deduce the direction (forward or reverse) of the
signal based upon which wave is read “high” rel-
ative to the other. For instance, with some film
equipment, when the device is running forward,
it will generate a Bi-Phase signal where the “A”
wave leads the “B” wave—that is, where the A
wave peaks before the B wave peaks. When the
device is in reverse, the B wave will lead the A
wave.
However, some film equipment works in the op-
posite manner, which is why the SYNC periph-
eral Input Signals option lets you make the ap-
propriate selection (Fwd = A leads B, or Fwd = B
leads A).
Calculating the direction of a Tach signal is
slightly different. As you may recall, Tach also
uses two signals. The “A” signal is a square wave
that provides clock information; the “B” signal
is in a steady state (high or low) that indicates
the direction. Unfortunately, not all Tach-gen-
erating equipment uses the B signal in the same
Bi-Phase/Tach signals
Square Wave A
Square Wave B