Avid Technology Digidesign USD, Руководство пользователя, Страница: 40 / 96

Universal Slave Driver 36
Using the front panel controls:
1
Using the front panel Clock Reference
switch, select BI PHASE/TACH.
2
Select the appropriate Pulse Per Frame
and Input Signals parameters, as described
in “Bi-Phase/Tach Starting Frame” on
page 42 and “Bi-Phase/Tach Signal” on
page 43.
▲
If the Bi-Phase/Tach reference clock source
is not valid for any reason (such as a poor con-
nection or other signal transmission problem),
the Locked LED on the far-right of the USD
front panel will flash.
To select Bi-Phase/Tach as the positional
reference from Pro Tools:
■
In the USD Setup area of Pro Tools Ses-
sion Setup window, click on the Clock Ref-
erence pop-up and select Bi-Phase.
Additional Bi-Phase/Tach Information
Bi-Phase/Tach is used with mag ma-
chine,16-, 35- and 70mm projectors, flat-
bed editing systems and other types of mo-
tor-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 an-
other. As a Bi-Phase-generating device
plays it outputs a steady stream of square
waves that the USD can use as its clock ref-
erence, at nearly any speed including
still/paused.
The USD uses the phase relationship be-
tween the two square waves to determine
the device’s direction (forward or reverse).
However, this is relevant only when the
USD 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, indica-
tor.The USD uses this rate signal when re-
solving to Tach as a clock reference.
There are several different standards for the
number of pulses-per-frame for Bi-Phase or
Tach devices. Using USD Setup’s Pulse Per
Frame setting, you can set the USD to oper-
ate from 2 to 254 pulses per frame to match
the PPF rate of the external device’s Bi-
Phase/Tach encoder.
☞
For additional Bi-Phase/Tach signal informa-
tion, see “Bi-Phase/Tach” on page 70 in Ap-
pendix A.
Internal Clock, Generating and
Regenerating
The USD can use its own, crystal-refer-
enced, internal clock as a master clock
source. When USD Clock Reference is set to
Internal:
• Word clock, Super clock, and AES/EBU
digital clock outputs are simultaneously
driven from the internal crystal refer-
ence.
– and –
• If the Positional Reference is set to Gen-
erate, generated LTC, MTC, VITC count,
and Window Dub outputs are resolved to
the same internal crystal reference.