Avid Technology Digidesign USD, User Manual, Page: 67 / 96

Chapter 5: Additional Operational Information 63
The clock reference (labelled Sample Clock
Resolver Circuit in Figure 3 on page 62) is
selectable at all times. You can decide
which input signal to use to generate the
digital clock signal.
However, when the clock reference is set to
Video, the positional (time code) reference
circuitry (labelled Time Code and Window
Dub Circuit in the illustration) is not swit-
chable. This is because the positional (time
code) reference circuitry is always used to
derive time code, whether the USD is read-
ing incoming time code or generating new
time code. Even in Generate mode, the
USD needs to use this circuitry to detect the
frame edge of the video, in order to gener-
ate time code.
Using Fader Start
The USD provides six GPI outputs in total,
two TTL-level and four relays. Together,
this combination of outputs makes it possi-
ble for the USD to provide Fader Start capa-
bility.
☞
Utilization of Fader Start has specific wiring
requirements. See “GPI Relay Wiring for Fader-
Start” on page 88.
Fader Start allows faders in Pro Tools to
trigger external devices to play and stop.
To implement Fader Start, Pro Tools maps
the first two visible auxiliary input chan-
nels in a session to GPI Relay outputs 0 and
1 (first being left-to-right in the Mix win-
dow, top-to-bottom in the Edit window).
Example Fader Start Application
In a typical scenario, the Fader Start feature
controls playback of a CD player. The CD
player outputs are routed into a Pro Tools
stereo Aux Input. As the Aux channel fader
is moved above -120 dB, playback of the
CD player is automatically triggered. Like-
wise, as the fader is moved below -120 dB,
playback is automatically stopped.
✽ To rearrange tracks, drag the Track Name
plate left or right in the Mix window, or up or
down in the Edit window. Refer to your
Pro Tools Reference Guide if you need addi-
tional information.
To configure Pro Tools tracks for Fader Start
Play and Stop:
1
Use the New Track dialog to create two
new auxiliary input tracks. If you already
have aux tracks, you will use the first and
second (top-most in the Edit window, left-
most in the Mix window).
2
When the first visible aux input in a
Pro Tools session is above -120 dB, GPI Re-
lay output 3 (Fader Start #1) will be en-
abled; otherwise, it will be disabled.
Similarly, when the second visible aux in-
put in a Pro Tools session is above -120 dB,
GPI Relay output #4 (Fader Start #2) will be
enabled; otherwise, it will be disabled.
If you rearrange channel strips in the
Pro Tools Mix or Edit windows, the two
GPI outputs will update dynamically to re-
flect the current state. The Fader Start
channel must be in a Show Track state (not
hidden).
Refer to “GPI Relay Wiring for Fader-Start”
on page 88 for additional GPI information.