Studio Technologies 780-03 V.4.15 - Manual (Page 13)

Model 780-03/790 User Guide Issue 1, April 2015
Studio Technologies, Inc. Page 13
for Surround
Sync Input
The Model 780-03 requires a timing refer-
ence (sync) source so that the digital audio
input and digital monitor output signals
will be handled correctly. A configuration
setting allows the source of sync to be
selected. The default setting uses the L/R
input of the currently selected digital input
source which can be either of the surround
inputs or the stereo input. While this is ac-
ceptable, audio artifacts (clicks or noise)
will typically occur when switching between
input sources. A better method is to con-
nect a dedicated timing reference signal to
the Model 780-03’s sync input connector.
The connected sync source must maintain
a stable relationship between itself and the
digital audio inputs. The actual sync source
can be in one of several formats: word
clock, DARS (AES11), bi-level video, or
tri-level video.
An overview of the various compatible
timing reference signals might prove
worthwhile. Word clock is a digital signal
that is locked in phase and frequency to
the sample rate of the associated digital
audio sources. DARS (digital audio refer-
ence source) is a timing signal compliant
with the AES11 standard. It’s sometimes
referred to as “AES3-black.” Technically it is
similar to an AES3 signal but is generated
specifically as a timing reference signal.
Bi-level video sync signals were originally
provided to support NTSC (United States)
and PAL (European) analog broadcast
applications, although they continue to be
used by contemporary digital video equip-
ment. Tri-level sync signals were primarily
associated with facilities that upgraded to
support high-definition (HD) video signals,
however the need for this type of sync sig-
nal seems to be waning. The Model 780-03
supports both bi-level and tri-level signals
at numerous rate combinations, allowing
for compatibility with various worldwide
video formats.
With the wide range of allowable sync
sources proper Model 780-03 operation
should be easy to obtain. Extensive testing
has been done using many different sync
source types and rates. Interested users
can refer to Appendix B of this user guide
for details.
An external sync reference source should
be connected to the sync input BNC con-
nector located on the Model 780-03’s back
panel. For flexibility the Model 780-03’s
sync input can be configured to be termi-
nated with an impedance of 75 ohms or
be high-impedance (“floating”) so as to
not load the source. A sync source that is
dedicated for use by the Model 780-03’s
sync input would typically want to have
the input termination enabled. If the sync
signal connected to the Model 780-03 is
being connected (“multed”) to other inputs
it may be desirable that the termination be
disabled. (A general “rule of thumb” is that
termination should be applied only at the
location of the last physical device using a
specific sync signal.)
Remote Control Inputs
Support is provided for two remote control
input functions: remote mute all and re-
mote dim. These functions only impact
the post-fader digital and analog moni-
tor outputs. The Model 780-03’s remote
control inputs use logic circuitry, “pulled
up” to 3.3 Vdc by way of resistors, which
are active whenever they are brought to
their logic low state. Inputs of this type are
commonly referred to as GPI inputs. While
the input circuitry is protected from over-
current and static discharge (ESD), care