User Guide

Issue 4, December 2020 Model 780-01/790 User Guide
Page 12 Studio Technologies, Inc.
for Surround
be connected to the inputs of loudspeak-
ers that contain integrated amplifiers with
digital audio input capability.
Sync Input
The Model 780-01 requires a timing refer-
ence (sync) source so that the audio input
and monitor output signals will be inter-
preted correctly. A configuration setting
allows the source of sync to be selected.
The default setting uses the L/R input of
the currently selected input source which
can be either of the surround inputs or
the stereo input. While this is acceptable,
audio artifacts (clicks or noise) will typi-
cally occur when switching between input
sources. A better method is to connect a
dedicated timing reference signal to the
Model 780-01’s sync input connector. The
connected sync source must maintain a
stable relationship between itself and the
connected audio sources. 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 tim-
ing reference signals might prove worth-
while. Word clock is a digital signal that
is locked in phase and frequency to the
sample rate of the associated audio sourc-
es. DARS (digital audio reference 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 specifi-
cally as a timing reference signal. Bi-level
video sync signals were originally provided
to support NTSC (United States) and PAL
(European) analog broadcast applica-
tions, although they continue to be used by
contemporary digital video equipment. Tri-
level sync signals were primarily associ-
ated with facilities that upgraded to support
high-definition (HD) video signals, however
the need for this type of sync signal seems
to be waning. The Model 780-01 sup-
ports 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 780-01 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 780-01’s back
panel. For flexibility the Model 780-01’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 780-01’s
sync input would typically want to have
the input termination enabled. If the sync
signal connected to the Model 780-01 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 con-
trol input functions: remote mute all and
remote dim. These functions only impact
the post-fader monitor outputs. The Model
780-01’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.