Studio Technologies 76DBA V.3.00 - Manual (Page 11)

Model 76DBA/77B User Guide Issue 1, November 2010
Studio Technologies, Inc. Page 11
for Surround
It’s important to note that there is one
limitation regarding stereo input C. Unlike
stereo inputs A and B, it can only be used
as a stereo source. Its left and right chan-
nels can’t be independently monitored over
the center channel of the surround moni-
tor outputs. (The configuration function
doesn’t allow this anyway so there is no
potential for a problem to develop.) Also,
the left and right channels of stereo input
C can’t be independently monitored by way
of the auxiliary stereo digital and analog
monitor outputs. It follows a left-in-to-left-
out, right-in-to-right-out scheme.
Nine BNC jacks on the Model 76DBA’s
back panel are used to interface with the
18 channels associated with the digital
audio signal sources; each BNC connector
carries two audio channels. The digital
audio inputs are intended for connection
with unbalanced digital audio sources that
are compatible with the AES3id standard.
In broadcast or post-production environ-
ments these signals may also be referred
to as following the SMPTE 276M standard.
This signal type has a nominal impedance
of 75 ohms with a nominal signal level of
1 Vpp. As expected, these digital audio
sources should be provided in the form of
coaxial cables with BNC plugs attached.
Balanced AES3 digital audio signals can
also be used with the Model 76DBA’s
inputs if external coupling transformers
(“baluns”) are utilized. These impedance-
matching (110 ohms to 75 ohms) and
level-attenuating transformer assemblies
typically provide a 3-pin female XLR con-
nector on their input and a female BNC
connector on their output.
Digital Monitor Outputs
The 25-pin D-subminiature connector
labeled Digital Monitor Outputs provides
access to the Model 76DBA’s 16 channels
of digital audio monitor output: pre-fader
surround, post-fader surround, auxiliary
stereo, and stereo input C direct. The pre-
fader surround digital monitor output
channels are intended for connection to
metering or monitoring equipment that
requires uninterrupted full-level signals. The
post-fader surround digital monitor output
channels are intended to connect to a 5.1
loudspeaker system.
The auxiliary stereo digital monitor output is
provided to support a separate set of stereo
monitor loudspeakers, the primary applica-
tion intended to allow monitoring of inter-
or intra-facility communications.
The stereo input C direct digital monitor
output is essentially a unity gain copy of the
signal connected to stereo input C. Howev-
er, the signal does pass through the sample
rate conversion (SRC) and input delay cir-
cuitry. The impact made by these functions
will depend on the specific input signal and
the Model 76DBA’s configuration settings.
For flexibility the digital monitor outputs
are transformer-coupled and can be con-
figured to act as AES3 or AES3id digital
audio sources. The digital monitor outputs
are configured in two groups with separate
choices available for the pre-fader surround/
stereo input C direct group and post-fader
surround/auxiliary stereo group. When a
group is set for AES3 (110 ohms/5 Vpp)
the signals are compatible with AES3
interfaces. Signals of this type are normally
interconnected using shielded twisted-pair
cable terminated with 3-pin XLR connec-
tors. When a group is configured for AES3id
(75 ohms/1 Vpp) the source impedance and