User Guide

Issue 13, December 2020 Model 76D/77 User Guide
Page 10 Studio Technologies, Inc.
for Surround
There is, however, an exception worth
noting. Circuitry associated with stereo input
C has sample rate conversion (SRC) ca-
pability, allowing virtually any digital audio
signal to be connected. A signal connected
to stereo input C can have an independent
sample rate and timing reference and still
be monitored correctly. Refer to the Techni-
cal Notes section of this guide for a detailed
review of the SRC capability.
Nine BNC jacks on the Model 76D’s back
panel are used to interface with the 18
channels associated with the digital audio
signal sources; each BNC connector car-
ries two audio channels. The digital audio
inputs are intended for connection with
unbalanced digital audio sources that are
compatible with the AES3 standard. In
broadcast or post-production environments
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 76D’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 connector on
their input and a female BNC connector
on their output.
Monitor Outputs
The 25-pin D-subminiature connector la-
beled Digital Monitor Outputs provides
access to the Model 76D’s 16 channels
of digital audio monitor output: pre-fader
surround, post-fader surround, post-fader
stereo, and stereo input C direct. The pre-
fader surround monitor output channels
are intended for connection to metering or
monitoring equipment that requires uninter-
rupted full-level signals.
The post-fader surround monitor output
channels are intended to connect to a 5.1
loudspeaker system. The post-fader stereo
monitor output is provided to support a sep-
arate set of stereo monitor loudspeakers.
The stereo input C direct monitor output is
essentially a unity gain copy of the signal
connected to stereo input C. However, the
signal does pass through the sample rate
conversion (SRC) and input delay circuitry.
The impact made by these functions will
depend on the specific input signal and the
Model 76D’s configuration settings.
For flexibility the monitor outputs are trans-
former-coupled and can be configured
to act as balanced or unbalanced AES3
digital audio sources. The monitor outputs
are configured in two groups with separate
choices available for the pre-fader sur-
round/stereo input C direct group and post-
fader surround/post-fader stereo group.
When a group is set for balanced AES3
operation the signals have a nominal im-
pedance of 110 ohms and a nominal level
of 5 Vpp. 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 unbal-
anced AES3 operation the signals have
a nominal impedance of 75 ohms and a
nominal level of 1 Vpp. These signals are
typically interconnected using coaxial cable
terminated with BNC connectors. For de-
tails on how a Model 77 Control Console
is used to select the monitor output types
refer to the Configuration section of this
user guide.