Studio Technologies 76DA V.4.00 - Manual (Page 10)

Issue 3, July 2012 Model 76DA/77 User Guide
Page 10 Studio Technologies, Inc.
for Surround
maintain a common sample rate and tim-
ing reference. Having all signals “locked”
together helps to ensure proper handling
by the Model 76DA’s all-digital signal
control path.
There is, however, an exception worth
noting. Circuitry associated with stereo
input C has sample rate conversion (SRC)
capability, allowing virtually any digital
audio signal to be connected. A signal
connected to stereo input C can have an
independent sample rate and timing refer-
ence and still be monitored correctly. Refer
to the Technical Notes section of this guide
for a detailed review of the SRC capability.
Nine BNC jacks on the Model 76DA’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 76DA’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 76DA’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 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 post-fader
stereo digital monitor output is provided to
support a separate set of stereo monitor
loudspeakers.
The stereo input C direct digital 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 76DA’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 sur-
round/stereo input C direct group and post-
fader surround/post-fader 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 connectors. When a group is con-
figured for AES3id (75 ohms/1 Vpp) the
source impedance and signal level are