Studio Technologies StudioComm 780-01 User manual

50390-1220, Issue 4
© 2020 by Studio Technologies, Inc., all rights reserved
www.studio-tech.com
Model 780-01 Central Controller and
Model 790 Control Console
User Guide
Issue 4, December 2020
This User Guide is applicable for systems consisting of:
Model 780-01: serial number M780-01-00151 and later with
software version 1.00 and higher and FPGA version 4.15 and higher;
Model 790: serial number M790-00151 and later with software version 1.00 and higher
for Surround

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Model 780-01/790 User Guide Issue 4, December 2020
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Table of Contents
Revision History ........................................................... 4
Introduction ................................................................... 5
Installation .................................................................... 9
Configuration ................................................................16
Operation ......................................................................35
Technical Notes ............................................................41
Specifications ...............................................................45
Appendix A—Connection Pin-Out Charts .....................47
Appendix B—Sync Input Sources ................................48
Appendix C—Downmix Formulas ................................49

Issue 4, December 2020 Model 780-01/790 User Guide
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Revision History
Issue 4, December 2020:
• Revised how dim values are stated. Now are four positive dB values. Operation does not
change. For clarification only.
Issue 3, October 2016:
• Revised text for error codes Err1, Err2, and Err3; added text for error code Err4.
Issue 2, April 2015:
• Revised specifications to reflect final audio performance measurements.
• Text clarifications.
Issue 1, January 2015:
• Initial release.

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Introduction
What This User Guide Covers
This User Guide is designed to assist
you when installing and using the Model
780-01 Central Controller and one or more
associated Model 790 or Model 71 Control
Consoles.
Overview
Creating and distributing eight channel
(7.1) surround audio material has become
common for entertainment, cinema, and
allied applications. As such, the ability to
simply and effectively monitor these sourc-
es is imperative during the recording and
post-production process. Studio Technolo-
gies has addressed these needs with the
StudioComm for Surround Model 780-01
Central Controller and the Model 790 and
Model 71 Control Consoles. With digital
audio inputs, digital monitor outputs, sup-
port for multiple user control surfaces, and
an extensive set of resources it’s a simple
task to integrate a monitoring system into
virtually any facility. The carefully selected
group of features, including two surround
(7.1) and one stereo input, configurable
input-source time delay, LFE low-pass
filter, pre- and post-fader surround outputs,
configurable downmix and mute/solo func-
tions, and bass management, along with
a multi-format sync input, make the system
powerful yet simple to operate. And by
using the best of contemporary technology,
as well as following rigorous design
practices, the system’s audio quality is
excellent.
A StudioComm for Surround system starts
with the Model 790 Control Console. It’s
the system’s “command center” and is
designed to reside at a user’s location,
allowing fingertip selection of all monitoring
functions. Numerous LEDs provide com-
plete status information. A 4-digit numeric
display indicates the level of the post-fader
monitor output. A major strength of the
Model 790 is its ability to configure, under
software control, many important operat-
ing parameters. Intended for secondary
monitoring locations that don’t require all
of the Model 790’s features, the Model 71
Control Console is a compact user control
surface. It provides three of the most basic
functions: a rotary level control, dim on/off
button, and reference level on/off button.
Most installations will use only one Model
790 Control Console. However, up to three
additional Model 790 or Model 71 Control
Consoles can also be connected. This
provides multiple users with control over
a facility’s monitor system. And to make
installation simple, the Model 780-01 pro-
vides power for all connected Model 790
or Model 71 units.
The core of this StudioComm for Surround
system is the Model 780-01 Central Con-
troller. The one-rack-space unit contains
circuitry that supports balanced digital
audio inputs, balanced digital monitor
outputs, digital audio and control process-
ing, and interfacing for the user control
surface(s). The Model 780-01 provides two
surround (7.1) and one stereo digital audio
inputs. These balanced digital inputs are
AES3-compliant; sources of this type are
ubiquitous in many post-production and
audio facility environments. The inputs
allow a sample rate of 44.1, 48, 88.2 or
96 kHz and a bit depth of up to 24 to
be supported. Circuitry associated with
the stereo input provides sample rate
conversion (SRC) capability, allowing a
wide range of digital audio sources to be
monitored. To compensate with processing

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Figure 1. Model 780-01 Central Controller Front Panel
Figure 2. Model 780-01 Central Controller Back Panel
Sync status
LED
Control console
status LED
Sync
input
Digital
monitor outputs
To/from
Models 790 &
71 Control
Consoles
AC mains
Remote control inputs
Digital surround (7.1)
inputs A & B
Stereo
input
delays (latency) associated with associ-
ated video displays up to 340 milliseconds
of input delay can be selected. For flex-
ibility, two delay values can be configured,
allowing real-time selection as desired. A
number of different signals can serve as
the Model 780-01’s digital audio timing
reference. For synchronization with a mas-
ter timing reference a dedicated source of
word clock, DARS (AES11), bi-level video,
or tri-level video can be connected. Alter-
nately, the L/R connection of the actively
selected surround or stereo input source
can serve as the timing reference.
Two surround (7.1) digital monitor outputs
are provided. The pre-fader monitor output
can be used with metering systems that
require signals that aren’t impacted by
level control or other monitoring functions.
The post-fader monitor output is intended
for connection to the inputs on a monitor
loudspeaker system. Both the pre- and
post-fader monitor outputs are compat-
ible with equipment that requires balanced
AES3 digital audio signals with an output
impedance of 110 ohms and a signal level
of 5 volts peak-to-peak (Vpp).
A sophisticated bass management function
is integral to the Model 780-01’s design
and can be enabled if desired. The overall
goal of bass management is very simple:
ensure that the entire audio bandwidth of
all channels can be accurately monitored.
Many loudspeaker systems have inher-
ent low-frequency limitations, preventing a
true sonic “picture” of the source material
from being presented. To overcome this,
the low-frequency energy from the seven
channels associated with the surround
inputs and the two channels associated
with the stereo input can be separated and
routed to the subwoofer (SUB) channel of
the post-fader monitor output. Several of
the bass management functions can be
configured to match the requirements of
specific installations.

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Figure 3. Model 790 Control Console Front Panel
Channel mute/solo
Mute/solo
mode
Post-fader surround
monitor output
• Surround/stereo
• Reference level
• Mute all
• Dim
• Rotary level control
Monitor output
level display
Input source
select
Downmix
Great care was taken in designing the
system’s architecture, ensuring that the
character of the audio input signals was
preserved. All audio processing, including
bass management, is performed in 32-bit
logic using a high-speed field-program-
mable gate array (FPGA) integrated circuit.
High-performance integrated circuits are
used to perform input, output, and clocking
tasks.
The Model 780-01 occupies one space
(1U) in a standard 19-inch rack. Digital
audio sources are interfaced with the Model
780-01 using one 25-pin female D-sub-
miniature connector and one 3-pin female
XLR connector. A BNC connector is used to
interface with an external sync source. Pre-
and post-fader digital monitor output signal
connections are made using a 25-pin fe-
male D-subminiature connector. One 9-pin
female D-subminiature connector is used to
connect the Model 780-01 with a maximum
of four Model 790 or Model 71 Control Con-
soles. A second 9-pin “D-sub” connector
is used to interface with remote control
signals. AC mains power is connected
directly to the Model 780-01, with an ac-
ceptable range of 100 to 240 V, 50/60 Hz.
Additional Details
The Model 790 provides three buttons
and associated LEDs for selection of the
source to be monitored. The choices are
the two surround inputs and the stereo
input; only one source can be monitored
at a time. It’s interesting to note that while
the surround inputs have an LFE channel
associated with them, the corresponding
post-fader monitor output channel is des-
ignated as subwoofer (SUB), rather than
LFE. This terminology was selected to
highlight the fact that this output channel
may include more than just LFE content.
The bass management function, if en-
abled, will redirect low-frequency energy
from the main channels, combine it with
the contents from the LFE input channel,
and route the combination to the post-
fader monitor output’s subwoofer (SUB)
channel.

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An LFE low-pass filter function is provided
as a means of checking the audio content
in the LFE channel of a selected surround
input. The user can enable and disable the
function as required, helping to ensure that
the proper signals are being mixed to the
LFE channel. Having the correct audio con-
tent in the LFE channel can be critical as
the LFE channel is typically band-restricted
during distribution.
The post-fader monitor output levels can be
controlled by way of a large, easy-to-use
rotary control. The control, actually a digital
encoder, allows level selection in precise
0.5-dB steps. The auto mute all function
causes the post-fader monitor output chan-
nels to automatically mute whenever the
output level control reaches maximum at-
tenuation. Using the reference level func-
tion, the post-fader monitor output levels
can be set to a pre-configured value. This
is provided for audio-with-picture applica-
tions that require a specific monitor output
level. The reference level is easily config-
ured by taking an electronic “snapshot”
of the desired monitor output level. For
user confirmation, the 4-digit LED display
will show the level of the post-fader moni-
tor output channels. To match the needs
of a facility, the display can be configured
to show either the attenuation level or the
sound pressure level (SPL).
The dim function allows the post-fader
monitor output level to be reduced by a
fixed dB amount. The dim level is config-
ured from among four available values.
A mute all function allows the post-fader
monitor output channels to be simultane-
ously muted. The input mute/solo section
allows an input channel to be muted or
monitored as desired. Multiple channels
can also be simultaneously selected for
muting or “soloing.”
Two output mute functions are also pro-
vided. One button allows the seven main
channels of the post-fader monitor output
to be muted. A second button allows the
subwoofer (SUB) channel of the post-fader
monitor output to be muted. The output
mute functions, along with the input mute/
solo function, allow a user complete flex-
ibility when checking an input source and
its path to the loudspeaker system. These
mute and solo resources are crucial in a
multichannel environment, especially when
signals are passing through the bass man-
agement function.
Three downmix functions allow the selected
input source to be checked for compatibility
with common audio channel formats. This
can help ensure that surround and stereo
mixes correctly “fold down” into formats
that utilize less channels than the original.
Errors can be quickly identified and then
corrected. The downmix functions, To 5.1
and To Stereo, apply only to the two sur-
round (7.1) sources. The To Mono downmix
function applies to the surround and stereo
inputs. Several of the downmix parameters
can be configured to best meet the needs
of an application. The downmix functions al-
ways impact the post-fader monitor output.
A configuration setting allows the pre-fader
monitor output to be selected for pre- or
post-downmix operation.
For flexibility, the StudioComm for Surround
system is designed to easily integrate with
equipment such as production intercom
systems, on-air or recording tally signals,
and audio consoles. Two remote-control
inputs provide access to the mute all and
dim functions. By providing access to these
functions, talkback or slate activity from an
audio console or other communications
system can control the level of the post-
fader monitor outputs.

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Installation
In this section you will be installing the
Model 780-01 Central Controller in an
equipment rack. Connections to the sur-
round and stereo audio inputs and pre-
and post-fader surround monitor outputs
will be made. A dedicated digital audio tim-
ing reference signal can be connected to
the sync input. If desired, external equip-
ment will be interfaced to the remote con-
trol inputs. A location will be selected for
the first Model 790 Control Console and
it will be connected to the Model 780-01.
AC mains power will be connected to the
Model 780-01. For advanced applications
up to three additional Model 790 or Model
71 Control Console units can be connected
to the Model 780-01.
System Components
The main shipping carton contains one
each of the following: Model 780-01
Central Controller, Model 790 Control Con-
sole, 9-pin D-subminiature interconnecting
cable (approximately 20 feet (6 meters) in
length), and a user guide. Also included
in the shipping carton is a North-Ameri-
can-standard AC mains cord. Your dealer
or distributor should provide an AC mains
cord appropriate for destinations outside of
North America. Any additional Model 790 or
Model 71 Control Consoles will be shipped
in separate cartons.
Mounting the Model 780-01
The Model 780-01 Central Controller
requires one space (1U) in a standard
19-inch (48.3 cm) equipment rack. Secure
the Model 780-01 into the equipment rack
using two mounting screws per side. Select
a location that is convenient for making
connections to the audio signals as well
as interfacing with the first (or only) Model
790 Control Console. A cable is supplied
to connect the Model 780-01 to the Model
790. If the needs of a specific installation
dictate, an alternate-length interconnecting
cable can be fabricated and used.
Audio Connections
Audio input connections are made by way
of one 25-pin female D-subminiature con-
nector and one 3-pin female XLR connec-
tor. Audio monitor output connections are
made by way of one 25-pin female D-sub-
miniature connector. The connectors are
located on the Model 780-01’s back panel.
Refer to Figure 2 for a detailed view of
these connectors.
Audio Inputs
Two balanced digital surround (7.1) and
one balanced digital stereo audio source
can be connected. Users will be able to
monitor them, one at a time, using the pre-
and post-fader monitor outputs. A one-to-
one relationship is maintained between the
input and output channels, i.e., left input to
left monitor output, right input to right moni-
tor output, center input to center monitor
output, etc. (Of course this won’t be true in
the case where the user has enabled one
of the three downmix functions.)
The audio inputs support digital audio
signals with sample rates of up to 44.1,
48, 88.2, and 96 kHz and a depth (word
length) of up to 24 bits. It’s recommended
that the connected signal sources maintain
a common sample rate and timing refer-
ence. Having all signals “locked” together
helps to ensure proper handling by the
Model 780-01’s all-digital signal path.

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There is, however, an exception worth
noting. Circuitry associated with the stereo
input has sample rate conversion (SRC)
capability, allowing virtually any stereo digi-
tal audio signal to be connected. A signal
connected to the stereo input can have an
independent sample rate and timing refer-
ence while still being monitored correctly.
Refer to the Technical Notes section of this
user guide for a detailed review of the SRC
capability.
The Model 780-01’s audio inputs are in-
tended for connection with balanced digital
audio sources that are compatible with the
AES3 standard. This type of signal has
a nominal impedance of 110 ohms and a
nominal signal level of 5 Vpp.
One 25-pin female D-subminiature con-
nector (DB-25F) is used to interface with
the 16 channels associated with surround
input A and surround input B. Each of
the eight connections supports two audio
channels. Often a wiring assembly pre-
pared for these digital audio inputs would
be identical to that of a TASCAM®-type
(AES59-compliant) input assembly. A typi-
cal assembly of this type will often have
eight 3-pin female XLR connectors on one
end and a 25-pin male D-subminiature
connector (DB-25M) on the other. Refer
to Figure 4 or Appendix A for details on
connecting with the 25-pin female D-sub-
miniature connector.
Note that unlike a TASCAM-type assem-
bly, the two threaded fasteners associated
with the Model 780-01’s D-subminiature
connector use 4-40 threads. This complies
with the original design standard for D-sub
connectors.
On the Model 780-01 the stereo input uses
a 3-pin female XLR connector for interfac-
ing with a digital audio source. The mating
cable should have a 3-pin male XLR con-
nector wired such that the + signal goes
to pin 2, the – signal to pin 3, and shield
to pin 1.
Unbalanced AES3 digital audio signals
can also be used with the Model 780-01’s
inputs if external coupling transformers
(“baluns”) are utilized. These impedance-
matching (75 ohms to 110 ohms) and level
step-up transformer assemblies typically
provide a BNC connector on their input
and a 3-pin male XLR connector on their
output.
Monitor Outputs
The 25-pin female D-subminiature con-
nector on the back panel labeled Digital
Monitor Outputs provides access to the
Model 780-01’s pre- and post-fader digi-
tal audio monitor outputs. The channels
are organized as two 8-channel surround
(7.1) sources, one pre-fader (fixed level)
Signal Signal
Connections Channel High (+) Low (–) Shield
Surround Input A L/R 1 24 12 25
Surround Input A C/LFE 2 10 23 11
Surround Input A SL/SR 3 21 9 22
Surround Input A BL/BR 4 7 20 8
Surround Input B L/R 5 18 6 19
Surround Input B C/LFE 6 4 17 5
Surround Input B SL/SR 7 15 3 16
Surround Input B BL/BR 8 1 14 2
Notes: 1) All signals transformer-coupled digital audio;
balanced AES3 (110 ohms, 5 Vpp) compatible.
2) Connector type on Model 780-01 is 25-pin female
D-subminiature (DB-25F). Installer must provide male
(DB-25M). Connector uses 4-40 threaded inserts for
locking with mating plug.
3) Wiring scheme follows AES59-2012 convention.
Standard TASCAM-type wiring harnesses are directly
compatible, with the possible exception of 4-40 screw
threads being required.
Figure 4. Connections for Surround A and
Surround B Digital Inputs

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and the other post-fader (level adjustable
by the user). The pre-fader monitor output
channels are intended for connection to
metering or monitoring equipment that re-
quires uninterrupted full-level signals. The
post-fader monitor output channels are
intended to be connected to a loudspeaker
system that provides seven main channels
and one subwoofer channel.
The monitor outputs are transformer-
balanced AES3 digital audio signals with
a source impedance of 110 ohms and
a nominal signal level of 5 Vpp. Signals
of this type are normally interconnected
to destination equipment using shielded
twisted-pair cable terminated with 3-pin
male XLR connectors.
A cable assembly with a 25-pin male
D-subminiature connector (DB-25M) on
one end and the desired connectors on
the other end will be used for connecting
to the monitor outputs. The D-sub connec-
tor follows the TASCAM-type wiring con-
vention, organizing the 25 pins into eight
groups of three pins each; one pin remains
unused. Each set of three pins provides an
independent AES3 balanced signal. In the
analog world this would allow eight audio
channels to be transported. But with AES3
digital audio signals this allows support
for 16 audio channels; eight signals each
supplying the pre- and post-fader monitor
outputs.
A wiring assembly prepared for the Model
780-01’s monitor outputs would typically
be identical to that of a TASCAM-type
output assembly. An assembly of this type
would often have a 25-pin male D-submin-
iature connector (DB-25M) on one end and
eight 3-pin male XLR connectors on the
other.
For compatibility with AES3 balanced
digital audio signals connect the D-sub’s
+ connections as signal high and the
– connections as signal low. In most appli-
cations a 3-pin male XLR connector will be
used. In this case the + connections would
go to pin 2 of each XLR, the – connection
to XLR pin 3, and the shield connection to
XLR pin 1. Refer to Figure 5 or Appendix A
for the connection details.
Signal Signal
Connections Channel High (+) Low (–) Shield
Pre-Fader L/R 1 24 12 25
Pre-Fader C/SUB 2 10 23 11
Pre-Fader SL/SR 3 21 9 22
Pre-Fader BL/BR 4 7 20 8
Post-Fader L/R 5 18 6 19
Post-Fader C/SUB 6 4 17 5
Post-Fader SL/SR 7 15 3 16
Post-Fader BL/BR 8 1 14 2
Notes: 1) All signals transformer-coupled digital audio;
balanced AES3 (110 ohms, 5 Vpp) compatible.
2) Connector type on Model 780-01 is 25-pin female
D-subminiature (DB-25F). Installer must provide male
(DB-25M). Connector uses 4-40 threaded inserts for
locking with mating plug.
3) Wiring scheme follows AES59-2012 convention.
Standard TASCAM-type wiring harnesses are directly
compatible, with the possible exception of 4-40 screw
threads being required.
Figure 5. Connections for Digital Monitor
Outputs
Pre-Fader Monitor Output
The pre-fader monitor output channels are
intended to connect to metering, measure-
ment, or other signal monitoring equipment
that requires uninterrupted, full-level digital
audio signal sources.
Post-Fader Monitor Output
The post-fader monitor output channels
are designed for connection to digital
inputs on audio amplifiers associated with
monitor loudspeakers. Alternately, they can

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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.

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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 should be taken to
prevent nasty signals from reaching them.
The inputs are active only when held in
the low state; they can’t be configured to
change state (“latch”) in response to a
logic pulse.
A 9-pin D-subminiature connector (DE-9F)
is used for the remote control inputs. Refer
to Figure 6 or Appendix A for connection
details. Note that pin 4 (remote common)
connects to the Model 780-01’s internal
circuit common connection as well as to
the Model 780-01’s chassis and mains
earth connections. Figure 6 also shows
two spare remote control inputs (pins 8
and 9). These are provided for future ap-
Control Consoles. Refer to Figure 7 or
Appendix A for details. A 9-pin female
D-sub connector (DE-9F) labeled To/From
Central Controller, is provided on the back
panel of each Model 790 Control Console.
A cable with 9-pin male D-sub (DE-9M)
connectors on each end is used to inter-
connect the Model 780-01 with the Model
790 units. A cable, approximately 20 feet
(6 meters) in length, is included in the ship-
ping carton. The cable implements all nine
connector pins in a one-to-one manner.
Should an interconnecting cable of a
different length be required there’s no
problem for one to be fabricated and used.
While it can be wired in a one-to-one fash-
ion supporting all nine pins, only four con-
nections are actually required: pin 1 (data
+), pin 6 (data –), pin 4 (DC +), and pin 9
(DC –). The Model 780-01’s connector pin-
out scheme was designed to allow creation
of an interconnecting cable which uses
commonly available 2-pair audio cable.
This cable, consisting of two twisted pairs
each with an individual shield, is typically
small in diameter, flexible, and available in
many colors. One pair and shield can be
used for the data connection (pins 1 and 6)
while the other pair and shield can be used
for the DC connections (pins 4 and 9). This
Signal Pin Direction
Data Shield 1 Shield
Remote Mute All 5 Input
Remote Dim 6 Input
Remote Spare 1 8 Input
Remote Spare 2 9 Input
Remote Common 4 Common
Note: Connector type on Model 780-01 is 9-pin female
D-subminiature (DE-9F). Connector uses 4-40
threaded inserts for locking with mating plug.
Figure 6. Connections for Remote Control
Inputs
Signal Pin Direction
Data + (RS-485) 1 To/From Models 790/71
Data – (RS-485) 6 To/From Models 790/71
Data Shield 2 To/From Models 790/71
DC + (12 V) 4 To Models 790/71
DC – (12 V Return) 9 To Models 790/71
DC Power Shield 5 To/From Models 790/71
Note: Connector type on Model 780-01 is 9-pin female
D-subminiature (DE-9F). Connector uses 4-40
threaded inserts for locking with mating plug.
Figure 7. Connections between Model 780-01
and Model 790 and Model 71
plications and should remain unconnected.
Connecting the Model 780-01
to the Model 790
A 9-pin female D-subminiature connector
(DE-9F), labeled To/From Control Con-
soles, is provided on the back panel of the
Model 780-01 Central Controller. This is
used to interface the unit with Model 790

Issue 4, December 2020 Model 780-01/790 User Guide
Page 14 Studio Technologies, Inc.
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implementation has the advantages of
providing a shield for the data path and a
more robust common (return path) connec-
tion (two conductors including the shield)
for the DC power circuit.
A few simple calculations are required to
determine the maximum cable length when
fabricating a cable to be used when con-
necting a Model 780-01 to a Model 790.
The differential transmission scheme used
by the system’s RS-485 interface makes
an interconnection in excess of 1000 feet
(>300 meters) easily possible. The limiting
factor is typically the ability of the wiring to
pass the DC power supplied by the Model
780-01 to a Model 790. The Model 780-01
supplies 12 Vdc, 500 milliamperes (mA)
maximum.
The Model 790 requires a minimum of
9 Vdc, 100 mA maximum, for operation.
(The voltage must be measured directly at
the Model 790’s 9-pin D-subminiature con-
nector.) So the maximum interconnecting
cable length is directly related to the resis-
tive voltage losses associated with the two
DC-carrying conductors (supporting pins 4
and 9). As the Model 780-01 supplies 12 V
and the Model 790 requires 9 V minimum,
this leads to a 3 Vdc maximum drop due
to the interconnecting cable. Using Ohm’s
law it’s quite easy to determine if a desired
cable length can be supported. Calculate
the voltage drop by multiplying the total
resistance (in ohms) of the proposed cable
by 0.1 (the Model 790’s required current in
amperes). Remember to include the resis-
tance in both conductors (DC + and DC –)
when calculating the voltage drop. If the
voltage drop in the cable is 3 V or less it
should function correctly. If it’s greater than
3 V the cable is too long or the wire gauge
is too small.
Additional Control Consoles
Some installations may benefit from the
Model 780-01’s ability to be controlled by
additional control consoles. At least one
Model 790 Control Console must be con-
nected to the Model 780-01 Central Con-
troller. After this requirement has been met
a combination of up to three additional
Model 790 or Model 71 Control Consoles
can also be connected to and powered by
the Model 780-01.
When connecting multiple control consoles
to a Model 780-01 all nine pins of each
interconnecting cable can be connected
in parallel (“multed”). Using this arrange-
ment the data and 12 Vdc power signals
between all the units will be connected in
parallel. A custom cable implementation
requires just four pins to be connected:
pin 1 (data +), pin 6 (data –), pin 4 (DC +),
and pin 9 (DC –).
To make installation simple, a “bus” cable
assembly can be created using a short
length of ribbon cable with one 9-pin male
and multiple 9-pin female D-subminiature
insulation-displacement connectors at-
tached. Then standard 9-pin cables can
link the control consoles with the connec-
tors on the bus cable.
Refer to the previous paragraphs of this
user guide where the issues involving
Model 780-01 to Model 790 cable length
are discussed. Note the required current
for a Model 790 is 100 mA while a Model
71 requires only 35 mA. It’s important to
review this information prior to selecting or
fabricating the interconnection cables that
will be used when installing multiple Model
790 or Model 71 units.

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AC Mains Power
The Model 780-01 operates directly from
AC mains power over a range of 100 to
240 V, 50/60 Hz. Being a “universal in-
put” device, there are no switches to set
or jumpers to install to match a location’s
mains voltage. The unit uses a 3-pin IEC
320 C14-type inlet connector to mate with
a detachable mains cord. All units are sup-
plied with a mains cord that has a North-
American-standard plug (NEMA 5-15L) on
one end and an IEC 320 C13 socket on the
other. Units bound for other destinations will
require that the appropriate cord be used.
The wire colors in the mains cord must con-
form to the internationally recognized color
code and should be terminated accordingly:
Connection Wire Color
Neutral (N) Light Blue
Line (L) Brown
Protective Earth (E) Green/Yellow
Safety Warning: The Model 780-01
does not contain an AC mains discon-
nect switch; the AC mains cord plug
serves as the disconnection device.
Safety considerations require that the
plug and associated outlet be eas-
ily accessible to allow rapid discon-
nection of AC mains power should it
prove necessary.
As soon as mains power is applied the
Model 780-01 will perform a power-up
sequence. The two LEDs on the right side
of the front panel will momentarily light in a
test sequence. Then the two LEDs will flash
in cadence while the firmware loads into
the Model 780-01’s main logic device. After
a few seconds initial system operation will
commence and the two LEDs will perform
their intended functions. Once operating
data is being interchanged with the one
or more connected Model 790 or Model
71 Control Consoles the control console
status LED will light. The sync status LED
will light if a valid sync source has been
recognized. The sync status LED will flash
if a valid sync source is not recognized.
Also upon application of mains power, all
connected Model 790 units will go through
a power-up sequence, lighting each of its
LEDs in succession. Using its 4-digit dis-
play, each Model 790 will then momentarily
display its address, its software version,
and the main and logic device software
versions of the associated Model 780-01.
All connected Model 71 units will also go
through a power-up sequence after mains
power is applied to the Model 780-01.
Each of the Model 71’s three LEDs will
light momentarily. After these LEDs have
lit, the device address will be shown briefly
using the dim and reference level LEDs, as
shown in Figure 8 in the Configuration sec-
tion. When this is complete the Model 71
will begin normal operation. Its status LED
will light if communication is established
with the Model 780-01. If the Model 71’s
status LED does not light check to see if
there is a device address conflict among
all connected control consoles and that all
cables are implemented properly. Refer to
the Configuration section of this user guide
for details on selecting the device address.
Should an error be detected during the
start-up process the two LEDs located on
the right side of the Model 780-01’s front
panel will remain flashing in cadence. On
the Model 790 units a diagnostic code may
be displayed. Refer to the Technical Notes
section of this user guide for details.

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Only after the Model 780-01 and all con-
nected Model 790 and Model 71 units
have correctly powered up will full system
operation begin.
Configuration
After the physical installation has been
completed it’s important that the system’s
configuration options be carefully re-
viewed. In most cases one or more of the
operating parameters will be revised to
meet the needs of the specific installa-
tion. Many of the configuration parameters
will impact the signal flow in to and out
of the Model 780-01 Central Controller.
Other parameters affect how the one or
more Model 790 Control Consoles will
display status conditions and respond to
user commands. Most of the configuration
choices will be made using a Model 790
Control Console. However, two configura-
tion choices are available for any connect-
ed Model 71 Control Consoles.
Configurable Parameters
Many StudioComm functions can be
configured to meet the exact needs of an
installation. A Model 790 Control Console
is used to display and select the desired
system configuration. Here’s an overview
of what can be configured:
• Model 790 Device Address (must be
unique for each unit!)
• Stereo Input Sample Rate Converter
• Bass Management
• Sync Source
• Sync Input Termination
• Audio-Synced-to-Video Sample Rate
• Reference Level
• Overall Display Mode
• Reference Level in dB SPL
• Auto Reference Level Off
• Dim Level
• Remote Inputs
• LFE Downmix Level
• Pre-Fader Monitor Output Mode
• Input Delay Settings
• Post-Fader Monitor Output Channel
Level Offsets
The configuration diagrams, located later
in this section, give details on setting each
parameter. An overview of each configu-
rable parameter is provided in the following
paragraphs.
Entering and Exiting the
Configuration Mode
A small button is located on the back of
each Model 790 Control Console, adjacent
to its 9-pin female D-subminiature con-
nector. On any connected Model 790 unit
pressing and holding its configure button
for two seconds places both this specific
unit and the Model 780-01 into their con-
figuration modes. Other connected Model
790 and Model 71 units will enter a stand-
by mode. When the Model 780-01 enters
its configuration mode it will immediately
mute the pre- and post-fader monitor out-
puts, providing an equipment and speaker
protection measure. When a specific Mod-
el 790 has entered the configuration mode
its array of buttons and LEDs will no longer
perform their normal functions, instead
being used to display the configuration
settings and reflect changes as they are
being made.

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As a user aid, a Model 790 that has entered
the configuration mode will have its mode
mute and mode solo LEDs (associated with
the input mute/solo section) light in an alter-
nating manner. Other connected Model 790
units will indicate that they have entered the
standby mode by simultaneously flashing
their mode mute and mode solo LEDs.
To leave the configuration mode and return
the system to normal operation requires a
final action to be made. On the Model 790
unit that’s in its configuration mode press
and hold its configure button for two sec-
onds. At this time any configuration changes
will be stored in nonvolatile memory and
normal operation, using the stored configu-
ration settings, will resume.
Our apologies to those of you who find the
configure button a pain to use, but it’s sup-
posed to be that way! Seriously, the top of
the button is slightly recessed from the back
panel, making accidental activation unlikely.
We didn’t want normal operation to cease
because someone pushed a Model 790
into a “rats nest” of schedules, memos from
management, and empty coffee cups! But
a firm press with the fleshy part of an index
finger should do the trick.
There is no problem frequently “tweak-
ing” the StudioComm system’s operating
parameters to achieve the desired perfor-
mance. The configuration data is stored
in nonvolatile memory, which is rated for
many thousands of read and write cycles
and a retention time in tens of years. Note
that memory integrated circuits are located
in the Model 780-01 Central Controller as
well as the Model 790 and Model 71 Control
Consoles. Only the individual device ad-
dresses are stored in each Model 790 and
Model 71. All other configuration param-
eters are stored in the Model 780-01.
Model 790 Device Address
A unique device address must be assigned
to each Model 790 Control Console that is
connected to a Model 780-01. The address
choices are A1, A2, A3, or A4, with the
default address being A1. As most installa-
tions will utilize only one Model 790 its de-
fault setting is appropriate. For installations
that use two, three, or four Model 790 units
it’s important that each be configured with
a unique device address. Problems will
occur if more than one unit has the same
address. It’s important to highlight the fact
that the device address is the only set-
ting that must be done on each individual
Model 790 unit. All other settings can be
made on any one of the connected Model
790 units. Be sure that any selected ad-
dress does not conflict with addresses that
are, or will be, assigned to Model 71 units.
Stereo Input Sample Rate
Converter
Circuitry associated with the stereo input
can provide sample rate conversion (SRC)
for digital audio signals connected to that
input. The acceptable input range for
sample rate conversion is very wide, but
is dependent upon the output sample rate.
With an output sample rate of 48 kHz any
signal with a sample rate over a range of 8
to 216 kHz can be properly monitored by
the system. This capability can be espe-
cially useful with signals that are not syn-
chronized with respect to the other signals
that are connected to the Model 780-01,
even if their sample rates are identical.
The only compromise is that the SRC pro-
cess adds a fixed input-to-output (group)
delay of approximately 1 millisecond, a val-
ue that shouldn’t impact most applications.
By default SRC is enabled and it’s recom-
mended that it remains that way. However

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there might be cases where this resource
isn’t desired and it can be disabled.
Bass Management
The Model 780-01 incorporates flexible
and sonically excellent bass management
capabilities. One configuration parameter
is used to enable or disable bass manage-
ment while three others are used to select
the characteristics of the associated au-
dio filters. While the settings are simple
to make, great care must be taken to first
review the entire monitor system. Only
after obtaining a full understanding of the
performance of the associated loudspeaker
system can a plan for the bass manage-
ment functions be selected.
The bass management function impacts
only the post-fader monitor output and by
default is disabled. The crossover point of
the seven main channels’ bass manage-
ment filters can be selected from among
four choices: 40, 50, 60, or 80 Hz. The
default value is 80 Hz. The slope of the
low-pass and high-pass filters associated
with the seven main channels’ bass man-
agement filters can be, as a group, select-
ed. The choices are 12 dB-per-octave or
24 dB-per-octave with the latter being the
default value. Setting the slopes to different
values (asymmetrical filtering on the seven
main channels) can be appropriate for
some loudspeaker systems.
Sync Source
The Model 780-01 requires that a designat-
ed external timing reference (sync) signal
be defined. Three of the choices—video,
DARS, and word clock—are associated
with a signal that is connected to the sync
input BNC connector. The fourth choice al-
lows the L/R input of the currently selected
surround or stereo input to also serve
as the system’s sync source. This fourth
choice is the default value.
Sync Input Termination
The sync input circuitry can be configured
to provide a 75 ohm termination impedance
to a connected source. When the sync input
is not terminated the input impedance is
very high, essentially applying no load to
the source. If the sync source is connected
only to the Model 780-01’s BNC input con-
nector then enabling termination is typically
appropriate. However, if the sync source is
being “shared” by multiple inputs then care
must be taken so that the signal is only
terminated by one device. By default sync
termination is enabled.
Audio-Synced-to-Video
Sample Rate
If a video sync signal is connected to the
sync input and video is selected as the
Model 780-01’s timing reference the sample
rate of the connected digital audio signals
must be explicitly specified. In most cases
the default value of 48 kHz will be appropri-
ate. But alternately 44.1, 88.2, or 96 kHz
can also be selected. This setting enables
the internal clock and timing circuitry to cor-
rectly interpret the video sync signal’s rela-
tionship to the connected audio sources.
Reference Level
For consistent monitoring of audio signals
it’s often beneficial for users to be able to
easily set the post-fader monitor output
level to a known value. This is sometimes
referred to as “mixing to 85 dB on the moni-
tors,” but the exact value will depend on
the application. The StudioComm system
allows a precise post-fader monitor output

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level to be stored and then enabled by
pressing the Model 790 button labeled
Reference Level. Setting the reference
level is very simple but care is required:
1. Set up a precision sound pressure
level (SPL) measuring device at the
desired listening location.
2. Ensure that the StudioComm system
is in its normal operating mode, not the
configuration mode. Be certain that the
dim, mute all, reference level, down-
mix, input mute/solo, and output mute
functions are not active. The remote
mute all and remote dim functions
must also not be active.
3. Use the Model 790 Control Console to
select the input source that contains
the desired reference signal source,
e.g., pink noise. This would typically be
one of the surround inputs rather than
the stereo input.
4. Observing the SPL meter, adjust the
Model 790’s rotary level control until
the desired loudspeaker system refer-
ence level has been reached.
5. Being careful not to disturb the posi-
tion of the rotary level control, enter the
configuration mode by pressing and
holding the configuration button for two
seconds. Once the configuration mode
has been entered the pre- and post-
fader monitor outputs will mute.
6. Press and hold the reference level
button; its associated LED will begin to
flash. After five seconds the LED will
light steadily to indicate that a “snap-
shot” of the new reference level has
been taken. The Model 790’s numeric
display will then show the value of the
new reference level. The value shown
will always be a negative number as
it’s always a value less than the maxi-
mum output level. The reference level
button can now be released.
7. To complete the process the con-
figuration mode must be exited. This
is performed by again pressing and
holding the configuration button for
two seconds. The new reference level
is now stored in the Model 780-01’s
nonvolatile memory. Only by repeating
the entire procedure can the value be
changed.
Once the configuration mode has been
exited, the monitor outputs will again be-
come active. Confirm that the correct level
has been stored by pressing the reference
level button. The SPL meter should display
the desired level. If not, repeat the calibra-
tion procedure to achieve the desired goal.
You might wonder why you have to press
and hold the reference level button for
five seconds before the selected value is
recognized. This is provided specifically so
that unauthorized users won’t accidentally
change the reference level while they ex-
periment with the configuration mode. Only
if you know the “secret” will you be able to
store a new value.
Overall Display Mode
The Model 790’s 4-digit numeric display
can be configured to display the post-fader
monitor output level in either an attenua-
tion mode or an SPL mode. In the attenua-
tion mode (the default), the output level
is shown as a reduction in level, in dB,
relative to the maximum output level.
When the rotary control is used to set the
output level to its maximum the display will
show 0.0. As the rotary control is turned in
the counterclockwise direction the display

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will show negative values, reaching –70.0
before the full mute function automatically
mutes the post-fader monitor outputs.
In the SPL mode the display can be con-
figured to allow the output level to be
presented to users in terms of an actual
sound pressure level (SPL). It is used in
conjunction with the reference level in dB
SPL configuration and the stored reference
level. The SPL mode allows a user to see
a visual representation of the SPL level
that is present in the listening environment.
While it takes a little more care to correctly
implement the SPL display mode, it can
offer an enhanced experience for Studio-
Comm users.
Reference Level in dB SPL
The reference level in dB SPL configu-
ration allows a specific SPL value to be
associated with the stored reference level
value. In this way whenever the post-fader
monitor outputs are at their reference level,
either through activating the reference lev-
el function or manually adjusting the rotary
level control, the Model 790’s display will
show the configured SPL level. Whenever
the post-fader monitor output is not at the
reference value the display will show the
current value, in dB, relative to the refer-
ence level. The reference level in dB SPL
can be configured over a range of 70.0 to
100.0 dB in 1.0-dB steps. In many applica-
tions using the default value of 85 would
be appropriate, reflecting the widely used
audio-for-picture 85 dB monitoring refer-
ence level. (Typically this 85 dB is really
85 dBC, indicating that a C-weighting filter
has been applied to the measurement.)
Other common reference SPL values,
such as 82 dB and 87 dB, are well within
the allowable range.
Auto Reference Level Off
When auto reference level off is enabled,
the function automatically turns the refer-
ence level function off if a change is made
to the rotary level control while the refer-
ence level function is active. This is pro-
vided strictly as a user convenience that
may, or may not, be desired. The default
configuration is for the auto reference level
off function to be disabled.
Dim Level
The dim function is used to reduce the
post-fader monitor output levels by a pre-
set amount. The reduction is in dB relative
to the post-fader monitor outputs’ current
level. There are four dim level values avail-
able: 10, 15, 20, and 25 dB. The default
value is 20 dB.
Remote Mute All
Two configuration choices are associated
with the remote mute all function: disabled
and enabled. The default setting has the
function enabled.
Remote Dim
Two configuration choices are associated
with the remote dim function: disabled and
enabled. The default setting has the func-
tion enabled.
LFE Downmix Level
By default, when the To Stereo or the To
Mono downmix functions are active the
LFE channel associated with the selected
surround input is fully attenuated (muted).
This removes LFE content from the “down-
mixed” signal. In most applications this is
appropriate. However, for special situa-
tions a configuration mode allows the LFE
channel to be included. In this scenario,