Studio Technologies StudioComm 780-02 User manual

50392-1220, Issue 4
© 2020 by Studio Technologies, Inc., all rights reserved
www.studio-tech.com
Model 780-02 Central Controller and
Model 790 Control Console
User Guide
Issue 4, December 2020
This User Guide is applicable for systems consisting of:
Model 780-02: serial number M780-02-00151 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 780-02/790 User Guide Issue 4, December 2020
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Table of Contents
Revision History ........................................................... 4
Introduction ................................................................... 5
Installation .................................................................... 8
Configuration ................................................................15
Operation ......................................................................34
Technical Notes ............................................................40
Specifications ...............................................................44
Appendix A—Connection Pin-Out Charts .....................46
Appendix B—Sync Input Sources ................................47
Appendix C—Downmix Formulas ................................48

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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 780-02
Central Controller and one or more associ-
ated 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 780-02
Central Controller and the Model 790 and
Model 71 Control Consoles. With digital
audio inputs, analog monitor output, 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,
analog surround (7.1) monitor output, con-
figurable downmix and mute/solo functions,
and bass management, along with a multi-
format sync input, make the system power-
ful 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, al-
lowing fingertip selection of all monitoring
functions. Numerous LEDs provide com-
plete status information. A 4-digit numeric
display indicates the level of the monitor
output. A major strength of the Model 790
is its ability to configure, under software
control, many important operating param-
eters. Intended for secondary monitoring
locations that don’t require all of the Model
790’s features, the Model 71 Control Con-
sole 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 780-02 pro-
vides power for all connected Model 790
or Model 71 units.
The core of this StudioComm for Surround
system is the Model 780-02 Central Con-
troller. The one-rack-space unit contains
circuitry that supports balanced digital
audio inputs, a balanced analog monitor
output, digital audio and control process-
ing, and interfacing for the user control
surface(s). The Model 780-02 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 780-02 Central Controller Front Panel
Figure 2. Model 780-02 Central Controller Back Panel
Sync status
LED
Control console
status LED
Sync
input
Analog
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 780-02’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.
One analog surround (7.1) monitor outputs
is provided. It’s intended for connection to
analog inputs on a monitor loudspeaker
system. Electrically balanced, the monitor
output signals provide low-noise, low-dis-
tortion, and high-headroom performance.
A sophisticated bass management function
is integral to the Model 780-02’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 inherent
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 chan-
nels 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 moni-
tor output. Several of the bass management
functions can be configured to match the
requirements of specific installations.
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.

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Figure 3. Model 790 Control Console Front Panel
Channel mute/solo
Mute/solo
mode
Monitor output
• Surround/stereo
• Reference level
• Mute all
• Dim
• Rotary level control
Monitor output
level display
Input source
select
Downmix
The Model 780-02 occupies one space
(1U) in a standard 19-inch rack. Digital
audio sources are interfaced with the
Model 780-02 using one 25-pin female
D-subminiature connector and one 3-pin
female XLR connector. A BNC connector
is used to interface with an external sync
source. Analog monitor output signal con-
nections are made using a 25-pin female
D-subminiature connector. One 9-pin fe-
male D-subminiature connector is used to
connect the Model 780-02 with a maximum
of four Model 790 or Model 71 Control
Consoles. A second 9-pin “D-sub” connec-
tor is used to interface with remote control
signals. AC mains power is connected di-
rectly to the Model 780-02, with an accept-
able 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
monitor output channel is designated 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 enabled, will re-
direct low-frequency energy from the main
channels, combine it with the contents
from the LFE input channel, and route the
combination to the monitor output’s sub-
woofer (SUB) channel.
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 content in the LFE channel can
be critical as the LFE channel is typically
band-restricted during distribution.

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The level of the channels associated with
the monitor output 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 monitor output channels to automati-
cally mute whenever the output level con-
trol reaches maximum attenuation. Using
the reference level function, the monitor
output level can be set to a pre-configured
value. This is provided for audio-with-
picture applications that require a specific
monitor output level. The reference level
is easily configured 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 mon-
itor 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 monitor output
level to be reduced by a fixed dB amount.
The dim level is configured from among
four available values. A mute all function
allows the monitor output channels to be
simultaneously muted. The input mute/solo
section allows an input channel to be mut-
ed or monitored as desired. Multiple chan-
nels 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 monitor output to be mut-
ed. A second button allows the subwoofer
(SUB) channel of the monitor output to be
muted. The output mute functions, along
with the input mute/solo function, allow a
user complete flexibility when checking an
input source and its path to the loudspeak-
er system. These mute and solo resources
are crucial in a multichannel environ-
ment, especially when signals are passing
through the bass management function.
Three downmix functions allow the select-
ed input source to be checked for compat-
ibility 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 func-
tions, To 5.1 and To Stereo, apply only
to the two surround (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.
For flexibility, the StudioComm for Sur-
round system is designed to easily inte-
grate 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 communi-
cations system can control the level of the
monitor outputs.
Installation
In this section you will be installing the
Model 780-02 Central Controller in an
equipment rack. Connections to the sur-
round and stereo audio inputs and the
surround monitor output will be made. A
dedicated digital audio timing reference
signal can be connected to the sync in-
put. If desired, external equipment will be
interfaced to the remote control inputs. A
location will be selected for the first Model
790 Control Console and it will be connect-
ed to the Model 780-02. AC mains power

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will be connected to the Model 780-02. For
advanced applications up to three additional
Model 790 or Model 71 Control Console
units can be connected to the Model 780-02.
System Components
The main shipping carton contains one
each of the following: Model 780-02 Cen-
tral Controller, Model 790 Control Console,
9-pin D-subminiature interconnecting cable
(approximately 20 feet (6 meters) in length),
and a user guide. Also included in the ship-
ping carton is a North-American-standard
AC mains cord. Your dealer or distributor
should provide an AC mains cord appropri-
ate for destinations outside of North Amer-
ica. Any additional Model 790 or Model 71
Control Consoles will be shipped in separate
cartons.
Mounting the Model 780-02
The Model 780-02 Central Controller re-
quires one space (1U) in a standard 19-inch
(48.3 cm) equipment rack. Secure the Model
780-02 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 780-02 to the Model 790. If the needs
of a specific installation dictate, an alternate-
length interconnecting cable can be fabri-
cated and used.
Audio Connections
Digital audio input connections are made by
way of one 25-pin female D-subminiature
connector and one 3-pin female XLR con-
nector. Analog monitor output connections
are made by way of one 25-pin female D-
subminiature connector. The connectors are
located on the Model 780-02’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
analog monitor output. A one-to-one rela-
tionship 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 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 com-
mon sample rate and timing reference.
Having all signals “locked” together helps
to ensure proper handling by the Model
780-02’s all-digital signal path.
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 780-02’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.

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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 chan-
nels. A wiring assembly prepared for these
digital audio inputs would be identical to
that of a TASCAM®-type (AES59-compli-
ant) input assembly. A typical 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-subminiature connector.
Note that unlike a TASCAM-type assem-
bly, the two threaded fasteners associated
with the Model 780-02’s D-subminiature
connector use 4-40 threads. This complies
with the original design standard for D-sub
connectors.
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 780-02 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
On the Model 780-02 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 780-02’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 Output
The 25-pin female D-subminiature connec-
tor on the back panel labeled Analog Moni-
tor Outputs provides access to the Model
780-02’s surround (7.1) monitor output.
The eight output channels are intended for
connection with inputs on a loudspeaker
system that provides seven main channels
and one subwoofer channel.
The monitor output channels are designed
for connection to audio amplifiers associ-
ated with monitor loudspeakers or to the
inputs of loudspeakers that contain inte-
grated amplifiers. The outputs are analog,
electronically balanced and will perform
optimally when driving loads of 2000
(2 k) ohms or greater. In most applications
3-pin male XLR connectors will be used to
interface with the inputs on the associated
amplifiers or amplified speakers. In this
case the + terminal would go to pin 2 of
the XLR, the – terminal to XLR pin 3, and
the shield terminal to XLR pin 1.

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Balanced operation of the monitor outputs
is the preferred connection method but un-
balanced operation does not pose a prob-
lem. To connect to an unbalanced load
connect the + terminal as signal high, and
only the Model 780-02’s shield terminal as
the signal low/shield. Leave the – terminal
unconnected. For correct unbalanced op-
eration, it is important not to connect – and
shield together
A wiring assembly prepared for the Model
780-02’s monitor outputs would typically
be identical to that of a TASCAM-type
output assembly. An assembly of this type
would have a 25-pin male D-subminiature
connector (DB-25M) on one end and eight
3-pin male XLR connectors on the other.
Please refer to Figure 5 for the exact con-
nection details. Again note that unlike a
TASCAM-type assembly, the Model 780-
02’s D-sub connectors use 4-40 threads.
Sync Input
The Model 780-02 requires a timing refer-
ence (sync) source so that the audio input
signals will be interpreted correctly. A con-
figuration 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 typically
occur when switching between input sources.
A better method is to connect a dedicated
timing reference signal to the Model 780-
02’s sync input connector. The connected
sync source must maintain a stable relation-
ship 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 worthwhile.
Word clock is a digital signal that is locked
in phase and frequency to the sample rate
of the associated audio sources. 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 specifically as a timing refer-
ence signal. Bi-level video sync signals were
originally provided to support NTSC (United
States) and PAL (European) analog broad-
cast applications, although they continue to
be used by contemporary digital video equip-
ment. Tri-level sync signals were primarily
associated with facilities that upgraded to
support high-definition (HD) video signals,
however the need for this type of sync sig-
nal seems to be waning. The Model 780-02
supports both bi-level and tri-level signals
at numerous rate combinations, allowing for
compatibility with various worldwide video
formats.
Signal Signal
Connections Channel High (+) Low (–) Shield
Left (L) 1 24 12 25
Right (R) 2 10 23 11
Center (C) 3 21 9 22
Subwoofer (SUB) 4 7 20 8
Surround Left (SL) 5 18 6 19
Surround Right (SR) 6 4 17 5
Back Left (BL) 7 15 3 16
Back Right (BR) 8 1 14 2
Notes: 1) Connector type on Model 780-02 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.
2) 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 Analog Monitor
Outputs

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With the wide range of allowable sync
sources proper Model 780-02 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 780-02’s back
panel. For flexibility the Model 780-02’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 780-02’s
sync input would typically want to have
the input termination enabled. If the sync
signal connected to the Model 780-02 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. The Model 780-02’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. 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 780-02’s internal
circuit common connection as well as to
the Model 780-02’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-
plications and should remain unconnected.
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 780-02 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
Connecting the Model 780-02
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 780-02 Central Controller. This
is used to interface the unit with Model
790 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 780-02 with the Model
790 units. A cable, approximately 20 feet
(6 meters) in length, is included in the ship-

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ping carton. The cable implements all nine
connector pins in a one-to-one manner.
Should an interconnecting cable of a differ-
ent length be required there’s no problem
for one to be fabricated and used. While
it can be wired in a one-to-one fashion
supporting all nine pins, only four connec-
tions are actually required: pin 1 (data +),
pin 6 (data –), pin 4 (DC +), and pin 9
(DC –). The Model 780-02’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 imple-
mentation has the advantages of providing
a shield for the data path and a more
robust common (return path) connection
(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
connecting a Model 780-02 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 780-02 to
a Model 790. The Model 780-02 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 780-02 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 volt-
age 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 resistance in both
conductors (DC + and DC –) when calculat-
ing 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 780-02’s ability to be controlled by
additional control consoles. At least one
Model 790 Control Console must be con-
nected to the Model 780-02 Central Control-
ler. 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
780-02.
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 780-02 is 9-pin female
D-subminiature (DE-9F). Connector uses 4-40
threaded inserts for locking with mating plug.
Figure 7. Connections between Model 780-02
and Model 790 and Model 71

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When connecting multiple control consoles
to a Model 780-02 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 780-02 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.
AC Mains Power
The Model 780-02 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
supplied 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 conform to the internationally
recognized color code and should be termi-
nated accordingly:
Connection Wire Color
Neutral (N) Light Blue
Line (L) Brown
Protective Earth (E) Green/Yellow
Safety Warning: The Model 780-02
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 780-02 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 780-02’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

Model 780-02/790 User Guide Issue 4, December 2020
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4-digit display, each Model 790 will then
momentarily display its address, its soft-
ware version, and the main and logic
device software versions of the associated
Model 780-02.
All connected Model 71 units will also go
through a power-up sequence after mains
power is applied to the Model 780-02.
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 780-02. 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 780-02’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.
Only after the Model 780-02 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 780-02 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
• Input Delay Settings
• Monitor Output Channel Level Offsets

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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 780-02 into their con-
figuration modes. Other connected Model
790 and Model 71 units will enter a standby
mode. When the Model 780-02 enters its
configuration mode it will immediately mute
the monitor outputs, providing an equip-
ment and speaker protection measure.
When a specific Model 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.
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 chang-
es 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
supposed to be that way! Seriously, the
top of the button is slightly recessed from
the back panel, making accidental activa-
tion unlikely. We didn’t want normal opera-
tion to cease because someone pushed a
Model 790 into a “rats nest” of schedules,
memos from management, and empty cof-
fee 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 780-02 Central Controller as
well as the Model 790 and Model 71 Con-
trol Consoles. Only the individual device
addresses are stored in each Model 790
and Model 71. All other configuration pa-
rameters are stored in the Model 780-02.
Model 790 Device Address
A unique device address must be assigned
to each Model 790 Control Console that is
connected to a Model 780-02. 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
default setting is appropriate. For installa-
tions 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

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setting that must be done on each individu-
al 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 in-
put 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 780-02,
even if their sample rates are identical. The
only compromise is that the SRC process
adds a fixed input-to-output (group) delay
of approximately 1 millisecond, a value that
shouldn’t impact most applications. By de-
fault SRC is enabled and it’s recommended
that it remains that way. However there
might be cases where this resource isn’t
desired and it can be disabled.
Bass Management
The Model 780-02 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
audio 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 the
analog monitor output channels and by de-
fault is disabled. The crossover point of the
seven main channels’ bass management
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 management
filters can be, as a group, selected. 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 780-02 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 780-02’s BNC input con-
nector then enabling termination is typically
appropriate. However, if the sync source is
being “shared” by multiple inputs then care

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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 780-02’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 monitor output level to a
known value. This is sometimes referred
to as “mixing to 85 dB on the monitors,” but
the exact value will depend on the applica-
tion. The StudioComm system allows a pre-
cise monitor output 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, downmix,
input mute/solo, and output mute func-
tions 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 monitor output
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 780-02’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

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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 monitor
output level in either an attenuation mode
or an SPL mode. In the attenuation 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 counter-
clockwise direction the display will show
negative values, reaching –70.0 before the
full mute function automatically mutes the
monitor output.
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 configuration
allows a specific SPL value to be associ-
ated with the stored reference level value.
In this way whenever the monitor output
channels are at their reference level, either
through activating the reference level func-
tion or manually adjusting the rotary level
control, the Model 790’s display will show
the configured SPL level. Whenever the
monitor output is not at the reference value
the display will show the current value,
in dB, relative to the reference 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 applications using the
default value of 85 would be appropriate,
reflecting the widely used audio-for-picture
85 dB monitoring reference 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
monitor output level by a preset amount.
The reduction is in dB relative to the moni-
tor outputs’ current level. There are four
dim level values available: 10, 15, 20, and
25 dB. The default value is 20 dB.

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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,
when the To Stereo downmix function is
active, LFE is reduced in level by 6 dB
and routed to both the left (L) and right
(R) monitor output channels. When in this
mode and the To Mono downmix function
is active the level of the LFE channel is
reduced by 6 dB and routed to the center
(C) monitor output channel.
Input Delay
A time delay can be added to the input
signals, allowing compensation for delays
that may be present on associated video
signals. The time delay applies to all input
sources and associated channels and can-
not be applied selectively. A configured de-
lay time is referenced to a sample rate of
48 kHz. In the case of input signals with a
sample rate of 48 kHz the delay range is 0
to 340 milliseconds in 1-millisecond steps.
For other sample rates the time must be
linearly scaled. For example, for a sample
rate of 96 kHz the actual time range is 0 to
170 milliseconds. In this case selecting a
delay of 120 on the Model 790 will result in
an actual time delay of 60 milliseconds.
For operating flexibility two different input
delay values can be selected and stored
during the configuration process. These
can then be enabled as required by the
user during normal system operation. The
default value for both delay A and delay
B is 0 milliseconds. Typical applications
would require only one input delay to be
configured. But in other cases two differ-
ent, both non-zero, input delay values can
be selected. This could be appropriate in
applications where multiple video display
systems are being used in the same con-
trol room or monitoring facility. Each video
display may exhibit its own processing
latency and audio would need to be “lined
up” accordingly. During normal Studio-
Comm operation a user can select the ap-
propriate input delay for the display system
currently being utilized.
Monitor Output Level Offsets
To provide assistance during room calibra-
tion, the relative output levels of the moni-
tor output channels can be adjusted over
a limited range. The eight channels can
be adjusted in 0.5-dB steps over a
±12-dB range. The default, of course, is
0 dB for all channels. During configuration
the displayed value represents the dB level
difference as compared to the nominal
output level. In most cases one channel
should serve as the overall reference level
and not be changed. This is typically the
center channel.