for Surround - Studio Technologies

for Surround - Studio Technologies
for Surround
Model 76 Central Controller and
Model 77 Control Console
User Guide
Issue 7, August 2012
This User Guide is applicable for systems consisting of:
Model 76: serial number M76-00151 and later with software version 1.10;
Model 77: M77-00151 and later with software version 2.01 and later
© 2012 by Studio Technologies, Inc., all rights reserved
www.studio-tech.com
50224-0812, Issue 7
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for Surround
Table of Contents
Introduction ................................................................... 5
Installation .................................................................... 8
Advanced Installation ...................................................12
Configuration ................................................................13
Operation ......................................................................27
Technical Notes ............................................................32
Specifications ...............................................................34
Block Diagrams
Model 76 Central Controller
Model 77 Control Console
Model 76/77 User Guide
Studio Technologies, Inc.
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Model 76/77 User Guide
Studio Technologies, Inc.
for Surround
Introduction
What This User Guide Covers
This User Guide is designed to assist you
when installing and using the Model 76
Central Controller and one or more associated Model 77 Control Consoles.
Overview
As the production of both multi-channel
surround (5.1) and 2-channel stereo audio
material has become a day-to-day reality,
the need for monitoring these sources is
imperative for recording, post-production,
and broadcast facilities. Studio Technologies has addressed this need with the
StudioComm for Surround Model 76
Central Controller and Model 77 Control
Console. With its digital audio inputs and
analog outputs, it’s a simple task to integrate the system into virtually any facility.
The carefully selected group of features,
including downmix, channel mute/solo,
and reference level, make the system both
powerful and simple to use. And by using
the best of contemporary technology, as
well as following rigorous design practices,
the system’s audio quality is simply excellent. With the StudioComm for Surround
system any audio console, disk-based
recording system, or broadcast facility can
have a complete multi-channel monitor
system.
A StudioComm for Surround system starts
with the Model 76 Central Controller. It occupies just one rack space but allows connection of two surround (5.1) inputs and
three stereo inputs, along with separate
surround and stereo monitor outputs. The
surround and stereo inputs are digital and
compatible with AES3id sources. These
unbalanced digital signals utilize BNC
Model 76/77 User Guide
Studio Technologies, Inc.
connectors and are ubiquitous in most
post-production and broadcast environments. Sample rates of up to 192 kHz and
bit depth of up to 24 are directly supported.
And with the system’s dynamic range of
greater than 106 dB, there isn’t a problem ensuring that a source’s audio quality
is maintained. The monitor outputs are
analog, balanced line-level, with a maximum signal level of +26 dBu. They include
power-up/power-down protection circuitry
to help maintain the health of the connected loudspeaker systems.
Digital audio signals are interfaced with
the Model 76 using nine BNC connectors.
Analog monitor output signal connections
are made using one 25-pin D-subminiature
connector. An advanced flash-based
microcontroller integrated circuit provides
the logic “horsepower” for the unit. AC
mains power is connected directly to the
Model 76, which is factory selected for
100, 120, or 220/240 V operation. The
internal power supply utilizes two toroidal
mains transformers for quiet audio operation. One 9-pin D-subminiature connector
is used to connect the Model 76 with up to
four Model 77 Control Consoles. A second
9-pin “D-sub” connector is used to interface
remote control signals with the Model 76.
The Model 77 Control Console is the
“command center” that is designed to
reside at an operator’s location. It allows
fingertip selection of all monitoring functions. Numerous LED indicators provide
complete status information. A 4-digit
numeric display indicates the monitor
output level in real time. While most installations will use only one Model 77 Control
Console, up to four can be connected
to a Model 76 Central Controller. This provides multiple users with full control over
the monitoring system. Each Model 77
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connects to a Model 76 Central Controller
using a 9-pin cable. A major strength of the
Model 77 is its ability to configure, under
software control, many important operating
parameters.
Additional Details
The Model 77 provides five buttons and
associated LEDs for selection of the surround and stereo input sources to be monitored. While in most cases only one input
source will be monitored at a time, stereo
input C can be selected for simultaneous
monitoring with one of the two surround
or other two stereo inputs. This allows
the two selected inputs to be combined
(“summed”).
The surround and stereo monitor output
levels can be controlled by way of a large,
easy-to-use rotary control. The level control auto mute all function ensures that
the monitor output channels automatically
mute whenever the output level is set to
the full attenuation (minimum) position. By
using the reference level function, the monitor output level can set to a pre-configured
value. This is provided for audio-with-picture
applications that require a specific monitor
level. The reference level is easily configured by taking an electronic “snapshot” of
the desired monitor output level. For operator confirmation a 4-digit LED readout displays the level of the monitor output. It can
be configured to display 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 selected from four available
levels. A mute all function allows all monitor output channels to be simultaneously
muted.
The channel mute/solo section provides
individual channel control. One pushbutton
switch sets the operating mode for either
Figure 1. Model 76 Central Controller Front Panel
Control console
data active LED
Power
present LED
Figure 2. Model 76 Central Controller Back Panel
AC mains
input connection
To/from
Model 77
Control
Console
Analog monitor
output connections
Remote control
inputs
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Surround Input B
connections
Stereo Input C
connection
Stereo Input A and
Stereo Input B
connections
Surround Input A
connections
Model 76/77 User Guide
Studio Technologies, Inc.
for Surround
Channel mute/solo
Mute/solo
mode
Downmix
Input source
select
Monitor output
level display
Monitor Output
• Surround/stereo
• Reference level
• Mute all
• Dim
• Rotary level control
Figure 3. Model 77 Control Console Front Panel
mute or solo. In the mute mode, individual
channels can be muted as required. In
the solo mode, a single channel can be
monitored while the others are automatically muted. Depending on a configuration
setting, the mute/solo activity will impact
audio either pre (before) or post (after)
the downmix functions. In either solo mode
multiple channels can be simultaneously
selected for “soloing.” The flexibility of having both mute and solo available allows an
operator to quickly select the most comfortable and productive operating mode.
A special solo mode is also provided,
called channel pop solo, which offers a
unique aid in monitoring audio material.
Channel pop solo allows the level of a single channel to be raised while the level of
the other channels is reduced. This helps
to emphasize the content on one channel
without fully muting the others. Broadcast
applications can benefit from this solo
mode, allowing, for example, the center
channel to be highlighted while still maintaining some level on the other channels.
Model 76/77 User Guide
Studio Technologies, Inc.
The amount of level increase—the “pop”—
as well as the amount of attenuation can
be configured to meet the needs of specific
applications. Note that channel pop solo is
only available when the mute/solo function
is configured for post downmix.
Two functions allow the format of the
monitored sources to be checked for level
or phase inconsistencies. The surround to
stereo downmix function is used to create
a stereo signal from the selected surround
(5.1) source. The stereo to mono downmix
function allows audio on the left and right
channels to be added (summed) and monitored on the center output channel. The
two downmix functions can be simultaneously enabled, allowing a surround source
to be checked for mono compatibility. A
small speaker simulator feature is associated with the stereo to mono downmix
function. It is included to assist an operator in determining compatibility with “realworld” playback environments. It functions
by placing an audio bandpass filter into
the path of the mono signal, simulating the
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response of a loudspeaker associated with
an inexpensive television or clock radio.
Up to four Model 77 Control Consoles
can be connected to a Model 76 Central
Controller. The Model 76 can provide power
for the first two Model 77 units while an
external 12 volt DC source is required for
a third and fourth unit. The interconnecting
cables use 9-pin D-subminiature connectors that carry RS-485 data and DC power.
Remote control signals, including mute all
and dim, connect to the Model 76 using a
second 9-pin D-sub connector.
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,
audio consoles, and film motion-control
electronics. Two remote-control input functions are provided: mute all and dim. By providing access to these functions, talkback or
slate activity from an audio console or other
communications system can control the
monitor output level.
While the StudioComm for Surround
system for multi-channel monitoring will
do many wonderful things, it is not designed
to selectively route input signals to the different output channels. An input-channel-tooutput-channel relationship is maintained.
As an example, a signal that arrives on the
center channel of surround input A will output only on the center channel of the monitor output. Any rerouting of the input signals
must be done prior to their connection to
the StudioComm for Surround system. This
should not be a drawback in most facilities,
but it’s important to highlight this fact.
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Installation
In this section you will be installing the
Model 76 Central Controller in an equipment rack. Connections to the digital
audio inputs and analog monitor outputs
will be made. External equipment will be
interfaced to the remote control inputs. A
location will be selected for the first Model
77 Control Console and it will be connected to the Model 76. AC mains power will
be connected to the Model 76.
For advanced applications up to three
additional Model 77 Control Console units
can be connected to the Model 76. Please
refer to the Advanced Installation section
of this guide for details.
System Components
The main shipping carton contains one
each of the following: Model 76 Central
Controller, Model 77 Control Console,
20-foot (6.1 m) 9-pin D-sub interconnecting
cable, and user guide. Units destined for
North America also include an AC mains
cord. Your dealer or distributor should
provide an AC mains cord for destinations
outside of North America. Any additional
Model 77 Control Consoles will be shipped
in separate cartons.
Mounting the Model 76
The Model 76 Central Controller requires
one space in a standard 19-inch (48.3 cm)
equipment rack. Select a location that is
convenient for making connections to the
digital and analog audio signals as well as
interfacing with the Model 77 Control Console. A 20-foot (6.1 m) cable is supplied to
connect the Model 76 to the Model 77. If
the needs of a specific installation dictate,
an alternate-length interconnecting cable
Model 76/77 User Guide
Studio Technologies, Inc.
for Surround
can be fabricated and used. Secure the
Model 76 into the equipment rack using
two mounting screws per side.
Audio Connections
Audio signal connections are made by
way of multiple BNC jacks and a 25-pin
D-subminiature connector which are
located on the Model 76’s back panel.
Refer to Figure 2 for a detailed view of the
back panel. The BNC jacks will be used for
the digital audio signals. A cable assembly
with a 25-pin D-sub plug (male) on one
end and the desired connectors on the
other end will be used for connecting to
the analog monitor outputs.
Digital Audio Inputs
The nine female BNC connectors on the
Model 76’s back panel are used to interface with digital audio signal sources. Each
of the digital audio inputs is intended for
connection to an unbalanced digital audio
source that is compatible with the AES3id2001 standard. In broadcast environments
these signals may also be referred to as
following the SMPTE 276M standard. As
expected, these signal sources will be
provided in the form of coaxial cables with
BNC plugs attached. The Model 76 supports sampling rates of up to 192 kHz with
a word length (depth) of up to 24 bits. Note
that no master external synchronization
source is required as each input is independently self-clocking.
Balanced AES3 digital audio signals can
also be used with the Model 76’s inputs
so long as external coupling transformers
(“baluns”) are utilized. These impedancematching (110 ohms to 75 ohms) transformer assemblies typically provide a 3-pin
female XLR connector on their input and
a female BNC connector on their output.
Model 76/77 User Guide
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Monitor Outputs
The connector labeled Analog Monitor
Outputs provides access to the Model 76’s
6-channel (5.1) surround and 2-channel
stereo analog monitor outputs. The surround output channels are intended to
connect to the main surround loudspeaker
system incorporated in a facility. The stereo
output allows support for a secondary set
of stereo monitor loudspeakers.
The monitor output channels are designed
for connection to audio amplifiers associated with monitor loudspeakers, or to the
inputs of loudspeakers that contain integrated amplifiers. The monitor outputs are
electronically balanced and capable of
driving balanced or unbalanced loads of
600 ohms or greater. While balanced operation is preferred, unbalanced operation
does not pose a problem. To connect to
an unbalanced load connect the + terminal
as signal high, and both the – and shield
terminals as the signal low/shield. For
optimal unbalanced operation, it is important to connect both – and shield together
directly on the D-sub plug, not at the other
end of the harness.
Note that while the Model 76’s electronically balanced output circuits are capable
of driving loads of 600 ohms or greater
the output level will drop slightly as the
load impedance approaches 600 ohms.
A 0.5 dB difference in output level can be
expected as the load impedance changes
from 10 k ohms to 600 ohms.
The wiring scheme used by the D-subminiature connector complies with that
made popular by TASCAM® with their
DA-88® product. A wiring assembly prepared for the Model 76’s monitor outputs
is identical to that of a DA-88-style output
assembly. Please refer to Figure 4 for the
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Connections
Signal
High (+)
Signal
Low (–)
Shield
Surround L
24
12
25
Surround R
10
23
11
Surround C
21
9
22
Surround LFE
7
20
8
Surround LS
18
6
19
Surround RS
4
17
5
Stereo L
15
3
16
Stereo R
1
14
2
Notes: 1) Connector type on Model 76 is 25-pin D-subminiature
female. Installer must provide plug (male). Connector
uses 4-40 threaded inserts for locking with mating plug.
2) Wiring scheme follows TASCAM DA-88 convention.
Standard DA-88-type wiring harnesses are directly
compatible, with the exception of 4-40 screw threads
being required.
Figure 4. Connections for Analog Monitor
Outputs
exact connection details. Note that unlike
a DA-88-style assembly, the Model 76’s
D-sub connector uses 4-40 threads. This
complies with the original design standard
for D-subminiature connectors.
Remote Control Inputs
Support is provided for two remote control input functions: remote mute all and
remote dim. The inputs use logic gates,
“pulled up” to +5 volts DC 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 (ESD)
discharge, 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 female D-subminiature connector
is used to interface with the remote control
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Signal
Pin
Direction
RS-485 Data+
7
Input
RS-485 Data–
2
Input
Data Shield
1
Shield
Remote Mute All
5
Input
Remote Dim
6
Input
Remote Spare 1
8
Input
Remote Spare 2
9
Input
Remote Input Common
4
Common
Note: Connector type on Model 76 is 9-pin D-subminiature
female. Connector uses 4-40 threaded inserts for
locking with mating plug.
Figure 5. Connector Pin Out for Remote Control
Inputs (RS-485 connections not used)
inputs. This connector, labeled RS-485/
Remote Control Inputs, is located on the
back panel of the Model 76. Refer to
Figure 5 for the exact connection details.
Note that pin 4 (remote input common)
connects to the Model 76’s internal circuit common connection as well as the
Model 76’s chassis and mains earth connections. Figure 5 also shows two spare
remote control inputs (pins 8 and 9). These
are provided for future applications and
should remain unconnected. This connector also allows access to an RS-485 data
interface. This interface is not supported in
the Model 76 and, as such, pins 7 and 2
should remain unterminated.
Connecting the Model 76 to
the Model 77
A 9-pin female D-subminiature connector,
labeled To/From Control Console, is provided on the back panel of the Model 76
Central Controller. This is used to interface
the unit with a Model 77 Control Console.
A 9-pin female D-sub connector, labeled
To/From Central Controller, is provided
on the back panel of the Model 77 Control
Model 76/77 User Guide
Studio Technologies, Inc.
for Surround
Console. A cable with 9-pin male D-sub
connectors on each end is used to interconnect the Model 76 with the Model 77. A
20-foot (6.1-meter) cable is included in the
shipping 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 fashion
covering all nine pins, a minimum of only
four connections are required: pin 1 (data+),
pin 6 (data–), pin 4 (DC+), and pin 9 (DC–).
The Model 76’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 sleek, flexible,
and available in many colors. One pair and
shield can be used for the data connections
while the other pair and shield can be used
for the DC connections. This implementation has the advantages of providing a
shield for the data path and a more robust
common connection (two conductors including the shield) for the DC power circuit.
Refer to Figure 6 for details.
Signal
Pin
Data+
1
To/From Model 77
Data–
6
To/From Model 77
Data Shield
2
To/From Model 77
DC+
4
To Model 77
DC–
9
To Model 77
DC Power Shield
5
To/From Model 77
Note:
Direction
Connector type on Model 76 is 9-pin D-subminiature
female. Connector uses 4-40 threaded inserts for
locking with mating plug.
Figure 6. Connections between Model 76 and
Model 77
Model 76/77 User Guide
Studio Technologies, Inc.
A few simple calculations are required to
determine the maximum cable length when
connecting a Model 77 to a Model 76. 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 76
to the Model 77. The Model 76 supplies
12 volt DC nominal with a maximum current
of 200 milliamperes. The Model 77 requires
a minimum of 9 volts DC, 100 milliamperes
maximum for correct operation. (The voltage
must be measured directly at the Model 77’s
9-pin connector.) So the maximum interconnecting cable length is directly related to the
resistive voltage losses associated with the
two DC-carrying conductors. As the Model
76 supplies 12 volts and the Model 77 requires 9 volts minimum, this directly leads
to a 3 volt DC maximum drop due to the
interconnecting cable. Using Ohm’s law it’s
quite easy to determine whether the selected cable will support the desired interconnection length. Calculate the voltage drop by
multiplying the total resistance (in ohms) of
the proposed cable by 0.01 (the square of
the Model 77’s maximum required current).
Remember to include the resistance in both
the DC+ and DC– wires in the figure for the
total resistance.
AC Mains Power
The Model 76 is internally configured to
operate from nominal 100, 120, or 220/240
volts, 50/60 Hz. Units shipped to North
America are factory selected for 120 volt
operation. Units bound for Japan are generally selected for 100 volts while our friends
“down under” and in Europe receive units
set for 220/240 volts. Before connecting the
Model 76 to AC mains power, check to be
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certain that it is configured to match the local mains voltage. Look on the back panel
(adjacent to the power entry connector) for
an indication of the factory-configured voltage. Note that an incorrect configuration
could prevent operation or cause damage to the unit. Should it be necessary to
change the unit’s operating voltage it must
be performed only at the factory, or by a
factory-authorized service technician.
The Model 76 uses an IEC-standard C14
inlet connector to mate with the AC mains
cord. The AC mains cord should have a
C13 socket affixed with the wire colors
conforming to the internationally recognized CEE color code:
Connection
Neutral (N)
Line (L)
Protective Earth (E)
Wire Color
Light Blue
Brown
Green/Yellow
Safety Warning: The Model 76 does
not contain an AC mains disconnect
switch. As such, the AC mains cord
plug serves as the disconnection
device. Safety considerations require
that the plug and associated outlet
be easily accessible to allow rapid
disconnection of AC mains power
should it prove necessary.
As soon as AC mains power is applied,
the Model 76 Central Controller’s power
LED will light steadily. The control console data activity LED may also light. The
one or more connected Model 77 Control
Consoles will go through a power-up sequence, lighting each LED in succession.
Using its 4-digit display, each Model 77
will then momentarily display its software
version, unit address, and the software
version of the associated Model 76.
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Should an error be detected during a
Model 77’s start-up process Err1 may
be displayed. This would indicate a wiring
problem. Refer to the Technical Notes
section of this user guide for details.
Only after the Model 76 and at least one
connected Model 77 has correctly powered
up will system operation begin.
Advanced
Installation
Additional Model 77 Control
Consoles
Some installations will benefit from the
Model 76’s ability to be controlled by up
to four Model 77 Control Consoles. In
this section details on how to connect
additional Model 77 units will be reviewed.
While control of one Model 76 by up to
four Model 77 units is fully supported,
one limitation does exists. A Model 76
Central Controller is capable of providing
DC power for only one or two Model 77
units. Connecting a third or fourth Model
77 requires use of a separate source of
12 volt DC power. As each Model 77 unit
requires a maximum current of only 100
milliamperes, obtaining an external power
supply should not prove to be an issue.
Many low-cost external “wall wart” 12 volt
DC power supplies are available that will
be suitable to the task. For best operation
they should be a “switch-mode” type with
a filtered and regulated output.
As covered in a previous section of this
user guide, a 9-pin female D-subminiature
connector, labeled To/From Control Console, is provided on the back panel of the
Model 76 Central Controller. This is provided to interface the Model 76 with up to
Model 76/77 User Guide
Studio Technologies, Inc.
for Surround
four Model 77 Control Consoles. A 9-pin
D-sub connector, labeled To/From Central
Controller, is provided on the back panel
of each Model 77 Control Console. A cable
with 9-pin male D-sub connectors on each
end is used to interconnect each Model 77
with the Model 76. A 20-foot (6.1-meter)
cable is included in the main shipping
carton as well as each “solo” Model 77.
These cables implement all nine connector
pins in a one-to-one manner.
When connecting one or two Model 77
units to a Model 76 all nine pins of the
interconnecting cables can be connected
in parallel (“multed”). This will connect the
data signals between the units and route
the Model 76’s 12 volt DC power source to
both Model 77 units. A basic cable implementation would have pin 1 (data+), pin 6
(data–), pin 4 (DC+), and pin 9 (DC–)
connected. Connecting to a third and
fourth Model 77 requires that only pin 1
(data+) and pin 6 (data–) be connected
from the Model 76 to the third and fourth
Model 77 units. (This will connect the “data
bus” from the Model 76 to all the Model
77 Control Consoles.) An external 12 volt
DC source must provide power to the third
and fourth Model 77. This power source,
capable of supplying a minimum of 200
milliamperes of current (100 milliamperes
per Model 77), needs to connect to pin 4
(DC+) and pin 9 (DC–) on the third and
fourth unit.
Previous paragraphs of this user guide
discussed the Model 76 to Model 77 cable
length issues. Please review that information prior to creating the interconnection
scheme to be used for installing multiple
Model 77 units.
Model 76/77 User Guide
Studio Technologies, Inc.
Configuration
After the physical installation has been
completed it’s important that the system’s
configuration options be carefully reviewed.
In most cases one or more of the operating
parameters will need to be revised to meet
the needs of a specific installation. Many
of the parameters will impact the signal
flow in to and out of the Model 76 Central
Controller. Other parameters affect how the
one or more Model 77 Control Consoles
will display status conditions and respond
to user commands.
Configurable Parameters
Many StudioComm functions can be
configured to meet the exact needs of an
installation. The Model 77 Control Console
is used to display and select the desired
system configuration. Here’s an overview
of what can be configured:
• Model 77 Device Address
• Channel Mute/Solo Function
• Stereo Output
• Digital Input Reference Level
• Monitor Output Nominal Level
• Reference Level
• Overall Display Mode
• Reference Level in dB SPL
• Auto Reference Level Off
• Dim Level
• Remote Inputs
• LFE Downmix
• Channel Pop Solo Mode Offset Levels
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The configuration diagrams, located at the
end of this section, give details on setting
each parameter. An overview of each configurable parameter is provided in the following paragraphs.
Entering and Exiting the
Configuration Mode
A small button is located on the back of
each Model 77 Control Console, adjacent
to the 9-pin D-sub connector. Pressing and
holding this button for two seconds places
both the Model 76 and all the connected
Model 77 units into the configuration mode.
The Model 76 will immediately mute the
analog outputs as a protection measure.
In the configuration mode the Model 77’s array of buttons and LEDs no longer perform
their normal functions, instead allowing you
to observe and change many of the operating parameters. The mute and solo LEDs,
associated with the channel mute/solo
mode section, will light alternately to indicate that the configuration mode is active.
To leave the configuration mode and return
the Model 77 units to normal operation once
again press and hold the configure button
for two seconds. Note that configuration
changes are stored in nonvolatile memory
only after the configuration mode has been
exited.
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 it harder to accidentally
activate. We didn’t want normal operation to
cease because someone pushed the Model
77 into a “rats nest” of schedules, magazines, or burrito wrappers! But a firm press
with the fleshy part of an index finger should
do the trick.
Issue 7, August 2012
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There is no problem frequently “tweaking” the system’s operating parameters
to achieve the desired performance. The
configuration data is stored in nonvolatile memory, which is rated for thousands
of read and write cycles and a retention
time in tens of years. Note that memory
integrated circuits are located in both the
Model 76 Central Controller and the Model
77 Control Consoles. Only the individual
device address is stored in each Model
77. All other configuration parameters are
stored in the Model 76.
Model 77 Device Address
A unique device address must be assigned
to each Model 77 that is connected to a
Model 76. The choices are A1, A2, A3, or
A4, with the default address being A1. As
most installations will find only one Model
77 utilized, its default setting is appropriate. For installations that use a second,
third, or fourth Model 77 each unit must 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 setting that must be done on each
individual Model 77 unit. All other settings
can be made on any one of the connected
Model 77 units.
Channel Mute/Solo Function
The action of the channel mute/solo function can be configured. The default selection is for the mute/solo action to take
place post (after) the downmix functions.
Alternately, the function can be selected
such that mute or solo activity will be pre
(before) the downmix functions.
Model 76/77 User Guide
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for Surround
Stereo Output
In addition to a 6-channel surround monitor
output, a separate 2-channel stereo output is also provided. By default the stereo
output can be enabled by an operator. In
applications where stereo monitor loudspeakers are not connected to the stereo
output, the stereo output can be disabled.
This can minimize confusion, preventing
an operator from attempting to select the
stereo output.
Digital Input Reference Level
Configuring the digital input reference level
to match the sources associated with a
specific installation is an important step
toward achieving optimal audio performance. This ensures that the Model 76’s
digital audio receiver integrated circuits
are configured to match the digital input
source’s “0 VU” or average point. The digital input reference level can be selected
from four choices: –20.0, –18.0, –16.0, and
–14.0 dBFS. The Society of Motion Picture
and Television Engineers (SMPTE) recommends a reference level of –20 dBFS,
a value which is also extensively used
in professional audio applications. The
recommended digital reference level for
PAL broadcast applications is –18 dBFS.
The other two levels were included because… well, we can’t remember why! But
it seemed like a good idea at the time. If
you end up using the –16.0 or –14.0 dBFS
settings please let us know why and we’ll
add that information to the next version of
this user guide!
Monitor Output Nominal Level
The nominal level of the surround (5.1) and
stereo output channels is configured, as
a group, matching the requirements of an
installation. This setting defines the analog
Model 76/77 User Guide
Studio Technologies, Inc.
output level when a digital input source, at
its reference level, is connected and the
monitor output level is at its maximum. The
choices are 0.0 or +4.0 dBu. Most applications will find the +4.0 dBu setting correct
as it meets the dominant worldwide audio
standards. For broadcast applications that
follow the PAL standards the 0.0 dBu setting may be appropriate.
While sometimes not fully understood,
using the term dBu is more in line with
contemporary audio applications than the
outdated dBm and the “semi-pro” dBV
references; dBu refers to audio levels
without regard to their load impedance,
typical of situations where an output has a
low source impedance and is connected to
a high-impedance input. An analog audio
signal with a level of +4 dBu has an RMS
level of 1.228 volts. A 0 dBu signal has an
RMS level of 0.775 volts.
A final review of the two previously selected settings might now be in order. The
most common input and output combination will have a digital input reference level
of –20.0 dBFS and a monitor output nominal level of +4.0 dBu. For PAL broadcast
applications a setting of –18.0 dBFS for
the digital input and 0.0 dBu for the analog
outputs would be typical.
Reference Level
For audio-with-picture applications it’s
often beneficial for monitoring to be done
in reference to a known loudspeaker
level. This is often referred to as “mixing
to 85 dB” on the monitors. The StudioComm system allows a precise monitor
output level to be stored, and then enabled
by pressing the Model 77 button labeled
Reference Level. Setting the reference
level is very simple but care is required:
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1. Set up a precision sound pressure level
(SPL) measuring device at the desired
listening location.
2. Place the StudioComm system in the
normal operating mode, not the configuration mode. Be certain that the dim,
mute all, reference level, and downmix
functions are not active. The remote
mute all or remote dim functions must
not be active.
3. Use the Model 77 Control Console to
select the input source that contains the
desired reference signal source, e.g.,
pink noise.
4. Observing the SPL meter, adjust the
Model 77’s rotary level control until the
desired reference monitor system level
has been reached.
5. Being careful not to disturb the position
of the rotary level control, enter the configuration mode by pressing and holding
the configuration button located on the
Model 77’s back panel.
6. Once the configuration mode has been
entered, the monitor outputs will mute.
Press and hold the reference button; its
associated LED will begin to flash. After
five seconds the LED will light steadily
to indicate that a “snapshot” of the new
reference level has been taken. The
Model 77’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 maximum output level.
The reference level button can now be
released.
7. To complete the process the configuration mode must be exited. This is performed by again pressing and holding
the configure button for two seconds.
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The new reference level is now stored
in the Model 76’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 become
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 calibration
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 experiment with the configuration mode. Only
if you know the “secret” will you be able to
store a new value.
Overall Display Mode
The Model 77’s 4-digit numeric display can
be configured to display the output level in
either an attenuation mode or an SPL mode.
In the attenuation mode the output level is
shown as a reduction in value 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 moved in the counterclockwise direction the display will show negative
values, reaching approximately –69.5 dB
before the full mute function automatically
mutes the outputs.
In the SPL mode the display can be configured to allow the output level to be presented
to users in terms of the actual sound pressure level (SPL). Used in conjunction with
the reference level in dB SPL configuration
and the stored reference level, SPL mode
Model 76/77 User Guide
Studio Technologies, Inc.
for Surround
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 StudioComm users.
Reference Level in dB SPL
The reference level in dB SPL configuration allows a specific SPL value to be
associated with the stored reference level
value. In this way whenever the monitor output is at the reference level, either
through activating the reference level function or manually adjusting the rotary level
control, the Model 77’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 one-dB
steps. In many applications a 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 and 87, are well within
the allowable range.
Auto Reference Level Off
When auto reference level off is enabled,
the function automatically turns the reference level function off if a change is made
to the rotary level control while the reference level function is active.
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
Model 76/77 User Guide
Studio Technologies, Inc.
monitor output’s current level. There are
four dim level values available: –10.0,
–15.0, –20.0, and –25.0 dB.
Remote Mute All
Two configuration choices are associated
with the remote mute all function: disabled
and enabled. To utilize the remote mute all
function simply requires you to select the
enabled setting.
Remote Dim
Two configuration choices are associated
with the remote dim function: disabled and
enabled. To utilize the remote dim function
simply configure it for enabled.
LFE Downmix
When the surround to stereo downmix
mode is active the LFE channel typically
mutes. When the LFE downmix mode is
configured for enabled, the LFE channel
is attenuated by 3 dB and mixed into the
left and right channels. This is provided for
special applications and won’t typically be
used.
Channel Pop Solo Mode
Offset Levels
Two parameters can be configured that set
how the channel pop solo function will impact audio levels. The up offset level sets
the amount of increase (gain) that a channel will experience when it is soloed in the
channel pop solo mode. The down offset
level sets the amount of decrease (attenuation) the non-soloed channels experience
when a channel is active in the channel
pop solo mode.
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Configuration—Entering and Exiting Configuration Mode
and hold the configuration
 Press
button for 2 seconds to enter or
exit the configuration mode.
These LEDs will light alternately
when configuration mode is active.
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Model 76/77 User Guide
Studio Technologies, Inc.
for Surround
Configuration—Model 77 Device Address, Channel Mute/Solo
Function, and Stereo Output
and hold the Mute/Solo button
 Press
to display and configure the Model 77’s
device address, channel mute/solo
function, and stereo output function.
When the Mode button is pressed, use the Channel Mute/Solo L and R
buttons to select the channel mute/solo function. Use the buttons to
change the configuration. LED L lit means pre downmix channel mute/
solo; LED R lit means post downmix channel mute/solo.
When the
Mode button is
pressed, these
LEDs display
the status of the
stereo output
function. When
LED Surround
is lit the stereo
output function cannot be
enabled. When
LED Stereo is lit
the stereo output
function can be
enabled. Use the
button to change
the configuration.
When the mode button is pressed, use
the Level control to change this specific
Model 77’s device address.
Address can be either A1, A2, A3, or A4.
Default:
Device address A1.
Post downmix channel mute/solo.
Stereo output can be enabled.
Note:
The Model 77’s device address is the only parameter stored in the Model 77. All other parameters are stored
in the Model 76.
Model 76/77 User Guide
Studio Technologies, Inc.
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Configuration—Digital Input Reference Level and Monitor
Output Nominal Level
When the Stereo to Mono button is pressed, use the Channel
Mute/Solo L and R buttons to select the monitor output nominal
level. Use the buttons to change the configuration. LED L lit means
nominal level is 0.0 dBu; LED R lit means nominal level is +4.0 dBu.

Press and hold
the Stereo to
Mono button
to display and
select the
digital input
reference level
and monitor
output nominal
levels.
When the Stereo to Mono button is pressed, use the Level
control to adjust the digital input reference level. Available
levels are –20.0 dBFS, –18.0 dBFS, –16.0 dBFS, and
–14.0 dBFS.
Default:
–20.0 dBFS digital input reference level.
+4.0 dBu monitor output nominal level.
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Model 76/77 User Guide
Studio Technologies, Inc.
for Surround
Configuration—Reference Level
and hold the Reference Level button for 5 seconds to take a “snapshot”
 Press
of the current monitor output level at the time configuration mode was entered.
The Reference Level LED will flash when the button is initially pressed and
then light steadily when the “snapshot” has been taken.
Default:
Reference level set for –60.0 dB monitor output level.
Note:
The 5-second delay is a safety feature ensuring that the reference level will not be accidently changed.
To permanently store the new value, you must still exit the configuration mode.
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Studio Technologies, Inc.
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Configuration—Overall Display Mode, Reference Level in
dB SPL, and Auto Reference Level Off
When the Mute All button is pressed, use the Channel
Mute/Solo L and R buttons to select the overall display
mode. LED L lit means attenuation mode is selected;
LED R lit means SPL mode is selected. Use the buttons
to change the configuration.
When the Mute
All button is
pressed, use the
Reference Level
button to enable
or disable auto
reference level
off. When the
Reference Level
LED is lit auto
reference level
off is enabled.
Press and hold the Mute All button to
 display
and set the overall display mode,
the reference level in dB SPL, and auto
reference level off.
Default:
When the Mute All button is pressed,
use the Level control to adjust the
reference level in dB SPL.
Attenuation display mode selected.
85.0 dB SPL reference level.
Auto ref level off disabled.
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Model 76/77 User Guide
Studio Technologies, Inc.
for Surround
Configuration—Dim Level, Remote Mute All, and Remote Dim
This LED displays the configuration
of remote mute all. LED not lit means
remote mute all is disabled; LED lit
means enabled. Use the button to
change the configuration.
and hold the Dim button to
 Press
display and select the dim level,
remote mute all, and remote dim
input configurations.
Default:
This LED displays the configuration
of remote dim. LED not lit means
remote dim is disabled; LED lit
means enabled. Use the button to
change the configuration.
When the Dim button is pressed, the 4-digit
display shows the currently selected dim
level. Use the Level control to adjust the
dim level. Available dim levels are –10.0 dB,
–15.0 dB, –20.0 dB, and –25.0 dB.
–20.0 dB dim level.
Remote mute all disabled.
Remote dim disabled.
Model 76/77 User Guide
Studio Technologies, Inc.
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Configuration—LFE Downmix
This LED displays the configuration
of the LFE downmix mode. LED not lit
means LFE downmix mode is disabled;
LED lit means enabled. Use the button
to change the configuration.

Press and hold
the Surround to
Stereo button to
display and set
the LFE downmix
mode.
Default:
LFE downmix disabled.
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Model 76/77 User Guide
Studio Technologies, Inc.
for Surround
Configuration—Channel Pop Solo Mode Offset Levels

Press and hold
the Surround A
button to display
and select the
channel pop solo
up offset level.

Press and hold
the Surround B
button to display
and select the
channel pop solo
down offset level.
When the Surround A button is pressed, use the level
control to adjust the channel pop solo up offset level. The
range is 0.0 to 12.0 in 0.5 dB steps.
When the Surround B button is pressed, use the level
control to adjust the channel pop solo down offset level.
The range is –0.0 to –12.0 in 0.5 dB steps and full mute.
Full mute is selected by adjusting the level control past
–12.0, at which point the display will show ‘– – – –’.
Default:
6.0 dB channel pop solo up offset level.
–6.0 dB channel pop solo down offset level.
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Studio Technologies, Inc.
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Configuration—Restore Factory Defaults
and hold both the Surround/Stereo and Dim buttons for 5 seconds
 Press
to restore Model 77 factory defaults. Once defaults have been restored,
the associated LEDs will light. After the buttons are released, configuration mode will be exited and normal operation will resume.
Factory Defaults: Device address A1.
Post downmix channel mute/solo.
Stereo output can be enabled.
–20.0 dBFS digital input reference level.
+4.0 dBu monitor output nominal level.
Reference level is set for –60.0 dB monitor output level.
Attenuation display mode selected.
85.0 dB SPL reference level.
Auto reference level off disabled.
–20.0 dB dim level.
Remote mute all disabled.
Remote dim disabled.
LFE downmix disabled.
6.0 dB channel pop solo up offset level.
–6.0 dB channel pop solo down offset level.
Warning:
Each Model 77 unit must have a unique address. Restoring factory defaults will reset only this
specific Model 77 to device address A1. If another connected unit is already configured for
address A1, normal system operation will stop.
Note:
The 5-second button-press delay is a safety feature ensuring that the factory defaults will not be
accidently restored.
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Model 76/77 User Guide
Studio Technologies, Inc.
for Surround
Operation
Now that you’ve installed and configured
the system, you’re ready to go. You should
find operation very easy. However, taking
time to study this section of the guide may
prove valuable.
Upon power up the system will return to
the last operating condition, including all
selected sources, downmix modes, etc.
As a precaution, however, the monitor
output level will always return to its minimum value. The rotary level control or the
reference level button must then be used
to return the system to the desired monitor
output level.
Model 76 Central Controller
The Model 76’s front panel contains two
LEDs. The power LED should be lit whenever AC mains power is connected. The
data LED will light steadily whenever the
Model 76 is communicating correctly with
the one or more connected Model 77 units.
The data LED will remain off during the
system power-up process, something
that typically takes several seconds to
complete.
Model 77 Control Console
StudioComm for Surround operation is
controlled using Model 77 Control Consoles and, if connected, the remote control inputs. In most installations only one
Model 77 will be present but, as previously
discussed, up to four can be connected
to one Model 76. To make things easy to
describe, we’ve divided the operator functions into six main groups: input source
selection, downmix, monitor output general
functions, channel mute/solo, display and
display mode, and remote control inputs.
Model 76/77 User Guide
Studio Technologies, Inc.
Any change made to any one Model 77
will be reflected in the status LEDs and
displays on all the connected units. And
note that all Model 77 units function simultaneously—there is no priority of one unit
over the others.
Input Source Selection
To select an input source press one of the
five input source buttons. The corresponding LED will light to indicate that the input
has been selected. Typically, only one
source will be selected for monitoring at
any one time. However, input stereo C can
be selected by itself, or mixed (summed)
with one of the other four inputs. To accomplish this selection of two inputs is easy:
simply press and hold input stereo C then
press the button associated with the other
desired input source. The two corresponding LEDs will light. Alternately, press and
hold the first desired input (other than input
stereo C) and then press the input stereo
C button.
Downmix
Two downmix functions allow users to perform “real-world” audio format compatibility
checks. One function allows a surround
(5.1) signal to be “folded down” (mixed)
to stereo (2-channels). The other allows a
stereo (2-channel) signal to be converted
to mono. Using the downmix functions
simply requires pressing the desired button. The buttons are set to always “latch”
the functions on and off. An LED is located
above to each button and lights whenever
its respective function is active. Please
refer to the Technical Notes section of this
guide for a detailed description on how the
downmix functions perform their tasks.
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Surround to Stereo
When the surround to stereo downmix
function is enabled the LS, RS, and C
channels associated with a surround
signal are combined (“folded down”) with
the L and R signals to create a 2-channel
stereo (left and right) signal. The resulting
stereo signal, sometimes known as LoRo,
is routed to the L and R monitor output
channel. The C, LFE, LS, and RS monitor
output channels are muted. By utilizing this
downmix function phase relationships and
inter-channel level issues can be quickly
observed.
Note that a configuration setting allows the
LFE channel to be routed to both the L and
R outputs when surround to stereo downmix is active. As such, if this configuration
is selected the LFE channel won’t mute
when the surround to stereo downmix
function is active.
Stereo to Mono
The stereo to mono downmix function
combines the left and right audio channels
to create a single-channel monaural signal. This signal is sent out the C (center)
monitor output channel while the L, R, LS,
RS, and LFE monitor output channels are
muted.
Note that when a surround input source
is selected for monitoring, the surround
to stereo downmix function will automatically enable whenever the stereo to mono
downmix function is enabled. This ensures
that an operator will hear a mono signal
created by folding down all channels associated with the selected surround input.
The Model 77 associates the state of the
downmix functions with the currently selected input. For example, if surround B is
the selected input source and surround to
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stereo downmix is enabled, the condition
will be “remembered” when switching to a
stereo input source. Upon returning to surround B as the input source, the surround
to stereo downmix function will again become active.
Note that a specific downmix function can
only be enabled when it is applicable for
the currently selected input source. This
means that the surround to stereo downmix function can only be enabled when a
surround (5.1) input source is selected.
Bandpass Filter for Stereo to Mono
Downmix
A bandpass filter can be inserted into the
path of the stereo to mono downmix signal.
This allows the simulation of the response
of a loudspeaker associated with an inexpensive monaural television or portable
radio. This special feature has been included to assist an operator in determining compatibility with “real-world” playback
environments. The filter passes signals in
the range of 100 Hz to 5 kHz, while rejecting those above and below. For a detailed
technical description of the bandpass filter
please refer to the Technical Notes section
of this guide.
To enable the bandpass filter feature
requires knowing a “secret” button push
method. But it’s not much of a secret, as
you simply press and hold the stereo to
mono downmix button for two seconds
to enable the function. From that point
forward, whenever the stereo to mono
downmix function is enabled the bandpass
filter will also be enabled. To indicate that
the bandpass filter is enabled, the LED
associated with the downmix mono button
will flash whenever its associated function is enabled. To disable the bandpass
function, press and hold the stereo to
Model 76/77 User Guide
Studio Technologies, Inc.
for Surround
mono downmix button for two seconds. The
change will be indicated by the LED, which
will now light steadily whenever the stereo
to mono downmix function is enabled.
Monitor Output General
Functions
Four buttons and one rotary control are
associated with the monitor output functions. The buttons control operation of the
surround and stereo outputs, reference
level, mute all, and dim functions. The
rotary level control is used to manually
set the monitor output level.
Surround and Stereo Outputs
The surround/stereo function allows selection between two different loudspeaker systems. When the surround output is selected
the six surround (5.1) output channels are
active. The two channels associated with the
stereo output are muted. When the stereo
output is selected the left and right channels
associated with the stereo output become
active; the six channels of the surround
output mute.
Remember that the Model 77 Control Console can be configured to disable the surround/stereo button. If the button is pressed
and nothing happens, this must be the case!
Reference Level
The reference level button sets the monitor
output level to a preset value. Technical personnel, using a sound pressure level (SPL)
meter and precision signal source, should
have set this level to meet the requirements
of the specific monitoring environment. The
LED associated with the reference level
button will light whenever the function is
active. Whenever the reference level mode
is active the rotary level control is disabled.
Model 76/77 User Guide
Studio Technologies, Inc.
The 4-digit display will indicate the reference
output level. Note that the system’s default
reference level is –60.0 dB so “out of the
box” the Model 77 will display –60.0 when
reference level mode is enabled.
The reference level LED also serves as a
calibration aid. If the reference level mode is
not active, whenever the monitor output level
is precisely the same as that stored for the
reference value the reference LED will flash.
Mute All
The mute all function is highly complicated
to operate—not! Pressing the mute all button causes all monitor output channels to
mute. The 4-digit display indicates the mute
condition by showing four horizontal dashes.
The mute all button is always set to “latch”
the function on and off. The LED associated
with the mute all button will light whenever
mute all is active. Note that if mute all is
enabled via the remote mute all function,
the mute all LED will flash.
Dim
The dim function is provided for user convenience, allowing the monitor output level to
be reduced by a fixed amount. The Model
77’s configuration mode allows the dim level
to be selected from among four choices:
–10.0, –15.0, –20.0, or –25.0 dB. Pressing the dim button will enable the function.
The dim button is always set to “latch” the
function on and off. The 4-digit display will
indicate the revised monitor output level.
If the “dimmed” output level is equal to or
less than the minimum attenuated level, the
monitor output will go into full mute and the
display will show four horizontal dashes.
When dim is active the monitor output level
reduction will apply no matter whether the
monitor output level is being set by the
rotary level control or by the reference level
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button. The LED associated with the dim
button will light whenever dim is active. If
dim mode is enabled via the remote dim
function the dim LED will flash.
amount of level change in dB per step. A
little experimentation will allow the user to
acquire a good “feel” for how best to use the
control.
It’s worth using a few sentences to discuss
the auto dim off function. Whenever dim
is enabled due to the dim button being
pressed, as well as the rotary level control
being active (reference level mode is not
active), changing the setting of the rotary
level control will automatically turn off dim.
The auto dim off function is a unique attempt at protecting the aural health of
users. No longer will there be a heartstopping blast of audio when the dim button is pressed, supposedly to enable dim,
but actually turning dim off because it was
already enabled. It’s hard to explain unless
you’ve experienced this in person—trust
us, this situation can and does happen!
The reference level LED will flash when the
rotary level control sets the output level to
be the same as the stored reference level.
Note that the rotary level control is not active
when the reference level function is on and
auto reference level off is off. Whenever the
rotary level control is used to set the output
level for minimum, the monitor output channels will automatically mute. Technically, this
has the same effect as when the mute all
function is active.
Note that the auto dim off function is not
active whenever dim is enabled due to
the remote dim function being active. This
allows remote control equipment, such
as a talkback system, to reliably dim the
monitor outputs.
Rotary Level Control
The rotary level control is used to manually
adjust the monitor output level. The level
control provides the ability to adjust the
monitor output level over a 70 dB range.
Technically the rotary level control is a
24-step-per-revolution mechanical encoder. The amount of level change in dB per
step (“click”) will depend on how quickly
the control is turned. When changed slowly, each step represents a 0.5 dB change
in level. In this case, to traverse the entire
level range would require rotating the control more than four full turns. But the Model
77’s software detects when the control is
rotated more quickly and increases the
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Channel Mute/Solo
The mute/solo mode button and the six
monitor output channel buttons, along with
associated LEDs, work together to provide
excellent operating flexibility. Depending
on the configuration of the mute/solo function, mute or solo activity will take place pre
(before) or post (after) the downmix functions. When the mute/solo function has been
configured to post downmix the channel pop
solo mode can also be enabled.
The channel mute/solo mode button allows
the operator to select between the mute
and solo functions. It is also used to select
which solo mode, normal or channel pop,
is active. Going from mute mode to solo
mode, or vice-versa, clears all active mutes
or solos. Pressing the mode button twice is
a legitimate means of quickly clearing muted
or soloed channels.
In the mute mode, multiple channels can
be muted simultaneously. A channel that
is muted has its associated LED turned
on. In solo mode multiple channels can
be soloed simultaneously. A channel that
is soloed has its associated LED flash on
Model 76/77 User Guide
Studio Technologies, Inc.
for Surround
and off, while the LEDs on the non-soloed
channels are not lit.
The channel pop solo function is available
when the mute/solo function is configured
for post downmix. In this case, the system can be changed between normal solo
mode and channel pop solo mode. Simply
press and hold the mute/solo mode button for a few seconds until the solo LED
lights in the desired manner; steady for
normal solo mode and flashing for channel
pop solo mode. Once the state of the LED
changes (steady-to-flashing or vice-versa)
the desired solo mode becomes active.
The selected solo mode will be maintained
even after the system is powered down and
subsequently powered up.
Display and Display Mode
The Model 77’s 4-digit LED display shows
the output level as either the amount of attenuation or the sound pressure level (SPL).
Both figures will indicate level in dB. What
the digits actually represent will depend on
how the Model 77 has been configured.
If configured for the attenuation mode the
display will show the output level as an
attenuation value in reference to the maximum output. This is in the form of 0.5 db
steps less than 0.0 dB. So a display of -40.5
would indicate that the output is set to be
40.5 dB below the maximum level. As the
rotary level control is moved counterclockwise the output level will go down and the
indicated value will get more negative.
If the Model 77 is configured to display
the output level in SPL, the 4-digit display
will always show the output level in positive numbers. These numbers are intended
to represent the sound pressure level in
dB SPL, a figure that should directly relate
to the actual sound pressure level that the
loudspeaker system is presenting to users.
Model 76/77 User Guide
Studio Technologies, Inc.
(Typically, the level value would actually
be in dBC, the C-weighted sound pressure
level.) When the reference level button is
enabled, or the rotary level control is set so
that the reference level has been reached,
the display will typically show something
in the range of 82 to 87 dB. Assuming that
the monitoring environment has been correctly calibrated, this would indicate that
an average listening level of 85 dB, for
example, had been achieved.
As has been previously discussed, the
channel pop solo mode offers a unique
way of sonically highlighting an individual
channel. A channel selected for soloing
in this mode will have its level increased
while the other non-soloed channels will be
reduced in level. To highlight this condition
the letters POP will appear in the 4-digit
display whenever a channel is actively
being soloed in the channel pop solo
mode. This ensures that a user will understand that the monitor outputs no longer
represent the true inter-channel level
relationships.
Remote Control Inputs
Two remote control signals can be connected to the StudioComm system and
configured for operation. The two functions
are remote mute all and remote dim. When
an external signal activates remote mute
all the LED on the Model 77 associated
with the mute all button will flash. If mute
all was already active when the remote
mute all function is activated, the LED will
change from being steadily lit to flashing.
When an external signal activates remote
dim the LED on the Model 77 associated
with the dim button will flash. If dim was
already active when remote dim is activated, the LED will change from being
steadily lit to flashing.
Issue 7, August 2012
Page 31
for Surround
Technical Notes
Downmix
The downmix functions are implemented in
the Model 76 Central Controller’s hardware
using analog circuitry. The surround to stereo downmix function performs this action:
center (C) dropped in level by 6 dB and
routed to the left (L) and right (R) monitor
outputs; left surround (LS) dropped in level
by 3 dB and routed to the L monitor output;
right surround (RS) dropped in level by
3 dB and routed to the R monitor output;
low-frequency-enhancement (LFE) input
muted. A configuration choice allows the
LFE channel to be dropped by 3 dB and
routed to the L and R monitor outputs. This
will be generally enabled only for special
applications.
The stereo to mono downmix function
performs this action: L dropped in level by
3 dB and routed to the C monitor output;
R dropped in level by 3 dB and routed to
the C monitor output; L, R, LFE, LS and
RS monitor outputs mute; C input muted.
Bandpass Filter
The bandpass filter associated with the
stereo to mono downmix mode is created
by cascading (connecting in series) a
high-pass and a low-pass active filter.
Each filter is a Sallen-Key type, with a
12 dB-per-octave response. The high-pass
filter has a nominal –3 dB point at 100 Hz;
the low-pass at 5 kHz. For a detailed
description of the filters, refer to page 7
of the Model 76 schematic diagram.
Issue 7, August 2012
Page 32
“Hot” Disconnection of
Model 77 Control Consoles
There’s no problem relocating a Model 77
Control Console while the StudioComm for
surround system is powered up and operating. You can disconnect the 9-pin interconnecting cable from a Model 77, move
the unit, and then re-connect without issue.
If only one Model 77 is present, disconnecting it from the Model 76 will cause
the monitor outputs to mute. No clicks,
pops, or other noises will occur when the
Model 77 is again connected. The Model
77 will go through its standard power-up
sequence and then normal operation will
resume. If more than one Model 77 is connected, disconnecting one unit won’t cause
any change to the system’s operation. Only
when there are no Model 77 units connected to a Model 76 will the outputs mute. Of
course, any time a Model 77 is connected
it will go through its standard power-up
sequence prior to continuing with normal
operation.
Monitor Output Transient
Protection
The Model 76 Central Controller contains a
power-up/power-down transient protection
feature. This limits the chance of damage
to the monitor loudspeakers during the
time when AC mains voltage is connected,
disconnected, or has changed significantly
from nominal. A combination of hardware
and software is used to monitor the internal DC power supply “rails.” Until the DC
“rails” exceed their nominal operating voltage range, electromechanical relays maintain a short-circuit condition on the monitor
Model 76/77 User Guide
Studio Technologies, Inc.
for Surround
outputs. After the DC voltages are recognized as valid, a short delay takes place
before the relays are allowed to function
normally. Whenever the AC mains input
drops below its nominal operating voltage range, the DC “rails” will drop and the
relays will almost immediately go into their
muted state. During testing it was found
that upon AC mains power up the monitor
outputs remained very quiet; during power
down a small to moderate “tick” was the
worst that was heard.
Model 76 to Model 77
Connections
Figure 6 gives a detailed description of
the signals that connect the Model 76
Central Controller to the one or more
Model 77 Control Consoles. The Model
76 provides a 12 volt DC, 200 milliampere
maximum power source for use by one
or two Model 77 units. The DC output is
current-limited to minimize the chance
that a short-circuit condition will damage
the Model 76’s circuitry. An asynchronous,
bi-directional data interface links the
units. This uses an RS-485 hardware
connection scheme that operates at a
rate of 115.2 kbit/s and uses an 8-N-1
data format. The Model 76 communicates
with each Model 77 20 times-per-second,
receiving button and rotary level control
information and sending LED and 4-digit
display status data.
Mono-to-Center Polarity
It’s worthwhile to note that a polarity inversion takes place whenever the stereo to
mono downmix function is active; the left
(L) and right (R) input signals experience
a 180-degree inversion in the Model 76’s
Model 76/77 User Guide
Studio Technologies, Inc.
combining circuitry. This should not cause
a problem as monitoring audio signals over
a single loudspeaker is considered polarity
insensitive. Only during electrical testing
would this condition be detected.
Power-Up Messages and
Error Codes
Upon mains power being applied to the
Model 76 all connected Model 77 units
will go through a power-up sequence.
The sequence starts by each of the individual LEDs lighting in a “walk-through”
sequence. At the same time the 4-digit
display tests all its LED segments. Then,
a set of messages provide details on the
specific Model 77 and connected Model 76
software versions:
1. Displays 77
2. Displays Model 77’s software version
3. Displays Model 77’s unit address
(A1, A2, A3, or A4)
4. Displays 76
5. Displays Model 76’s software version
After a successful system power-up
sequence normal operation will then commence. Should a problem be encountered
during power up an error code may show
on the Model 77’s 4-digit display. If Err1
displays it indicates that communication
is not taking place with the Model 76. The
most likely cause would be incorrect wiring of the data pair linking the two units.
This could be caused by one or both of the
wires being open (not connected) or the
data pair being reversed.
Issue 7, August 2012
Page 33
for Surround
Specifications
Model 76 Central Controller
General Audio:
Frequency Response: digital inputs to monitor
outputs loaded with 10 k ohms
32 to 48 kHz Sample Rate: 20 Hz-20 kHz
±0.05 dB
88.2 to 96 kHz Sample Rate: 20 Hz-40 kHz
±0.05 dB
Downmix:
Functions: surround (5.1) to stereo, stereo to
mono
Surround to Stereo: LS @ –3 dB summed with L;
RS @ –3 dB summed with R; C @ –6 dB summed
with L and R; C, LFE, LS, and RS monitor outputs
mute
Stereo to Mono: L @ –3 dB summed with R @
–3 dB to C; L, R, LS, RS, and LFE monitor outputs
mute; C input mutes
176.4 to 192 kHz Sample Rate: 20 Hz to 40 kHz
±0.05 dB; down 0.5 dB at 80 kHz
Stereo to Mono Bandpass Filter:
Response: –3 dB @ 100 Hz and 5 kHz, nominal,
12 dB/octave
Distortion (THD+N): 0.004%, ref 1 kHz, +4 dBu
output
Control Console Interface:
Power: 12 volts DC, 200 milliamperes maximum
S/N Ratio: 86 dB, ref +4 dBu output
Dynamic Range: greater than 106 dB
Crosstalk: 104 dB at 1 kHz; 90 dB at 20 kHz,
ref –1 dBFS input
Digital Audio Inputs: 5
Configuration: organized as two surround (5.1)
and three stereo (2-channel)
Supported Sample Rates: 32, 44.1, 48, 88.2, 96,
176.4, and 192 kHz
Word Length: 24 bits maximum
Type: AES3id-2001 (SMPTE 276M)
Impedance: 75 ohms, unbalanced
Reference Level: –20.0, –18.0, –16.0, or
–14.0 dBFS, selectable
Sync Source: all inputs independently self-clocking
Monitor Outputs: 8
Configuration: organized as one surround (5.1)
and one stereo (2-channel)
Type: electronically balanced, compatible with
balanced or unbalanced loads
Nominal Level: 0.0 or +4.0 dBu, selectable
Maximum Level: +26 dBu into 600 ohms or
greater
Remote Control Inputs: 4
Functions: remote mute all, remote dim, two spare
Type: +5 V logic, activates on closure to system
common
Issue 7, August 2012
Page 34
Control Data Type: RS-485
Control Data Rate/Format: 115.2 kbit/s, 8-N-1
Polling Interval: 50 milliseconds
Connectors:
Digital Audio Inputs: 9, 75 ohm BNC
Monitor Outputs: 25-pin D-subminiature female
Control Console: 9-pin D-subminiature female
Remote Control Input: 9-pin D-subminiature
female
AC Mains: 3-blade, IEC 320 C14-compatible
(mates with IEC 320 C13)
AC Mains Requirement: 100, 120, or 220/240 V,
±10%, factory configured, 50/60 Hz, 30 watts
maximum
Dimensions (Overall):
19.00 inches wide (48.3 cm)
1.72 inches high (4.4 cm)
8.75 inches deep (22.2 cm)
Mounting: one space in a standard 19-inch rack
Weight: 8.8 pounds (4.0 kg)
Model 77 Control Console
Application: up to four Model 77 Control Consoles
can be connected to Model 76 Central Controller
(two can be powered by Model 76)
Power: 12 volts DC, maximum current 100
milliamperes, typically provided by Model 76
Central Controller
Model 76/77 User Guide
Studio Technologies, Inc.
for Surround
Control Data:
Type: RS-485
Data Rate/Format: 115.2 kbit/s, 8-N-1
Connector: 9-pin D-subminiature female
Dimensions (Overall):
7.20 inches wide (18.3 cm)
2.20 inches high (5.6 cm)
5.40 inches deep (13.7 cm)
Weight: 1.7 pounds (0.8 kg)
Specifications and information contained in this
User Guide subject to change without notice.
Model 76/77 User Guide
Studio Technologies, Inc.
Issue 7, August 2012
Page 35
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