76/77 User Guide_3 - Studio Technologies

76/77 User Guide_3 - Studio Technologies
for Surround
Model 76 Central Controller and
Model 77 Control Console
User Guide
Issue 3, July 2008
This User Guide is applicable for systems consisting of:
Model 76: serial number M76-00151 and later with software version 1.02;
Model 77: M77-00151 and later with software version 1.01
© 2008 by Studio Technologies, Inc., all rights reserved
www.studio-tech.com
50224-0708, Issue 3
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for Surround
Table of Contents
Introduction ................................................................... 5
Installation .................................................................... 8
Advanced Installation ...................................................12
Configuration ................................................................13
Operation ......................................................................27
Technical Notes ............................................................31
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
mute or solo. In the mute mode, individual
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
channels can be muted as required. In
the solo mode, a single channel can be
monitored while the others are automatically muted. 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. The amount of level increase—the
“pop”—as well as the amount of attenuation can be configured to meet the needs
of specific applications.
Model 76/77 User Guide
Studio Technologies, Inc.
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
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
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for Surround
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 motioncontrol 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 inputchannel-to-output-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.
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
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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 American. 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
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
Model 76/77 User Guide
Studio Technologies, Inc.
for Surround
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.
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.
Model 76/77 User Guide
Studio Technologies, Inc.
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
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.
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Connections
Signal
High (+)
Signal
Low (–)
Shield
L
24
12
25
R
10
23
11
C
21
9
22
LFE
7
20
8
LS
18
6
19
RS
4
17
5
LB
15
3
16
RB
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
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
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
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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)
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
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.
Model 76/77 User Guide
Studio Technologies, Inc.
for Surround
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.
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
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.
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 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 factoryconfigured voltage. Note that an incorrect
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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
also momentarily display its address, it’s
software version, and the software version
of the associated Model 76.
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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
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
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for Surround
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.
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
Model 76/77 User Guide
Studio Technologies, Inc.
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
• Digital Input Reference Level
• Monitor Output Nominal Level
• Reference Level
• Overall Display Mode
• Reference Level in dB SPL
• Dim Level
• Remote Inputs
• LFE Downmix
• Channel Pop Solo Mode Offset Levels
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
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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.
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.
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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.
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!
Model 76/77 User Guide
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for Surround
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
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
Model 76/77 User Guide
Studio Technologies, Inc.
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:
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.
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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.
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
Issue 3, July 2008
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sound pressure level (SPL). Used in conjunction with the reference level in dB SPL
configuration and the stored reference
level, 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 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.
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 monitor output’s current level. There are four
dim level values available: –10.0, –15.0,
–20.0, and –25.0 dB.
Model 76/77 User Guide
Studio Technologies, Inc.
for Surround
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.
Model 76/77 User Guide
Studio Technologies, Inc.
Issue 3, July 2008
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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
and hold the Mute/Solo
Press
button to display and select the
Model 77’s device address.
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.
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.
Issue 3, July 2008
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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.
Issue 3, July 2008
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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 fully attenuated (minimum) 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.
Model 76/77 User Guide
Studio Technologies, Inc.
Issue 3, July 2008
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for Surround
Configuration—Overall Display Mode and Reference Level
in dB SPL
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.
and hold the Mute All button to
Press
display and set the overall display mode
and the reference level in dB SPL.
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.
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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.
Issue 3, July 2008
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for Surround
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.
Issue 3, July 2008
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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.
Model 76/77 User Guide
Studio Technologies, Inc.
Issue 3, July 2008
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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.
–20.0 dBFS digital input reference level.
+4.0 dBu monitor output nominal level.
Reference level is set for fully attenuated (minimum) monitor output level.
Attenuation display mode selected.
85.0 dB SPL reference level.
–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 delay is a safety feature ensuring that the factory defaults will not be accidently
restored.
Issue 3, July 2008
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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.
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.
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.
Model 76/77 User Guide
Studio Technologies, Inc.
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.
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,
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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 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.
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.
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.
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
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.
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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 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.
Model 76/77 User Guide
Studio Technologies, Inc.
for Surround
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.
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. The 4-digit display will
indicate the reference output level. Note
that the system’s default reference level is
full mute so “out of the box” the Model 77
will display four horizontal lines 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
Model 76/77 User Guide
Studio Technologies, Inc.
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
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.
It’s worth using a few sentences to discuss
the auto dim off function. Whenever dim
Issue 3, July 2008
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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 heart-stopping 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!
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. It is active
whenever the reference level function is
not active. 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 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.
Issue 3, July 2008
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The reference level LED will flash when the
rotary level control sets the output level to
be the same as the stored reference level.
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.
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. 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
and off, while the LEDs on the non-soloed
channels are not lit.
If the system has been selected for the
normal solo mode the solo LED associated
with the mute/solo mode button will light
steadily. If the system has been selected
for the channel pop solo mode the LED
will flash. At any time 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
Model 76/77 User Guide
Studio Technologies, Inc.
for Surround
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.
(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.
Model 76/77 User Guide
Studio Technologies, Inc.
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.
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
Issue 3, July 2008
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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.
“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
Issue 3, July 2008
Page 32
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
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 76/77 User Guide
Studio Technologies, Inc.
for Surround
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
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.
Model 76/77 User Guide
Studio Technologies, Inc.
Issue 3, July 2008
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
Control Data Type: RS-485
Dynamic Range: greater than 106 dB
Control Data Rate/Format: 115.2 kbit/s, 8-N-1
Crosstalk: 104 dB at 1 kHz; 90 dB at 20 kHz,
ref –1 dBFS input
Polling Interval: 50 milliseconds
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 3, July 2008
Page 34
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 3, July 2008
Page 35
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