Studio Technologies 761 User Manual

for Surround
Model 761 Central Controller and
Model 771 Control Console
User Guide
Issue 1, March 2008
This User Guide is applicable for systems consisting of:
Model 771: M771-00151 and later
© 2008 by Studio Technologies, Inc., all rights reserved
www.studio-tech.com
50226-0308, Issue 1
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for Surround

Table of Contents

Introduction ................................................................... 5
Installation .................................................................... 9
Confi guration ................................................................15
Operation ...................................................................... 29
Technical Notes ............................................................35
Specifi cations ...............................................................37
Appendix A ...................................................................38
Block Diagrams
Model 761 Central Controller
Model 771 Control Console
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Introduction

What This User Guide Covers
This User Guide is designed to assist you when installing and using the Model 761 Central Controller and the Model 771 Control Console.
Overview
As production of both 5.1 surround and 2-channel stereo audio material becomes a day-to-day reality, the need for monitor­ing these sources is imperative for broad­cast and post-production facilities. Studio Technologies has addressed this need with the StudioComm for Surround Model 761 Central Controller and Model 771 Control Console. While this system was designed to support the needs of a major televi­sion network, it should fi nd a comfortable home in many other applications as well. About the only system features that were selected to directly match this network’s re­quirements are related to the input source/ monitor output organization and naming conventions. However this implementation should match the needs of others too. With its digital audio inputs, analog outputs, and Dolby® E dialnorm support, it’s a simple task to integrate the system into a variety of facilities. The carefully selected feature set provides the most-needed resources and presents them in a way that remains simple to use. In addition, by using the best of contemporary technology, as well as following rigorous design practices, the system’s audio quality is simply excellent.
This version of the StudioComm for Sur­round system starts with the Model 771 Control Console, the “command center” that is designed to reside at the operator’s location. It allows fi ngertip selection of
all monitoring functions. Numerous LED indicators provide complete status infor­mation. A 4-digit numeric display indicates the monitor output or dialnorm level in real time. A major strength of the Model 771 is its ability to confi gure, under software control, a number of operating parameters. Using a 9-pin cable, the Model 771 con­nects to a Model 761 Central Controller.
The Model 761 Central Controller occupies just one rack space but allows connec­tion of two 5.1 surround inputs and three 2-channel stereo inputs. In addition, a 5.1 surround and special 2-channel stereo “di­rector cue” monitor output are provided.
All the 5.1 and stereo inputs are digital and are compatible with AES3id sources. These unbalanced digital signals utilize BNC connectors and are ubiquitous in most broadcast and many post-production environments. Sample rates of up to 192 kHz and bit depths of up to 24 are sup­ported. With the system’s dynamic range of greater than 106 dB, there isn’t a problem ensuring that the quality of all connected audio sources is maintained. The monitor outputs are analog, balanced line level, and have a maximum level of +26 dBu. They include power-up/power-down pro­tection circuitry to help maintain the health of the connected loudspeaker systems.
A source of Dolby E metadata can be connected to the Model 761 Central Con­troller. This RS-485/RS-422 115.2 kbit/s compatible signal carries numerous data elements, including one that represents the average dialog level of an associated audio program. This dialog normalization or “dialnorm” value is an integral part of many broadcast distribution systems, end­ing up in the audio playback systems of consumers. Hardware and software within
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the Model 761 separates out the dialnorm element that relates to one of the con­nected 5.1 surround audio sources. This dialnorm level value can then be displayed on the Model 771 Control Console, as well as used to automatically adjust the monitor output level. This provides a unique solution to the broadcast and post­production world, allowing a professional environment to accurately simulate an end user’s experience.
Digital audio sources are interfaced with the Model 761 using nine BNC connectors. Analog monitor output signal connections are made using one 25-pin D-subminia­ture connector. One 9-pin D-subminiature connector is used to link the Model 761 to the Model 771 Control Console. A second 9-pin D-sub connector is used to interface metadata and remote control signals with
the Model 761. An advanced fl ash-based microcontroller integrated circuit provides the logic “horsepower” for the unit. AC mains power is connected directly to the Model 761, 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.
Additional Details
The Model 771 provides four buttons and associated LEDs for selection of the input source to be monitored. A total of six sources can be monitored, one being active at a time. Two of the sources are 5.1 surround, while the other four are monau­ral. For fl exibility, one of the 5.1 inputs can be confi gured to be directly compatible with a 2-channel stereo source.
Figure 1. Model 761 Central Controller Front Panel
Figure 2. Model 761 Central Controller Back Panel
AC mains
input connection
To/from
Model 771
Control
Console
RS-485 and
remote control
inputs
Analog monitor
output connections
Stereo Input C
connection
Surround Input B
connections
Control console
to/from data
active LED
Surround Input A
connections
Metadata
active
LED
Stereo Input A and
Stereo Input B
connections
Powe r
present
LED
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Director cue
output enable
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Channel solo
Downmix
Input select
Figure 3. Model 771 Control Console Front Panel
The 5.1 monitor output levels can be controlled by way of a large, easy-to-use rotary control. The level control auto mute all function ensures the monitor output channels automatically mute when­ever the rotary level control is in its fully counterclockwise (minimum) position. By using the reference level function, the monitor output level can be set to a pre-confi gured value. This is provided for audio-with-picture applications which require a specifi c monitor level. The refer­ence level is easily confi gured by taking an electronic “snapshot” of the position of the rotary level control. For operator confi rma­tion, a 4-digit LED display shows the level of the monitor output. The display can be confi gured for either an attenuation mode or a direct db SPL value.
The dim function allows the monitor output level to be reduced by a fi xed dB amount. The dim level is selected from four avail­able levels. A mute all function allows all
Display mode
Dialnorm and monitor output level display
Monitor Output
• Dialnorm enable
• Reference level
• Mute all
• Dim
• Rotary level control
monitor output channels to be simultane­ously muted. The channel solo function allows one or more specifi c channels to be monitored while the others are auto­matically muted.
Two functions allow the format of the monitored sources to be checked for level or phase inconsistencies. The 5.1 to ste­reo downmix function is used to create a stereo signal from the selected 5.1 sur­round source. The stereo to mono down­mix function allows audio on the left and right channels to be added (summed) and monitored on the monitor’s system’s center channel. The two downmix functions can be simultaneously enabled, allowing a 5.1 surround source to be checked for mono compatibility.
A special “director cue” output function is provided. This allows a monaural or stereo input to be connected to the Model 761 Central Controller, which also has
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a dedicated 2-channel stereo output as­sociated with it. A button on the Model 771 Control Console allows on/off control of this signal. This is useful when control rooms need to monitor auxiliary audio signals, such as site-event cue signals, through an independent set of loudspeak­ers. For additional fl exibility, two remote control input functions are provided: mute all and dim. By providing access to these functions, talkback or communications activity from an audio console or matrix intercom system can control the level of the system’s 5.1 monitor outputs.
The Model 771 Control Console connects to, and is powered by, the Model 761 Cen­tral Controller. The interconnecting cable uses 9-pin D-subminiature connectors and carries RS-485 data and DC power. The Dolby E-compatible metadata connects to the Model 761 by way of a second 9-pin D-sub connector. Remote control signals, including mute all and dim, also connect to the Model 771 using the second 9-pin D-sub connector.
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Installation

In this section you will be installing the Model 761 Central Controller in an equip­ment rack. Connections to the digital audio inputs and analog monitor outputs will be made. A location will be selected for the Model 771 Control Console and it will be connected to the Model 761. If applicable, a source of Dolby E metadata may be con­nected. In addition, external equipment will be interfaced to the remote control inputs. AC mains power will be connected to the Model 761.
System Components
The shipping carton contains one each of the following: Model 761 Central Con­troller, Model 771 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.
Mounting the Model 761
The Model 761 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 to the Model 771 Control Console. A 20-foot (6.1 m) cable is supplied to con­nect the Model 761 to the Model 771. If the needs of a specifi c installation dictate, an alternate-length interconnecting cable can be fabricated and used. Secure the Model 761 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 761’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 761’s back panel are used to in­terface with digital audio signal sources. Please refer to Figure 4 for details on the supported inputs and the exact connectors to be used.
Note that the input source titles in Figure 4 refer to the button selections on the Model 771 Control Console. It includes support for three input sources each for both SD (standard-defi nition) and HD (high-defi ni­tion) programming. For SD the primary source is either 5.1 surround or 2-channel stereo while for HD the primary source is intended to be 5.1 surround. In both SD and HD the SAP (secondary audio program) and INTL (international) inputs are monaural. Of course, technically, all the digital audio inputs on the Model 761 provide the same excellent audio quality. The titles refer only to the intended signal sources.
Each of the available digital audio inputs is intended for connection to an unbal­anced digital audio source that is compat­ible with the AES3id-2001 standard. In broadcast environments these signals may also be referred to as following the SMPTE
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SD–Primary
This input selection allows a 5.1 surround or 2-channel stereo audio source to be monitored.
Left Source: Channel 1, Surround A L/R input
Right Source: Channel 2, Surround A L/R input
Center Source: Channel 1, Surround A C/LFE input
LFE Source: Channel 2, Surround A C/LFE input
LS Source: Channel 1, Surround A LS/RS input
RS Source: Channel 2, Surround A LS/RS input
SD–SAP
This input selection allows a mono audio source to be monitored.
Source: Channel 1, Stereo A L/R input
SD–INTL
This input selection allows a mono audio source to be monitored.
Source: Channel 2, Stereo A L/R input
HD–Primary
This input selection allows a 5.1 surround audio source to be monitored.
Left Source: Channel 1, Surround B L/R input
Right Source: Channel 2, Surround B L/R input
Center Source: Channel 1, Surround B C/LFE input
LFE Source: Channel 2, Surround B C/LFE input
LS Source: Channel 1, Surround B LS/RS input
RS Source: Channel 2, Surround B LS/RS input
HD–SAP
This input selection allows a mono audio source to be monitored.
Source: Channel 1, Stereo B L/R input
HD–INTL
This input selection allows a mono audio source to be monitored.
Source: Channel 2, Stereo B L/R input
Director Cue
This input selection allows a 2-channel stereo audio source to be monitored using separate analog outputs.
L Source: Channel 1, Stereo C L/R input
R Source: Channel 2, Stereo C L/R input
Figure 4. Model 761 Digital Audio Inputs
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276M standard. As expected, these signal sources will be provided in the form of coaxial cables with BNC plugs attached. The Model 761 supports sampling rates of up to 192 kHz with a word length (bit depth) of up to 24. Note that no external synchronization source is required as the inputs are all self-clocking.
Balanced AES3 digital audio signals can also be used with the Model 761’s inputs so long as external coupling transformers (“baluns”) are utilized. These impedance­matching (110 ohms to 75 ohms) trans­former assemblies typically use 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 761’s 5.1 surround and 2-channel stereo director cue monitor outputs. The surround output channels are intended to connect to the main surround loudspeaker system incorporated in a facility. The director cue output channels are provided to support a separate set of loudspeakers, allowing monitoring of inter- or intra-facility communications.
The monitor output channels are intended for connection to audio amplifi ers associ­ated with monitor loudspeakers, or to the inputs of loudspeakers that contain inte­grated amplifi ers. 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 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 761’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 761’s monitor outputs is identical to that of a DA-88-style output assembly. Please refer to Figure 5 for the exact connection details. Note that unlike a DA-88-style assembly, the Model 761’s D-sub connector uses 4-40 threads. This complies with the original design standard for D-subminiature connectors.
Signal Signal Connections High (+) 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
Director Cue L 15 3 16
Director Cue R 1 14 2
Notes: 1) Connector type on Model 761 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 5. Connections for Monitor and Director Cue Outputs
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Metadata Input
The Model 761 allows a source of Dolby E metadata to be directly connected. Hard­ware and software inside the Model 761 extracts (“parses”) a dialnorm data ele­ment from the connected metadata signal. This dialnorm value can then be viewed on the Model 771 and, if desired, used to control the monitor output levels. Refer to the Technical Notes section of this guide for details.
The metadata must be in the form of an RS-485 or RS-422 asynchronous serial signal. This differential signal must have a data rate of 115.2 kbit/s and a data for­mat of 8 data bits, no parity, and 1 stop bit (8-N-1). A metadata signal of this type is commonly available on metadata­generating or de-embedding equipment from broadcast equipment manufacturers such as Dolby Laboratories, Evertz, and NVISION.
While technically the Model 761’s RS-485 connection is bi-directional, in software it’s confi gured to only receive data. This means that there’s no reason why a signal already connected between two pieces of equipment can’t be connected in parallel (“bridged”) with the Model 761’s metadata input. Refer to Figure 6 for exact connec­tion details. While only the data+ and data– connections are absolutely necessary, a shield connection can also be made. Note that the connections for the metadata signal are reminiscent of the SMPTE 207M standard.
Note that Studio Technologies has found documentation supplied with some meta­data-generating equipment has incorrect pin-out information. This resulted in much head scratching and hair pulling. As such, it may be valuable to use a logic analyzer
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 761 is 9-pin D-subminiature female. Connector uses 4-40 threaded inserts for locking with mating plug.
Figure 6. Connector Pin Out for Metadata Input and Remote Control Inputs
or oscilloscope to confi rm that the meta­data source is terminated as expected prior to connecting it to the Model 761.
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 V 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 confi gured 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 761. Refer to Figure 6 for exact connection details. Note that pin 4 (remote input common) connects to the Model 761’s internal circuit com-
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mon connection as well as the Model 761’s chassis and mains earth connection. The two spare inputs are provided for future special applications. As such, pins 8 and 9 should remain unconnected.
Connecting the Model 761 to the Model 771
A 9-pin female D-subminiature connector, labeled To/From Control Console, is pro­vided on the back panel of the Model 761 Central Controller. Another 9-pin D-sub connector, labeled To/From Central Con­troller, is provided on the back panel of the Model 771 Control Console. A cable with 9-pin male D-sub connectors on each end is used to interconnect the two units. A 20-foot (6.1-meter) cable is included in the shipping carton of each system. This 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: data+, data–, DC+, and DC–. The Model 761’s connector pin-out scheme was designed to allow creation of an interconnecting cable which uses commonly available two­pair audio cable. This cable, consisting of two twisted pairs each with an individual shield, is often sleek, fl exible, and available in many colors. One pair and shield can be used for the data connections and 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 7 for details.
It’s hard to specify a maximum intercon­necting cable length. The data connections won’t be the limiting factor as the differ­ential transmission scheme of an RS-485 interface makes an interconnection in excess of 1000 feet (300+ meters) eas­ily possible. The culprit is the DC current supplied by the Model 761 to power the Model 771. This nominal 12 volt DC, 100 milliamperes maximum signal is subject to the resistive voltage losses associated with the interconnecting cable. For correct Model 771 performance the voltage sup­plied to the Model 771, when measured directly at the Model 771’s 9-pin connector and at full load, must be 9 volts minimum. This requires that the voltage drop due to the interconnecting cable be no more than 3 volts DC. Using Ohm’s law, it’s quite easy to determine whether the selected cable will support the desired interconnection length. To calculate the voltage drop, mul­tiply the total resistance (in ohms) of the proposed cable by 0.01 (the square of the maximum current). Remember to include the resistance in both the DC– and DC+ wires.
Signal Pin Direction
Data+ 1 To/From Model 771
Data– 6 To/From Model 771
Data Shield 2 To/From Model 771
DC+ 4 To Model 771
DC– 9 To Model 771
DC Power Shield 5 To/From Model 771
Note: Connector type on Model 761 is 9-pin D-subminiature female. Connector uses 4-40 threaded inserts for locking with mating plug.
Figure 7. Connections between Model 761 and Model 771
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AC Mains Power
The Model 761 is internally confi gured to operate from nominal 100, 120, or 220/240 V, 50/60 Hz. Units shipped to North America are factory selected for 120 V operation. Units bound for Japan are generally selected for 100 V while our friends “down under” and in Europe re­ceive units set for 220/240 V. Before con­necting the Model 761 to AC mains power, check to be certain that it is confi gured to match the local mains voltage. Look on the back panel (adjacent to the power entry connector) for the factory-confi gured volt­age. Note that an incorrect confi guration 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.
As soon as AC mains power is applied, the Model 761 Central Controller’s power LED will light steadily. The two activity LEDs may also light. The Model 771 Control Console will go through a power­up sequence, lighting each LED in succes­sion. Using its 4-digit display, the Model 771 will momentarily display both its, and the Model 761’s, software revisions.
The Model 761 uses an IEC-standard C14 connector to mate with the AC mains cord. The AC mains cord should have a C13 socket. The wire colors should conform to the internationally recognized CEE color code and be wired accordingly:
Connection Wire Color Neutral (N) Light Blue Line (L) Brown Protective Earth (E) Green/Yellow
Safety Warning: The Model 761 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.
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Confi guration
After the physical installation has been completed it’s important that the system’s confi guration 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 specifi c installation. Many of the parameters will impact the signal fl ow in to and out of the Model 761 Central Controller. Other parameters affect how the Model 771 Console will display status conditions and respond to user commands.
Confi gurable Parameters
Many StudioComm functions can be con­fi gured to meet the exact needs of an in­stallation. The Model 771 Control Console is used to display and select the desired system confi guration. Here’s an overview of what can be confi gured:
• Digital Input Sample Rate
• Digital Input Reference Level
• Monitor Output Nominal Level
Entering and Exiting the Confi guration Mode
A small button is located on the back of the Model 771 Control Console, adjacent to the 9-pin D-sub connector. Pressing and holding this button for two seconds places both the Model 761 and the Model 771 into the confi guration mode. The Model 761 will immediately mute the analog out­puts as a protection measure. In the con­fi guration mode the Model 771’s array of buttons and LEDs no longer perform their normal functions, instead they allow you to observe and change many of the operating parameters. The dialnorm and output level LEDs, associated with the display mode section, will light alternately to indicate that the confi guration mode is active.
To leave the confi guration mode and return the Model 771 to normal operation once again press and hold the confi gure button for two seconds. Note that confi guration changes are stored in nonvolatile memory only after the confi guration mode has been exited.
• SD Primary Input Type
• Director Cue Output Nominal Level
• Reference Level
• Overall Display Mode
• SPL Reference Level
• Dialnorm Reference Level
• Dim Level
• Remote Inputs
The confi guration diagrams, located at the end of this section, give details on set­ting each parameter. An overview of each confi gurable parameter is provided in the following paragraphs.
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Our apologies to those of you who fi nd the confi gure 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 771 into a “rats nest” of sched­ules, magazines, or burrito wrappers! But a fi rm press with the fl eshy part of an index fi nger should do the trick.
There is no problem frequently “tweak­ing” the Model 771’s operating parameters to achieve the desired performance. The confi guration data is stored in nonvola­tile memory, which is rated for thousands of read and write cycles and a retention
for Surround
time in tens of years. Note that the actual memory integrated circuit is located in the Model 761 Central Controller, rather than in the Model 771 Control Console.
Digital Input Sample Rate
The Model 761’s digital audio inputs are compatible with signals that have sample rates spanning the professional digital audio range of 32 to 192 kHz. A confi gura­tion setting allows the performance of the digital audio receiver integrated circuits to be optimized for three sample rate zones within the overall range. The choices are 32 to 48 kHz, 88.2 to 96 kHz, and 176.4 to 192 kHz. Note that selecting the 88.2 to 96 kHz setting will also allow signals with a sample rate of 32 to 48 kHz to be received. But audio performance of those lower-rate signals may be compromised by clock rate confusion in the receiver cir­cuitry. This situation also holds true for the
176.4 to 192 kHz setting which will allow signals with sample rates all the way down to 32 kHz to be received. But again the audio performance of the lower-rate sig­nals could suffer from clocking errors. Note that the inputs are confi gured as a group; no individual receivers can be confi gured to a range different from the others. This is generally not an issue as a single sample rate is typically selected for each facility.
Digital Input Reference Level
Confi guring the digital input reference level to match that of a specifi c installation is an important step toward achieving optimal audio performance. This ensures that the Model 761’s digital audio receiver integrat­ed circuits are set 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. 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 levels please let us know why.
Monitor Output Nominal Level
The nominal level of the six monitor output channels can be confi gured, as a group, to match the requirements of an installation. This setting defi nes the analog output level when a digital input source, at its refer­ence level, is connected and the monitor output level control is at its maximum. The choices are 0.0 dBu and +4.0 dBu. Most applications will fi nd 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 will have an RMS level of 0.775 volts.
A fi nal review of the selected setting might now be in order. The most common input and output combination will have a digital input reference level of –20 dBFS and a monitor output nominal level of +4 dBu.
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For PAL broadcast applications a setting of –18 dBFS for the digital input and 0 dBu for the analog outputs would be typical.
SD Primary Input Type
The type of source connected to the digital audio input connectors associated with the SD primary input selection can be con­fi gured. The choices are 5.1 surround or 2-channel stereo. When selected for 5.1 surround six input channels are associated with SD primary: L, R, C, LFE, LS, and RS. Selecting 5.1 surround as the input type also allows the 5.1 to stereo downmix function to be enabled. When the input type is selected for 2-channel stereo only the L and R channels are active for SD primary; C, LFE, LS, and RS are disabled. In addition, the 5.1 to stereo downmix function is disabled.
system allows a precise monitor output level to be stored, and then enabled by pressing the Model 771 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 confi g­uration mode. Be certain that the dim, mute all, reference, dialnorm enable, and downmix functions are not active. The remote mute or remote dim func­tions must also not be active.
3. Use the Model 771 Control Console to select the input source that contains the desired reference signal source, e.g., pink noise.
Director Cue Output Nominal Level
The nominal level of the director cue out­put can be confi gured from four available settings: +4.0 dBu, 0.0 dBu, –6 dBu, and –12.0 dBu. This range of settings is pro­vided so that compatibility can be achieved with a variety of connected devices. The +4.0 dBu and 0.0 dBu settings are ap­propriate for device inputs that expect to receive full line-level signals. Devices such as amplifi ed speakers will often perform better when receiving signals with a lower nominal level. In the latter case the ability to comfortably use a level potentiometer may be greatly enhanced using the –6.0 dBu or, especially, the –12.0 dBu setting.
Reference Level
For audio-with-picture applications it’s often benefi cial 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
4. Observing the SPL meter, adjust the Model 771’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 confi guration mode by pressing and holding the confi guration button located on the Model 771’s back panel.
6. Once the confi guration mode has been entered, the monitor outputs will mute. Press and hold the reference button; the associated LED will begin to fl ash. After fi ve seconds the LED will light solidly to indicate that a “snapshot” of the new reference level has been tak­en. The level 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 button can now be released.
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7. To complete the process the confi gura­tion mode must be exited. This is per­formed by again pressing and holding the confi gure button for two seconds. The new reference level is now stored in the Model 761’s nonvolatile memory. Only by repeating the entire procedure can the value be changed.
Once the confi guration mode has been exited, the monitor outputs will again be­come active. Confi rm that the correct level has been stored by pressing the reference button. The SPL meter should display the desired level. If not, repeat the calibration procedure to achieve the goal.
You might wonder why you have to press and hold the reference button for fi ve seconds before the selected value is rec­ognized. This is provided specifi cally so that unauthorized users won’t accidentally change the reference level while they ex­periment with the confi guration mode. Only if you know the “secret” will you be able to store a new value.
Overall Display Mode
The Model 771’s 4-digit numeric display can be confi gured 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 level control is at its fully clockwise position the maximum output level is obtained and the display will show
0.0. As the rotary control moves 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 confi gured to allow the output level to be presented to a user in terms of the actual sound pressure level (SPL). Used in conjunction with the SPL reference level confi guration and the stored confi guration level, SPL mode allows a user to see a vi­sual representation of the SPL level that is present in the listening environment. While correct implementation of the SPL display mode takes a little more care, it can offer an enhanced experience for StudioComm users.
SPL Reference Level
The SPL reference level confi guration allows a specifi c SPL number to be associ­ated with the stored reference level value. In this way whenever the monitor output is at the stored reference level, either through activating the reference level function or manually adjusting the rotary level con­trol, the Model 771’s display will show the confi gured 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 SPL reference level can be confi gured over a range of 70.0 to 100.0 dB in one-dB steps. In many applications a value of 85 would be appropriate, refl ecting the widely used audio-for-picture 85 dB monitoring refer­ence level. (Typically this 85 dB is really 85 dBC, indicating that a C-weighting fi lter has been applied to the measurement.) Other common reference SPL values, such as 82 and 87, are well within the allowable range.
Dialnorm Reference Level
The dialnorm reference level parameter is provided so that the StudioComm system can be confi gured to match a facilities’ or
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“plant” default dialnorm level. This value is used as a reference against which the sur­round monitor output level will, if enabled, be adjusted up or down in response to an incoming dialnorm value. The dialnorm reference level parameter can be adjusted over the entire –31 to –1 dB range but typical values will be in the range of –27 to –24. Implementation purists might want to select –31 dB as it may well be the “truest” implementation of the dialnorm scheme. In this way the system will, when enabled, reduce the monitor output level whenever dialnorm is different than –31 dB. But as bar fi ghts have broken out over decisions such as this we’ll leave the choice up to you! For additional information about dial­norm refer to the Technical Notes section of this user guide.
Dim Level
Restore Factory Defaults
The restore factory defaults function is pro­vided primarily for factory use. In this way a system can be shipped with the default settings selected. While you are welcome to use this function, be careful that your confi guration efforts aren’t wasted. Spe­cifi cally, be aware that the reference level is reset to minimum level. All the other parameters are fairly easy to set up, but resetting the reference level would require getting out an SPL meter and connecting a calibrated signal source. This is a hassle you may not need!
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.
Remote Mute All
Two confi guration 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 confi guration choices are associated with the remote dim function: disabled and enabled. To utilize the remote dim function simply confi gure it for enabled.
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Model 771 Confi guration—Entering and Exiting Confi guration Mode
Press and hold the confi guration
button for 2 seconds to enter or exit the confi guration mode.
These LEDs will light alternately when confi guration mode is active.
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Model 771 Confi guration—Digital Input Sample Rate, Digital Input Reference Level, and Monitor Output Nominal Level
When the Mute All button is pressed, the 4-digit display shows the currently selected digital input reference level. Use the 5.1 to Stereo button to increase the reference level. Use the Stereo to Mono button to decrease the reference level. Available digital input reference levels are –20.0 dBFS, –18.0 dBFS, –16.0 dBFS, and –14.0 dBFS.
When the Mute All button is pressed, use the Channel Solo L and R buttons to select the monitor output nominal level. Use the buttons to change the confi guration. LED L lit means nominal level is 0.0 dBu; LED R lit means nominal level is +4.0 dBu.
When the Mute All button is pressed, use these buttons to select the digital input sample rate. INTL lit means 32 to 48 kHz; SAP lit means 88.2 to 96 kHz; Primary lit means 176.4 to 192 kHz.
Default: 32 to 48 kHz digital input sample rate. –20.0 dBFS digital input reference level. +4.0 dBu monitor output nominal level.
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Press and hold the Mute All button
to display and select the digital input sample rate, digital input reference level, and monitor output nominal levels.
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Model 771 Confi guration—SD Primary Input Type
Use the 5.1 to Stereo and Stereo to Mono buttons to set the SD primary input type. 5.1 to Stereo LED lit means SD primary is 5.1; Stereo to Mono LED lit means SD primary is stereo.
Press and hold the HD/SD and Primary buttons to display and select the SD primary input type.
Default: Stereo SD primary input type.
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Model 771 Confi guration—Director Cue Output Nominal Level
Press and hold the Director Cue Output
Enable button to display and select the director cue output nominal level.
When the Director Cue Output Enable button is pressed, the 4-digit display shows the selected director cue output nominal level. Use the
5.1 to Stereo button to increase the nominal level. Use the Stereo to Mono button to decrease the nominal level. Available director cue output nominal levels are: +4.0 dBu, 0.0 dBu, –6.0 dBu, and –12.0 dBu.
Default: +4.0 dBu director cue output nominal level.
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Model 771 Confi guration—Reference Level
Press and hold the Reference Level button for 5 seconds to take a
“snapshot” of the level control’s setting at the time confi guration mode was entered. The Reference Level LED will fl ash when the button is initially pressed and then light solid 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 confi guration mode.
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Model 771 Confi guration—Overall Display Mode and Reference Level in dB SPL
When the Display Mode button is pressed, use the Channel 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 confi guration.
When the Display Mode button is pressed, use the
5.1 to Stereo but­ton to increase the reference level in dB SPL. Use the Stereo to Mono button to decrease the reference level. The range is 70.0 to
100.0 dB in one-dB steps.
Press and hold the Display Mode button to display and set the overall display mode and the SPL reference level.
Default: Attenuation display mode selected.
85.0 dB SPL reference level.
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Model 771 Confi guration—Dialnorm Reference Level
When the Dialnorm Enable button is pressed, use the 5.1 to Stereo button to increase the dialnorm reference level. Use the Stereo to Mono button to decrease the dialnorm refer­ence level. The range is –31 to –1 dB in one-dB steps.
Press and hold the Dialnorm
Enable button to display and set the dialnorm reference level.
Default: –31 dB dialnorm reference level.
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Model 771 Confi guration—Dim Level, Remote Mute All, and Remote Dim
This LED displays the confi guration of remote mute all. LED not lit means remote mute all is disabled; LED lit means enabled. Use the button to change the confi guration.
This LED displays the confi guration of remote dim. LED not lit means remote dim is disabled; LED lit means enabled. Use the button to change the confi guration.
When the Dim button is pressed, the 4-digit display shows the currently selected dim level. Use the 5.1 to Stereo button to decrease the dim level. Use the Stereo to Mono button to increase the dim level. Available dim levels are –10.0 dB, –15.0 dB, –20.0 dB, and –25.0 dB.
Default: –20.0 dB dim level. Remote mute all disabled. Remote dim disabled.
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Press and hold the Dim button to display
and select the dim level, remote mute all, and remote dim input confi gurations.
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Model 771 Confi guration—Restore Factory Defaults
Press and hold both the Dialnorm Enable and Dim buttons for 5 seconds
to restore Model 771 factory defaults. Once defaults have been restored, the associated LEDs will light. After the buttons are released, confi gura­tion mode will be exited and normal operation will resume.
Factory Defaults: 32 to 48 kHz digital input sample rate. –20.0 dBFS digital input reference level. +4.0 dBu monitor output nominal level. Stereo SD primary input type. +4.0 dBu director cue output nominal level. Reference level set for fully attenuated (minimum) monitor output level. Attenuation display mode selected.
85.0 dB SPL reference level.
–31 dB dialnorm reference level. –20.0 dB dim level. Remote mute all disabled. Remote dim disabled.
Note: The 5-second delay is a safety feature ensuring that the factory defaults will not be accidently restored.
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Operation

Now that you’ve installed and confi gured the system, you’re ready to go. You should fi nd operation very easy. However, taking time to study this section of the guide may prove valuable, especially regarding the system’s support for dialnorm.
Model 761 Central Controller
The Model 761’s front panel contains three LEDs. The power LED should be lit whenever AC mains power is connected. The control console activity LED will light steadily whenever the Model 761 is com­municating correctly with the Model 771. This LED will remain off during the system power-up process, something that typically takes several seconds to complete. The metadata activity LED will light whenever an active metadata signal has been con­nected and valid sync word information is being received.
Model 771 Control Console
StudioComm operation is controlled using the Model 771 Control Console and, if con­nected, the remote control inputs. To make things easy to describe, we’ve divided the StudioComm functions into seven main groups: input source selection, downmix, monitor output general functions, channel solo, director cue output, display and dis­play mode, and remote control inputs.
Input Source Selection
Four input select buttons work together to allow monitoring of up to six input sources. One source can be selected for monitor­ing at any one time. The input sources are grouped into two sets of three with the groups labeled SD and HD. Each group’s three input sources are labeled primary,
SAP, and international (INTL). The titles were selected to match the names com­monly assigned to sources in broadcast facilities. The SD (standard defi nition) primary input supports either a 5.1 sur­round or 2-channel stereo source. The HD (high defi nition) primary input supports a
5.1 surround source. The SD and HD SAP and international inputs each support a single-channel monaural source. SAP is a broadcast-derived acronym for secondary audio program. An “international” source simply refers to an alternate source that is typically associated with remotely origi­nated broadcast material. Note that, as would be expected, the titles of the actual sources connected to a specifi c Studio­Comm system may not match the Model 771’s descriptions. Local technical person­nel should be familiar with the actual con­nected sources.
The SD/HD button is used to select the active group. Pressing the button will alternate between the groups. Two LEDs are associated with the SD/HD button and indicate which of the groups is active. Three buttons are used to select the spe­cifi c input source to be monitored. They are labeled primary, SAP, and INTL (inter­national). LEDs are associated with these buttons and indicate which is active. Note that the Model 771 “remembers” which specifi c input was last selected for each group, so changing between groups will switch between two specifi c inputs. This allows rapid switching between, as an example, SD primary and HD SAP.
Downmix
Two downmix functions allow users to per­form “real-world” audio format compatibility checks. One function allows a 5.1 surround signal to be “folded down” (converted) to
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stereo. The other allows a stereo signal to be converted to mono. Using the down­mix functions simply requires pressing the designated buttons. The buttons are set to “latch” the functions on and off. An LED is located adjacent to each button and lights whenever its respective function is active.
When the 5.1 to stereo downmix func­tion is enabled the LS and RS channel’s associated with a 5.1 surround signal is combined (“folded down”) with the L and R signals to create a 2-channel stereo (left and right) signal. The resulting stereo signal is routed to the left and right moni­tor output channels. The LS, RS, and LFE monitor output channels are muted. By uti­lizing this downmix function phase relation­ships and inter-channel level issues can be quickly observed.
The stereo to monaural downmix function combines the left and right audio channels to create a single-channel monaural signal. This signal is sent to the center channel monitor output. The L, R, LS, RS, and LFE channels are muted. Please refer to the Technical Notes section of the guide for a detailed description on how the downmix functions perform their tasks.
Note that when a 5.1 surround source is selected as the input source, the 5.1 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 input.
The Model 771 associates the state of the downmix functions with the currently selected input. For example, if HD primary is the selected input source and 5.1 to stereo downmix is enabled, that condition will be “remembered” when switching to
another input source. Upon returning to HD primary as the input source, the 5.1 to stereo downmix function will again become active.
Note that a specifi c downmix function can only be enabled when it is applicable for the currently selected input source. This means that the 5.1 to stereo downmix function can only be enabled when a 5.1 surround input source is selected. Neither of the downmix functions can be enabled when one of the SAP or international input sources is selected. This is because these inputs are already monaural and wouldn’t be subject to any additional fold down.
Monitor Output General Functions
Four buttons and one rotary control are associated with the monitor output func­tions. The buttons control operation of the dim, mute all, reference level, and dialnorm enable functions. The rotary level control is used to manually set the monitor output level.
Dim
The dim function is provided for user convenience, allowing the monitor output level to be reduced by a fi xed amount. The Model 771’s confi guration mode allows the dim level to be selected from among four choices: –10, –15, –20, or –25 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, when selected for output level mode, 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 a full mute and the display will show four horizontal dashes. When dim is active the monitor
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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 fl ash.
It’s worth a 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!
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.
Mute All
The mute all function is highly complicated to operate—not! Pressing the mute all but­ton causes all six 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 mute all 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 fl ash.
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 exact monitoring environment. The LED associated with the reference level button lights 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 771 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 level is precisely the same as that stored for the reference value the reference LED will fl ash. The monitor output level can reach this exact level through the use of the rotary level control by itself or through the setting of the rotary level control in conjunction with the dialnorm data and dim function. Whatever path the output level takes to reach the reference level value, it will cause the reference level LED to fl ash!
Dialnorm Enable
Enabling the dialnorm level function sim­ply requires pressing the dialnorm enable button. The button provides a “latching” function so that the selected state is main­tained. An associated LED will light when­ever the function is active. The dialnorm enable function is only active when the input source is selected for HD primary. (This is because dialnorm level data is available only for that specifi c source.)
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When enabled, and HD primary is the input source, as the dialnorm level changes the output level will automatically increase or decrease as is appropriate. During confi gu­ration of the system a dialnorm reference level was entered. This level, typically in the range of –27 to –24 dB, is compared to the incoming dialnorm level value. If the re­ceived dialnorm level is less than the refer­ence value the output level is increased by the difference. If the received dialnorm level is greater than the reference value the out­put level is decreased, again by the differ­ence. Note that dialnorm levels are limited to a range of –31 to –1 dB. This restricts the maximum amount of level control to 30 dB.
The 4-digit display, when selected for out­put level mode, will display all level changes as they occur, including level changes due to dialnorm activity. The received dialnorm level values can themselves be viewed by selecting the display dialnorm mode.
In either display mode the decimal point “dot” in the lower-right corner of the display will light whenever the input dialnorm value matches the dialnorm reference value. This topic is described in greater detail in the Display and Display Mode section of this section of this guide. The Technical Notes section of this guide also will provide addi­tional useful information about dialnorm.
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 an approximately 70 dB range. The reference LED will fl ash when the rotary level control sets the output level to be the same as the stored reference level. Whenever the rotary
level control is set to its fully counterclock­wise position, the monitor output channels automatically mute. Technically, this has the same effect as when the mute all func­tion is active.
Channel Solo
The channel solo function allows specifi c channels to be selected for individual or group “solo” monitoring. The function takes place electrically “after” the input source selection, downmix, and level control func­tions. A channel selected for solo actu­ally doesn’t change, but the solo function causes the non-soloed monitor output channels to mute. This leaves only the soloed output active. Six buttons and six LED indicators are associated with the channel solo function. To solo a channel simply requires pressing one of the solo buttons. The buttons function in a press­to-enable/press-to-disable “latching” mode. The LED associated with a soloed chan­nel will fl ash to indicate that solo is active. More than one output channel can be se­lected for soloing at a time. The Model 771 even allows all six monitor output channels to be simultaneously selected for solo. This seems like an “all soloed so none soloed” mode but this condition is specifi cally allowed so that an output channel mute function can be provided. By fi rst soloing all output channels an operator can then “un-solo” specifi c channels, directly muting them. It’s a bit confusing to describe in words but is very simple to use and can be very useful resource—try it out and you’ll see!
Director Cue
Controlling the on/off state of the director cue output is simply a matter of pressing the director cue button. It functions in an
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alternate action manner to change the current state of the output. An associ­ated LED lights whenever the director cue output is active. The director cue output is not impacted, nor does it impact any of the other Model 771 functions.
Display and Display Mode
The 4-digit LED display can be selected to show either the output level or the dialnorm level. The display mode button is used to select the desired mode. Two LEDs are associated with the button, indi­cating which mode is active. When select­ed for the output level display mode, what the digits actually show will depend on how the Model 771 is confi gured. If confi gured for the attenuation mode the display will show the output level as an attenuation value in reference to the maximum output. For example, when the rotary level control is set to its fully clockwise position the dis­plays will typically show 0.0. This indicates that no attenuation is taking place in the signal path. (The signal path starts with the selected input source and ends with the monitor outputs.) As the rotary level control is moved counterclockwise readings such as –20.0 or –35.0 would be typical.
If the Model 771 is confi gured 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 fi gure 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. Assuming that the monitoring environment has been correctly calibrated, this would indicate that an average listening level of 85 dB SPL, for example, had been achieved.
When the 4-digit display is set for the dial­norm display mode a much different piece of information will be shown to the user. It will show the somewhat obscure but im­portant dialnorm level parameter that’s as­sociated with the HD primary input source. As has been covered in other parts of this guide, dialnorm is intended to provide a numeric value that represents the aver­age dialog level associated with an audio­for-picture element. Technically, dialnorm values can range from –31 to –1 dB but during actual operation they will typically be in the range of –30 to –20 dB. The value may change frequently in conjunction with changes to the actual audio signal. In other situations the dialnorm level will only change when certain sources, such as a live 5.1 surround event, are being “aired.” On the extreme end, in some facilities the dialnorm level is fi xed and won’t ever change. That’s not really in the spirit of what dialnorm is supposed to accomplish, but c’est la vie. Whatever the dialnorm level—the Model 771 will display it!
In both display modes a special feature is provided to assist users in knowing if the current dialnorm level matches a facility’s “house” reference. This reference level, typically in the range of –24 to –27 dB, is entered as part of the Model 771’s confi guration process. The “dot” in the lower-right corner of the 4-digit display will light whenever the incoming dialnorm level matches the stored reference level. Refer to Figure 8. This feature can be useful in broadcast transmission and distribution applications. In theory, any time the
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Figure 8. Incoming dialnorm level match “dot”
dot in the lower-right corner is not lit the current dialnorm level value is causing a level adjustment to take place. This level adjustment can be taking place in the StudioComm system, if the dialnorm enable function is active, as well as in downstream users of the broadcast signal.
When an external signal activates remote dim the LED on the Model 771 associ­ated with the dim function will fl ash. If dim was already active when remote dim is activated, the LED will change from being steadily lit to fl ashing.
Note that if a valid dialnorm source is not available the 4-digit display, when selected to display dialnorm, will show four horizon­tal bars. This could be due to a problem with the metadata signal connected to the Model 761 Central Controller. But more fre­quently this will simply be the normal result that occurs when the Model 771’s input is not selected for HD primary.
Remote Control Inputs
Two remote control signals can be con­nected to the StudioComm system and confi gured 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 771 associ­ated with mute all will fl ash. If mute all was already active when the remote mute all function is activated, the LED will change from being steadily lit to fl ashing.
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Technical Notes

Dialnorm
A source of Dolby E metadata can be con­nected to the Model 761 Central Controller. Within this fl ow of metadata frames will be a “dialnorm” level value that’s associated with the 5.1 surround signal that serves as the Model 761’s HD primary input. The dialnorm level value can be displayed by the Model 771 Control Console and used to control the monitor output level.
Technically, the metadata is in the form of a 115.2 kbit/s RS-485/RS-422 signal that contains a number of data elements, including one or more that represent the average dialog level (dialog normalization or dialnorm) in the audio program signals being carried over the digital audio por­tion of the related Dolby E interface. These dialnorm levels are associated with spe­cifi c programs within the 8-channel audio “stream.” Firmware within the Model 761 is able to parse (separate) the data elements, specifi cally separating the fi rst dialnorm level value in the metadata frame from the one or more that may be present later. To clarify, any dialnorm level elements that occur later in the same metadata frame are ignored. This method was selected as it was assumed that the fi rst dialnorm level element will always be associated with a
5.1 program. There’s a technical basis for why this should be true. In Dolby E a 5.1 program is always assigned to the fi rst six channels (channels 1-6). While there may be separate dialnorm values associated with audio channels 7 and 8, they are not relevant for correct StudioComm system operation.
Downmix
The downmix functions are implemented in the Model 761 Central Controller’s hardware using analog circuitry. The 5.1 to stereo downmix function performs this action: center (C) dropped in level by 6 dB and routed to left (L) and right (R) monitor outputs; left surround (LS) dropped in level by 3 dB and routed to L monitor output; right surround (RS) dropped in level by 3 dB and routed to R monitor output; low­frequency-enhancement (LFE) input mut­ed. 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; C, LS, RS, and LFE inputs mute.
“Hot” Disconnection of the Model 771 Control Console
There’s no problem relocating the Model 771 Control Console while your Studio­Comm system is operating. You can dis­connect the 9-pin interconnecting cable, move the unit, and then re-connect without issue. Upon disconnection the Model 761 Central Controller will mute the moni­tor output channels as well as saving the current operating parameters. No clicks, pops, or other noises will occur when the Model 771 is again connected. The Model 771 will go through its standard power-up sequence and then normal operation will resume.
Monitor Output Transient Protection
The Model 761 Central Controller contains a power-up/power-down transient protec­tion feature. This limits the chance of
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damage to the monitor loudspeakers during the time when AC mains voltage is connected, disconnected, or has changed signifi cantly from nominal. A combination of hardware and software is used to moni­tor one of the power supply “rails.” Until the AC mains input exceeds its nominal operating voltage range, electromechanical relays maintain a short-circuit condition on the monitor outputs. After the input volt­age is 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 relays immediately go to their mute state. During testing it was found that upon power up the monitor outputs remained very quiet; during power down a small to moderate “tick” was the worst that was heard.
Mono-to-Center Polarity
It’s worthwhile to note that a polarity inver­sion takes place whenever the stereo to mono downmix function is active. By de­sign, the left (L) and right (R) input signals experience a 180-degree inversion in the Model 761’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 761 to Model 771 Connections
Figure 7 gives a detailed description of the signals that connect the Model 761 Central Controller to the Model 771 Control Console. The Model 761 provides a +12 volt DC power source for use by the Model 771’s circuitry. The DC output is current-limited to minimize the chance that a short-circuit condition will damage the Model 761’s circuitry. An asynchronous, bi-directional, data interface links the two units. The RS-485 hardware connection scheme operates at a rate of 115.2 kbit/s and uses an 8-N-1 data format. The Model 761 communicates with the Model 771 20 times per second, receiving button and rotary level control information and send­ing LED and 4-digit display status data.
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Specifi cations
Model 761 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
176.4 to 192 kHz Sample Rate: 20 Hz to 40 kHz ±0.05 dB; down 0.5 dB at 80 kHz
Distortion (THD+N): 0.004%, ref 1 kHz, +4 dBu output
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: 9 Confi guration: organized as two 5.1 surround, one
2-channel stereo, and two dual-channel monaural
Supported Sample Rates: 32, 44.1, 48, 88.2, 96,
176.4, and 192 kHz
Word Length: 24 bit
Type: AES3id-2001 (SMPTE 276M)
Impedance: 75 ohms, unbalanced
Reference Level: –20, –18, –16, or –14 dBFS,
selectable
Sync Source: all inputs independently self-clocking
Monitor Outputs: 8 Confi guration: organized as one 5.1 surround and
one 2-channel stereo
Type: electronically balanced, compatible with balanced or unbalanced loads
Maximum Level: +26 dBu into 600 ohms or greater
Nominal Level, Channels 1-6 (5.1 Surround): 0 or +4 dBu, selectable
Nominal Level, Channels 7 and 8 (Director Cue): –12, –6, 0, or +4 dBu, selectable
Remote Control Inputs: 4 Function: remote mute all, remote dim, two spare
Type: +5 V logic, activates on closure to system
common
AC Mains Requirement: 100, 120, or 220/240 V, ±10%, factory confi gured, 50/60 Hz, 30 watts maximum
Connectors: Digital Audio Inputs: 9, 75 ohm BNC (per IEC
60169-8 Amendment 2)
Monitor Outputs: 25-pin D-subminiature female
Control Console: 9-pin D-subminiature female
Metadata and Remote Control Input: 9-pin
D-subminiature female
AC Mains: 3-blade, IEC 320 C14-compatible (mates with IEC 320 C13)
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 771 Control Console
Application: supports Model 761 Central Controller
Power: +12 volts DC, 100 mA maximum, provided
by Model 761 Central Controller
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)
Specifi cations and information contained in this User Guide subject to change without notice.
Dolby E Metadata Input: Type: RS-485/RS-422
Data Rate/Format: 115.2 kbit/s, 8-N-1
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Appendix A

Target Application
The StudioComm for Surround Models 761 and 771 were designed in conjunction with a major North American television broadcast network. While the system supports their direct application, many features were also included to support the needs of a broad group of po­tential users. The one area that the “761/771” does exactly match the needs of this network is in the channel input designations and the monitor output assignments. A summary of that information may prove to be interesting reading. Note that Model 761’s Surround A C/LFE and LS/RS inputs are not used for this application.
Channel Group Description: Standard Defi nition (SD) Audio
Model 761 Model 761 Monitor Channel Type Description Input Connection Output Connection
1 Stereo Left (L) Surround A L/R 5.1 L (Channel 1)
2 Stereo Right (R) Surround A L/R 5.1 R (Channel 2)
3 Monaural Secondary Audio Stereo A L/R 5.1 C (Channel 3) Program (SAP)
4 Monaural International Stereo A L/R 5.1 C (Channel 3)
5 Monaural Director Cue Stereo C L/R Stereo L (Channel 7)
6 Monaural Future Use Stereo C L/R Stereo R (Channel 8)
7 --- Future Use --- ---
8 --- Future Use --- ---
Channel Group Description: High Defi nition (HD) Audio
Model 761 Model 761 Monitor Channel Type Description Input Connection Output Connection
1 5.1 Left (L) Surround B L/R 5.1 L (Channel 1)
2 5.1 Right (R) Surround B L/R 5.1 R (Channel 2)
3 5.1 Center (C) Surround B C/LFE 5.1 C (Channel 3)
4 5.1 Low-Frequency Surround B C/LFE 5.1 LFE (Channel 4) Enhancement (LFE)
5 5.1 Left Surround (LS) Surround B LS/RS 5.1 LS (Channel 5)
6 5.1 Right Surround (RS) Surround B LS/RS 5.1 RS (Channel 6)
7 Monaural Secondary Audio Stereo B L/R 5.1 C (Channel 3) Program (SAP)
8 Monaural International Stereo B L/R 5.1 C (Channel 3)
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