Studio Technologies 55 User Manual

Model 55 Central Controller,

Model 56 Control Console ,

and Related Components

User Guide

Issue 3, December 1996

This User Guide is applicable for serial numbers:

Model 55 M55-00151 and later
Model 56 M56-00151 and later

© 1996 by Studio Technologies, Inc., all rights reserved

5520 West Touhy Avenue

Skokie, Illinois 60077 U.S.A.

Telephone [phone]

Fax [phone]

www.studio-tech.com

50063-1296, Issue 3

Issue 3, December 1996 Model 55/56 User Guide
Page 2 Studio Technologies, Inc.

Tab le of Contents

Foreword

Introduction ................................................................. 7

What This User Guide Covers ................................ 7

System Overview .................................................... 7

System Features ..................................................... 8

Installation ................................................................... 12

Configuration............................................................... 17

Model 56 Configuration Chart—Main Functions ..... 2 1

Model 56 Configuration Chart—

Alternate Functions ............................................ 22

Operation .................................................................... 23

Model 55 Central Controller .................................... 2 3

Model 56 Control Console....................................... 23

Talent Amplifiers ..................................................... 2 5

Troubleshooting .......................................................... 26

Technical Notes .......................................................... 28

Specifications .............................................................. 3 3

Appendix A.................................................................. 36

MIDI Messages ....................................................... 38

Block Diagrams

Model 55 Central Controller

Model 56 Control Console

Model 35/Model 38 Talent Amplifiers

Model 70 Interface

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Issue 3, December 1996 Model 55/56 User Guide
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Forew ord

I am pleased to present the StudioComm series of products. As both president and owner
of Studio Technologies, I take a very personal approach when designing products. Getting
older (40 as of this writing) has increased my appreciation of the more subtle things in
life—be they a part of nature or the nuances contained in a well-designed piece of elec­tronic equipment. Do the technical and operational aspects of a product work together
to “feel” right? A Studio Technologies’ design is ready to go only when I am completely
satisfied. My entire focus for the StudioComm series was to make a system that you’d
really enjoy using, and one that would perform reliably for years. I hope you share my
enthusiasm.

Many fine people worked toward making the StudioComm “happen.” Mitch Budniak (ace
consulting engineer) designed many of the circuits. Jim Cunningham contributed to the
analog design. Carrie Loving provided engineering support. Barbara Govednik coordinated
the marketing communications aspects. Ben Kamen designed the automatic testing rou­tines. Larry Leviton wrote the excellent micro-controller software. Al Lux designed
the printed circuit boards. Jim McGuire designed the graphics. Fred Roeck performed the
mechanical design. Joe Urbanczyk coordinated the safety testing and agency approvals.

Many thanks to Bob Tjarks, professional audio sales manager at Gand Music & Sound,
Northfield, Illinois. Bob brought to my attention the need for a product to serve digital audio
workstations. His product idea evolved into the StudioComm series. Additional thanks to
Timothy Powell of Metro Mobile Recording, Glenview, Illinois, who provided his excellent
ears when issues of sonic quality arose. His extensive field and studio experience was
extremely helpful in keeping me on the audio “straight and narrow.”

Please contact me with your questions, comments, and suggestions. I can be
reached by voice at [phone], fax at [phone], or via the Internet
@ www.studio-tech.com.

Sincerely,
Gordon K. Kapes

President

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Issue 3, December 1996 Model 55/56 User Guide
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Introduction

The Model 55 Central Controller, along
with the companion Model 56 Control
Console, are members of the StudioComm
family of products. The Models 55 and 56
are specifically designed to work in con­junction with digital audio workstations to
provide a full set of monitoring and com­munications functions. Features include
control room monitoring, meter output, an
integrated headphone system, dubbing,
and communications functions that include
talk to phones and slate. All StudioComm
functions perform to a level that rivals
even the largest recording consoles. Many
of the functions are user configurable,
allowing unmatched flexibility.

What This User Guide Covers

This User Guide is designed to assist you
when installing, configuring, and using
the Model 55 Central Controller, Model 56
Control Console, Model 35 Talent Ampli­fier, Model 38 Talent Amplifier, and related
components. A limited amount of trouble­shooting and background technical infor­mation is also provided. Should you
require detailed technical information
please refer to the StudioComm Service
Guide covering the Models 55, 56, 35, and

38. The Service Guide contains detailed
service information, including schematic
diagrams. The Service Guide is not
shipped with each StudioComm system,
but is available from the factory upon
request. It is free of charge to purchasers
of StudioComm equipment. Give us a call
or send a fax if you need this highly excit­ing document!

System Overview

A complete StudioComm system consists
of a rack-mounted central controller, a
desktop control console, and one or more
portable talent amplifier units. The Model
55 Central Controller and the Model 56
Control Console work together, intercon­necting using a standard 5-pin MIDI-style
cable.

Circuitry in the Model 55 routes any of
four stereo inputs to the control room,
meter, headphone, and dub outputs, with
commands provided by the Model 56
Control Console. The Model 56 Control
Console’s built-in microphone lets you
talk to the headphone output. It also allows
you to talk to the dub output, or to the dub
and headphone outputs using the slate
function.

The Model 35 Talent Amplifier is a por­table amplifier unit capable of driving one
or two pairs of high-impedance stereo
headphones. A single microphone-type
cable links the Model 35 with the Model 55
Central Controller. The Central Controller
provides power and left and right audio
over just three wires.

The Model 38 Talent Amplifier takes the
basics from the Model 35 and adds a
unique stereo preamplifier section. This
allows each Model 38 user to create an
individual headphone mix, solving the
classic problem of wanting “more me” in
the phones! Like the Model 35, the Model
38 is linked to the Model 55 Central Con­troller by a single microphone-type cable.

Model 55/56 User Guide Issue 3, December 1996
Studio Technologies, Inc. Page 7

System Features

Stereo Line Inputs

The Model 55 contains four stereo line­level inputs which are compatible with both
balanced and unbalanced signals. Each
input is independently software config­urable for a nominal input level of –10dBV
or +4dBu. This allows direct connection
with virtually any audio source. Each input
can also be configured to operate as a
mono input. In this manner, a signal
connected to the left input is routed to both
the left and right outputs.

Control Room Monitoring

The control room section provides a ste­reo line-level output for driving a power
amplifier associated with monitor loud­speakers. Four buttons are used to select

the input source to be monitored. Nor­mally, only one of the four input sources is
selected for monitoring. For special appli­cations, the system can be configured to
allow two input sources to be simulta­neously monitored. The control room level
is adjusted using a smooth-feeling rotary
potentiometer. The Dim button allows the
control room level to be temporarily re­duced. The Mono button allows the sum
(L+R) of the selected source to be sent as
the control room output.

Meter Output

The meter output provides a stereo output
that “follows” the source(s) selected for the
control room. The signal is not affected by
the control room level circuitry, but is
“post-mono.” The meter output is intended
to be connected to VU- or PPM-type meter

Model 55 Front Panel

Power

present LED

Model 56 Control Console

and Talent Amplifier

over current LED

Model 55 Back Panel

AC mains

connection

Mains voltage

configuration chart

Input data

present LED

To/from Model 56

Control Console

Output to talent

amplifiers

Meter

output

Dub

output

Control room

output

Stereo line

inputs 1-4

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Page 8 Studio Technologies, Inc.

panels that contain series current-limiting
resistors or input buffer amplifiers.

Dub Output

A stereo line-level output is provided as a
dub (copy) output. Any of the four inputs
can be assigned to the dub output. The
slate function allows communications
(voice) audio to be sent out the dub output.

Communications Functions

The Model 56 Control Console contains
an internal microphone that is used in
conjunction with the two communications
functions. The talk to phones function
either interrupts the phones source or adds
(sums or mixes) to the phones source. The
slate function interrupts the dub source
and, if configured, the headphone source
and connects communications audio. The
audio level of each communications func­tion is individually adjustable.

• Each of the four stereo line inputs can

be independently set for –10dBV or
+4dBu operating levels.

• Each input can be set for either mono

or stereo operation. In the mono mode
a signal connected to the left input is
sent to the left and right outputs.

• The dub output level can be set for a

nominal –10dBV or +4dBu output level.

• Unique to the system is the ability to

configure the dim level to one of three
values, allowing a 15, 20, or 25dB
reduction when dim is active.

• Three functions can be set for push-to-

latch operation if desired: talk to
phones, slate, and control room mono.

• The auto dim off function, when config-

ured, allows any change in the control
room level potentiometer to automati­cally turn off an active dim state.

MIDI Control

All Model 55 Central Controller functions
are controlled using system-exclusive
MIDI messages. The Model 56 Control
Console “speaks” this language, and in
most applications a Model 56 will be uti­lized. In special applications the Model 55
Central Controller can be connected
directly to a MIDI bus, allowing the creation
of a fully automated recording or audio
routing system. For more information on
MIDI support, refer to Appendix A.

Configuration

The Model 56 Control Console can be
configured to make the system meet a
user’s exact operating environment. All
configuration parameters, along with
“power down” operation conditions, are
stored in nonvolatile memory.

• The slate function can be configured to

talk to the dub output, or talk to both the
dub and headphone outputs.

• The talk to phones function can be set

to interrupt the normal phones source or
add (sums) to the phones source.

• The system can be configured to allow

only one input source, or one or two
input sources to be selected as the
control room source(s).

Headphone Monitoring

The StudioComm system contains an
integrated, full-featured headphone (cue)
system. Up to four Model 35 or Model 38
Talent Amplifiers can be connected to
the Model 55’s talent amplifier output. A
single 3-conductor microphone-type cable
carries power and stereo audio.

Model 55/56 User Guide Issue 3, December 1996
Studio Technologies, Inc. Page 9

Model 56 Front Panel

Configure button switches
between normal operation

and configure mode

Built-in microphone for
communications functions
(talk to phones, slate)

Source selection

for control room (CR),

headphones, and dub;

three columns of LEDs

show the currently

selected sources

Model 56 Back Panel

Change the control room
level; listen in mono
(L+R); or reduce the level
by a preset amount

Talk to the headphones;
slate; set communications
levels

Connection

to the Model 55

Central Controller

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Page 10 Studio Technologies, Inc.

Using the Model 56 Control Console,
any of the four stereo inputs can be as­signed to the talent amplifier output. The
talk to phones and slate functions allow
communications (voice) audio to be sent
to the talent amps. The talent amplifier
output is short circuit protected. Error
conditions are displayed by the Over
Current LED on the Model 55’s front
panel.

Model 35 Front Panel

Each Model 35 and Model 38 Talent
Amplifier can drive two sets of high­impedance headphones (>150Ω). The
audio output is loud, and very “clean.”
The units feature a built-in level control,
a stereo/mono switch, and a power
present LED.

The Model 38 Talent Amplifier takes the
basics from the Model 35 and adds a
unique stereo preamplifier section. This

Power present

LED

Headphone output

level control

Switch between

stereo and mono

(L+R) output

Two headphone

outputs

Model 35 Back Panel

Connects to additional

talent amplifiers

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Studio Technologies, Inc. Page 11

Connects to the Model 55 or another talent

amplifier’s loop thru connector

allows a musician’s microphone or line­level signal to be “looped” through the
Model 38, boosted by its preamp, and then
combined with the stereo cue mix supplied
by the Model 55. This provides each
Model 38 with an individual headphone
mix, solving the classic problem of wanting
“more me” in the phones! Like the Model
35, the Model 38 is linked with a Model 55
Central Controller by a single cable.

Model 38 Front Panel

Installation

In this section you will be installing the
Model 55 Central Controller in an equip­ment rack. Audio input and output connec­tions will be made using the Model 55’s
multitude of jacks. One or more Model 35
or Model 38 Talent Amplifiers may be
connected. A location will be selected for

Power present

LED

Mic/Line button switches

the talent input between

microphone and line level

Model 38 Back Panel

Connects to additional

talent amplifiers

Talent level

to phones

Connects to the Model

55 or another talent
amplifier’s loop thru

connector

Switch between

stereo and mono

(L only) for the

talent input

Loop thru connectors parallel the

talent inputs for routing to a digital

audio workstation, effects device,

microphone preamp, etc.

Cue mix

level to
phones

Two headphone outputs

Switch between stereo

and mono (L+R) for

the cue mix

Connects to talent

sources such as key-

boards or microphones

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Page 12 Studio Technologies, Inc.

the Model 56 Control Console, and it will
be connected to the Model 55. AC mains
power will be connected to the Model 55.

System Components

The main StudioComm shipping carton
contains a Model 55 Central Controller,
Model 56 Control Console, 5-conductor
MIDI-style cable, User Guide, and war­ranty card. Units destined for North
America are shipped with an AC mains
cord. Your dealer or distributor will provide
an AC mains cord for non-North American
destinations. Model 35 and Model 38
Talent Amplifiers, along with accessories,
will be contained in separate cartons.
Please check to ensure you have every­thing you need.

Mounting the Model 55

The Model 55 requires one space in a
standard 19-inch (48.3cm) equipment
rack. Select a location near where the
Model 56 Control Console will be located.
A cable is provided to connect the Model
55 to the Model 56. You can supply a
longer cable, however 50 feet (15.3m) is
the recommended maximum length. It is
desirable to locate the Model 55 to allow
easy access to both the front and the back
panels. The back panel contains all of
the input and output connectors, while
the front panel contains several LED
indicators. The Model 55 is secured to
the equipment rack using two mounting
screws per side.

Audio Inputs and Outputs

The Model 55’s line-level audio input and
output connections are made using ¼-inch
3-conductor phone jacks. Don’t be con­cerned about our use of phone jacks as
part of a “professional” product. The jacks

Balanced Connection

(Input & Output)

Ring (–)

Tip ( + )

Sleeve

(Shield)

(Switchcraft No. 297, Neutrik NP3C, or equivalent)

used are manufactured by Neutrik, and
feature gold-plated contacts for high reli­ability.

Caution: For reliable audio intercon­nection, the plugs you use must comply
with industry standard RS-453.
Switchcraft No. 297, Neutrik NP3C, or
equivalent will work correctly. Refer to
the Technical Notes section for details.

Stereo Line Inputs

The Model 55 provides four stereo line­level inputs. Each input is electronically
balanced, and can be configured for com­patibility with –10dBV or +4dBu signal
levels. The Model 56 Control Console
gives you push-button control, so you can
easily change input sensitivities at any
time (refer to the Configuration section
under Input Sensitivity). Monaural sources
should be connected to the left (L) input
and configured for mono operation (refer
to the Configuration section under Stereo/
Mono Input).

Prepare the mating connectors (plugs)
so that tip is signal high (+ or hot), ring is
low (– or cold), and sleeve is shield. With
an unbalanced source connect the tip to

Model 55/56 User Guide Issue 3, December 1996
Studio Technologies, Inc. Page 13

high (+ or hot), and both the ring and
sleeve to shield. If connecting to an
unbalanced source in this manner results
in hum or noise, connect tip to high (+ or
hot) and ring to shield; leave the sleeve
unterminated.

The meter output utilizes two ¼-inch
3-conductor phone jacks for interconnec­tion. Prepare the mating connectors
(plugs) so that tip is signal high (+ or hot),
sleeve is low (– or cold); ring is not con­nected.

Control Room Output

The Model 55 contains a stereo line-level
output for connection to an audio power
amplifier. This audio amplifier serves a
pair of loudspeakers that are located in the
control room. (Of course the control room
output can be connected to loudspeakers
that contain integral power amplifiers, such
as the products from Genelec.)

The output is electronically balanced and
capable of driving loads of 600 ohms
or greater. In most situations best perfor­mance will be obtained if the audio amp­lifier’s input sensitivity is set to near
maximum. Refer to the Technical Notes
section for details on setting amplifier
sensitivity.

The control room output utilizes two
¼-inch 3-conductor phone jacks for inter­connection. Prepare the mating connec­tors (plugs) so that tip is signal high (+ or
hot), ring is low (– or cold), and sleeve is
shield. To connect to an unbalanced load
connect the tip to high (+ or hot), and both
the ring and sleeve to shield.

Meter Output

The meter output is intended to be con­nected to a VU- or PPM-type meter panel
that contains input buffer circuitry or series
current-limiting resistors. Each output is
unbalanced, has a nominal level of +4dBu,
and is capable of driving loads of 2k ohms
and greater.

Dub Output

The Model 55 contains a stereo line-level
output which is intended for connection to
a variety of analog audio devices. The dub
output is electronically balanced and cap­able of driving 600 ohm loads or greater.
With the input impedance of most audio
devices at 10k ohms or greater, the dub
output can easily drive 10 or more devices
simultaneously.

The dub output can be configured for a
nominal level of –10dBV or +4dBu, so you
can connect to all line-level inputs with no
hassle (refer to the Configuration section
under Dub Output Level ) .

The dub output utilizes two ¼-inch
3-conductor phone jacks for interconnec­tion. Prepare the mating connectors
(plugs) so that tip is signal high (+ or hot),
ring is low (– or cold), and sleeve is shield.
To connect to an unbalanced load connect
the tip to high (+ or hot), and both the ring
and sleeve to shield.

Talent Amplifier Output

Up to four Model 35 or Model 38 Talent
Amplifiers can be connected in any combi­nation to the Model 55’s talent amplifier
output. The output connector is a 3-pin
male XLR-type. For best performance,
use low-capacitance shielded microphone­type cable to distribute the talent amplifier
signal. If you have a choice, select cables
with the heaviest wire gauge commonly
available. This will reduce voltage drop

Issue 3, December 1996 Model 55/56 User Guide
Page 14 Studio Technologies, Inc.

when using long cable runs. Refer to the
Technical Notes section for additional
information.

The simplest installation would use a
microphone cable to connect the Model 55
to the first talent amplifier; the loop through
connector on that talent amp sending the
signal on to the next talent amp.

For convenience, you may want to wire
your facility to allow easy access to the
talent amplifier signal at all locations
where talent amplifiers might be used. The
talent amplifiers connect to the Model 55
in parallel, so the connectors on the distri­bution panels or mult boxes must be wired
in parallel.

Warning: Do not connect the Model
55’s talent amplifier output to anything
but Studio Technologies’ talent amplifi­ers. Some audio equipment may be
damaged by the +23Vdc contained on
pin 2 of the talent amplifier output
connector.

Several mounting options are available for
the Model 35 and 38 Talent Amplifiers. For
details refer to Mounting Options in this
section.

In special cases you may need to obtain
a stereo, balanced line level output signal
from the Model 55 talent amplifier output.
The Model 70 Interface is available for this
purpose. For details refer to the end of this
section.

Locating the Model 56 Control Console

The Model 56 was designed for desktop
use, however provision has also been
made for microphone-stand mounting.
For details refer to Mounting Options in
this section.

Connecting the Model 55 to the
Model 56

A standard 5-conductor MIDI-style cable
is used to connect the Model 55 to the
Model 56; a cable is included with your
system. Just connect the cable between
the female 5-pin DIN-type connectors on
the back of the Model 55 and 56, and
you’re done.

Note: If you require a longer cable, be
certain to buy a MIDI cable that has all 5
pins wired. If they aren’t all connected, the
Model 56 will not operate. This is because
the Model 55 powers the Model 56 with
the pins that aren’t used for MIDI data.

For best performance, the cable that
connects the Model 55 with the Model 56
should be limited to 50 feet (15.3m).
Should you need to exceed this length,
refer to the Technical Notes section of
this guide for details on the cable
requirements.

For more information on MIDI, and using
controllers other than the Model 56, please
refer to Appendix A.

AC Mains Power

The Model 55 is internally configured to
operate from either 100, 120, or 220/240V,
50/60Hz. In most cases, units shipped to
North America are factory selected for
120V operation. Units bound for Japan are
selected for 100V, while our friends “down
under” and in Europe receive units set for
220/240V. Before connecting the Model 55
to mains power, check that it is configured
to match the local mains voltage. Look on
the back panel, adjacent to the power
entry connector, for the configured
voltage(s). Note than an incorrect configu­ration could seriously damage the unit.
Should it be necessary to change the

Model 55/56 User Guide Issue 3, December 1996
Studio Technologies, Inc. Page 15

unit’s operating voltage it must be per­formed only at the factory or by an autho­rized service technician.

microphone stand. Please refer to the
Installation Guide provided in the Model
35’s shipping carton for details.

The Model 55 uses an IEC standard con­nector to mate with the AC mains cord.
The wire colors in the AC mains cord
should conform to the internationally
recognized CEE color code and must
be wired accordingly:

Connection Wire Color
Neutral (N) Light Blue

Line (L) Brown
Protective Earth (E) Green/Yellow

Safety Warning: The Model 55 does not
contain an AC mains disconnect switch.
As such the mains cord plug serves as
the disconnection device. Safety consid­eration requires that the plug and associ­ated outlet be easily accessible to allow
rapid disconnection of mains power
should it prove necessary.

As soon as mains power is applied, the
Model 55’s power present LED will light.
The Model 56 will go through its power-up
sequence lighting each LED in a rapid
sequence. The power present LEDs on the
talent amplifiers will also light.

The Over Current LED located on the front
panel of the Model 55 should not be lit.
If it is flashing, immediately refer to the
Troubleshooting section of this guide.
If everything appears to be functioning
properly you are now ready to configure the
system.

Model 35 Stand Mounting

Included with each Model 35 Talent Ampli­fier is a nifty mounting adapter that allows
the unit to be conveniently attached to a

Model 38 and Model 56 Mounting
Options

The Model 38 Talent Amplifier and the
Model 56 Control Console include provi­sions for mounting to microphone stands,
equipment consoles, etc. To avoid “rein­venting the wheel,” our products are com­patible with the 25 Series components
from OmniMount Systems, Tempe,
Arizona U.S.A. [phone], a supplier
of finely engineered mounting systems.
This firm makes many versions of the 25
Series; one of which should fit your needs.
If you desire microphone stand mounting
the following components would be appro­priate: 25RST-25H Straight Tube Reverse
Mount with Quick Release, along with a
25MA Microphone Stand Adapter. (If quick
adjustment is not required the 25RST
Straight Tube Reverse Mount can be used
in place of the first item.) When connecting
to metric-thread stands please contact
OmniMount for the correct part numbers.

The bottom surface of the Model 38 Talent
Amplifier contains two threaded inserts
that will accept English-standard ¼-20
screws. Using two,

5

/8-inch long, round-

head machine screws, the 25 Series
clamp assembly can be directly attached.
The cover of the Model 38 does not have
to be removed.

The design of the Model 56 did not allow
the inclusion of threaded inserts, so holes
of adequate size to allow

¼-20 round head

machine screws are provided. It is in­tended that screws of

5

/8-inch length, along

with lock washers and machine nuts, will
securely attach a 25 Series mounting

Issue 3, December 1996 Model 55/56 User Guide
Page 16 Studio Technologies, Inc.

clamp assembly. The cover of the Model
56 will have to be removed to gain access
to mounting holes. Be careful when select­ing the mounting screws—exceeding the
recommended

5

/8-inch length will cause

the mounting screws to damage the Model
56’s internal components.

Model 70 Interface

In most cases Model 35 and/or Model 38
Talents Amplifiers will be used to drive
headphones associated with a Studio­Comm installation. In special cases a line
level signal may be required to interface
the Model 55 Central Controller’s talent
amplifier output with other audio equip­ment. An example would be to use the
Model 55 with an existing headphone
system. The Model 70 Interface is used
to convert the talent amplifier signal to a
stereo, balanced line level signal.

Installation is very simple. Connect the
Model 70 to the Model 55 Central
Controller’s talent amplifier output using
a standard 3-conductor microphone-type
cable. For best performance, use low­capacitance shielded cable.

The Model 70 provides independent left
and right balanced outputs. Pin 1 is shield,
pin 2 is signal positive (+ or hot), and pin 3
is signal negative (– or cold). The elec­tronically balanced outputs have a nominal
signal level of +4dBu and are capable of
driving loads of 600 ohms or greater.

The Model 70 can be used by itself, or in
conjunction with up to four Model 35 or
Model 38 Talent Amplifiers. The loop
through connector on the Model 70 can
be used to connect to a Model 35 or 38
Talent Amplifier.

Model 70 Front Panel

Model 70 Back Panel

Configuration

Many StudioComm functions can be
configured to meet the exact needs of your
installation. Here’s an overview of what
you can configure:

• –10dBV or +4dBu sensitivity for each

input

• Stereo or mono for each input

• –10dBV or +4dBu level for the dub

output

• Dim level

• Momentary or latching operation for

mono, talk to phones, and slate buttons

• Auto dim off function

• Slate feed to phones

Model 55/56 User Guide Issue 3, December 1996
Studio Technologies, Inc. Page 17

• Talk to phones interrupts or adds to

phones source

• Allow simultaneous selection of two

control room sources

buttons that correspond to inputs 1
through 4. After you leave the configure
mode, inputs configured for a mono
source will flash during normal operation.

The Configure button allows the Model 56
to go into the configure mode. While in the
configure mode, all the Model 56’s buttons
and LEDs are associated with configure
functions. Refer to the Model 56 Configu­ration Chart later in this section.

To enter the configure mode, press and
hold the Configure button for two seconds.
While in the configure mode, all audio
outputs switch off and the orange LED
beside the Configure button will flash. As
you make changes, the Model 56 keeps
track of the new settings and updates the
system when you exit the configure mode.
You must exit the configure mode before
any changes take effect.

Input Sensitivity

The CR column of four red LEDs shows
you whether an input is set to be compat­ible with –10dBV or +4dBu signal levels.
When a red LED in the CR column is off,
it means the input is set to –10dBV. When
lit, the corresponding input is set to +4dBu.
Just press the CR buttons to toggle inputs
1 through 4 between –10dBV and +4dBu.

Stereo/Mono Input

The Phones column of green LEDs indi­cates whether an input is configured for
mono or stereo operation. When a green
LED in this column is off, the input is set
for stereo; the LED on means the corre­sponding input is set for mono. In mono
mode, the left input is sent out both the
left and right outputs. To toggle a channel
between stereo and mono, press and hold
the Phones button and press the CR

Dub Output Level

The Dub column of orange LEDs will help
you configure two options: dub output level
and dim level. The orange LED in the first
row (number 1 at the top) tells you
whether the dub output is set to –10dBV or
+4dBu. When the LED is off, the dub
output is set to –10dBV; when it’s on, the
dub output is configured for +4dBu.

Dim Level

The dim function is used to reduce the
control room output level a preset amount
whenever you press the Dim button. You
can take a quick phone call without using
the level control to change the control
room level. Also, any time you press the
talk to phones or slate buttons the dim
function is activated.

In the configure mode, LEDs 2 through 4
in the Dub column indicate the selected
dim level. Dim can only have a single
setting, so only one of the orange LEDs
is on at a time.

Row Number Dim Value (dB)

225
320
415

When the orange LED is on in row two,
dim is down 25dB. Dim is down 20dB in
row three, and 15dB in row four. To
change the dim level, hold down the Dub
button while pressing the CR button of
your choice.

Issue 3, December 1996 Model 55/56 User Guide
Page 18 Studio Technologies, Inc.

Mono Function

The Mono function allows the control room
output to be placed in the mono (L+R)
mode. When you’re in configure mode, the
red LED labeled Mono tells you whether
the Mono button works as a momentary or
latching button. When the button is set to
momentary, the LED will be off and mono
mode will only be active while you press
and hold the Mono button. When the LED
is on, the button is set to latch. With this
setting, you can press the Mono button
once and it will remain in mono mode until
you press it again.

Auto Dim Off

The auto dim off function is unique to
StudioComm products, making the dim
function respond to real world operating
conditions. When enabled the function
automatically turns the dim function off if
a change is made to the control room level
potentiometer while the unit is already in
dim mode. This prevents a heart-stopping
blast of audio when an engineer presses
the dim button to turn dim on, but actually
turns it off because the unit was already in
the dim mode. While it’s hard to explain
unless you’ve used a console and experi­enced this in person, trust us, this situation
does happen! Auto dim off is a wonderful
“real-world” function and in most cases
should be configured.

In the configure mode the Dim LED tells
you if auto dim off is enabled. When the
dim LED is off, the auto dim off function is
off; when the Dim LED is lit, the auto dim
off function is on.

Communications Functions

There are two Communications buttons at
the bottom center of the Model 56. Moving
from left to right, the buttons are talk to

headphones and slate. During configura­tion, LEDs above the Communications
buttons tell you whether the buttons will
latch when you press them. When an LED
is off, the button below it won’t latch. You
would have to press and hold the button
to activate the function. When an LED is
on, it indicates that the button will latch.
Pressing the button will activate the func­tion until it’s pressed again.

Alternate Configure Functions

To allow additional functions to be config­ured, an alternate configure mode is
utilized. By pressing and holding the
Level Up button the alternate functions
are accessed. This is like the ALT key
on your personal-computer keyboard.

Slate to Phones

When you press the slate button, the
Model 56’s microphone is fed to the dub
output. This is how you can record your
own voice for marking takes. But there are
times when it’s convenient to have the
slate provided in the headphone output as
well.

While holding Level Up, the Phones LED
is used to display whether the slate will go
to the phones. When the LED is off, slate
goes to the dub output only; when the LED
is on, slate goes to both the dub and head­phone outputs. While holding Level Up,
press the button below the LED to toggle
the setting.

Talk to Phones Interrupt or Add

The talk to phones function can be config­ured to either interrupt the source selected
for phones audio and connect communica­tions audio, or to have the communica­tions audio added (summed or mixed) with
the phones audio.

Model 55/56 User Guide Issue 3, December 1996
Studio Technologies, Inc. Page 19

While holding Level Up, the slate LED is
used to display whether talk to phones will
interrupt the phones source, or add to the
phones source. When the LED is off, the
selected phones source will be interrupted
and the communications audio source will
be connected; when the LED is on the
communications audio source will be add­ed (mixed) to the phones audio source.
While holding Level Up, press the button
below the LED to toggle the setting.

Allow Two Simultaneous Control Room
Sources

A feature has been added that allows any
two of the four input channels to be simul­taneously selected for monitoring over the
control room output. This was added for
applications where multiple “rough” or
“scratch” audio signals need to be moni­tored at the same time. This feature can
be enabled or disabled using the configu­ration procedure on the Model 56 Control
Console.

Reset Factory Defaults

Provision has been made to allow you to
return all configurable parameters to the
factory default values. With the Model 56
in the configure mode, press and hold both
the Dub and Phones buttons. After two
seconds the factory defaults will be stored
in memory, the configure mode will auto­matically end, and the Model 56 will return
to normal operation.

Issue 3, December 1996 Model 55/56 User Guide
Page 20 Studio Technologies, Inc.

Model 56 Configuration Chart—Main Functions

Press and hold

Configure for two seconds to enter

or exit the configure mode; while in

configure, LED will flash

Press and hold

Dub and Phones

for 2 seconds

to reset all

parameters to

factory defaults

Press Mono to toggle
between latching or
momentary operation;
LED on means the
Mono button is set
to latch

Press Dim to toggle
the automatic dim
off function; LED on
means auto dim
off function is active

Press CR 1 through 4 to

toggle each channel’s input

sensitivity between

–10dBV and +4dBu; LED on

means input is set to +4dBu

Press and hold Phones, then

press CR 1 through 4 to toggle

the inputs between stereo and

mono operation; LED on means

input is set to mono

Press and hold Dub, then

press CR 1 to toggle the

dub output between

–10dBV and +4dBu; LED

on means dub is set to

+4dBu

Press and hold Dub, then press CR 2

through 4 to select a dim level:

LED 2 is 25dB
LED 3 is 20dB
LED 4 is 15dB

Press and hold Level
Up to activate alternate
configure functions
(refer to next page)

Press a Communications

button to toggle between

latching or momentary

operation; LED on means

the button is set to latch

Model 55/56 User Guide Issue 3, December 1996
Studio Technologies, Inc. Page 21

Model 56 Configuration Chart—Alternate Functions

Press CR 1 to toggle between

allowing only one control room

source or allowing one or two

control room sources; LED on

means two sources are allowed

Press Talk to Phones to

toggle slate feed to

phones; LED on means

slate to phones is on

Press and hold Level
Up to activate alternate
configure functions

Press Slate to toggle

between phones interrupt

and phones add; LED on

means talk to phones is add

Issue 3, December 1996 Model 55/56 User Guide
Page 22 Studio Technologies, Inc.

Operation

Now that you’ve installed and configured
the system, you’re ready to go. You should
find operation very easy.

Model 55 Central Controller

The Model 55 front panel contains three
LEDs. The power present LED should be
lit whenever AC mains power is con­nected. During normal operation the Over
Current LED will not be lit. It will flash only
if there is a problem interfacing with the
Model 56 Control Console or the talent
amplifiers that you have connected. Refer
to Troubleshooting section if the Over
Current LED lights.

The Input Data LED will light whenever
a message is received. Refer to the
Troubleshooting section if the LED does
not flash in response to a message from
the Model 56 Control Console.

Model 56 Control Console

All StudioComm functions are controlled
using the Model 56 Control Console.
To make things easy, we’ve divided the
StudioComm functions into three main
groups: input-output selection, control
room output, and communications
functions.

Control Room/Meter Source Selection

To select an input for monitoring in the
control room, press one of the four C R
buttons. The corresponding LED in the
CR column will light to let you know which
input is selected. If the input is set for
mono the LED will continually flash on
and off as a warning. The same source
will be connected to the meter output.

The system may have been configured
to allow two control room sources to be
selected simultaneously. If so, select the
first source by pressing and holding one
of the four CR buttons. Then, while keep­ing the first button pressed, select the
second source by pressing one of the
three other CR buttons. The two sources
will be added (summed or mixed) to­gether: L+L, R+R.

Headphone Source Selection

To select an input source for the head­phone output, press and hold the Phones
button and press one of the four CR but­tons. In the Phones column, the LED for
the input you select will light. If the input is
set for mono the LED will continually flash
on and off as a warning.

A special function allows you to select no
input to be sent to the headphones. This
ensures a quiet feed to the phones, but
still allows the talk to phones function to
be used. To select no input, simply press
and hold the Phones button, then press
both Communications Level buttons at the
same time. The Level buttons are located
to the right of the two Communications
buttons. All LEDs in the Phones column
will be off when no input is selected. To
again select one of the four inputs, press
and hold the Phones button, then press
one of the four CR buttons.

Dub Source Selection

To select an input source for the dub
output, press and hold the Dub button and
press one of the four CR buttons. The
appropriate LED in the Dub column will
light. If the input is set for mono the LED
will continually flash on and off as a warn­ing. You can select no input just as you did

Model 55/56 User Guide Issue 3, December 1996
Studio Technologies, Inc. Page 23

for the headphones. Press and hold the
Dub button, then press both Level buttons
at the same time.

Control Room Output

Associated with the control room output
are two buttons and one level control. In
addition, the Communications Level but­tons are used. Use the Control Room
Level knob to set the control room output
level. There is no on/off switch. Just select
an input and turn the knob to the level you
want.

The Dim button lets you lower the control
room level by a fixed amount. The amount
of attenuation depends on the dim level
set in the configure mode (refer to the
Configuration section for help). The Dim
button is always set to latch the function
on or off.

If the auto dim off function is enabled,
whenever dim is on and the control room
level is changed, dim will automatically
return to the off state. Note that the auto
dim off function is not active whenever dim
is on due to one of the communications
functions being active.

The Mono button lets you send L+R to
both the left and right control room out­puts. The Mono button can be configured
for momentary or latching operation.

For diagnostic purposes, the control
room left-only or right-only mode can be
activated. To enter the mode you use the
Communications Level buttons. Press and
hold both Level buttons for two seconds.
The control room will switch from stereo
operation to the left-channel-only mode.
Press and hold the Level buttons again,
and the control room switches to right
channel only. Press and hold the Level

buttons a third time and the control room
switches back to stereo operation. The
Level buttons continue to cycle through
left, right, and stereo monitoring as you
press them.

The Mono LED indicates when you are in
left-only or right-only modes. During left­only operation the LED will flash once; in
right-only operation the LED will flash
twice.

Note that the mono function is disabled
during single-channel operation. If mono
is active when entering the single-channel
mode, the system will terminate the mono
mode.

Communications Functions

Four buttons are associated with the
communications functions. The two main
buttons are called talk to phones and
slate. They have symbols that represent
(from left to right) a pair of headphones
and a slate board (or “clapper”). Pressing
each button activates the Model 56’s built­in microphone and sends its audio to the
appropriate output(s). Press the button
under the headphone symbol to talk to the
headphones; press the button under the
clapper to slate. Remember that during a
slate, microphone audio goes to the dub
output or, depending on the configuration,
to the dub and phones output. When you
press one of the communications buttons,
the LED above it will come on to tell you
the function is active. Note that only one
communications function can be active at
a time.

When you press the communication but­tons, various things happen depending
on the Model 56’s configuration. Either of
these buttons may be configured to stay
on (latch) when you press them. Also, if

Issue 3, December 1996 Model 55/56 User Guide
Page 24 Studio Technologies, Inc.

the headphones are configured to receive
slate audio, both the phones and slate
LEDs will light when you press slate. The
communications level to the headphones
will be determined by the slate level set­ting (not the talk to phones level).

The talk to phones function is configured
to interrupt or to add to the selected head­phone source. If interrupt is selected,
activating talk to phones disconnects the
selected headphone source and connects
communications audio. If add is selected,
activating talk to phones leaves the head­phone source connected and adds (sums
or mixes) the communications audio.

You can independently set the output level
for the two communications functions. To
set the communications levels, press and
hold either the talk to phones or slate
button and press the Communications
Level buttons. (If the talk to phones or
slate buttons are set to latch, you won’t
have to hold them.) The LEDs above the
buttons will flash each time the level is
increased or decreased until you reach the
top or bottom of the range. At this point, if
you continue to press the same Level
button, the LED won’t flash, indicating
you’re at the top or bottom of the eight­step level range.

Headphone Level

The headphone output level is controlled
only at the Model 35 and Model 38 Talent
Amplifiers. There is no headphone level
adjustment using the Model 56.

Configure Mode

Refer to the Configuration section for an
understanding of how to use the Configure
button.

Talent Amplifiers

Warning: protect your ears! The

StudioComm talent amplifiers are ca­pable of driving headphones to extreme­ly high sound pressure levels. Hearing
experts advise against continuous ex­tended play, especially at high levels.

Model 35 Talent Amplifier

The power present LED should be lit
whenever the Model 35 is connected to
an operating Model 55. The Model 35 has
a Level control and a Stereo/Mono button.
You can plug in one or two pairs of head­phones with a total impedance of 75 ohms
or greater. Turn the knob to the output
level you want and select stereo or mono
by pressing the button. Both headphone
outputs are controlled by the one level
control. The Mono button sends L+R to
both the left and right output.

Model 38 Talent Amplifier

The Model 38 has the unique ability to pro­vide a personalized headphone mix for the
in-studio talent. The performer’s audio can
be connected to the talent inputs and
passively looped through to the control
room. This lets performers increase their
level in the headphone mix without an
engineer getting involved. The Model 38’s
circuitry was carefully designed to not
interfere with the talent audio as it passes
through.

The Model 38 has all the functions of the
Model 35, plus it provides personal mix
controls. The power present LED should
be lit whenever the Model 38 is connected
to an operating Model 55. You can plug in
one or two pairs of headphones with a
total impedance of 75 ohms or greater.

Model 55/56 User Guide Issue 3, December 1996
Studio Technologies, Inc. Page 25

The Cue Mix Level control sets the head­phone output level for the signal coming
from the Model 55. The Cue Mix Stereo/
Mono button switches both headphone
outputs between a stereo and mono (L+R)
feed of the cue mix.

The Model 38 allows connection of a
control Stereo or Mono talent signal at
microphone or line level. If your talent
source is stereo, connect it to the In Left/
Mono and In Right connectors and set the
Talent Stereo/Mono button for stereo
operation. With a mono source, use only
the In Left/Mono connector and set the
Stereo/Mono button for mono operation.
This will feed the mono talent source to
both left and right headphone channels.
Connect loop through cables as needed
for feeds to the control room.

The Talent Mic/Line button is used to
select an input sensitivity level for the
talent source. When you connect a micro­phone or direct box, select Mic. When
keyboards or other preamplified sources
are connected, select Line. The expected
signal level in the Mic position is –40 to
–60dBu. In the Line position it’s –10 to
+10dBu. If you are unsure of your signal
level, start with input sensitivity set for
Line. If the output level is not sufficient,
turn down the level control, switch to Mic,
then listen as again you raise the level
control.

The Talent Level control works just like
you would guess: turn it up for more talent
signal in the headphone mix, and turn it
down for less. The Talent and Cue Mix
level controls work like a mixer for the
headphone outputs, so you can have any
level you want of either source in the
headphone mix.

Troubleshooting

If you’re having problems getting the
StudioComm system up and running, this
section can help. If you haven’t read the
other sections of this guide, you should do
so before proceeding.

If the Model 56 Doesn’t Work At All

Your StudioComm system was supplied
with a 5-conductor DIN-type cable that is
used to connect the Model 56 Control
Console to the Model 55 Central Control­ler. This cable has an important character­istic; it implements all five conductors. This
means that all five pins on each plug
connect to each other using a length of
5-conductor cable. If you choose to use
your own cable it’s easy to get in trouble;
many MIDI cables only have three conduc­tors! You must use a 5-conductor MIDI­style cable or the Model 56 will not power
up and function. Five conductor MIDI
cables are not hard to find, but you must
ask for them and ensure that you get what
you asked for. Be warned!

Over Current LED

During normal operation the Over Current
LED, located on the front panel of the
Model 55, should not light. It will light,
flashing on and off, in response to prob­lems with the Model 56 Control Console
and/or the Talent Amplifier output.

The Over Current LED will light if the
power source that supplies the Model 56
Control Console is loaded to exceed its
maximum output current. The most com­mon reason for an over current condition
would be a shorted 5-conductor MIDI-style
interconnecting cable. A major fault in the
Model 56 would also cause the LED to
light.

Issue 3, December 1996 Model 55/56 User Guide
Page 26 Studio Technologies, Inc.

The Over Current LED will also light if the
talent amplifier output is loaded to exceed
its maximum output current. The most
common reason for an over current condi­tion would be a shorted interconnecting
cable. Also, connecting more than the
specified maximum of four Model 35 or
Model 38 Talent Amplifiers can also cause
the LED to light. Possible, but not likely,
would be a fault condition in a Model 35
or Model 38.

If the Over Current LED does light, trouble­shooting should prove quite simple. Begin
by disconnecting the cables that are
plugged into the Control Console/MIDI In
and the talent amplifier output connectors.
Perform the disconnection directly on the
Model 55’s back panel. The LED should
stop lighting. Now reconnect to Control
Console/MIDI In. If the LED again lights,
follow this paragraph. If the LED does not
light, skip to the next paragraph. Check the
interconnecting cable that links the Model
55 with the Model 56 Control
Console. You need to determine where the
short circuit condition is located. The Model
55 will not be damaged if the Over Current
LED is lighting so you should use it to help
you locate the fault. In just a few minutes
you should be able to isolate exactly if the
cable or the Model 56 is causing the prob­lem. Replace the cable if it proves to be
bad—remember you’ll need a MIDI-style
cable with all five conductors connected. If
the Model 56 appears to be at fault, it will
need to be returned to the factory for re­pair.

If the LED did not light when you recon­nected to Control Console/MIDI In, recon­nect to the talent amplifier output. The LED
should now light, identifying that the prob­lem is with the talent amplifiers or associ­ated cabling. In most cases you will find

that a cable is at fault. If a talent amplifier
is found to be at fault, it will need to be
returned to the factory for repair.

Input Data LED

The Input Data LED lights only when data
is received that is valid for the Model 55.
The Model 55 uses MIDI system-exclusive
messages to perform all operations. When
the Model 56 Control Console is con­nected to the Model 55, the LED will light
any time the Model 56 generates data.
This is because the Model 56 will only
generate data that is compatible with the
Model 55.

If you are not using the Model 56, and
instead are supplying MIDI data using
another device, the LED should prove
extremely useful when troubleshooting.
Only when the MIDI data conforms to the
Model 55’s MIDI system-exclusive format
will the LED light. Refer to Appendix A,
located at the end of this guide, for details
on how data must be sent to the Model 55.

Intermittent Audio Connections

Should you experience audio connections
that seem to be “flaky” or intermittent, refer
to the Technical Notes section of this
guide. The ¼-inch 3-conductor phone
jacks used on the StudioComm products
are of very high quality, conforming to the
industry standard EIA RS-453. Some
plugs do not meet this standard, specifi­cally in the shape of the tip conductor. In
rare cases you may have to replace plugs
on interconnecting cables or headphones
to remedy an interconnection problem.
Switchcraft No. 297 or Neutrik NP3C
phone plugs will function correctly.

Clicks in the Audio

As covered in the Configuration section of

Model 55/56 User Guide Issue 3, December 1996
Studio Technologies, Inc. Page 27

the manual, the four stereo line inputs can
be configured for –10dBV or +4dBu opera­tion. Setting an input for –10dBV, while
connecting an audio source with a +4dBu
nominal level will lead to distortion (“clip­ping”) of the signal. In this fault condition
the user would hear a harsh “clicking”
sounds in the audio, especially when peak
levels occur in the program material. To
remedy this problem simply use the Model
56 Control Console to configure the input
for +4dBu operation. The distortion will go
away and the gain structure of the
StudioComm system will be correctly
established.

Technical Notes

ing cables. Since cable is rated in ohms
per 1000 feet (or ohms per 1000 meters),
you need to know what the maximum
cable resistance is. This can be easily
calculated by dividing the maximum volt­age drop by the maximum current flow: 3V
divided by 0.2A = 15 ohms. For example,
a standard 20 AWG microphone cable is
Belden 8412, which has 10.9 ohms resis­tance per conductor per 1000 feet. Since
we’re using two conductors to carry the
signal (pins 1 and 2) you’d get 21.8 ohms
per 1000 feet of microphone cable. With
our 15 ohm maximum resistance you’d be
able to use 688 feet (210m) of this cable.

By using the numbers provided you can
select a cable, and its maximum length,
for your application.

Talent Amplifier Cable Length

There are no hard and fast rules defining
the maximum cable length when connect­ing Model 35 or Model 38 Talent Amplifi­ers to the Model 55 Central Controller.
The maximum cable length is directly
related to the amount of resistance in the
connecting cable; the lower the resistance
per foot (or meter), the longer the cable
can be. (Although cable capacitance
affects high frequency performance, resis­tance is the limiting factor is this case.)

To lay out the facts in grammar-school
story problem format: for correct opera­tion, a Model 35 or Model 38 needs to see
at least +20Vdc between pins 1 and 2 of
their input connector. The Model 55’s
talent amplifier output voltage across pins
1 and 2 is +23Vdc, with a maximum cur­rent draw of 0.2A (200mA). This difference
between the voltage supplied and the
voltage required results in a maximum
voltage drop of 3V over the interconnect-

Model 55 to Model 56 Cable Length

The Model 56 Control Console generates
system-exclusive MIDI messages which
are sent to the Model 55 Central Controller
using a 5-conductor MIDI-style intercon­necting cable. The MIDI signal is carried
on two of the five conductors. The three
remaining conductors are for common/
shield, DC power, and communications
audio. The limiting factor in the intercon­necting cable’s length is the transmission
of the MIDI data, which has a rate of
31,250 bits-per-second. The inter­conductor capacitance of the cable attenu­ates the data, and as the cable length
increases the data becomes unusable; the
cable serves as a low-pass filter. The MIDI
specification calls for a maximum cable
length of 50 feet (15.3m), which will work
fine connecting the Model 56 to the Model

55. There is really no reason why this
length can’t be increased, as long as good
low-capacitance, shielded cable is utilized.
Runs of 100 to 250 feet (30.5 to 76.2m)

Issue 3, December 1996 Model 55/56 User Guide
Page 28 Studio Technologies, Inc.

are possible using the latest sophisticated
cable. Test to ensure that the Studio­Comm system works correctly with the
desired cable length. There are too many
variables to give a simple formula—good
luck!

¼-Inch Plugs versus EIA RS-453

An incompatibility problem lurks between
some ¼-inch 2-conductor and 3-conductor
phone plugs and the jacks found on pro­fessional audio equipment. While all the
plugs seem to “look” the same, some do
not comply with the industry standard,
called EIA RS-453. This standard defines
the physical dimensions, including the
shape of the plug’s tip. It seems that some
plug manufacturers don’t bother to make
the tip comply with the standard. Why is
this relevant to you? Because the phone
jacks used on the Model 55 Central
Controller, Model 35 Talent Amplifier, and
Model 38 Talent Amplifier do comply with
the standard. They expect to be mated
with plugs that also meet the specification.

When interfacing your line inputs, line
outputs, or headphones be careful with
the plugs you utilize. Should a connection
appear “flaky,” sound noisy, or make an
intermittent contact, the most likely
problem is a non-standard phone plug.
Replace the plug if this is the case. You
should find that all plugs from Switchcraft
or Neutrik will work correctly, specifically
Switchcraft No. 297 or Neurtik NP3C. In
our experience, headphones are the most
likely place to find non-standard plugs—
we even found them on some “world­class” headphones that we use in our lab!

Definition of Level—dBu and dBV

Whenever possible, Studio Technologies
has opted to use the dBu designation as

it seems to be quite rational. Using dBm
was fine when all audio line outputs were
terminated with 600 ohm loads. In this
way it was easy to say that 0dBm is 1
milliwatt dissipated in the known load (i.e.,
0dBm across 600 ohms will measure

0.775V). In contemporary situations an
output is rarely terminated with 600 ohms;
generally 10k ohms or higher. The dBu
designation is better because it refers to
dB referenced to 0.775V, with no refer­ence to load impedance. This takes into
account today’s audio scene where sig­nals have
a low source impedance, and a high input
impedance. The dBu designation is be­coming the standard for the professional
audio industry.

StudioComm equipment is designed to
interface with audio signals that have
nominal signal levels of –10dBV and
+4dBu. You might wonder why dBV
came into the picture. Most people don’t
realize that equipment that utilizes “–10”
levels usually mean –10dBV—substan­tially different from –10dBu (–10dBV =
–7.78dBu). The dBV designation is simply
a different way of measuring signal level
and is often used when dealing with por­table or consumer audio equipment. The
dBV designation refers to dB referenced
to 1.0V, rather than dBu which refers to

0.775V.

“Hot” Disconnection of the Model 56
Control Console

Should you need to relocate the Model 56
while your StudioComm system is operat­ing, there is no reason why you can’t
disconnect the 5-conductor cable, move
the unit, and then connect it again. If
the Model 56 is disconnected while it is

Model 55/56 User Guide Issue 3, December 1996
Studio Technologies, Inc. Page 29

operating, the current operating param­eters are saved in nonvolatile memory
and the Model 55 Central Controller will
continue to operate as it did when the link
was broken. No clicks, pops, or other
noises will occur when the Model 56 is
again connected.

The Model 56 will go through its standard
power-up sequence, send a message to
reset power-up defaults, then send the
operating parameters as stored in its
memory. You may notice a brief interval
of silence while the Model 55 responds
to the reset defaults message.

Control Room Mono Function

Many arguments where had while design­ing the control room monaural function.
Was the function supposed to be a true
mono function, sending the sum of left
and right to a separate mono control room
output? Was mono to be the sum of left
and right sent to both left and right chan­nels? What about level build up with
phase coherent signals that are in both
the left and right channels? After much
head scratching it was realized that the
mono function that most people are ac­customed to is really a means of observ­ing the character of a stereo mix, and not
a “true” mono function. To observe the
stereo image of a mix you need to sum
the left and right signals, drop the level of
the sum by 6dB, and send the result out
the left and right outputs. This is what
virtually all recording consoles implement,
and is what the StudioComm does, too!

Talent Amplifier Mono Function

The Model 35 and Model 38 Talent Ampli­fiers each contain a monaural switch. The
mono function sums the left and right input
signals, drops the level of the sum by 6dB,

and sends the sum to both the left and
right outputs. This is consistent with the
mono methodology discussed in the previ­ous paragraph. Please refer to that note
for details.

Input Level and the Talent Amplifiers

Optimal performance of the Model 35 and
Model 38 Talent Amplifiers depend on the
headphone source signal levels being at
approximately the nominal input level,
either –10dBV or +4dBu, depending on
the configuration. The headphone volume
is adjusted only by the level controls on the
talent amplifiers. If the selected headphone
source signal level is significantly less than
nominal, the talent amplifier will simply not
be able to create the maximum volume in
the headphones. While there is some gain
in the talent amplifiers, optimal perfor­mance still requires an input close to
nominal.

The Model 38 Talent Amplifier can also
exhibit reduced performance if the level
of the headphone source is significantly
“hotter” than nominal. The entire system
has plenty of headroom, but maintaining
proper signal levels, as usual, is important.
If the source selected for headphones has
an average level that is excessive, a small
amount of bleed-through can be heard with
the Model 38’s cue mix level control set
fully counterclockwise. Instead of having
no sound in the phones, a bit of sound can
be heard. This is not a design problem; the
Model 38 has a sensitive preamplifier
section which doesn’t like excessive excur­sions in the left channel modulation of the
+23Vdc signal. The Model 38’s power
supply can reject the left channel modula­tion within the design parameters, creating
a clean reference voltage for the stereo
preamplifier. Modulation levels outside

Issue 3, December 1996 Model 55/56 User Guide
Page 30 Studio Technologies, Inc.

the design parameters show up in the
reference voltage!

Communication Switch Noise

During field trials of the StudioComm
components one item came up for discus­sion concerning “thumps” in the communi­cations functions. A brief discussion may
be useful. Electrically the Model 55 and
Model 56 electronics that support the
communications functions are quite quiet,
not adding appreciable “clicks, pops, or
thumps.” Software time delays are even
added to minimize noise when a button is
pressed. Mechanical noise being picked
up by the Model 56’s microphone can be
an issue. If the talk to phones or slate
buttons are pushed using a relatively light
touch no objectionable noise will be gener­ated; pressing the switches with “gusto”
will cause mechanical noise to be trans­ferred into the microphone. While the
Model 56’s microphone is of good quality,
shock mounting it was not possible using
a cost-effective method. The fact that the
Model 56 is physically small and the but­tons must be relatively close to the micro­phone adds to the difficulty. (Note that
most all recording consoles, both small
and large, share this condition.) So in
conclusion, use a light touch on the but­tons and everyone should stay reasonably
happy!

Power Amplifier Input Sensitivity

Optimum StudioComm performance is
obtained when the input sensitivity of the
control room power amplifier is adjusted to
match the Model 55’s output level. With
normal, but loud, listening levels you
should find the level potentiometer on the
Model 56 to be set to about 2 o’clock. If
you find that you don’t have to turn up the

Model 56’s control that high, reduce the
input sensitivity of the power amplifier until
you get to the 2 o’clock position. Most
power amplifiers have controls on their
inputs to allow easy adjustment of the
input sensitivity.

Control Room Output Transient
Protection

Unique to the Model 55 Central Controller
is a power up/power down transient pro­tection feature. It limits the chance of
damage to the control room loudspeakers
during the time when AC mains voltage is
connected, disconnected, or has signifi­cantly changed from nominal. A combina­tion of hardware and software is used to
monitor one of the power supply “rails.”
Until the rail voltage exceeds 81% of its
nominal value, an electromechanical relay
maintains a short circuit condition on the
control room output. After
a one-second delay the relay is released
to function normally. Whenever the rail
voltage drops below 79% of its nominal
value, the relay immediately goes to its
mute state. During testing it was found
that upon power up the control room
output remained very quiet; during power
down a moderate “tick” was the worst that
was heard.

Meter Output Calibration

At the factory a +4dBu signal is applied to
input 1, input 1 is selected as the control
room source, and the meter output is
monitored with an Audio Precision System
One (set for 100k ohm input impedance).
Trim potentiometers, located on the Model
55’s printed circuit board, are set to give
an output level of +4dBu. In this way input
1 becomes the “accurate” input when a
user views the meters. As input 1 serves
as the “calibrated” input for metering, it

Model 55/56 User Guide Issue 3, December 1996
Studio Technologies, Inc. Page 31

may impact which source you choose to
connect to it.

While a “precision” device, the Model 55
relies upon 1%-tolerance resistors for
signal level integrity. “Perfect” tracking of
the input levels, vis-a-vis the four inputs,
is simply not possible; deviations of up to
±0.5dB are considered normal. (In most
cases, the human ear is not aware of level
variations this small, especially when
comparing different program sources.)
Conclusion: The same input signal con­nected to multiple Model 55 input channels
may display slightly different levels on the
meters.

Direction Connection to Mechanical
Meters

As shipped from the factory, the meter
output is not intended to directly drive
VU- or PPM-type mechanical meter move­ments. These meters generally require a
series current-limiting resistor, such as the

3.6k ohm resistors commonly used with
VU-type meters. Provision has been made
on the Model 55 printed circuit board to
allow series resistors to be inserted. How­ever, 0 ohm resistors are inserted at the
factory. Refer to the Model 55 schematic
diagram, contained in the Service Guide,
for details.

prove to be a problem. However, it is
possible that someone connecting a very
“hot” signal to the Model 55, and selected
it as the control room source, might per­ceive that the circuitry “bleeds” signal even
when the control room level pot is turned
“all the way” down. This is due to the fact
that the input signal is being attenuated by
73dB, rather than being fully “muted.”

Maximum Output Attenuation

The meter output requires that the input
source(s) remain connected through the
Model 55’s switching circuitry at all times,
even when the level control is set to the
fully counterclockwise position. Instead
of fully muting the output, the control room
level is attenuated by approximately 73dB,
which is the maximum supported by the
voltage-controlled amplifiers (VCAs).
During normal operation this should not

Issue 3, December 1996 Model 55/56 User Guide
Page 32 Studio Technologies, Inc.

Specifications

Model 55 Central Controller

Mounting

One space in a standard 19-inch (48.3cm) rack

AC Mains Requirement

100, 120, or 220/240V, ±10%, factory configured,
50/60Hz, 100-120V 0.4A maximum, 220/240V

0.2A maximum

Fusing

Qty: 1
Type: 5 x 20mm time lag (Littelfuse 218-series or

equivalent)
Rating: 0.400A for 100 and 120V mains power,

0.200A for 220/240V mains power

Connectors

Audio Inputs and Outputs: dual, ¼-inch,
3-conductor phone jacks, gold-plated contacts
(Manufactured by Neutrik). Mates with all plugs
specified by EIA RS-453.

Talent Amplifier Output: 3-pin XLR-type, male
(Neutrik)

Control Console/MIDI In: 5-pin DIN-type, female
AC Mains: standard 3-blade plug, meets IEC 320

specifications

Audio Inputs

Qty: 4, stereo (separate left and right input
connectors)

Type: electronically balanced, direct coupled,
compatible with balanced or unbalanced signals

Impedance: 24k ohms
Nominal Input Level: –10dBV or +4dBu, each input

individually software configurable
Common Mode Rejection: 100dB @ DC and 60Hz,

70dB @ 20kHz, 62dB @ 40kHz (typical)

Control Room Output

Qty: 1, stereo (separate left and right output
connectors)

Type: electronically balanced, intended to drive
loads of 600 ohms or greater, balanced or
unbalanced

Output Level (input source at nominal level):
–69dBu at 0% rotation (fully counterclockwise),
–58dBu at 25% rotation, –37dBu at 50% rotation,
–17dBu at 75% rotation, +4dBu at 100% rotation
(fully clockwise)

Maximum Output Level: +27dBu into 10k ohms,
+26dBu into 600 ohms

Frequency Response: 10Hz-40kHz +0/–0.5dB
(down 1dB @ 80kHz)

Distortion (THD+N): 0.02% (measured at +4dBu
input, +4dBu output)

S/N Ratio: 87dB (20Hz-20kHz)

Dub Output

Qty: 1, stereo (separate left and right output
connectors)

Type: electronically balanced, intended to drive
loads of 600 ohms or greater, balanced or
unbalanced

Nominal Output Level: –10dBV or +4dBu, software
configurable

Maximum Output Level: +27dBu into 10k ohms,
+26dBu into 600 ohms

Frequency Response: 10Hz-40kHz +0/–0.5dB
(down 1dB @ 70kHz)

Distortion (THD+N): 0.004% (measured at +4dBu
input, +4dBu output)

S/N Ratio: 92dB (20Hz-20kHz)

Meter Output

Qty: 1, stereo (separate left and right output
connectors)

Type: unbalanced, intended to drive loads of 2k
ohms or greater

Nominal Output Level: +4dBu
Maximum Output Level: +21dBu into 10k ohms
Frequency Response: 10Hz-40kHz +0/–0.5dB

(down 1dB @ 70kHz)
Distortion (THD+N): 0.004% (measured at +4dBu

input, +4dBu output)
S/N Ratio: 92dB (20Hz-20kHz)

Model 55/56 User Guide Issue 3, December 1996
Studio Technologies, Inc. Page 33

Talent Amplifier Output

Application: provides power and audio signals for
up to 4 Model 35 or Model 38 Talent Amplifiers.
The output connector (3-pin XLR-type, male) has
common on pin 1, +23Vdc modulated with left
channel audio at –10dBu on pin 2, and right
channel audio at –10dBu on pin 3. Maximum
output current 200mA (nominal).

Model 35 Talent Amplifier

Mounting

Desktop. Provision for stand mounting available as
option.

Power Requirements

+20-32Vdc (modulated with left channel audio),
provided by Model 55 Central Controller

LED Indicators

Qty: 3, power present, over current, and input data
present

Dimensions (Overall)

19.00 inches wide (48.3cm)

1.72 inches high (4.4cm)

8.75 inches deep (22.2cm)
(1 standard rack space)

Weight

8.5 pounds (3.9kg)

Model 56 Control Console

Mounting

Desktop. Provision for stand mounting provided.

Power Requirements

15Vdc filtered and regulated, 75mA maximum,
provided by Model 55 Central Controller

Connectors

To Model 55 Central Controller: 5-pin DIN-type,
female

Internal Microphone

Type: electret condenser

Power Present LED

Red LED indicates presence of operating power

Connectors

Input (from Model 55): 3-pin XLR-type, female
(Neutrik)

Loop Thru: 3-pin XLR-type, male, connected in
parallel with input connector (Neutrik)

Headphone Outputs: 2, ¼-inch, 3-conductor
(stereo) phone jacks, gold-plated contacts
(Neutrik)

Headphone Output

Qty: 1, feeds two headphone jacks
Load: intended for connection to one or two pairs

of headphones with total impedance of 75 ohms or
greater

Output Level: user adjustable
Maximum Output Voltage: 16V peak-to-peak into

150 ohms @ 1% THD+Noise, 400Hz
Distortion (THD+N): 0.03%
Frequency Response: 20Hz-20kHz +0.5dB

Frequency Response: 3dB roll off at 105Hz

Dimensions (Overall)

7.2 inches wide (18.3cm)

2.2 inches high (5.6cm)

5.4 inches deep (13.7cm)

Weight

1.7 pounds (0.8kg)

Issue 3, December 1996 Model 55/56 User Guide
Page 34 Studio Technologies, Inc.

Dimensions (Overall)

4.2 inches wide (10.7cm)

2.0 inches high (5.1cm)

5.3 inches deep (13.5cm)

Weight

0.8 pounds (0.4kg)

Model 38 Talent Amplifier

Mounting

Desktop. Provision for stand mounting provided.

Power Requirements

+20-32Vdc (modulated with left channel audio),
provided by Model 55 Central Controller

Dimensions (Overall)

8.0 inches wide (20.3cm)

2.0 inches high (5.1cm)

5.4 inches deep (13.7cm)

Weight

1.5 pounds (0.7kg)

Power Present LED

Red LED indicates presence of operating power

Connectors

Cue Mix Input (from Model 55): 3-pin XLR-type,
female (Neutrik)

Cue Mix Input Loop Thru: 3-pin XLR-type male,
connected in parallel with input connector (Neutrik)

Talent Input (Left In/Mono and Right In): 3-pin
XLR-type, female (Neutrik)

Talent Input Loop Thru: 3-pin XLR-type male,
connected in parallel with input connectors
(Neutrik)

Headphone Outputs: 2, ¼-inch, 3-conductor
(stereo) phone jacks, gold-plated contacts
(Neutrik)

Cue Mix Input

Intended for connection only with Model 55 Central
Controller

Talent Input

Qty: 1, stereo or mono, switch selectable
Type: electronically balanced, capacitor coupled,

input impedance 20k ohms

Model 70 Interface

Power Requirements

+20-32Vdc (modulated with left channel audio),
provided by Model 55 Central Controller

Power Present LED

Red LED indicates presence of operating power

Connectors

Input (from Model 55): 3-pin XLR-type, female
(Neutrik)

Loop Thru: 3-pin XLR-type, male, connected in
parallel with input connector (Neutrik)

Left and Right Line Outputs: 3-pin XLR-type, male

Line Output

Qty: 1, stereo
Type: electronically balanced, intended to

drive loads of 600 ohms or greater, balanced
or unbalanced

Nominal Output Level: +4dBu
Maximum Output Level: +20dBu into 10k ohms,

+19dBu into 600 ohms
Frequency Response: 20Hz-20kHz +0/–0.5dB

Input level: switch selectable for microphone or
line-level signals. Expected signal level: Mic
position –40 to –60dBu, Line position –10 to
+10dBu.

Headphone Output

Qty: 1, feeds two headphone jacks
Load: intended for connection to one or two pairs

of headphones with total impedance of 75 ohms or
greater

Output Level: user adjustable
Maximum Output Voltage: 16V peak-to-peak into

150 ohms @ 1% THD+Noise, 400Hz
Distortion (THD+N): 0.1%
Frequency Response: 20Hz-20kHz +0.5dB

Model 55/56 User Guide Issue 3, December 1996
Studio Technologies, Inc. Page 35

Distortion (THD+N): 0.02%

Dimensions (Overall)

4.2 inches wide (10.7cm)

2.0 inches high (5.1cm)

5.3 inches deep (13.5cm)

Weight

0.8 pounds (0.4kg)

Specifications and information contained in this
User Guide subject to change without notice.

Appendix A

Controlling the Model 55

The Model 55 Central Controller uses
MIDI system-exclusive messages to con­trol all functions. The Model 56 Control
Console is programmed to generate a
subset of what the Model 55 is capable of
doing. By using standard MIDI messages,
the Model 55 can be used for a wide range
of special applications. Any device that
can be programmed to send system­exclusive MIDI messages can be used to
control the Model 55.

Note that the 5-pin connector on the Model
55’s back panel is wired somewhat differ­ently from a standard MIDI input. While
pins 4 and 5 meet the MIDI standard, the
three remaining pins are implemented for
use by the Model 56. Pin 1 supplies
+15Vdc power, pin 2 is shield (ground),
and pin 3 is communications audio input.

If you’re connecting your own controller,
such as a computer’s MIDI interface, you
might be concerned about the DC power
on pin 1. Because the MIDI standard
doesn’t use this pin, it is highly unlikely
that it will be connected inside your con­troller, so there’s little chance of the DC
causing damage. To be safe, you can use
a MIDI cable with only two or three wires
implemented.

The following pages provide a detailed list
of all Model 55 system-exclusive MIDI
messages.

Issue 3, December 1996 Model 55/56 User Guide
Page 36 Studio Technologies, Inc.

Date: July 1, 1993

Model 55 Central Controller MIDI Implementation Chart Version: 1.01

Function Transmitted Recognized Remarks

Basic Default Not Applicable Not Applicable
Channel Channel

Default Not Applicable Not Applicable

Mode Messages

Altered

Note Not Applicable Not Applicable
Number True Voice

Velocity Note ON Not Applicable Not Applicable

Note OFF

After Key’s Not Applicable Not Applicable
Touch Ch’s

Pitch Bender Not Applicable Not Applicable

Control
Change X X

Prog
Change True # X X

System Exclusive X O Refer to following pages
System Song Pos X X

Song Sel X X

Common Tune X X
System Clock X X

Real Time Commands X X
Aux Local ON/OFF X X

Mes- All Notes Off X X
sages Active Sense X X

Reset X X

Notes

Mode 1: OMNI ON, POLY Mode 2: OMNI ON, MONO O: Yes
Mode 3: OMNI OFF, POLY Mode 4: OMNI OFF, MONO X : No

Model 55/56 User Guide Issue 3, December 1996
Studio Technologies, Inc. Page 37

Model 55 Central Controller

MIDI Messages to be Acted Upon

General Notes:

1. All MIDI messages to be acted upon are system-exclusive type (F0H). No channel mode,
system common, or system real time messages are utilized.

2. Studio Technologies, Inc. manufacturer’s ID number is 00H 00H 56H.

3. The Model 55’s product device ID number is 02H.

Function: Reset to Power Up Default Configuration

Byte Value Description
1 F0H System-Exclusive Message
2 00H 1st Byte of Studio Tech ID
3 00H 2nd Byte of Studio Tech ID
4 56H 3rd Byte of Studio Tech ID
5 02H Product ID (Model 55)
6 00H Function: Restore Power Up Default Configuration
7 F7H EOX, End of System Exclusive

Action taken after Model 55 receives MIDI message:

1. Set control room level to minimum.

2. Set control room source 1 to no input.

3. Set control room source 2 to no input.

4. Set headphone source to no input.

5. Set dub source to no input.

6. Set control room output to off.

7. Set mono to off (stereo mode).

8. Set all input levels to +4.

9. Set dub output level to +4.

10. Set dim to normal, non-dim

11. Set dim level to 20dB.

12. Set talk to headphones to off.

13. Set slate to off.

Function: Input Level

Byte Value Description
1 F0H System-Exclusive Message
2 00H 1st Byte of Studio Tech ID
3 00H 2nd Byte of Studio Tech ID
4 56H 3rd Byte of Studio Tech ID
5 02H Product ID (Model 55)
6 01H Function: Input Level
7 0nH Input Channel, range 1-4, 1=input 1, 2=input 2, etc.
8 0nH Input Level, range 0-1, 0=–10, 1=+4
9 F7H EOX, End of System Exclusive

Issue 3, December 1996 Model 55/56 User Guide
Page 38 Studio Technologies, Inc.

Function: Dub Output Level

Byte Value Description
1 F0H System-Exclusive Message
2 00H 1st Byte of Studio Tech ID
3 00H 2nd Byte of Studio Tech ID
4 56H 3rd Byte of Studio Tech ID
5 02H Product ID (Model 55)
6 02H Function: Output Level
7 0nH Output Channel, range 1, 1=dub out
8 0nH Output Level, range 0-1, 0=–10, 1=+4
9 F7H EOX, End of System Exclusive

Function: Control Room Source 1

Byte Value Description
1 F0H System-Exclusive Message
2 00H 1st Byte of Studio Tech ID
3 00H 2nd Byte of Studio Tech ID
4 56H 3rd Byte of Studio Tech ID
5 02H Product ID (Model 55)
6 03H Function: Control Room Source 1
7 mnH Source Selected, m range 0-2: 0=stereo, 1=left only, 2=right only;

n range 0-4: 0=no input, 1=input 1, 2=input 2, etc.

8 F7H EOX, End of System Exclusive

Function: Control Room Source 2

Byte Value Description
1 F0H System-Exclusive Message
2 00H 1st Byte of Studio Tech ID
3 00H 2nd Byte of Studio Tech ID
4 56H 3rd Byte of Studio Tech ID
5 02H Product ID (Model 55)
6 04H Function: Control Room Source 2
7 mnH Source Selected, m range 0-2: 0=stereo, 1=left only, 2=right only;

n range 0-4: 0=no input, 1=input 1, 2=input 2, etc.

8 F7H EOX, End of System Exclusive

Model 55/56 User Guide Issue 3, December 1996
Studio Technologies, Inc. Page 39

Function: Headphone Source

Byte Value Description
1 F0H System-Exclusive Message
2 00H 1st Byte of Studio Tech ID
3 00H 2nd Byte of Studio Tech ID
4 56H 3rd Byte of Studio Tech ID
5 02H Product ID (Model 55)
6 05H Function: Headphone Source
7 mnH Source Selected, m range 0-2: 0=stereo, 1=left only, 2=right only;

n range 0-4: 0=no input, 1=input 1, 2=input 2, etc.

8 F7H EOX, End of System Exclusive

Function: Dub Source

Byte Value Description
1 F0H System-Exclusive Message
2 00H 1st Byte of Studio Tech ID
3 00H 2nd Byte of Studio Tech ID
4 56H 3rd Byte of Studio Tech ID
5 02H Product ID (Model 55)
6 06H Function: Dub Source
7 mnH Source Selected, m range 0-2: 0=stereo, 1=left only, 2=right only;

n range 0-4: 0=no input, 1=input 1, 2=input 2, etc.

8 F7H EOX, End of System Exclusive

Function: Control Room Level

Byte Value Description
1 F0H System-Exclusive Message
2 00H 1st Byte of Studio Tech ID
3 00H 2nd Byte of Studio Tech ID
4 56H 3rd Byte of Studio Tech ID
5 02H Product ID (Model 55)
6 07H Function: Control Room Level
7 0nH Level, MSB, range 0-3, see notes
8 nnH Level, LSB, range 00-7F, see notes
9 F7H EOX, End of System Exclusive

Notes:

MSB=0 allows LSB to control lower 128 level steps, MSB=1 allows LSB field to control upper 128 level
steps. During operation MSB=0/LSB=00 gives minimum output level (maximum attenuation), MSB=1/
LSB=7F gives maximum output level.

MSB=2 places function in reduced precision mode, where LSB=00 gives minimum output level (maximum
attenuation), LSB=7F is maximum output.

MSB=3 places function in reduced precision, reverse range mode, where LSB=7F gives minimum output
level (maximum attenuation), LSB=00 is maximum output.

Issue 3, December 1996 Model 55/56 User Guide
Page 40 Studio Technologies, Inc.

Function: Control Room Output Select

Byte Value Description
1 F0H System-Exclusive Message
2 00H 1st Byte of Studio Tech ID
3 00H 2nd Byte of Studio Tech ID
4 56H 3rd Byte of Studio Tech ID
5 02H Product ID (Model 55)
6 09H Function: Control Room Output Select
7 nnH Output Selected, Range 00-11:

L Ch. R Ch. Action
0 0 No Output
1 0 Left Only
0 1 Right Only
1 1 Left and Right

8 F7H EOX, End of System Exclusive

Function: Control Room Mono/Stereo Select

Byte Value Description
1 F0H System-Exclusive Message
2 00H 1st Byte of Studio Tech ID
3 00H 2nd Byte of Studio Tech ID
4 56H 3rd Byte of Studio Tech ID
5 02H Product ID (Model 55)
6 0AH Function: Control Room Mono
7 0nH Output Selected, Range 0-1, 0=stereo, 1=mono
8 F7H EOX, End of System Exclusive

Function: Control Room Dim

Byte Value Description
1 F0H System-Exclusive Message
2 00H 1st Byte of Studio Tech ID
3 00H 2nd Byte of Studio Tech ID
4 56H 3rd Byte of Studio Tech ID
5 02H Product ID (Model 55)
6 0BH Function: Control Room Dim
7 0nH Status, Range 0-1, 0=No Dim, 1=Dim
8 F7H EOX, End of System Exclusive

Model 55/56 User Guide Issue 3, December 1996
Studio Technologies, Inc. Page 41

Function: Talk to Headphones

Byte Value Description
1 F0H System-Exclusive Message
2 00H 1st Byte of Studio Tech ID
3 00H 2nd Byte of Studio Tech ID
4 56H 3rd Byte of Studio Tech ID
5 02H Product ID (Model 55)
6 0EH Function: Talk to Headphones
7 0nH Status, Range 0-2, 0=no talk to headphones, 1=talk to headphones (interrupt), 2=talk to

headphones (add)
8 0nH Level, range 1-8, 8 is loudest
9 F7H EOX, End of System Exclusive

Function: Slate

Byte Value Description
1 F0H System-Exclusive Message
2 00H 1st Byte of Studio Tech ID
3 00H 2nd Byte of Studio Tech ID
4 56H 3rd Byte of Studio Tech ID
5 02H Product ID (Model 55)
6 0FH Function: Slate
7 0nH Status, Valid Values 0, 1, and 3, 0=no slate, 1=slate to dub output,

3=slate to dub and headphone output
8 0nH Level, range 1-8, 8 is loudest
9 F7H EOX, End of System Exclusive

Function: Set Dim Level

Byte Value Description
1 F0H System-Exclusive Message
2 00H 1st Byte of Studio Tech ID
3 00H 2nd Byte of Studio Tech ID
4 56H 3rd Byte of Studio Tech ID
5 02H Product ID (Model 55)
6 10H Function: Set Dim Level
7 0nH Status, Range 0-5:

0=full mute (approx. 70dB)

1=30dB dim

2=25dB dim

3=20dB dim

4=15dB dim

5=10dB dim
8 F7H EOX, End of System Exclusive

Issue 3, December 1996 Model 55/56 User Guide
Page 42 Studio Technologies, Inc.