Studio Technologies 374A User manual

Copyright © 2019 by Studio Technologies, Inc., all rights reserved
www.studio-tech.com
50658-0819, Issue 3
User Guide
Issue 3, August 2019
This User Guide is applicable for serial numbers
M374A-02501 and later with application firmware 1.3 and later
Model 374A Intercom Beltpack

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Model 374A User Guide Issue 3, August 2019
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MODEL 374A
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Table of Contents
Revision History ............................................................ 4
Introduction ................................................................... 5
Getting Started .............................................................. 8
Operation ...................................................................... 13
Technical Notes ............................................................. 18
Specifications ................................................................ 23
Appendix A .................................................................... 24

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Revision History
Issue 3, August 2019:
1. Documents revision to STcontroller (version 2.02.00 and later) which separates
microphone power and microphone gain configuration.
Issue 2, April 2019:
1. Documents new receive and send call function.
Issue 1, June 2018:
1. Initial release.

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Introduction
The Model 374A Intercom Beltpack
begins with the features offered by tradi-
tional party-line intercom user devices and
adds a range of new capabilities along
with the advanced performance and flex-
ibility that Dante® audio-over-Ethernet
provides. With four independent talk and
listen channels the Model 374A bridges
the gap between typical single- and dual-
channel party-line devices and permanent-
ly installed multi-channel intercom panels.
Imagine the possibilities—four channels
of high-quality party-line intercom in a
compact, user-worn package.
Over a standard IP network, multiple
Model 374A units can be used in party-
line (PL) intercom applications with help
from an external Dante-enabled audio
matrix such as the Studio Technologies’
Model 5422 Dante Intercom Audio Engine.
Or, units can be used “point-to-point” or
interfaced with Dante-compatible matrix
intercom systems.
Only a single Power-over-Ethernet (PoE)
connection is required for operation. Key
user features can be easily configured us-
ing the STcontroller software application.
Configurable parameters include electret
microphone powering, microphone pre-
amplifier gain, talk button operation, and
headphone channel assignment. User
features include integrated sidetone, re-
mote mic kill (“talk off”), call function, and
monitor-only modes. The wide range of
capabilities, along with the excellent audio
quality provided by the digital audio signal
path, offers a unique and powerful user
experience.
Set up and configuration of the Model
374A is simple. An etherCON® RJ45
receptacle is used to interconnect with a
standard twisted-pair Ethernet port as-
sociated with a local-area network (LAN).
This connection provides both power and
bidirectional digital audio. A broadcast or
intercom-style stereo or monaural headset
with a dynamic or electret (DC-powered)
microphone interfaces with the unit using
a 5-pin XLR connector.
The STcontroller software application is
used to select the unit’s operating pa-
rameters. Four talk pushbutton switches
can be configured for optimal operation.
Four push-in/push-out (“pop out”) rotary
controls make it easy to set and maintain
the desired headphone output level. The
Model 374A’s enclosure is made from
an aluminum alloy which offers both light
weight and ruggedness. A stainless steel
“belt clip,” located on the back of the
unit, allows direct attachment to a user’s
clothing.
Figure 1. Model 374A Intercom Beltpack top and bottom views

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The audio quality of the Model 374A’s
four audio channels is excellent, with low
distortion, low noise, and high headroom.
Careful circuit design and rugged com-
ponents ensure long, reliable operation.
A wide range of applications can be sup-
ported, including sports and entertain-
ment TV and radio events, streaming
broadcasts, corporate and government AV
installations, and post-production facilities.
Dante Audio-over-Ethernet
Audio data is sent to and received from
the Model 374A using the Dante audio-
over-Ethernet media networking technol-
ogy. As a Dante-compliant device, the
Model 374A’s four audio output (Dante
transmitter) and four audio input (Dante
receiver) channels can be interconnected
(routed) with other devices using the
Dante Controller software application. The
Dante transmitter and receiver channels
are limited to supporting four Dante flows,
two in each direction. The digital audio’s
bit depth is up to 24 with a sampling rate
of 48 kHz. The Model 374A is AES67
compatible and compliant with the Dante
Domain Manager™ software application.
Two bi-color LEDs provide an indication
of the Dante connection status. The Dante
Controller’s Identify command takes on a
unique role with the Model 374A. Not only
will it cause the talk button LEDs to light
in a unique highly visible sequence, it can
also be configured to turn off any active
talk channels.
Audio Quality
The Model 374A’s completely “pro”
performance is counter to the less-than-
stellar reputation of typical party-line
(PL) intercom audio. A low-noise, wide
dynamic-range microphone preamplifier
and associated voltage-controlled-amplifier
(VCA) dynamics controller (compressor)
ensures that microphone audio quality is
preserved while minimizing the chance of
signal overload. DC power to support elec-
tret microphones can be enabled if neces-
sary. The output of the microphone preamp
and compressor is routed to an analog-to-
digital converter (ADC) section that sup-
ports a sampling rate of 48 kHz with a bit
depth of up to 24. The audio signal, now
in the digital domain, travels through the
processor and on to the Dante interface
section where it is packetized and prepared
for transport over Ethernet.
Audio input signals arrive via four Dante
receiver channels. The supported sampling
rate is 48 kHz with a bit depth of up to 24.
The audio signals pass into the Model
374A’s processor where channel routing,
headphone level control, and sidetone
creation are performed within the digital
domain. This provides flexibility, allowing
for precise control of the audio signals and
eliminates the need for the four rotary level
controls from having to directly handle
analog audio signals. The audio signals
destined for the 2-channel headphone out-
put are sent to a high-performance digital-
to-analog converter and then on to robust
driver circuitry. High signal levels can be
provided to a variety of headsets, head-
phones, and earpieces.
Call Function
A call function allows Model 374A users to
receive and send channel-specific visual
alert signals. Using 20 kHz tones, the call
signals are sent within the audio channels
(“in band”) allowing interoperability be-
tween multiple Model 374A units as well as
being compatible with legacy party-line in-
tercom systems. Call signals can be useful

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to indicate to users that they are needed
“on headset” or should be actively listen-
ing to an intercom channel. The call func-
tion can also be used to provide realtime
cues to production personnel during the
running of live events. Call signals present
on the four audio input (Dante receiver)
channels can be detected and displayed.
Pushbutton 4, on the Model 374A’s top
panel, can be configured to serve as a
call button. This allows a call signal to be
generated for talk channels 1, 2, and 3.
Configuration Flexibility
A highlight of the Model 374A is its ability
to be easily configured to meet the needs
of specific users and applications. All
configuration choices are made using
the STcontroller software application that
communicates with the Model 374A by
way of an Ethernet network connection.
Configurable parameters include micro-
phone power and preamplifier gain, side-
tone audio operation, talk button opera-
tion, and headphone monitoring.
The microphone input can be selected
for compatibility with dynamic or electret
(DC-powered) microphones. The gain of
the microphone preamplifier can be se-
lected from among four choices. These
allow compatibility with a variety of mi-
crophones that are part of broadcast and
intercom headsets.
A unique Model 374A feature is the ability
to individually configure the way in which
the four talk pushbutton switches function;
four choices are available. For standard
intercom beltpack operation either Push
to Talk or Push to Talk/Tap to Latch opera-
tion can be selected. For situations where
only monitoring of an intercom channel
is desired a Talk Disabled mode is avail-
able. And for advanced monitoring-only
situations the Talk Disabled/Phones Tap to
Latch mode can be selected such that a
button will serve in an audio on/off role.
Four audio channels arrive via Dante and
are destined for the 2-channel headphone
output. Each input source can be inde-
pendently routed to the left headphone
channel, right headphone channel, or both
the left and right headphone channels.
This flexibility allows a variety of listening
environments to be created, including
stereo, single-channel monaural, and
dual-channel monaural.
Ethernet Data and PoE
The Model 374A connects to an Ethernet
data network using a standard 100 Mb/s
twisted-pair Ethernet interface. The physi-
cal interconnection is made by way of
a Neutrik® etherCON RJ45 receptacle.
While compatible with standard RJ45
plugs, etherCON allows a ruggedized and
locking interconnection for harsh or high-
reliability environments. An LED displays
the status of the network connection.
The Model 374A’s operating power is
provided by way of the Ethernet interface
using the 802.3af Power-over-Ethernet
(PoE) standard. This allows fast and
efficient interconnection with the associ-
ated data network. To support PoE power
management, the Model 374A’s PoE
interface reports to the power sourcing
equipment (PSE) that it’s a class 1 (very
low power) device.

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Future Capabilities and
Firmware Updating
The Model 374A was designed such that
its capabilities and performance can be
enhanced in the future. A USB connector,
located on the unit’s main circuit board
(underneath the unit’s cover), allows the
application firmware (embedded software)
to be updated using a USB flash drive.
The Model 374A uses Audinate’s Ultimo™
integrated circuit to implement the Dante
interface. The firmware in this integrated
circuit can be updated via the Ethernet con-
nection, helping to ensure that its capabili-
ties remain up to date.
Getting Started
What’s Included
Included in the shipping carton are a
Model 374A Intercom Beltpack and a
printed copy of this guide. As a device
that is Power-over-Ethernet (PoE) powered,
no external power source is provided. In
most applications an Ethernet switch with
the required PoE capability will be utilized.
Connections
In this section signal interconnections will
be made using the two connectors located
on the bottom of the Model 374A’s enclo-
sure. An Ethernet data connection with
Power-over-Ethernet (PoE) capability will
be made using either a standard RJ45
patch cable or an etherCON protected
RJ45 plug. A dual-channel or single-
channel (dual- or single-ear) headset
will be connected using a cable-mounted
5-pin male XLR connector.
Ethernet Connection with PoE
A 100BASE-TX Ethernet connection that
supports Power-over-Ethernet (PoE) is re-
quired for Model 374A operation. This one
connection will provide both the Ethernet
data interface and power for the Model
374A’s circuitry. A 10BASE-T connection is
not sufficient and a 1000BASE-T (“GigE”)
connection is not supported unless it can
automatically “fall back” to 100BASE-TX
operation. The Model 374A supports Eth-
ernet switch power management, enumer-
ating itself as a PoE class 1 device. Any
source that is compliant with the IEEE®
802.3af standard will function correctly.
Should the selected Ethernet switch port
support Energy-Efficient Ethernet (EEE) it
must be disabled to help ensure reliable
Dante operation.
The Ethernet connection is made by way
of a Neutrik etherCON protected RJ45
receptacle that is located on the bottom
of the Model 374A’s enclosure. This allows
connection by way of a cable-mounted
etherCON connector or a standard RJ45
plug. The Model 374A’s Ethernet interface
supports auto MDI/MDI-X so that a cross-
over cable will never be required.
Headset Connection
The Model 374A provides a 5-pin female
XLR connector that interfaces with the
microphone and headphone connec-
tions of an intercom or broadcast-style
headset. Refer to Figure 2 for connection
details. The microphone input connections
are compatible with most unbalanced
dynamic or electret (low-voltage DC-pow-
ered) microphones. A balanced dynamic
microphone should, in most cases, also
function correctly if the signal – (low) is
connected to Model 374A’s mic in –/shield

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connection. No support is provided for
microphones that require P12 or P48
phantom power.
To allow users of stereo (dual-earpiece or
“double muff”) headsets to hear a monau-
ral version of the two headphone output
channels does not require special wiring
of the 5-pin male XLR mating connector.
The headset’s left headphone channel
should always be wired to pin 4 and the
right headphone channel to pin 5. Con-
figuration choices, discussed later in this
guide, can then be used to create the
desired monaural output. It’s important
not to connect together (short) pins 4 and
5 of the Model 374A’s headset connector
as damage to the Model 374A’s output
circuitry could result.
Monaural (single-earpiece or “single
muff”) headsets should be wired such that
its headphone is wired only to pin 4; pin 5
should be remain unused. Configuration
choices, discussed later in this guide, can
be used to create a monaural output.
It’s possible that some Beyerdynamic
headset interconnecting cable assemblies
terminate the earpiece’s left and right con-
nections opposite from what the Model
374A and other broadcast equipment
require. These cables may terminate the
left earpiece to pin 5 of the XLR connec-
tor and the right earpiece to pin 4. If this
condition is present it will require reversing
or “flipping” the two wires in a headset’s
5-pin male XLR connector such that the left
earpiece connects to pin 4 and the right
earpiece to pin 5.
Dante Configuration
For audio to pass to and from the Model
374A requires that several Dante-related
parameters be configured. These configu-
ration settings will be stored in non-volatile
memory within the Model 374A’s circuitry.
Configuration will typically be done with
the Dante Controller software application
which is available for download free of
charge at www.audinate.com. Versions of
Dante Controller are available to support
Windows® and OS X® operating systems.
The Model 374A uses the Ultimo 4-input/
4-output integrated circuit to implement
the Dante architecture.
The four Dante transmitter (Tx) channels
associated with the Model 374A’s Dante
interface must be assigned to the desired
receiver (Rx) channels. This achieves rout-
ing the Model 374A’s four talk output audio
channels to the device (or devices) that will
be “listening” to them. Within Dante Con-
troller a “subscription” is the term used for
routing a transmitter flow (a group of out-
put channels) to a receiver flow (a group of
input channels). The number of transmitter
flows associated with an Ultimo integrated
circuit is limited to two. These can either be
unicast, multicast, or a combination of the
two. If the Model 374A’s transmitter chan-
nels need to be routed using more than
two flows it’s possible that an intermediary
device, such as the Studio Technologies’
Model 5422 Dante Intercom Audio Engine,
can be used to “repeat” the signals.
Figure 2. Headset connection pinout chart

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The four Dante receiver (Rx) channels
associated with the Model 374A’s audio in-
puts also need to be routed to the desired
Dante transmitter (Tx) channels. These four
audio signals can be sent to the Model
374A’s 2-channel headphone output.
The Model 374A supports an audio sample
rate of 48 kHz with no pull-up/pull-down
values available. The Model 374A can
serve as the clock master for a Dante net-
work but in most cases it will be configured
to “sync” to another device that is serving
as the “grand master.”
The Model 374A has a default Dante
device name of ST-M374A- followed by a
unique suffix. The suffix identifies the spe-
cific Model 374A that is being configured.
The suffix’s actual alpha and/or numeric
characters relate to the MAC address of
the unit’s Ultimo integrated circuit. The four
Dante transmitter (Tx) channels have de-
fault names of Ch1, Ch2, Ch3, and Ch4.
The four Dante receiver (Rx) channels have
default names of Ch1, Ch2, Ch3, and Ch4.
Using Dante Controller the default device
name and channel names can be revised
as appropriate for the specific application.
Model 374A Configuration
Many of the Model 374A’s operating pa-
rameters can be configured to match
the needs of specific applications. The
STcontroller software application is used
to observe a unit’s current configuration
and perform any changes that are required.
No DIP switch settings or other local ac-
tions are used to configure the unit. This
makes it imperative that STcontroller be
available for convenient use in a personal
computer that’s connected to the related
LAN.
STcontroller is available free of charge on
the Studio Technologies’ website (www.
studio-tech.com/stcontroller-application/)
and is compatible with personal comput-
ers running Windows operating systems
that are version 7 and later. STcontroller
versions 2.02.00 and later are required
to fully support the Model 374A. If neces-
sary, download and install STcontroller
onto a designated personal computer. This
personal computer must be on the same
local area network (LAN) and subnet as
the Model 374A unit or units that are to be
configured.
STcontroller allows observation and selec-
tion of functions that include:
• Microphone Input – Electret Power
• Microphone Input – Gain
• Headphone Output Channel Routing
• Sidetone – Level
• Button Operation
• System – Mic Kill
Changes made using STcontroller will be
immediately reflected in the unit’s opera-
tion; no Model 374A “reboot” is required.
Each time a change is made the four talk
buttons on the top panel will momentarily
flash orange in a distinctive pattern to indi-
cate that a command from STcontroller has
been received.
Using STcontroller
Immediately after starting STcontroller
the application will locate and display the
devices that it can control. The one or more
Model 374A units that are recognized will
appear in the device list. Use the Identify
command to allow easy recognition of a
specific Model 374A unit. Double clicking
on a device name will cause the associated

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configuration menu to appear. Review the
current configuration and make changes
as required.
Microphone Input – Electret Power
Choices are Enabled or Disabled.
If the headset has an electret microphone
that requires a source of low-voltage DC
power for operation enable the Electret
Power check box. If the associated head-
set has a dynamic (non-powered) micro-
phone do not enable the Electret Power
check box. Most broadcast headsets that
terminate on a 5-pin male XLR connector
will not require microphone power. The
on/off status is displayed by way of a red
LED, labeled MIC POWER, that is located
adjacent to the headset connector.
Note that the Model 374A cannot supply
P12 or P48 phantom power that may be
required for balanced condenser (capaci-
tor) microphones. This should not pose an
issue as this type of microphone is essen-
tially never associated with a headset that
would be used for intercom applications.
Microphone Input – Gain
Choices are 22 dB, 30 dB, 42 dB, and
48 dB.
Dynamic microphones have an output
level that is typically lower than that pro-
vided by electret microphones. As such,
the 42 or 48 dB gain settings will probably
be appropriate for them. Electret micro-
phones often have internal circuitry which
provides a relatively high output level. The
22 and 30 dB gain settings will typically be
appropriate with this type of microphone.
When a dynamic microphone is con-
nected to the Model 374A the 42 dB gain
setting may be correct for many applica-
tions. Setting the gain for 48 dB may be
helpful in some applications, such as with
headsets that have a low microphone out-
put level. The 48 dB gain setting may also
be useful when the Model 374A is going
to be deployed at events where users are
not able to speak at normal levels, e.g.,
sporting events such as golf tournaments
where “whispering” may be necessary.
Electret microphones typically have a
higher output level due to their internal
preamplifier circuitry. As such, less pream-
plifier gain may be required. Selecting the
22 or 30 dB gain setting will probably be
appropriate in these cases.
The compressor active LED, labeled
COMP and visible adjacent to the headset
connector, can act as a guide when set-
ting the microphone preamplifier gain.
During normal talk operation the com-
pressor active LED should light intermit-
tently. If, for example, with a dynamic
microphone the LED rarely lights and the
preamp gain is set to 42 dB it might be a
good idea to change it to 48 dB. If the LED
is lit fully during normal talking in a situ-
ation where the headset has an electret
microphone and the gain is set for 30 dB,
changing it to 22 dB might be warranted.
Headphone Output Channel Routing
Choices are Left, Right, and Left and Right.
Four audio input sources (Dante receiver
channels) can be assigned to the head-
phone output channels using the Dante
Controller application. How these four
audio signals are routed to the Model
374A’s headphone output channels can
be configured using this configuration
choice. The three options provide flexibility
in how the audio sources are presented
to the user. When using a stereo (“double
muff”) headset it’s common for the audio

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input sources to be routed to both the left
and right channels. But the Model 374A’s
flexibility allows each source to be inde-
pendently configured for sending to the
left only, right only, or both left and right
headphone channels.
When using a stereo headset sending all
inputs to both channels is often referred to
as a dual-channel mono output. If a mon-
aural (“single muff”) headset is used the
Left configuration option allows the four
input channels to be combined to monau-
ral so that the listener can simultaneously
hear both sources.
Sidetone – Level
Choices are Off, Low, Medium Low,
Medium, Medium High, and High.
The Model 374A includes a sidetone
function that allows microphone audio
coming from the microphone preampli-
fier to be sent to the both channels of
the headphone output. This serves as a
user confirmation that they are actively
sending audio to one or more of the talk
output channels. Sidetone audio will only
be routed to the headphone output when
at least one of the talk channels is ac-
tive. The level of the sidetone audio can
be selected from among five values. The
correct value is simply the one that makes
the user most comfortable. Sidetone
audio can also be disabled by selecting
Off. Selecting Off would be useful only
in special applications such as during
troubleshooting or where user talk audio is
being returned as part of their listen audio
signals. The four rotary level controls will
not impact the sidetone level.
Button Operation
Choices are Push to Talk, Push to Talk/
Tap to Latch, Talk Disabled, Talk Disabled/
Phones Tap to Latch, and Call (button 4
only).
This configuration section allows indepen-
dent selection of how the four buttons will
function. When the Push to Talk mode is
selected the operation is self-explanatory.
Only when a button is pressed and held
will talk audio be sent out its associated
Dante transmitter channel.
When the Push to Talk/Tap to Latch mode
is selected a “hybrid” function of sorts is
enabled. Pressing and holding the button
will enable audio to be sent out its associ-
ated Dante transmitter channel. When the
button is released audio will stop being
sent out its associated transmitter channel.
Tapping (momentarily pressing) the button
will cause the function to “latch” into the
talk active mode. Tapping the button again
will cause the function to “unlatch” and
talk will no longer be active.
Many applications are best served when
the buttons are configured in the Push
to Talk mode. This ensures that a chan-
nel can’t accidentally be left in its active
mode. But there are certainly valid situa-
tions when the Push to Talk/Tap to Latch
mode setting will prove to be very useful.
When the Talk Disabled mode is selected
microphone audio will never be sent out
the associated Dante transmitter channel.
This can be useful when the audio input
associated with this channel is going to
be monitored but talk audio is not allowed
to “join” this specific intercom channel.
When the Talk Disabled/Phones Tap to
Latch mode is selected the associated
button will not impact talk audio but will

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MODEL 374A
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instead control the on/off state of the audio
being sent to the headphone output. In this
mode talk audio will never be sent out the
associated Dante transmitter channel. This
is an interesting mode, allowing one or
more Model 374A audio channels to serve
in a “monitor mixer” function. The button
will allow quick on/off control while the ro-
tary level control can remain in its desired
position.
When button 4 has been selected to the
Call mode it will serve as a call enable
button for talk channels 1, 2, and 3; micro-
phone audio will never be sent out Dante
transmitter channel 4. In the Call mode
button 4 will operate in a push-to-activate
manner and whenever it is active and
channels 1, 2, and/or 3 are active a 20 kHz
tone (call signal) will be added to the active
audio paths. It will not display a call signal
that’s present on audio input channel 4.
System – Mic Kill
Choices are Off, Device ID, Global Kill
Command, and Device ID/Global Kill
Command.
The mic kill function allows an enabled
talk channel to be disabled by remote
control. Specifically, it’s possible to re-
motely change all active (on) talk channels
to their off state. This function is sometimes
referred to as a “talk off” function. There
are two means available to remotely dis-
able all active talk channels. The Device
ID method uses the identification com-
mand generated by the Dante Controller
or STcontroller applications as a “trigger”
to disable any active talk channels. The
Global Kill Command can be generated by
applications that incorporate the Studio
Technologies’ proprietary method. This
method utilizes sending a data command
over the Ethernet connection. Select the
desired mic kill configuration from the four
choices. Off simply means that no remote
talk control is supported.
Operation
At this point everything should be ready
and Model 374A operation can commence.
An Ethernet connection with Power-over-
Ethernet (PoE) capability should have been
made. A headset terminated on a 5-pin
male XLR connector should be plugged
into the headset connector.
Using the Studio Technologies’ STcontroller
software application the unit’s configura-
tion should have been selected to meet
the needs of the specific application. The
Model 374A’s Dante configuration set-
tings should have been selected using the
Dante Controller software application. In
this way the unit’s four audio output chan-
nels (Dante transmitter channels) and four
audio input channels (Dante receiver chan-
nels) should have been routed, by way of
Dante “subscriptions,” to the receiver and
transmitter channels on associated Dante-
enabled equipment.
Initial Operation
The Model 374A will start to function
as soon as a Power-over-Ethernet (PoE)
power source is connected. However, it
may take 20 to 30 seconds for full opera-
tion to commence. Upon initial power up
the three status LEDs located on the bot-
tom panel below the etherCON RJ45 re-
ceptacle will begin to light as network and
Dante connections are established. The
green and orange LEDs that illuminate the
four pushbutton switches on the top panel
may initially light randomly and then will
light in a test sequence to indicate that the
application firmware (embedded software)

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MODEL 374A
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has started. Once the entire sequence has
completed and the Dante connection has
been established full operation will begin.
Ethernet and Dante Status
LEDs
Three status LEDs are located below the
etherCON RJ45 receptacle on the Model
374A’s bottom panel. The LINK ACT LED
will light green whenever an active con-
nection to a 100 Mb/s Ethernet network
has been established. It will flash in re-
sponse to Ethernet data packet activity.
The SYS and SYNC LEDs display the
operating status of the Dante interface and
associated network. The SYS LED will light
red upon Model 374A power up to indi-
cate that the Dante interface is not ready.
After a short interval it will light green to
indicate that it is ready to pass data with
another Dante device. The SYNC LED
will light red when the Model 374A is not
synchronized with a Dante network. It will
light solid green when the Model 374A is
synchronized with a Dante network and an
external clock source (timing reference)
is being received. It will slowly flash green
when this specific Model 374A is serving
as the clock master for the network. It’s
possible that up to 30 seconds may be
required for the SYNC LED to reach its
final state.
Compressor Active LED
A yellow LED indicator is located on the
bottom panel adjacent to the headset con-
nector. Labeled COMP, the LED displays
the status of the microphone audio com-
pressor function. It will light whenever the
input level from the microphone, along
with the configured preamplifier gain, is
such that the dynamic range of the talk
signal is being controlled. It’s perfectly
acceptable for this LED to light intermit-
tently whenever a user is talking at a
normal voice level into the associated
microphone. But if the COMP LED lights
solid while a user is talking at a normal
voice level this will typically indicate that
the mic preamp gain setting should be
reduced. Conversely, if the COMP LED
almost never lights when normal talking
is taking place, it’s possible that changing
the mic preamp gain to the higher setting
would be beneficial. Note that due to the
design of the circuitry the compressor ac-
tive LED will function whether or not any
of the four talk channels are active.
Headphone Output
Four rotary potentiometers (“pots”),
located on the Model 374A’s top panel,
allow individual adjustment of the level of
the four audio input signals as they are
sent to the 2-channel headphone output.
Depending on the configuration of the
unit, each audio input can be sent to the
left channel, the right channel, or both the
left and right channels of the headphone
output. The pots are “push-in/push-out”
type which allow their associated knobs
to be in their “out” position to be adjusted
and then moved to their “in” position when
protection from an unwanted change is
desired.
Users should find the headphone output
audio quality to be excellent, with high
maximum output level and low distor-
tion. Audio signals do not pass directly
through the level pots. The position of the
pots is recognized by the Model 374A’s
processor which then adjusts the signal
level within the digital domain. When a
pot is in its fully counterclockwise posi-
tion the associated audio signal is fully
muted. In most cases the on/off status of

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the four talk channels does not impact the
headphone output. However, one button
configuration setting (Talk Disabled/Phone
Tap to Latch) assigns the associated button
to function as a channel listen audio on/off
selector.
Button Operation
Four pushbutton switches are associated
with the Model 374A’s four channels. How
they function will depend on the configura-
tion of the unit. Each button can be config-
ured independently.
Push to Talk
When a button has been configured for the
Push to Talk mode how it functions is pretty
self-explanatory. Press and hold the button
when headset microphone audio is to be
sent out the associated Dante audio output
(transmitter) channel. The button’s green
LED will light to indicate that the output is
active. The button will not be lit when the
function is not active.
Push to Talk/Tap to Latch
If a button has been configured for the
Push to Talk/Tap to Latch mode operation
is a bit different and certainly more flex-
ible. Press and hold the button to activate
the talk function. When released the talk
function will turn off. Momentarily pressing
(“tapping”) the button will cause the func-
tion to change states; off-to-on or on-to-off.
Whenever the talk function is active the
green LED will light. The button will not be
lit when the function is not active.
Talk Disabled
A button that is configured to the Talk
Disabled mode will never allow talk audio
to be sent to the associated Dante audio
output channel. But to provide “feedback”
that the button has been pressed the
button’s green LED will flash rapidly three
times. This says, in effect, “Yes, I recog-
nize that you pressed the button but I’m
not going to do anything in response!”
Talk Disabled/Phones Tap to Latch
In the Talk Disabled/Phones Tap to Latch
mode the button will never allow talk
audio to be sent to the associated Dante
audio output channel. Instead the button
will operate in a tap to enable/tap to dis-
able (alternate action or “toggle”) manner
and provide an audio channel listen on/off
function. The button’s orange LED will
light whenever audio is being sent to the
headphone output. The headphone output
level will continue to follow the setting of
the associated rotary level control.
Call (Button 4 Only)
When button 4 is configured for the Call
mode it will allow call signals to be gener-
ated whenever talk channels 1, 2, and/or 3
are active. The button functions in a
push-to-call manner and will light orange
whenever it is pressed and held. No mi-
crophone audio will be routed to audio
output 4. Button 4 will never light in re-
sponse to a call signal being present on
audio input 4. The headphone output level
will continue to follow the setting of the
rotary level control associated with audio
input 4.
Sidetone Function
The Model 374A includes a sidetone func-
tion that sends microphone audio to both
the left and right headphone output chan-
nels whenever one or more of the talk
buttons are active. The quality of the side-
tone audio should be excellent and will
provide Model 374A users with a confi-
dence signal that they are actively talking
to other intercom users. Sidetone audio

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Page 16 Studio Technologies, Inc.
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will always be sent to both headphone
channels and is not a configurable choice.
This is because the function is trying to
simulate what a user would hear if they
didn’t have a headset covering their ears.
It is not intended to indicate to the user
which Dante audio output (transmitter)
channel or channels are actively sending
audio.
The exact sidetone level is configured
from among five values within the STcon-
troller application. There is also a selection
choice for turning off sidetone. There is
no means of adjusting the sidetone level
using any physical buttons or controls on
the Model 374A unit. Also, the four head-
phone level controls on the top panel of
the unit do not impact the sidetone level.
In most cases the exact sidetone level
setting is not critical and typical users will
not be concerned about revising it to a
specific value. But setting the sidetone
level to something reasonable is impor-
tant. Setting the level too low will encour-
age users to speak too loudly; setting
it too high and users will be tempted to
speak hesitantly. And while the user isn’t
provided with a sidetone level control or
other adjustment means, should the need
arise STcontroller allows rapid adjustment
of the sidetone level. In most cases the
default sidetone level, Medium, should
provide an appropriate level.
Call Function
An integrated call function allows Model
374A users, and users of compatible
equipment, to signal to each other visu-
ally. A call receive function is provided for
each of the four channels. Any combina-
tion of the four can have their call function
active at any one time. Technically, call is
achieved by sending a 20 kHz audio tone
on the desired audio output channel. This
signal is summed (mixed) with normal talk
audio. The Model 374A’s four audio input
channels continually monitor for the pres-
ence of 20 kHz. A call signal is recognized
when a continuous 20 kHz tone is detected
on the audio input for that channel. Any
channel that has been configured to Talk
Disabled/Phones Tap to Latch mode will not
respond to call signals. Also, if channel 4
has been configured to the Call mode that
channel will not respond to a call signal on
audio input 4.
Normal talk audio signals will not be con-
fused with a call signal. Digital filters within
the Model 374A’s processor integrated
circuit limits the high-frequency response,
helping to ensure that false call detection
won’t take place. Digital filtering is also per-
formed on the audio input (Dante receiver)
signals before they are sent to the head-
phone outputs. This prevents users with
extended high-frequency sensitivity, such
as hosts and guests associated with dog
shows, from receiving undesirable audio
content.
The Model 374A allows a call signal to be
sent on channels 1, 2, and 3. This requires
that button 4 be configured to the Call
mode. To send a call signal is simple: just
enable any combinations of call channels
1, 2, and/or 3 and simultaneously press
and hold button 4. When call sending is
active the orange LED associated with but-
ton 4 will light. At the same time the chan-
nel or channels that are active in their talk
mode (from among channels 1, 2, and 3)
will add 20 kHz to their audio output chan-
nels and have their associated orange LED
flash. Release button 4 and the sending
of all call signals will cease. As expected,
pressing button 4 when no talk channels
are active will result in no action occurring.

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Whenever a Model 374A audio input chan-
nel receives a call signal (20 kHz audio
tone) the orange LED on its companion talk
button will first flash and then light continu-
ally. The only exception is if button 4 has
been set to the Call mode. (In this mode
button 4 will allow call signals to be gener-
ated on talk channels 1, 2, and 3.) It will
not light in response to a call signal being
present on audio input channel 4.
By using a 20 kHz tone for call signaling
the Model 374A is compatible with legacy
intercom equipment, including the vener-
able RTS BP-325 beltpack. When intercon-
necting Model 374A and BP-325 units using
an appropriate Dante-enabled interface,
such as the Studio Technologies’ Model
45DR Intercom Interface, call signaling
is fully compatible. Compatibility with the
Clear-Com® method of call functionality
is also possible by using the Model 45DC
Intercom Interface. (It converts the DC call
signal associated with pin 3 of a Clear-Com
party-line circuit to a 20 kHz tone.) Also,
devices such as the Studio Technologies’
Model 44D Audio Interface will send and
receive 20 kHz signals that are be compat-
ible with the Model 374A. The Model 44D
responds to the state of its GPI (general-
purpose input) signals and activate 20 kHz
tones, summing them with the audio sig-
nals which are then transported “in band”
via the Dante audio paths. Audio signals re-
ceived by the Model 44D will be monitored
for the presence of 20 kHz call signals. If
call signals are detected the GPO (general-
purpose output) signals will activate.
How to Identify a Specific
Model 374A
The Dante Controller software application
offers an Identify command that can be
used to help locate a specific Model 374A.
When Identify is selected it will send a
command to a single Model 374A unit.
On that specific unit the four pushbut-
ton LEDs will light in a unique pattern. In
addition, the SYS and SYNC status LEDs,
located directly below the etherCON RJ45
receptacle on the bottom panel, will slowly
flash green. After a few seconds the LED
identification pattern will cease and normal
Model 374A button LED and Dante status
LED operation will resume.
If configured, the Identify command can
also cause the mic kill function to activate.
For details please refer to the next para-
graph of this guide.
Mic Kill Function
The Model 374A includes a mic kill func-
tion, allowing talk buttons that have been
placed in their enabled (on) state to be
remotely changed to their disabled (off)
state. This allows one or more talk chan-
nels on a specific Model 374A that have
been enabled to be remotely disabled.
The reason for this function is simple. It’s
common in intercom applications for users
to enable a talk channel and then go “off
headset,” forgetting that they’ve left the
talk channel enabled. While they take a
break or go to lunch, all other users listen-
ing to that channel may hear unwanted
audio! Having the ability to disable this
talk channel can be very useful.
A configurable choice in the STcontroller
software application is used to select
which of the mic kill methods, Device ID
or Global Kill Command, will be active.
Either or both can be enabled as desired.
It’s also possible to disable the mic kill
function.
If the Device ID method of activating
mic kill is enabled, whenever the specific

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Model 374A is identified using the Iden-
tify command within Dante Controller or
STcontroller all enabled talk channels will
be forced to their disabled state. If the
Global Kill Command method is enabled
the Model 374A will respond to any such
request and force all talk channels to their
disabled state.
Technical Notes
IP Address Assignment
By default the Model 374A’s Ethernet in-
terface will attempt to automatically obtain
an IP address and associated settings
using the DHCP (Dynamic Host Configu-
ration Protocol). If a DHCP server is not
detected an IP address will automatically
be assigned using the link-local protocol.
This protocol is known in the Microsoft®
world as Automatic Private IP Addressing
(APIPA). It is also sometimes referred to
as auto-IP. Link-local will randomly assign
a unique IP address in the IPv4 range of
169.254.0.1 to 169.254.255.254. In this
way multiple Dante-enabled devices can
be connected together and automatically
function, whether or not a DHCP server
is active on the LAN. Even two Dante-
enabled devices that are directly intercon-
nected using an RJ45 patch cable will,
in most cases, correctly acquire IP ad-
dresses and be able to communicate
with each other.
An exception does arise when trying to
directly interconnect two Dante-enabled
devices that use Ultimo integrated circuits
to implement Dante. The Model 374A
uses the Ultimo “chip” and, as such, a
direct one-to-one interconnection to an-
other Model 374A (or other Ultimo-based
product) is not supported. An Ethernet
switch linking the two units is required to
successfully interconnect two Ultimo-based
devices. The technical reason that a switch
is required relates to the need for a slight
latency (delay) in the data flow. And an
Ethernet switch will provide this. While this
is certainly an anomaly, since PoE power
is required for Model 374A operation it’s
highly unlikely that an application would
use two Model 374A units without a PoE-
enabled Ethernet switch being present.
Using the Dante Controller software ap-
plication the Model 374A’s IP address and
related network parameters can be manu-
ally set for a fixed (static) configuration.
While this is a more-involved process than
simply letting DHCP or link-local “do their
thing,” if fixed addressing is necessary then
this capability is available. But in this case
it’s highly recommended that each unit be
physically marked, e.g., directly using a
permanent marker or “console tape,” with
its specific static IP address. If knowledge
of a Model 374A’s IP address has been
misplaced there is no reset button or other
method to easily restore the unit to a de-
fault IP setting.
In the unfortunate event that a device’s IP
address is “lost,” the Address Resolution
Protocol (ARP) networking command can
be used to “probe” devices on a network
for this information. For example, in Win-
dows OS the arp –a command can be
used to display a list of LAN information
that includes MAC addresses and cor-
responding IP addresses. The simplest
means of identifying an unknown IP ad-
dress is to create a “mini” LAN with a
small PoE-enabled Ethernet switch con-
necting a personal computer to the Model
374A. Then by using the appropriate ARP
command the required “clues” can be
obtained.

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Optimizing Network
Performance
For best Dante audio-over-Ethernet
performance a network that supports VoIP
Quality-of-service (QoS) capability is rec-
ommended. This can be implemented
on virtually all contemporary managed
Ethernet switches. There are even special-
ized switches that are optimized for enter-
tainment-associated applications. Refer to
the Audinate website (www.audinate.com)
for details on optimizing networks for Dante
applications. Also, disable Energy-Efficient
Ethernet (EEE) support on all Ethernet
switch ports that are associated with Dante
devices. Some implementations of EEE
can incorrectly interpret that a connected
device is not present and prevent proper
Dante operation.
Application Firmware Version
Display
There are two ways in which the version
number of the Model 374A’s application
firmware (embedded software) can be
identified. One requires only the Model
374A unit and involves a button-press
sequence performed upon power up.
The other method utilizes the Model 374A
and the STcontroller software application.
Either method may prove to be useful
when working with factory personnel on
application support and troubleshooting.
As part of the Model 374A’s power-up
sequence the unit’s application firmware
(embedded software) version number
can be displayed. This is useful when
working with factory personnel on applica-
tion support and troubleshooting. Before
connecting the PoE-enabled Ethernet ca-
ble, press and hold the channel 4 button.
Then connect the Ethernet cable. Upon ap-
plication of PoE power the Model 374A will
go through its normal power-up sequences
followed by a display of the firmware ver-
sion. The LED associated with the channel
1 button will “flash” to display the major
version number. Then the LED associated
with the channel 2 button will “flash” to dis-
play the minor version number. Once the
version number has been displayed button
4 can be released and normal operation
will begin. As an example of what would
be a typical application firmware display,
if the channel 1 button “flashes” once fol-
lowed by the channel 2 button “flashing”
two times this would indicate that applica-
tion firmware version 1.2 was present in
the Model 374A.
A selection in the STcontroller software
application allows the Model 374A’s ap-
plication firmware version to be identi-
fied. Connect the Model 374A unit to the
network and let it connect and start to
function. Then, after starting STcontroller,
review the list of identified devices and
select the specific Model 374A that inter-
ests you. Then select Version under the
Device tab. A page will then display that
will provide lots of useful information. This
includes the application firmware version
and well as details on the firmware present
in the Ultimo integrated circuit.
Application Firmware Update
Procedure
It’s possible that updated versions of the
application firmware (embedded software)
that is utilized by the Model 374A’s proces-
sor (microcontroller or MCU) integrated
circuit will be released to add features or
to correct issues. Refer to the Studio Tech-
nologies’ website for the latest application
firmware file. The unit has the ability to load
a revised file into the MCU’s non-volatile

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flash memory by way of a USB interface.
The Model 374A implements a USB host
function that directly supports connection
of a USB flash drive. The Model 374A’s
MCU updates its application firmware
using a file named M374A.bin.
The update process begins by preparing
a USB flash drive. The flash drive doesn’t
have to be empty (blank) but must be in
the personal-computer-standard FAT32
format. Save the new application firmware
file in the root directory with a name of
M374A.bin. Studio Technologies will sup-
ply the application firmware file inside
a .zip archive file. While the application
firmware file inside of the zip file will ad-
here to the naming convention required
by the Model 374A, the name of the
zip file itself will include the file’s ver-
sion number. For example, a file named
M374Av1r2MCU.zip would indicate that
version 1.2 of the application firmware
(M374A.bin) is contained within this zip
file.
Once the USB flash drive is inserted into
the USB interface, located on the main cir-
cuit board under the cover, the unit must
be powered off and again powered on.
At this point the file will automatically load
into the processor’s flash memory. The
precise steps required will be highlighted
in the next paragraphs of this guide.
To install the application firmware file
follow these steps:
1. Disconnect power from the Model
374A. This will entail removing the
Ethernet connection that is providing
PoE power.
2. Remove the cover from the Model
374A. Begin by removing the four Phil-
lips-head machine screws (#1 screw
driver tip), two per side. Be certain to
save the screws so that re-assembly
will be fast and painless. Then carefully
slide the cover forward to separate it
from the level controls and buttons and
then lift it off.
3. Locate the USB connector on the main
circuit board. It’s near the channel 1
button. Insert the prepared USB flash
drive into it.
4. Apply power to the Model 374A by
connecting to a Power-over-Ethernet
(PoE) Ethernet source.
5. After a few seconds the Model 374A
will run a “boot loader” program
that will automatically load and save
the new application firmware file
(M374A.bin). This will take only a few
seconds. During this time period the
channel 4 button LED will flash slowly
in alternating colors. Once the entire
process is over, taking approximately
10 seconds, the Model 374A will re-
start using the newly saved application
firmware.
6. At this time the Model 374A is operat-
ing under the newly saved application
firmware and the USB flash drive can
be removed. But to be conservative,
remove PoE power first and then re-
move the USB flash drive.
7. Confirm that the desired application
firmware version has been correctly
saved. This can be done by pressing
and holding the channel 4 button, ap-
plying PoE power to the Model 374A,
and then “reading” the application firm-
ware version number by first observing