Studio Technologies 381 User manual

Copyright © 2019 by Studio Technologies, Inc., all rights reserved
www.studio-tech.com
User Guide
Issue 1, January 2019
This User Guide is applicable for serial numbers
M381-00151 and later with application firmware 1.1 and later
50663-0119, Issue 1
Model 381 On-Air Beltpack

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Model 381 User Guide Issue 1, January 2019
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MODEL 381
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Table of Contents
Revision History ........................................................... 4
Introduction ................................................................... 5
Getting Started ............................................................. 8
Operation ...................................................................... 14
Technical Notes ............................................................ 18
Specifications ............................................................... 22
Appendix A ................................................................... 23

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Revision History
Issue 1, January 2019:
• Initial release.

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Introduction
The Model 381 On-Air Beltpack offers a
unique combination of audio resources
to directly support a complete broadcast
“stand-up” on-air position. Using Dante®
audio-over-Ethernet technology, the unit
provides main and talkback output channels,
talent cue (IFB) input, and sidetone capabili-
ties, as well as essential user controls in
a compact, portable package. The Model
381 is compatible with the Dante Domain
Manager™ (DDM) software application and
is AES67-compliant for direct integration into
many contemporary networked audio appli-
cations.
Optimized for broadcast sports and live en-
tertainment events, eSports, news-gathering,
and streaming broadcast applications, the
Model 381 allows incredibly simple deploy-
ment while maintaining “pro” audio quality
and an intuitive user experience. With just
a Power-over-Ethernet (PoE) connection, a
dynamic or phantom-powered microphone,
and a pair of headphones or an earpiece,
the unit will be ready for “on-air” deploy-
ment. The STcontroller software application
is used for configuring operating parameters
including microphone preamplifier gain, P48
phantom power, headphone signal routing,
sidetone operation, and talkback button
action. The Model 381’s audio quality is
excellent, with low distortion, low noise, and
high headroom. Careful circuit design and
rugged components ensure long, reliable
operation.
Applications
The Model 381 provides an “all-Dante”
solution for one on-air talent location. Two
Dante audio input channels supply the user
with their talent cue (IFB) signals. Should
the cue signal be “mix-minus” an integrated
sidetone function can provide the user with
a microphone confidence signal. Two Dante
audio output channels, one designated
as main (for “on-air” use) and the other
talkback, are routed via the associated
local-area network (LAN) to inputs on
Dante-compatible devices. A pushbutton
switch, located on the Model 381’s top
panel, provides a combination talkback
and “cough” function. When talkback is
not active audio associated with the micro-
phone preamplifier is routed to the Dante
main output channel; the Dante talkback
output channel is muted. When the talkback
function is active audio is muted on the
Dante main output channel and activated
on the Dante talkback output channel. The
audio switching is performed in the digital
domain and is virtually “click-free.”
Figure 1. Model 381 On-Air Beltpack top and bottom views

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Setup and Operation
Set up and operation of the Model 381 is
simple. An etherCON® RJ45 jack is used
to interconnect with a standard twisted-pair
Ethernet port associated with a PoE-enabled
network switch. This connection provides
both power and bidirectional digital audio.
A broadcast headset or handheld (“stick”)
microphone can be directly connected to the
unit’s 3-pin XLR microphone input connec-
tor. This input is compatible with dynamic or
condenser microphones. An integrated P48
phantom power source can be enabled if
desired. Stereo headphones, the headphone
connections from a stereo or monaural
headset, or even a monaural earpiece are
connected to the headphone output jack.
Two “push-in/push-out” rotary controls (po-
tentiometers or “pots”) make it easy to set
the level of the talent cue signals level being
sent to the 2-channel headphone output.
The STcontroller software application is
used to configure the wide range of Model
381 operating parameters. This allows the
unit’s performance to be optimized to meet
the needs of specific applications. The
Model 381’s ultra-compact enclosure is
made from an aluminum alloy which offers
both light weight and ruggedness. A stain-
less steel “belt clip,” located on the back
of the unit, allows direct attachment to a
user’s clothing. The top surface is curved
to minimize the chance of the unit interfering
with clothing or being readily observable
“on camera.”
Ethernet Data and PoE
The Model 381 connects to a local area net-
work (LAN) by way of a standard 100 Mb/s
twisted-pair Ethernet interface. The physical
100BASE-TX interconnection is made by
way of a Neutrik® etherCON RJ45 connec-
tor. While compatible with standard RJ45
plugs, etherCON allows a ruggedized and
locking interconnection for harsh or high-
reliability environments. The Model 381’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
associated data network. To support PoE
power management, the Model 381’s PoE
interface enumerates (reports) to the power
sourcing equipment (PSE) that it’s a class 2
(low power) device.
Dante Audio-over-Ethernet
Audio data is sent to and received from
the Model 381 using the Dante audio-over-
Ethernet media networking technology.
The Model 381’s two Dante output (trans-
mitter) and two Dante input (receiver) audio
channels can be assigned to other devices
(routed) using the Dante Controller soft-
ware 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 44.1, 48, 88.2, or 96 kHz.
Two bi-color LEDs provide an indication of
the Dante connection status.
The Model 381 is compatible with the AES67
interoperability standard. In this mode the
two transmitter (output) channels will func-
tion in multicast; unicast is not supported.
In addition, the unit is compatible with the
Dante Domain Manager (DDM) software
application.
Audio Quality
The Model 381’s performance is completely
“pro,” making it appropriate for use in a
wide-range of applications. A low-noise, wide
dynamic-range microphone preamplifier
and associated voltage-controlled-amplifier
(VCA) dynamics controller (“compressor”)
circuit ensures that mic input audio quality

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is preserved while minimizing the chance
of signal overload. A configuration choice
allows selection of the signal source for the
Dante main output channel. The choices
are either the output of the microphone
preamp or the output of the compressor
circuit. These choices are referred to as
“pre-compressor” or “post-compressor.” The
ADC section utilizes a high-performance
integrated circuit that supports sampling
rates of 44.1, 48, 88.2, and 96 kHz with
a bit depth of up to 24. The audio signal,
now in the digital domain, routes through a
32-bit microprocessor and on to the Dante
interface section where it is packetized and
prepared for transport over Ethernet.
Audio input signals arrive via the Dante
receiver channels and pass into the Model
381’s microprocessor. As with the Dante
audio output channels, the sampling rate
can be 44.1, 48, 88.2, or 96 kHz with a bit
depth of up to 24. Channel routing, head-
phone level control, and sidetone creation
are performed in the digital domain. This
provides flexibility, allows precise control,
and keeps the two controls from having
to directly handle analog audio signals.
The audio channels destined for the head-
phone output channels 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, headphones, and earpieces.
Configuration Flexibility
The Model 381 can be configured to meet
the needs of specific applications and user
preferences. All configuration tasks are
performed using the STcontroller personal
computer software application which is
compatible with version 7 and later of the
Windows® operating systems. There are
no mechanical switch settings or button-
press sequences required to configure how
the unit functions. Selectable parameters
include microphone preamplifier gain, P48
phantom power on/off, headphone output
performance, sidetone operation, button
action, and main output audio source.
The gain of the microphone preamplifier
can be selected from among five choices.
This allows the Model 381 to match the out-
put sensitivity of a range of handheld and
headset-associated microphones. A low-
noise source of P48 phantom power can
be enabled if required to support condenser
(capacitor) microphones. The two Dante
input audio sources and the way in which
they are assigned to the headphone output
channels can be configured. In addition,
the operation of the two rotary controls can
be selected. These unique choices allow
almost any required headphone monitoring
situation to be implemented. Whether for
use in on-air sports, in an eSports broad-
cast, or as a production support tool, the
Model 381 should be able to achieve the
desired configuration.
The integrated sidetone function can be
configured to operate from among three
choices. This allows audio associated with
the microphone input and microphone pre-
amplifier to be returned to the headphone
output as required. Sidetone can be impor-
tant as some applications may provide a
“mix-minus” talent cue signal that doesn’t
include the user’s own voice content. A
configuration selection allows the talkback
button to be selected for a push to mute or
latching operation. The Dante main output
channel can be selected to its audio source
to be “pre-” or “post-” the dynamics control
circuitry.

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Future Capabilities and
Firmware Updating
The Model 381 was designed so that its
capabilities and performance can be en-
hanced 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 381 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 will be a
Model 381 On-Air Beltpack and a printed
copy of this guide. As a device that is
Power-over-Ethernet (PoE) powered,
no external power source is provided.
Connections
In this section signal interconnections will
be made using the three connectors located
on the bottom of the Model 381’s enclosure.
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 microphone will be connected using a
cable-mounted 3-pin male XLR connector.
A set of headphones or an earpiece will be
connected by way of a 2- or 3-conductor
¼-inch plug.
Ethernet Connection with PoE
A 100BASE-TX Ethernet connection that
supports Power-over-Ethernet (PoE) is
required for Model 381 operation. This one
connection will provide both the Ethernet
data interface and power for the Model
381’s circuitry. A 10BASE-T connection is
not sufficient as Dante does not support
this Ethernet protocol. And a 1000BASE-T
(“GigE”) connection is not supported unless
it can automatically “fall back” to 100BASE-
TX operation. The Model 381 supports
Ethernet switch power management,
enumerating itself as a PoE class 2 device.
The Ethernet connection is made by way
of a Neutrik etherCON protected RJ45 con-
nector that is located on the bottom of the
Model 381’s enclosure. This allows connec-
tion by way of a cable-mounted etherCON
connector or a standard RJ45 plug. The
Model 381’s Ethernet interface supports
auto MDI/MDI-X so that a “cross-over” or
“reversing” cable will never be required.
Ethernet Connection without PoE
As previously discussed in this guide, the
Model 381 was designed such that the
Ethernet connection will provide both data
and Power-over-Ethernet (PoE) power.
There may be situations where the as-
sociated Ethernet switch does not provide
PoE power. In such cases an external PoE
midspan power injector can be used. If the
selected midspan power injector is 802.3af-
compatible it should function correctly.
Midspan units are available from a variety
of sources, including many online retailers.
Microphone Input
The Model 381 provides a 3-pin female
XLR connector which allows a balanced dy-
namic or phantom-powered condenser mi-
crophone to be connected. The microphone
can be a standalone handheld (“stick”) type
or can be part of a broadcast-style head-
set. The Model 381’s microphone input is
directly compatible with balanced dynamic

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or P48 phantom powered microphones. A
microphone should be connected such that
its common is on connector pin 1, its signal
high (+) is on connector pin 2, and its sign
low (–) is on connector pin 3. An STcon-
troller configuration setting allows the P48
microphone power sources to be enabled or
disabled as desired. Details on configuring
the unit will be described later in this guide.
Headphone Output
The Model 381 provides a 2-channel
(“stereo”) headphone output by way of a
3-conductor ¼-inch phone jack. Devices
such as stereo headphones or “dual-ear”
broadcast-style headsets can be directly
connected using a 3-conductor ¼-inch
plug. Following the usual convention the
left channel should be terminated on the
tip lead, the right channel on the ring lead,
and common on the sleeve lead.
It’s also possible to use a monaural (“single-
ear”) headset or broadcast-type single
earbud as long as sufficient care is taken.
If a 3-conductor ¼-inch plug is used by the
device it should be wired such that the tip
lead is connected to the positive terminal
of the transducer and the sleeve lead is
connected to the negative or common lead
of the transducer; the plug’s ring should
be left unconnected. But it’s also likely that
the monaural device will be terminated on
a 2-conductor (tip and sleeve) ¼-inch plug.
When a plug of this type is inserted into the
Model 381’s headphone output connector
(jack) the Model 381’s right headphone out-
put channel will be shorted. (This will occur
since the ring lead will be directly shorted to
the sleeve lead.) This can lead to stress on
the Model 381’s right channel headphone
output circuitry as well as drawing extra cur-
rent from the output stage. To prevent this
condition the Headphone Output – Controls
(A/B) mode configuration choice should be
set for Single-Channel Mono. This disables
the right headphone output channel and
sends the listen audio source or sources
only to the left headphone output channel.
Refer to a later section in this guide for de-
tails on configuring the headphone output.
Dante Configuration
For audio to pass to and from the Model
381 requires configuration of several
Dante-related parameters. These configu-
ration settings will be stored in non-volatile
memory within the Model 381’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 Con-
troller are available to support Windows and
OS X® operating systems. The Model 381
uses the Ultimo 2-input/2-output integrated
circuit to implement the Dante architecture.
The two Dante transmitter (Tx) channels
associated with the Model 381’s Dante
interface must be assigned to the desired
receiver (Rx) channels. This achieves rout-
ing the Model 381’s two output audio chan-
nels to the device (or devices) that will be
“listening” to them. Within Dante Controller
a “subscription” is the term used for routing
a transmitter flow (a group of output chan-
nels) 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 uni-
cast, multicast, or a combination of the two.
If the Model 381’s Dante transmitter chan-
nels need to be subscribed (routed) to more
than two flows it’s possible that an interme-
diary device, such as the Studio Technolo-
gies’ Model 5422 Dante Intercom Audio
Engine, can be used to “repeat” the signals.
The two Dante receiver (Rx) channels as-
sociated with the Model 381’s audio inputs

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also need to be subscribed (routed) with
the desired Dante transmitter (Tx) chan-
nels. These two audio signals will provide a
Model 381 user with their headphone cue
signals.
The Model 381 has a default Dante device
name of ST-M381- and a unique suffix.
The suffix identifies the specific Model 381
that is being configured. The suffix’s actual
alpha and/or numeric characters relate to
the MAC address of the unit’s Ultimo inte-
grated circuit. The two Dante transmitter
(Tx) channels have default names of Main
and Talkback. The two Dante receiver (Rx)
channels have default names of Head-
phone Ch1 and Headphone Ch2. Using
Dante Controller, the default device name
and channel names can be revised as ap-
propriate for the specific application.
The Model 381 supports audio sample rates
of 44.1, 48, 88.2, and 96 kHz. A setting in
Dante Controller is used to configure the
desired sample rate. The Model 381 can
serve as the clock master for a Dante net-
work but in most cases, it will be configured
to “sync” to another device. No clock config-
uration settings associated with the Model
381 will typically require configuration within
Dante Controller.
Model 381 Configuration
The STcontroller software application is
used to configure the way in which the Mod-
el 381 functions. No DIP switch settings or
other local actions are used to configure the
unit. This makes it imperative that STcon-
troller be available for convenient use in a
personal computer that’s connected to the
related LAN.
Installing STcontroller
STcontroller is available free of charge on
the Studio Technologies website (www.
studio-tech.com/stcontroller). STcontroller
versions 1.08.00 and later will fully support
the Model 381. If required, download and in-
stall STcontroller onto a designated personal
computer. This personal computer must be
on the same local area network (LAN) and
subnet as the Model 381 unit or units that
are to be configured. Immediately after start-
ing STcontroller the application will locate the
devices that it can control. The Model 381 unit
or units will appear in the device list. Use the
Identify command to allow easy recognition of
a specific Model 381 unit. Double-clicking on
a device name will cause the associated con-
figuration menu to appear. Review the current
configuration and make changes as required.
Parameters
The configurable functions include:
• P48 phantom power on/off status
• Microphone preamplifier gain
• Headphone output routing and level
control operation
• Sidetone operation and level
• Talkback button operation
• Main output audio source
Changes made using STcontroller will be
immediately reflected in the unit’s operation.
No “reboot” of the Model 381 is required.
Each time a change is made the talkback
button on the top panel will flash orange in
two quick sequences to indicate that a com-
mand from STcontroller has been received.
Microphone Input – P48 Phantom Power
STcontroller allows selection of the on/off
status of the microphone input’s P48 phantom
power source. The on/off status is displayed
by way of an LED, red in color, located on
the bottom panel adjacent to the microphone
input connector. Select the status of the P48
source to meet the needs of the connected
microphone.

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Microphone Input – Gain
Choices are 36 dB, 42 dB, 48 dB, 54 dB,
and 60 dB.
The gain of the Model 381’s microphone
preamplifier can be selected from among
five choices. The compressor active LED,
orange in color and visible on the bottom of
the Model 381’s enclosure adjacent to the
microphone input connector, can act as a
guide when setting the preamp gain. When
a voice signal at a normal level is present
on the microphone input the compressor
active LED should light intermittently. If, for
example, it rarely lights and the gain is set
to 42 dB, it might be a good idea to change
the setting to 48 dB. If the LED is lit fully
while speaking at a normal level into the
microphone and the gain is set for 54 dB
or 60 dB, changing the gain to one of the
lower values might be warranted. There’s
no “hard and fast” rule about which gain
setting is appropriate. But unless otherwise
indicated, 42 dB is typically a good initial
choice.
Headphone Output – Routing
Choices are Dual-Channel Stereo, Dual-
Channel Mono, and Single-Channel Mono.
STcontroller allows selection from among
three headphone output modes. Each mode
is distinct and careful selection will help op-
timize the Model 381’s operation for a range
of applications.
Dual-Channel Stereo
The Dual-Channel Stereo mode is provided
for on-air applications where two indepen-
dent audio sources need to be routed to the
two headphone output channels. Dante
audio input channel 1 will be routed to the
left headphone output channel and Dante
audio input channel 2 will be routed to the
right headphone output channel. Note that
in this mode the sidetone audio signal will
be routed to both the left and right head-
phone output channels.
Dual-Channel Mono
The Dual-Channel Mono mode can be use-
ful in applications where the same audio
signals need to be provided to the user on
both the left and right headphone output
channels. In this mode Dante audio inputs
1 and 2 are combined (mixed together or
“summed”) and routed to both the left and
right headphone output channels. Note that
in this mode the sidetone audio signal will
be routed to both the left and right head-
phone output channels.
Single-Channel Mono
The Single-Channel Mono mode is spe-
cifically provided for applications where a
2-conductor ¼-inch plug is being used with
the connected headphones, headset, or
a broadcast-style earpiece. In this mode
Dante audio inputs 1 and 2 are combined to
monaural and routed to only the left channel
of the headphone output; no audio signal
is routed to the right channel of the head-
phone output. Note that in this mode the
sidetone audio signal will be routed to only
the left headphone output channel.
Headphone Output – Controls (A/B)
Choices are Ch 1 Level / Ch 2 Level, Ch 1
& 2 Level / Balance, and Ch 1 & 2 Level /
Sidetone Level.
Three configuration choices in STcontroller
allow selection of the manner in which the
two rotary controls (“pots”), labeled A and B,
will function.
Ch 1 Level / Ch 2 Level
This mode is provided for on-air applica-
tions where independent control of the
channel 1 and channel 2 input signals is
required. The control on the left, labeled
A, will allow adjustment of input channel 1.

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The control on the right, labeled B, will allow
adjustment of input channel 2. Note that in
this mode the level of the sidetone audio sig-
nal will be determined by the configuration of
the Fixed Sidetone Level setting.
Ch 1 & 2 Level / Balance
This mode is provided primarily for use
in “stereo” applications such as live music
events or radio broadcasts. In these applica-
tions it’s typical to want the user to have
a single control to simultaneously adjust
the level of both input channels 1 and 2
with a separate control used to adjust the
left/right level balance. When the Head-
phone Output – Routing configuration is
set for Dual-Channel Stereo the control on
the left, labeled A, will be used to adjust the
level of both input channels 1 and 2. The
control on the right, labeled B, will be used
to adjust the balance of the channel levels.
If the Headphone Output – Routing configu-
ration is set to either of the mono choices
the action of the balance control, on the right
and labeled B, will simply change the level
ratio of input 1 versus input 2. Also note that
in this mode the level of the sidetone audio
signal will be determined by the configura-
tion of the Fixed Sidetone Level setting.
Ch 1 & 2 Level / Sidetone Level
This mode is provided for applications where
the user needs to adjust the level of both the
audio input channels and the sidetone signal
as they are sent to the headphone output
channel or channels. The control on the left,
labeled A, will be used to adjust the level of
both input channels 1 and 2. The control
on the right, labeled B, will be used to adjust
the level of the sidetone signal.
Note that in this mode the configuration
choice for Fixed Sidetone Level will be
“grayed out” (become inactive) as it will
not be utilized.
Headphone Output – Sidetone Mode
Choices are Main Active, Talkback Active,
and Always Active.
The overall mode of the Model 381’s side-
tone function can be configured. Sidetone is
audio from the microphone input that is sent
to the headphone output channel or chan-
nels. This can be important, allowing the user
to “hear” themselves for performance confir-
mation and comfort. Making a specific selec-
tion from among the three available modes
will depend on the needs of the application.
If a “full mix” is being provided to the Model
381’s audio inputs then locally provided side-
tone won’t be needed when “on air,” i.e., the
main output is enabled. The user will hear
themselves by way of the audio signals being
routed to the Dante audio input channels.
But if a “mix-minus” is being supplied to the
Model 381 then having one of the sidetone
modes enabled can be an important means
of establishing user confidence. There are
also cases where a “full mix” is provided but
the user desires to hear themselves when
the talkback function is active.
Note that the actual level of sidetone audio
as it is sent the headphone output will be
determined by the configuration of the Head-
phone Output – Controls (A/B) selection. It
will either follow the Fixed Sidetone Level
configuration or the position of the level con-
trol that is located on the right and labeled B.
STcontroller allows selection from among
three sidetone modes:
Main Active
In this mode the sidetone function will be
active whenever the main output is active,
i.e., audio signal associated with the micro-
phone input is present on the Dante main
output. Whenever the talkback function is
active sidetone audio will not be enabled.

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Talkback Active
In this mode the sidetone function will be ac-
tive whenever the talkback function is active
and the audio signal is present on the Dante
talkback output channel. Whenever the main
output function is active sidetone audio will
not be enabled.
Always Active
In this mode the sidetone function will always
be active and sidetone audio will be continu-
ously routed to the headphone output.
Headphone Output – Fixed Sidetone
Level
Choices are Off, Low, Medium Low, Medium,
Medium High, and High.
When the configuration for the Headphone
Output – Controls (A/B) is set for either of
the dual-channel modes the level of the
sidetone audio will follow the Fixed Side-
tone Level setting. This level 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 dis-
abled by selecting the Off choice. Selecting
Off is useful for applications such as when
user microphone audio (a “full mix”) is being
returned as part of their listen audio signals.
As previously discussed, the Fixed Sidetone
Level choice will be “grayed out” and inac-
cessible if the Ch 1 & 2 / Sidetone mode
is selected for the Headphone Output –
Controls (A/B) configuration choice. In this
case the rotary control on the right, labeled
B, will be used to adjust the sidetone level.
Button Operation – Talkback
Choices are Push to Mute and Latching.
STcontroller allows the operating configura-
tion of the talkback button to be selected.
There are two choices available.
Push to Mute
If this mode is selected when the talkback
button is not pressed the microphone signal
will be sent to the Dante main output chan-
nel and the Dante talkback output channel
will be muted. The green LED associated
with the talkback button will be lit. When-
ever the talkback button is pressed and
held the audio signal will mute on the Dante
main output channel and the audio signal
will become active on the Dante talkback
output channel. In addition, the talkback
button will light orange.
Latching
If this mode is selected the talkback func-
tion will alternate between its on (active)
and off (inactive) states whenever the
button is momentarily pressed. The button
will light green whenever the main output
is active and light orange whenever the
talkback output is active. Upon power being
initially applied to the Model 381 the main
output function will be active and the talk-
back button will be lit green.
System Mode – Main Output Source
Choices are Pre-Compressor and Post-
Compressor.
This STcontroller selection allows the audio
source for the main output channel to be
selected. There are two choices available.
In most cases the post-compressor selec-
tion will be appropriate. In all cases the out-
put of the compressor circuitry will be used
by the talkback output (transmitter) channel.
Pre-Compressor
When selected for Pre-Compressor the
audio source for the Dante main output
channel will be the output of the micro-
phone preamplifier. No dynamic range
control is performed on the signal that is
provided to the main output. This selection

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can be appropriate when the most accu-
rate representation of the microphone input
signal is desired. This would allow maxi-
mum “downstream” control of a signal that
is to be used for “on-air” or other primary
purposes. Any processing of audio coming
from the main output channel would need
to be performed in equipment that’s “post”
(after) the Model 381 in the audio chain.
The downside of selecting pre-compressor
is an increased risk of signal overload.
Post-Compressor
When selected for Post-Compressor the
audio source for the Dante main output
channel will be the output of the dynamics
control (compressor) circuitry. This can help
prevent excessive signal levels from being
sent out the main output channel and on to
the next audio device in the signal “chain.”
With a threshold of just above the nominal
digital output level and a “gentle” compres-
sion ratio of just 2 to 1, in most cases the
impact of the compressor on voice audio
signals will be minimal while helping to
prevent audio overloads.
Operation
At this point everything should be ready
such that Model 381 operation can com-
mence. An Ethernet connection with Power-
over-Ethernet (PoE) capability should have
been made. A microphone and headphones
or an earbud should have been connected.
Alternately, a broadcast-style headset may
be utilized.
The Model 381’s Dante configuration set-
tings should have been selected using
the Dante Controller software application.
In this way the unit’s two audio output chan-
nels (Dante transmitter channels) and two
audio input channels (Dante receiver chan-
nels) should have been routed (subscribed)
to the Dante receiver and Dante transmitter
channels on associated equipment. The
Model 381’s operating configuration should
have been established using the STcon-
troller application. This will ensure that
the unit will meet the needs of the specific
application.
Initial Operation
The Model 381 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 operation to com-
mence. Upon initial power up the three
status LEDs located on the bottom panel,
below the etherCON RJ45 jack, will begin to
light as the network and Dante connections
are established. The COMP LED, adjacent
to the microphone input connector, may or
may not flash momentarily. The P48 LED,
also located adjacent to the microphone
input connector, will flash once to indicate
that it is functioning. The green and orange
LED indicators within the talkback pushbut-
ton switch will each light once to indicate
that the main operating firmware (embed-
ded software) has started functioning. Once
the power-up sequence has completed and
the Dante connection has been established
full operation will begin. The unit’s various
LEDs will become operational, displaying
the status of their designated functions.
How to Identify a Specific
Model 381
Functions within the Dante Controller and
STcontroller software applications allow
a specific Model 381 unit to be identified.
Each application provides an “eyeball” icon
that when selected (“clicked”) will activate
the Identify function. When Identify is se-
lected it will send a command to the des-
ignated Model 381 unit. On that unit the
orange LED associated with the talkback

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ON-AIR BELTPACK
pushbutton switch will flash on and off ap-
proximately eight times. (Of course, the
Identify command will not change the on/off
status of the button.) In addition, the SYS
and SYNC status LEDs, located directly
below the etherCON RJ45 connector on the
bottom panel, will slowly flash green. After a
few seconds this LED identification pattern
will cease and normal Model 381 talkback
button LED and Dante status LED operation
will resume.
Ethernet and Dante Status
LEDs
As previously mentioned, there are three sta-
tus LEDs located below the etherCON RJ45
connector on the Model 381’s bottom panel.
The LINK ACT LED lights green whenever
an active connection to a 100 Mb/s Ethernet
network has been established. It will flash
in response to Ethernet data packet activ-
ity. The SYS and SYNC LEDs display the
operating status of the Dante interface and
associated network. The SYS LED will light
red upon Model 381 power up to indicate
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 381 is not synchronized with a
Dante network. It will light solid green when
the Model 381 is synchronized with a Dante
network and an external clock source (tim-
ing reference) is being received. It will slowly
flash green when the Model 381 is part of a
Dante network and it is serving as a clock
master. It’s possible that up to 30 seconds
may be required for the SYNC LED to reach
its final state.
P48 Status LED
A red LED indicator is located on the
bottom panel adjacent to the microphone
input connector. It is labeled P48 and will
light whenever the P48 phantom power
source is active and providing power to
the microphone input.
Compressor Active LED and
Mic Preamp Gain
An orange LED indicator is located on the
bottom panel, also adjacent to the micro-
phone input connector. It is labeled COMP
and displays the status of the microphone
audio compressor function. This function
controls the dynamic range of the audio
signal that is sent to the talkback output
channel as well as being used by the side-
tone function. This signal may also, depend-
ing on a configuration setting, be present on
the Dante main output (transmitter) channel.
The compressor LED will light whenever the
input signal from the microphone, along with
the configured mic preamp gain, is of suf-
ficient level such that the dynamic range of
the microphone signal is being actively con-
trolled. It’s perfectly acceptable for this LED
to light intermittently whenever a user is talk-
ing at a normal voice level into an associat-
ed microphone. But if the COMP LED lights
solid orange while a user is talking at a nor-
mal voice level this will typically indicate that
the mic gain should be reduced. Conversely,
if the COMP LED almost never lights when
normal talking is taking place, it’s likely that
changing the gain to a higher value would
be beneficial. Note that due to the design of
the circuitry the compressor active LED will
function whether or not the main, talkback,
or sidetone functions are active.
Headphone Output – General
Users should find the headphone output
audio quality to be excellent, with high maxi-
mum output level and low distortion. Two
rotary controls (potentiometers or “pots”) are
located on the top panel and are “push-in/
push-out” type. This allows their associated

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knobs to be in the “out” position when the
level needs to be adjusted and in the “in”
position when protection from an unwanted
change is desired. Analog audio signals do
not pass directly through the two controls.
The position of the controls is recognized
by the Model 381’s processor which then
adjusts the actual signal level within the
digital domain.
Headphone Output – Routing
and Controls (A/B)
How the two rotary controls function will
depend on two configuration settings as
made using the STcontroller application.
The Headphone Output – Routing mode
configures how the two Dante audio inputs,
Ch 1 and Ch 2, are assigned to the two
headphone output channels. The Head-
phone Output – Controls (A/B) configuration
determines exactly the way in which the two
controls will function. Since the two configu-
rations each offer three choices, this pro-
vides nine separate configurations that each
provide a unique operating scenario.
When Headphone Output – Routing is
configured to the Dual-Channel Stereo
mode:
• In the Ch 1 Level / Ch 2 Level mode the
control on the left, labeled A, is used to ad-
just the level of the channel 1 input audio
signal as it is being sent to the left chan-
nel of the headphone output. The control
on the right, labeled B, is used control the
level of the channel 2 input audio signal
as it is sent to the right headphone output.
Sidetone audio, whose level will follow the
Fixed Sidetone Level configuration, will be
sent to both the left and right headphone
output channels.
• In the Ch 1 & 2 Level / Balance mode the
control on the left, labeled A, adjusts the
level of the Ch 1 input audio signal as it
is being sent to the left headphone output
and the Ch 2 input audio signal as it is
being sent to the right headphone output.
The control on the right, labeled B, will
adjust the level balance of both audio input
Ch 1 and audio input Ch 2 as they are sent
to the headphone output channels. The
level of the sidetone audio will follow the
Fixed Sidetone Level configuration and
will be sent to both the left and right head-
phone output channels.
• In the Ch 1 & 2 Level / Sidetone Level
mode the control on the left, labeled A, ad-
justs the level of both the Ch 1 input audio
signal as it is being sent to the left head-
phone output and the Ch 2 input audio
signal as it is being sent to the right head-
phone output. The control on the right,
labeled B, adjusts the level of the sidetone
audio as it is being sent to both the left and
right channels of the headphone output.
In this mode the Fixed Sidetone Level
configuration will be ignored.
When Headphone Output – Routing is
configured to the Dual-Channel Mono
mode:
• In the Ch 1 Level / Ch 2 Level mode the
control on the left, labeled A, is used to ad-
just the level of the channel 1 input audio
signal as it is being sent to both the left
and right headphone output channels. The
control on the right, labeled B, controls the
level of the channel 2 input audio signal
as it is sent to both the left and right head-
phone output channels. Sidetone audio,
whose level will follow the Fixed Sidetone
Level configuration, will be sent to both the
left and right headphone output channels.

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MODEL 381
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balance of audio input Ch 1 and audio
input channel 2. The level of the sidetone
audio will follow the Fixed Sidetone Level
configuration and will be sent to the left
headphone output channel.
• In the Ch 1 & 2 Level / Sidetone Level
mode the control on the left, labeled A,
adjusts the level of both the Ch 1 and
Ch 2 input audio signals as they are sent
to the left headphone output channel. The
control on the right, labeled B, adjusts the
level of the sidetone audio as it is being
sent to the left headphone output chan-
nel. In this mode the Fixed Sidetone Level
configuration will be ignored.
Sidetone Function Activity
The Model 381’s sidetone function is used
to send post-compressor microphone audio
to the headphone output as a user confir-
mation signal. When sidetone audio will be
actively sent to the headphone output will
depend on the configuration of the Head-
phone Output – Sidetone Mode in the
STcontroller application. The Sidetone
Mode can be configured such that sidetone
audio will be active only when the main
output is active, is active only when the
talkback output is active, or is active at all
times.
Whether sidetone audio will be sent to the
left and right headphone output channels or
only the left headphone output channel will
depend on the configuration of the Head-
phone Output – Routing configuration in
STcontroller. As expected, when the Head-
phone Output – Routing mode is configured
for Dual-Channel Stereo or Dual-Channel
Mono sidetone audio will be sent to both the
left and right headphone output channels.
When configured for Single-Channel Mono
sidetone audio will be sent only to the left
headphone output channel.
• In the Ch 1 & 2 Level / Balance mode the
control on the left, labeled A, adjusts the
level of both the Ch 1 and Ch 2 input audio
signals as they are sent to both the left and
right headphone output channels. The con-
trol on the right, labeled B, will adjust the
level balance of audio input Ch 1 and audio
input channel 2. The level of the sidetone
audio will follow the Fixed Sidetone Level
configuration and will be sent to both the
left and right headphone output channels.
• In the Ch 1 & 2 Level / Sidetone Level
mode the control on the left, labeled A,
adjusts the level of both the Ch 1 and
Ch 2 input audio signals as they are sent
to both the left and right headphone output
channels. The control on the right, labeled
B, adjusts the level of the sidetone audio
as it is being sent to both the left and right
channels of the headphone output. In this
mode the Fixed Sidetone Level configura-
tion will be ignored.
When Headphone Output – Routing is
configured to the Single-Channel Mono
mode:
• In the Ch 1 Level / Ch 2 Level mode the
control on the left, labeled A, is used to
adjust the level of the channel 1 input
audio signal as it is being sent to the left
headphone output channel. The control
on the right, labeled B, controls the level
of the channel 2 input audio signal as it is
sent to the left headphone output channel.
Sidetone audio, whose level will follow the
Fixed Sidetone Level configuration, will be
sent to the left headphone output channel.
• In the Ch 1 & 2 Level / Balance mode the
control on the left, labeled A, adjusts the
level of both the Ch 1 and Ch 2 input audio
signals as they are sent to the left head-
phone output channel. The control on
the right, labeled B, will adjust the level

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orange, microphone audio will be sent out
the Dante talkback output channel; and the
Dante main output will be muted.
Latching
If the Talkback button has been configured
for the latching mode its operation is a bit
different. Momentarily pressing (“tapping”)
the button will cause the talkback func-
tion to change states: off-to-on or on-to-off.
Whenever microphone audio is being sent
only to the Dante main output channel the
button will light green. The button will light
orange when the talkback function is en-
abled and microphone audio is being sent
out the Dante talkback output channel while
the Dante main output channel is muted.
Technical Notes
IP Address Assignment
By default, the Model 381’s Ethernet inter-
face will attempt to automatically obtain an
IP address and associated settings using
DHCP (Dynamic Host Configuration Pro-
tocol). 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 (PIPPA).
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, wheth-
er or not a DHCP server is active on the
LAN. Even two Dante-enabled devices that
are directly inter-connected using an RJ45
patch cord will, in most cases, correctly
acquire IP addresses and be able to com-
municate with each other.
Depending on the configuration of the
Headphone Output – Controls selection in
STcontroller, the level of the sidetone audio
will be determined either by the selected
value in the Fixed Sidetone Level configu-
ration or by adjustment of the right control,
labeled B, that is located on the top panel.
Typically, providing a precise sidetone level
is not important and most users will not
be concerned about setting it to a specific
value. But ensuring that the level of the side
tone audio is reasonable is important. Set-
ting the level too low will encourage a user
to speak too loudly; setting it too high and
the user will be tempted to speak hesitantly.
Talkback Button
The Talkback pushbutton serves as both
a main output mute and a talkback enable
function. When “talkback” is active audio
is no longer sent out the Dante main out-
put channel but instead is routed to the
Dante talkback output channel. In this way
the “on-air” channel is muted and the talk-
back channel is active. When the button’s
LED is lit green audio is being sent out the
main output channel and no audio is being
sent out the talkback output channel. The
button’s LED will light orange when the main
output is muted and audio is present on the
talkback output channel. The button’s spe-
cific action in response to being pressed will
depend on its configuration as made using
STcontroller.
Momentary
When the Button Operation – Talkback
selection has been configured for Push
to Mute its functionality will be pretty self-
explanatory. When the button is not pressed
its LED is lit green and audio is sent out the
Dante main output channel. Press and hold
the button to enable the talkback function.
When talkback is enabled its LED will be lit

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Optimizing Network
Performance
For best Dante audio-over-Ethernet perfor-
mance a network that supports VoIP QoS
capability is recommended. In applica-
tions that utilize multicast Ethernet traffic
enabling IGMP snooping can be valuable.
These protocols can be implemented on
virtually all contemporary managed Ether-
net switches. There are even specialized
switches that are optimized for entertain-
ment-associated applications. Refer to the
Audinate website (www.audinate.com) for
details on optimizing networks for Dante
applications.
Application Firmware Version
Display
There are two ways in which the version
number of the Model 381’s application firm-
ware (embedded software) can be identi-
fied. One requires only the Model 381 unit
and involves a button press sequence per-
formed upon power up. The other method
utilizes the Model 381 and the STcontroller
software application. Either method may
prove to be useful when working with fac-
tory personnel on application support and
troubleshooting.
As part of the Model 381’s power-up se-
quence the unit’s application firmware can
be directly displayed. Before connecting
the PoE-enabled Ethernet cable, press and
hold the talkback button. Then connect the
Ethernet cable. Upon application of PoE
power the Model 381 will not go through
its normal power-up sequence but instead
will display the firmware version. The LED
associated with the talkback button will
“flash” green in color to display the major
version number and then “flash” orange
to display the minor version number. Then
the LED will remain off until the talkback
An exception does arise when trying to
directly interconnect two Dante-enabled
devices that use Ultimo integrated circuits
to implement Dante. The Model 381 uses
the Ultimo “chip” and, as such, a direct one-
to-one interconnection to another 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; an Ethernet
switch will provide this.
Using the Dante Controller software ap-
plication, the Model 381’s IP address and
related network parameters can be 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 capabil-
ity is available. But in this case it’s highly
recommended that every 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
381’s IP address has been misplaced there
is no reset button or other method to easily
restore the unit to a default 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 Windows
OS the arp –a command can be used to
display a list of LAN information that in-
cludes MAC addresses and corresponding
IP addresses. The simplest means of iden-
tifying an unknown IP address is to create a
“mini” LAN with a small PoE-enabled Ether-
net switch connecting a personal computer
to the Model 381. Then by using the appro-
priate ARP command the required “clues”
can be obtained.

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The processor in the Model 381 is compat-
ible with both USB 2.0, USB 3.0, and USB
3.1-compliant Flash drives. Save the new
firmware file in the root directory with a
name of m381.bin. Studio Technologies will
supply the application firmware file inside
a .zip archive file. While the firmware file
inside of the zip file will adhere to the nam-
ing convention required by the Model 381,
the name of the zip file itself will include the
file’s version number. For example, a file
named m381v1r2MCU.zip would indicate
that version 1.2 of the application firmware
(m381.bin) is contained within this zip file.
Once the USB flash drive is inserted into
the USB interface, located on the main
circuit board under the cover, the unit must
be powered off and again powered on. At
this point the file will automatically load. 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 381.
This will entail removing the Ethernet
connection that is providing PoE power.
2. Remove the cover from the Model 381.
Begin by removing the four Phillips
head 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 con-
trols and button and then lift it off.
3. Locate the USB connector on the main
circuit board. It’s near the top of the unit,
directly between the two rotary level
controls. Insert the prepared USB flash
drive into it.
4. Apply power to the Model 381 by con-
necting to a Power-over-Ethernet (PoE)
Ethernet source.
button is released. Once the talkback but-
ton is released normal operation will then
take place. As an example of what would
be a typical firmware display, if the talkback
button’s LED “flashes” green once followed
by the LED “flashing” orange once it would
indicate that application firmware version
1.1 is present in the Model 381.
A selection in the STcontroller software ap-
plication allows the Model 381’s application
firmware version to be identified. Connect
the Model 381 unit to the network and let
it connect and start to function. Then, after
starting STcontroller, review the list of identi-
fied devices and select the specific Model
381 from which you want to determine its
application firmware version. 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
Dante interface firmware.
Application Firmware Update
Procedure
It’s possible that updated versions of the
application firmware (embedded software)
that is utilized by the Model 381’s processor
(microcontroller or MCU) integrated circuit
will be released to add features or correct
issues. Refer to the Studio Technologies
website for the latest application firmware
file. The unit has the ability to load a revised
file into the MCU’s non-volatile memory by
way of a USB interface. The Model 381
implements a USB host function that direct-
ly supports connection of a USB flash drive.
The Model 381’s MCU updates its firmware
using a file named m381.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.