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Model 373A Intercom Beltpack
Featuring Dante® Technology
Key Features
• Dante audio-over-Ethernet technology
• One talk and two listen channels
• Supports dynamic and electret microphones
• 4-pin male XLR headset connector
• 3.5 mm 4-conductor TRRS headset connector
• Call receive and display function
• Excellent audio quality
• Uses STcontroller for configuration
• AES67 and Dante Domain Manager™ (DDM) support
• Power-over-Ethernet (PoE) powered
Introduction
The Model 373A Intercom Beltpack is a highly compact userworn device that combines a single channel of talk and two
channels of listen. The unit begins with the features offered by
traditional analog party-line (PL) intercom user devices and adds
a range of new capabilities, along with the advanced perfor
mance and flexibility that Dante® audio-over-Ethernet provides.
Over a standard IP network, multiple Model 373A and other
compatible Studio Technologies’ beltpack units can be used to
create party-line intercom applications with help from an external
Dante-enabled audio matrix such as the Studio Technologies’
Model 5422 Dante Intercom Audio Engine. Alternately, Model
373A units can be used “point-to-point” or interfaced with
Dante-compatible matrix intercom systems.
Having one talk and two listen channels may seem unconven
tional. But it can be ideal for many “real-world” applications.
Often an intercom user is primarily listening and non-verbally
responding to requests made by producers, directors, or stage
managers. Typically, the Model 373A will be configured to be
part of one talk-and-listen party-line intercom channel. During
the time that an event is taking place the listen function will
serve a much more important role; the talk function will rarely
be utilized. However, the second listen channel will often be
important. Typically, it will be designated as a program-listen or
“show audio” channel. The two listen channels, along with the
ability to receive and display call signals, allow the Model 373A
to very effectively support production personnel in a compact
and cost-effective manner.
Only a single Power-over-Ethernet (PoE) connection is required
for operation. Key user features can be easily configured using
the STcontroller software application. Configurable parameters
include electret microphone powering, microphone preamplifier
gain, talk button operation, and headphone channel assignment.
Features include integrated sidetone, call signal receive display,
and remote mic kill (“talk off”). The range of capabilities, along
with the excellent audio quality provided by the digital audio
signal path, offers a unique and powerful user experience.
Setting up and configuring a Model 373A is simple. An ether
CON® RJ45 receptacle is used to interconnect with a standard
twisted-pair Ethernet port associated with a local-area network
(LAN). This connection provides both power and bidirectional
digital audio. The Model 373A is compatible with both broadcast
and “gaming” headsets.
A broadcast or intercom-style monaural headset with a dynamic
or electret (DC-powered) microphone can be interfaced with
the Model 373A using a 4-pin XLR connector. The Model 373A
also directly supports connection of stereo earbuds or gaming
headsets that utilize a 3.5 mm 4-conductor TRRS plug. These
moderately priced devices, commonly associated with mobile
phones or personal computers, are often of high-quality and
may be preferred for some applications. With the Model 373A’s
moderate price and ability to support a broad range of headset
devices the overall cost of deploying an intercom system can
often meet budget goals.
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The STcontroller software application is used to select the unit’s
operating parameters. The talk pushbutton switch can be config
ured for optimal operation. Two “push-in/push-out” (“pop-out”)
rotary controls make it easy to set and maintain the desired
headphone output level. The Model 373A’s compact 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.
channel routing, headphone level control, and sidetone creation
are performed within the digital domain. This provides flexibility,
allowing precise control of the audio signals and eliminating the
need for the two rotary level controls from having to directly
handle analog audio signals. The audio signals destined for the
2-channel headphone output 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.
The audio quality of the Model 373A is excellent, with low
distortion, low noise, and high headroom. Careful circuit design
and rugged components ensure long, reliable operation. A wide
range of applications can be supported, including education
and commercial theater, sports and entertainment TV and radio
events, streaming broadcasts, corporate and government AV,
post-production, and aerospace.
Dante Audio-over-Ethernet
Audio data is sent to and received from the Model 373A using
the Dante audio-over-Ethernet media networking technology.
As a Dante-compliant device, the Model 373A’s one audio
output (Dante transmitter) channel and two 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 support
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ing 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
373A is AES67 compatible and compliant with the Dante Domain
Manager™ software application.
Two bi-color LEDs provide status indications of the Dante inter
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face. The Dante Identify command takes on a unique role with
the Model 373A. Not only will it cause the talk pushbutton’s
orange LED to light in a highly visible sequence, it will also turn
off (“kill”) the talk function if it is active.
Audio Quality
The Model 373A offers “pro” audio performance that is not
found in typical party-line (PL) intercom beltpacks. A low-noise,
wide dynamic-range microphone preamplifier and associated
voltage-controlled-amplifier (VCA) dynamics controller (com
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pressor) ensures that microphone audio quality is preserved
while minimizing the chance of signal overload. DC power to
support electret microphones can be enabled as required. The
output of the microphone preamp and compressor is routed to
an analog-to-digital converter (ADC) section that supports 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.
Call Function Receive
A call receive function allows Model 373A users to be provided
with a visual indication that a call signal is active. The orange
LED within the pushbutton switch
will first flash then light
solid whenever a call signal is detected on either of the Dante
receiver (input) channels. Using 20 kHz tones, the call signals
are sent within the Dante audio channels (“in band”) allowing
interoperability between multiple Studio Technologies’ beltpack
units as well as being compatible with legacy party-line intercom
systems. Call signals can be useful to indicate to users that they
are needed “on headset” or should be actively listening to an
intercom channel. The call function can also be used to provide
real-time cues to production personnel during the running of
live events.
Configuration Flexibility
A highlight of the Model 373A 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 373A by way of an
Ethernet network connection. Configurable parameters include
microphone power and preamplifier gain, headphone monitoring,
sidetone audio operation, and talk button operation.
The microphone input can be selected for compatibility with
dynamic or electret (DC-powered) microphones. The gain of
the microphone preamplifier can be selected from among five
choices. These choices allow compatibility with the variety of
microphones that are part of broadcast, intercom, and computer
gaming headsets.
To support optimum user performance, the Model 373A’s talk
pushbutton switch can be configured from among three choices:
Push to Talk, Latching, or Push to Talk/Tap to Latch. Two audio
channels arrive via Dante receivers (inputs) and are destined
for the 2-channel headphone output. Each input source can
be independently routed to the left headphone channel, right
headphone channel, or both the left and right headphone chan
nels. This flexibility allows a variety of listening environments
to be created, including stereo, single-channel monaural, and
dual-channel monaural.
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Audio input signals arrive via two 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 373A’s processor where
Studio Technologies, Inc. Model 373A Intercom Beltpack, Issue 1, Page 2
Note that the left headphone output is sent to both the 4-pin
male XLR connector (Headset A) and the 3.5 mm 4-conductor
TRRS jack (Headset B). However, the right headphone output
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channel only connects to the 3.5 mm 4-conductor TRRS jack
(Headset B).
Ethernet Data and PoE
The Model 373A connects to an Ethernet data network using a
standard 100 Mb/s twisted-pair Ethernet interface. The physi
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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 373A’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 373A’s PoE interface reports to the power sourcing
equipment (PSE) that it’s a class 1 (very low power) device.
Future Capabilities and Firmware
Updating
The Model 373A 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 373A uses Audinate’s Ultimo™ integrated circuit to
implement the Dante interface. The firmware in this integrated
circuit can be updated via the Ethernet connection, helping to
ensure that its capabilities remain up to date.
Model 373A Specifications
Power Source:
Power-over-Ethernet (PoE): class 1 (very low power, ≤3.84 watts)
per IEEE® 802.3af
Network Audio Technology:
Type: Dante audio-over-Ethernet
AES67-2013 Support: yes
Dante Domain Manager (DDM) Support: yes
Bit Depth: up to 24
Sample Rate: 48 kHz
Number of Transmitter (Output) Channels: 1
Number of Receiver (Input) Channels: 2
Dante Audio Flows: 4; 2 transmitter, 2 receiver
Network Interface:
Type: 100BASE-TX, twisted-pair Ethernet, Power-over-Ethernet
(PoE) supported
Data Rate: 100 Mb/s (10 Mb/s and 1000 Mb/s “GigE” Ethernet
not supported)
Compatibility – Headset A: monaural single- or dual-ear
broadcast-style with dynamic or electret (low-voltage DC-powered)
microphone: pin 1 mic –/shield/screen; pin 2 mic +; pin 3 phones –;
pin 4 phones +
Compatibility – Headset B: CTIA™/AHJ configuration (typically
uses electret powered mic): tip phones left; ring 1 phones right; ring
2 common; sleeve mic
Audio Channels: 1 talk, 2 listen
Microphone Input:
Compatibility: dynamic or electret (low-voltage DC-powered)
microphones
Type: unbalanced
Electret Microphone Power: 5 volts DC via 2.21 k resistor,
selectable on/off
Impedance: 1 k ohms, nominal, microphone power off; 690 ohms,
nominal, microphone power on
Gain: 24, 30, 36, 42, or 48 dB, selectable, ref. –60 dBu input to
Dante output (–20 dBFS nominal)
Frequency Response: 40 Hz to 20 kHz, –3 dB
Distortion (THD+N): <0.02% (at minimum gain)
Dynamic Range: 91 dB of dynamic range
Compressor:
Application: applies to Dante transmitter (output) channel and
sidetone audio
Threshold: 1 dB above nominal level (–19 dBFS)
Slope: 2:1
Status LED: compressor active
Headphone Output:
Type: 2-channel
Compatibility: intended for connection to stereo (dual-channel)
or monaural (single-channel) headsets with nominal impedance
of 50 ohms or greater
Maximum Output Voltage: 3.8 Vrms, 1 kHz, 150 ohm load
Frequency Response: 20 Hz to 10 kHz, –3 dB
Distortion (THD+N): <0.002%
Dynamic Range: >100 dB
Call Receive Function:
Implementation: monitors both Dante receiver (input) channels for
presence of call signals
Signaling Method: 20 kHz, ±800 Hz, within audio channels
Call Receive Level: –27 dBFS minimum
Connectors:
Headset A: 4-pin male XLR
Headset B: 4-conductor (TRRS) 3.5 mm jack, per Japanese
standard JEITA/EIAJ RC-5325A
Ethernet: Neutrik NE8FBH etherCON RJ45 receptacle
USB: type A receptacle (located inside Model 373A’s enclosure and
used only for application firmware updates)
Configuration: requires Studio Technologies’ STcontroller
software application, version 2.01.00 and later
Environmental:
Operating Temperature: 0 to 50 degrees C (32 to 122 degrees F)
Storage Temperature: –40 to 70 degrees C (–40 to 158 degrees F)
Humidity: 0 to 95%, non-condensing
Altitude: not characterized
Dimensions (Overall):
3.1 inches wide (7.9 cm)
1.5 inches high (4.0 cm) without belt clip; 1.8 inches (4.6 cm) with
belt clip
4.9 inches deep (12.5 cm)
Deployment: intended for portable applications; contains integral
belt clip
Weight: 0.5 pounds (0.23 kg)
Specifications subject to change without notice.
Studio Technologies, Inc.
Skokie, Illinois USA
© by Studio Technolog
ies, Inc., April 2019
studio-tech.com
Studio Technologies, Inc. Model 373A Intercom Beltpack, Issue 1, Page 3
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