studio-tech 372A Intercom Beltpack Instructions
- May 15, 2024
- studio-tech
Table of Contents
Model 372A
Intercom Beltpack
User Guide
Issue 2, June 2023
This User Guide is applicable for serial numbers
M372A-00151 and later with application firmware 2.1 and later
Copyright © 2023 by Studio Technologies, Inc., all rights reserved
studio-tech.com
Revision History
Issue 2, June 2023:
- Adds screen capture for the STcontroller application.
- Miscellaneous improvements and clarifications.
- Updated to meet latest document format.
Issue 1, April 2019:
- Initial release.
Introduction
The Model 372A Intercom Beltpack is a highly compact user-worn 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
performance and flexibility that Dante® audio-over-Ethernet provides. Over a
standard IP network, multiple Model 372A 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 5422A Dante Intercom Audio Engine. Alternately,
Model 372A units can be used “point-to-point” or interfaced with Dante-
compatible matrix intercom systems.
Having one talk and two listen channels may seem unconventional. 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 372A 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 372A 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 372A is simple. An etherCON® RJ45 jack 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 372A is compatible with both broadcast
and “gaming” headsets.
A broadcast or intercom-style headset with a dynamic or electret (DC-powered)
microphone can be interfaced with the Model 372A using a 5-pin XLR connector.
The Model 372A also directly supports connection of 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 372A’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.
The STcontroller software application is used to select the unit’s operating
parameters. The talk pushbutton switch can be configured 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 372A’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.
The audio quality of the Model 372A 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 372A using the Dante audio-
over-Ethernet media networking technology. As a Dante-compliant device, the
Model 372A’s one Dante audio transmitter (output) channel and two Dante audio
receiver (input) channels can be interconnected (routed) with other devices
using the Dante Controller software application. The Dante transmitter
(output) and receiver (input) 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 372A is AES67 compatible and compliant with
the Dante Domain ManagerTM software application.
Two bi-color LEDs provide status indications of the Dante interface. The Dante
Identify command takes on a unique role with the Model 372A. 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 372A 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 voltagecontrolled-amplifier (VCA) dynamics
controller (compressor) 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.
Audio input signals arrive via two Dante receiver (input) channels. The
supported sampling rate is 48 kHz with a bit depth of up to 24. The audio
signals pass into the Model 372A’s processor where 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.
Call Function Receive
A call receive function allows Model 372A 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 372A 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 372A 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 372A’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 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 372A connects to an Ethernet data network using a standard 100 Mb/s
twisted-pair Ethernet interface. The physical interconnection is made by way
of a Neutrik® etherCON RJ45 jack. 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 372A’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 372A’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 372A was designed such that its capabilities and performance can be
enhanced in the future. A USB receptacle, 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 372A uses Audinate’s UltimoTM 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.
Getting Started
What’s Included
Included in the shipping carton are a Model 372A Intercom Beltpack and
instructions on how to obtain an electronic 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 may be made using the three
connectors located on the bottom of the Model 372A’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 dual-
channel or single-channel (dual- or single-ear) headset will be connected
using a cable-mounted 5-pin male XLR connector. Alternately, a headset with a
3.5 mm 4-conductor TRRS plug can be used. (The headset’s plug needs to follow
the CTIATM/AHJ configuration standard.)
Ethernet Connection with PoE
A 100BASE-TX Ethernet connection that supports Power-over-Ethernet (PoE) is
required for Model 372A operation. This one connection will provide both the
Ethernet data interface and power for the Model 372A’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 372A supports Ethernet switch power management, enumerating 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
jack that is located on the bottom of the Model 372A’s enclosure. This allows
connection by way of a cable-mounted etherCON connector or a standard RJ45
plug. The Model 372A’s Ethernet interface supports auto MDI/MDI-X so that a
crossover cable is not required.
Headset Connections
The Model 372A allows two different types of headsets to be connected. A 5-pin
female XLR connector is provided to support connection of a standard
broadcast- or intercom-style communications headset. A 3.5 mm 4-conductor TRRS
jack allows a computer gaming headset to be directly connected. The Model
372A’s two headset connectors are electrically wired in parallel. As such,
only one type of headset should be connected at one time.
Headset A
The Model 372A provides a 5-pin female XLR connector that interfaces with the
microphone and headphone connections of a single- or dual-ear intercom- or
broadcast-style headset. The connector is labeled Headset A. Refer to Figure 2
for connection details. The microphone input connections are compatible with
most unbalanced dynamic or electret (low-voltage DC-powered) microphones. A
balanced dynamic microphone should, in most cases, also function correctly if
its signal (low) is connected to Model 372A’s mic in /shield 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
monaural 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. Configuration 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 headset’s connector as damage to the Model 372A’s
output circuitry could result.
A monaural (single-earpiece or “single muff”) headset 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.
Figure 2. Headset A connection pinout chart
It’s possible that some beyerdynamic headset interconnecting cable assemblies
terminate the earpiece’s left and right connections opposite from what the
Model 372A and other broadcast equipment require. These cables may terminate
the left earpiece to pin 5 of the 5-pin male XLR connector 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 connector such that the left earpiece
connects to pin 4 and the right earpiece to pin 5.
If a separate microphone and pair of headphones need to be connected an
adapter cable assembly should be fabricated. It would consist of a 5-pin male
XLR connector wired to both a 3-pin female XLR connector for the microphone
and a ¼-inch or 3.5 mm TRS jack for the headphones. In this scenario, the
microphone would in most cases be a dynamic type as the Model 372A provides
only low-voltage DC “electret” power. Phantom-powered (P12 or P48) microphones
would not be compatible. Most handheld or “stick” microphones are dynamic and
should function correctly.
Headset B
The Model 372A also allows direct connection of gaming headsets that are
ubiquitous in the personal computer world. The 3.5 mm 4-conductor TRRS jack,
labeled Headset B, is compatible with the CTIATM/ AHJ configuration standard
which has the headphone left channel on the tip connection, the headphone
right channel on the ring 1 connection, common on the ring 2 connection, and
the microphone on the sleeve connection. Compatible headsets are readily
available, typically described as personal computer or gaming headsets. The
microphones used in these headsets are electret type which require a low-
voltage DC source for operation. The Model 372A is able to provide this power
and requires only that the appropriate setting in STcontroller be selected.
Refer to Figure 3 for a detailed description of the compatible TRRS plug.
Figure 3. Headset B connection pinout chart
Dante Configuration
For audio to pass to and from the Model 372A requires that several Dante-
related parameters be configured. These configuration settings will be stored
in nonvolatile memory within the Model 372A’s circuitry. Configuration will
typically be done with the Dante Controller software application which is
available for download free of charge at audinate.com. Versions of Dante
Controller are available to support Windows® and OS X® operating systems. The
Model 372A uses the Ultimo 2-input/2-output integrated circuit to implement
the Dante architecture. One transmitter (output) channel and both receiver
(input) channels are utilized.
The Dante transmitter (output) channel associated with the Model 372A’s Dante
interface must be assigned to the desired Dante receiver (input) channel. This
achieves routing the Model 372A’s one talk output audio channel to the device
(or devices) that will be “listening” to it. Within Dante Controller a
“subscription” is the term used for routing a transmitter flow (a group of
output 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 372A’s Dante transmitter (output) channel needs to be routed using
more than two flows it’s possible that an intermediary device, such as the
Studio Technologies’ Model 5422A Dante Intercom Audio Engine, can be used to
“repeat” the signals. (Use the Model 5422A’s pass-thru group configuration
mode to provide this resource.)
The two Dante receiver (input) channels associated with the Model 372A’s audio
inputs also need to be routed to the Dante transmitter (output) channels
provided by the desired source device. These two audio signals can be sent to
the Model 372A’s 2-channel headphone output.
The Model 372A supports an audio sample rate of 48 kHz with no pull-up/pull-
down values available. The Model 372A can serve as the Leader clock or a Dante
network, but in most cases it will be configured to “sync” to another device
that is serving as the “grand Leader” for the Dante implementation.
The Model 372A has a default Dante device name of ST-M372A- followed by a
unique suffix. The suffix identifies the specific Model 372A 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 one Dante transmitter
(output) channel has a default name of Ch1. The two Dante receiver (input)
channels have default names of Ch1 and Ch2. Using the Dante Controller
application the default device name and channel names can be revised as
appropriate for the specific application.
Model 372A Configuration
Many of the Model 372A’s operating parameters 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 actions are used to configure
the unit. This makes it imperative that the STcontroller software application
be available for use in a personal computer that’s connected to the related
LAN.
STcontroller is available free of charge on the Studio Technologies’ website
(studio-tech.com/stcontroller) and is compatible with personal computers
running Windows® and macOS® operating systems. If necessary, 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
372A unit or units that are to be configured.
Changes made using STcontroller will be immediately reflected in the unit’s
operation; no Model 372A “reboot” is required. Each time a change is made the
talk button, located on the top panel, will momentarily flash orange to
indicate 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. All Model 372A units that are present
on the network will be recognized and display on the device list. Use the
Identify command to allow easy recognition of a specific Model 372A unit.
Double clicking on a device name will cause the associated 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. In
virtually all cases a gaming or computer headset that uses a 3.5 mm TRRS plug
will require microphone power. If the associated headset has a dynamic (non-
powered) microphone do not enable the Electret Power check box. Most broadcast
headsets that terminate on 5-pin male XLR connectors 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 A connector.
Note that the Model 372A cannot supply P12 or P48 phantom power that may be
required for balanced condenser (capacitor) microphones. This should not pose
an issue as this type of microphone is essentially never associated with a
headset that would be used for intercom applications.
Microphone Input Gain
Choices are 24 dB, 30 dB, 36 dB, 42 dB, and 48 dB.
Dynamic microphones have an output level that is typically lower than that
provided by electret microphones. As such, the 36, 42, or 48 dB gain settings
will probably be appropriate for them. Electret microphones often have
internal circuitry which provides a relatively high output level. The 24 and
30 dB gain settings will typically be appropriate for use with this type of
microphone.
When a dynamic microphone is connected to the Model 372A the 42 dB gain
setting should be appropriate for many applications. The 36 dB choice may be
correct should the connected microphone have a high sensitivity (high output
level for a given acoustical input) or an enthusiastic user routinely talks
loudly into the microphone. Setting the gain for 48 dB may be helpful in some
applications, such as with headsets that have a low microphone output level.
The 48 dB gain setting may also be useful when the Model 372A 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 preamplifier gain may be
required. Selecting the 24 or 30 dB gain setting will probably be appropriate
in these cases.
The compressor active LED, labeled COMP and visible adjacent to the HEADSET A
connector, can act as a guide when setting the microphone preamplifier gain.
During normal talk operation the compressor active LED should light
intermittently. 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 situation
where the headset has an electret microphone and the gain is set for 30 dB,
changing it to 24 dB might be warranted.
Headphone Output Channel Routing
Choices are Left, Right, and Left and Right.
Two Dante transmitter (output) channels can be assigned to the Model 372A’s
two Dante receiver (input) channels using the Dante Controller application.
How these two audio signals are routed to the Model 372A’s headphone output
channels can be independently configured. For flexibility, each input source
has three routing options. They can be independently configured for sending
only to the left channel, only to the right channel, or sending to both the
left and right headphone output channels.
In some applications, split-mono or stereo operation will be desired. In this
case, input channel 1 might be routed to the left headphone output while input
channel 2 might be routed to the right headphone output. When using a stereo
or dual-ear headset sending both inputs to both headphone output channels is
often referred to as a dual-channel mono output. If a monaural (“single muff”)
headset is used, the Left configuration option allows the two input channels
to be combined to monaural and sent to just the left headphone output channel.
Sidetone Level
Choices are Off, Low, Medium Low, Medium, Medium High, and High.
The Model 372A includes a sidetone function that allows microphone audio
coming from the microphone input section to be sent to the headphone output.
This serves as a user confirmation that they are actively sending audio to the
talk output channel. Sidetone audio will only be routed to the headphone
output when the talk channel is active. 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 two rotary level controls will not impact
the sidetone level.
Button Operation Talk
Choices are Push to Talk, Latching, and Push to Talk/Tap to Latch.
This configuration section allows selection of how the talk button will
function. When the Push to Talk mode is selected, the operation is self-
explanatory. Only when the talk button is pressed and held will talk audio be
sent out the Dante transmitter (output) channel.
When the Latching mode is selected, 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.
When the Push to Talk/Tap to Latch mode is selected, a “hybrid” function of
sorts is enabled. Pressing and holding the talk button will enable audio to be
sent out the Dante transmitter (output) channel. When the button is released,
audio will stop being sent out the 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 channel can’t accidentally be left in its
talk active mode. There are certainly valid situations when the Latching mode
or Push to Talk/Tap to Latch mode settings will prove to be very useful.
Operation
At this point everything should be ready and Model 372A operation can
commence. An Ethernet connection with Power-over-Ethernet (PoE) capability
should have been made. A headset terminated with a cable-mounted 5-pin male
XLR connector may be plugged into the Headset A connector. Alternately, a
gaming or computer-type headset will be connected to Headset B using a 3.5 mm
4-conductor TRRS plug.
Using the Studio Technologies’ STcontroller software application, the unit’s
configuration should have been selected to meet the needs of the specific
application. The Model 372A’s Dante configuration settings should have been
selected using the Dante Controller software application. In this way, the
Model 372A’s Dante audio transmitter (output) channel and two Dante audio
receiver (input) channels should have been routed, by way of Dante
“subscriptions,” to the receiver and transmitter channels on associated Dante-
enabled equipment.
Initial Operation
The Model 372A 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 commence. Upon initial power-up the three status LEDs, located on
the bottom panel below the etherCON RJ45 jack, will begin to light as network
and Dante connections are established. The compressor active LED might
somewhat randomly flash for a brief period. The green and orange LEDs that
illuminate the talk pushbutton switch will light as part of a short test
sequence to indicate that the application firmware (embedded software) has
started. The mic power LED will also light for a short interval to indicate
that it is functioning. Once the test 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 jack on the Model 372A’s
bottom panel. The LINK ACT LED will light green whenever an active connection
to a 100 Mb/s Ethernet network has been established. It will flash in response
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 372A 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 372A is not synchronized with a Dante network. It will light solid green
when the Model 372A 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 372A is serving as the Leader clock 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
A connector. Labeled COMP, the LED displays the status of the microphone
preamplifier compressor 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 intermittently whenever a user is talking at
a normal voice level into the connected 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 active
LED will function whether or not the talk channel is active.
Headphone Output
Two rotary potentiometers (“pots”), located on the Model 372A’s top panel,
allow individual adjustment of the level of the two 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 distortion. Audio signals do not pass
directly through the level pots. The position of the pots is recognized by the
Model 372A’s processor which then adjusts the signal level within the digital
domain. When a pot is in its fully counterclockwise position the associated
audio signal is fully muted. The on/ off status of the talk channel does not
impact the headphone output.
Button Operation
A pushbutton switch is associated with the Model 372A’s talk channel. How the
switch functions will depend on the configuration of the unit.
Push to Talk: When the 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 Dante audio transmitter
(output) 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.
Latching: If the button has been configured for the Latching mode, operation
momentarily pressing (“tapping”) the button will cause the function 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.
Push to Talk/Tap to Latch: If the button has been configured for the Push to
Talk/Tap to Latch mode, operation is a bit different and certainly more
flexible. 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 function to change states: off-to-on or on-to-off.
Whenever the talk function is active the pushbutton will light green. The
button will not be lit when the function is not active.
Sidetone Function
The Model 372A includes a sidetone function that sends microphone audio to the
headphone output whenever the talk function is active. The quality of the
sidetone audio should be excellent and will provide Model 372A users with a
confidence signal that they are actively talking to other intercom users.
Sidetone audio will always be sent to both the left and right headphone output
channels. This is because the function is trying to simulate what a user would
hear if they didn’t have a headset covering both their ears.
An exception is if both Dante input channels are routed to only the left
headphone output channel. In this case, sidetone audio will only be sent to
the left headphone output channel.
The exact sidetone level is configured from among five values within the
STcontroller application. There is also a selection choice for turning off
sidetone. There is no means of adjusting the sidetone level using a physical
button or control on the Model 372A unit. Also, the two headphone 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 typically
users will not be concerned about revising it. But setting the sidetone level
to something reasonable is important. Setting the level too low will encourage
users to speak too loudly; setting it too high and users will be tempted to
speak hesitantly. And while users aren’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 Detection Display
A Model 372A function allows a call signal that’s present on either Dante
receiver (input) channel to cause the pushbutton switch’s LED to light.
Whenever a call signal is detected the button’s orange LED will first flash
and then light continually. Technically, a call signal is achieved by sending
a 20 kHz audio tone on the desired Dante audio channel. This signal is summed
(mixed) with normal talk audio. The Model 372A’s two audio input channels
continually monitor the audio input for the presence of 20 kHz.
The detection circuitry will not confuse normal talk audio signals with a call
signal. Digital filters within the Model 372A’s processor integrated circuit
help to ensure that false call detection won’t take place. Digital filtering
is also performed on the microphone audio output signals as well as the Dante
audio receiver (input) signals before they are sent to the headphone outputs.
This prevents users with extended high-frequency sensitivity, such as hosts
and guests associated with dog shows, from receiving undesirable audio
content.
By using a 20 kHz tone for call signaling the Model 372A is compatible with
legacy intercom equipment, including the venerable RTS BP-325 beltpack. When
interconnecting Model 372A and BP-325 units using an appropriate Dante-enabled
interface, such as the Studio Technologies’ Model 545DR Intercom Interface,
call signaling is fully compatible. Compatibility with the Clear-Com® method
of call functionality is also possible by using the Model 545DC 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 544D Audio Interface will send and receive 20 kHz signals
that are be compatible with the Model 372A. The Model 544D converts its GPI
(generalpurpose input) signals to 20 kHz tones and sums them with the audio
signals which are then transported “in band” via the Dante audio paths.
How to Identify a Specific Model 372A
Both the Dante Controller and STcontroller software applications offer a
command that can be used to help locate a specific Model 372A. When the
Identify command is selected it will send a message to a single Model 372A
unit. On that specific unit the pushbutton switch’s orange LED will flash
rapidly. In addition, the SYS and SYNC status LEDs, located directly below the
etherCON RJ45 jack on the bottom panel, will slowly flash green. After a few
seconds the LED identification pattern will cease and normal Model 372A button
LED and Dante status LED operation will resume.
Mic Kill Support
The Model 372A includes a mic kill function, allowing the talk button, if it
has been placed in its enabled (on) state, to be remotely forced to its
disabled (off) state.
This function is sometimes referred to as a “talk off” function. Two actions
can enable the mic kill function. Any time a Model 372A receives a Dante
Identify command it will cause both an LED pattern to start as well as
enabling the mic kill function. The second “trigger” method uses the Studio
Technologies’ Global Mic Kill command. This command can be activated from a
menu choice in the STcontroller software application.
The reason for the Model 372A to offer a mic kill function is simple. It’s
common in intercom applications for users to enable (“latch on”) a talk
channel and then go “off headset,” forgetting that they’ve left that talk
channel enabled. While they take a break or go to lunch, all other users are
forced to listen to that channel which may include unwanted audio. This makes
having the ability to disable a talk channel very useful. The Dante Identify
command allows a “latched on” talk channel on a specific Model 372A to be
remotely disabled. Alternately, by using the Global Mic Kill command a large
group of units can simultaneously have their talk channels disabled. This
would include any Studio Technologies’ compatible device that follows this
protocol.
Technical Notes
IP Address Assignment
By default, the Model 372A’s Ethernet interface will attempt to automatically
obtain an IP address and associated settings using the DHCP (Dynamic Host
Configuration 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 interconnected using an RJ45
patch cable will, in most cases, correctly acquire IP addresses 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 372A
uses Ultimo and a design limitation in it prevents a one-to-one
interconnection with another Model 372A (or any other Ultimo-based product).
An Ethernet switch linking the two Ultimo-based units is required to
successfully interconnect them. 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. While this is certainly an anomaly, since PoE power
is required for Model 372A operation it’s highly unlikely that an application
would use two Model 372A units without a PoE-enabled Ethernet switch being
present.
Using the Dante Controller software application, the Model 372A’s IP address
and related network parameters can be manually set for a fixed (static)
configuration. While this is a more-involved process than simply letting DHCP
or link-local automatically assign an IP address, if fixed IP addressing is
necessary then this capability is available. 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 372A’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 includes MAC addresses
and corresponding IP addresses. The simplest means of identifying an unknown
IP address is to create a “mini” LAN with a small PoE-enabled Ethernet switch
connecting a personal computer to the Model 372A. Then by using the
appropriate ARP command the required “clues” can be obtained.
Optimizing Network Performance
For best Dante audio-over-Ethernet performance a network that supports VoIP
Quality-of-service (QoS) capability is recommended. This can be implemented on
virtually all contemporary managed Ethernet switches. There are even
specialized switches that are optimized for entertainment-associated
applications. Refer to the Audinate website (audinate. com) for details on
optimizing networks for Dante applications. Also, be certain to disable
EnergyEfficient Ethernet (EEE) support on all Ethernet switch ports that are
associated with Dante devices. Some implementations of EEE can incorrectly
interpret that a connected Dante device is not present and prevent proper
operation.
Application Firmware Version Display
There are two ways in which the version number of the Model 372A’s application
firmware (embedded software) can be identified. One requires only the Model
372A unit and involves a button-press sequence performed upon power up. The
other method utilizes the Model 372A 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 372A’s power-up sequence the unit’s application firmware
(embedded software) version number can be displayed. Before connecting the
PoE-enabled Ethernet cable, press and hold the talk pushbutton. Then connect
the Ethernet cable. Upon application of PoE power the Model 372A will go
through its normal power-up sequences followed by a display of the firmware
version. The LED associated with the talk button will “flash” green to display
the major version number. Then, after a short pause, the talk button’s LED
will “flash” orange to display the minor version number. Once the version
number has been displayed the talk button can be released and normal operation
will begin. As an example of what would be a typical application firmware
display, if the LED in the talk button first “flashes” green two times then
“flashes” orange one time this would indicate that application firmware
version 2.1 was present in the Model 372A.
A selection in the STcontroller software application allows the Model 372A’s
application firmware version to be identified. Connect the Model 372A 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 372A that interests you. Then select Version under the Device tab. A
page will then display that will provide a lot 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 372A’s processor (microcontroller or
MCU) integrated circuit will be released to add features or to 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 its MCU’s non-
volatile flash memory by way of a USB receptacle. The Model 372A implements a
USB host function that directly supports connection of a USB flash drive. The
Model 372A’s MCU updates its application firmware using a file named
M372A.bin. (Note for geeks: the suffix .bin indicates that it’s a binary
file.)
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 M372A.bin. Studio Technologies will supply the application
firmware file inside a .zip archive file. While the application firmware file
inside of the zip file will adhere to the naming convention required by the
Model 372A, the name of the zip file itself will include the file’s version
number. For example, a file named M372Av2r1MCU. zip would indicate that
version 2.1 of the application firmware (M372A.bin) is contained within this
zip file.
Once a correctly prepared USB flash drive is inserted into the USB receptacle,
located under the cover of the Model 372A’s main circuit board, the unit must
be powered off and again powered on. At this point the file will automatically
be loaded into the processor’s flash memory. The precise steps required will
be highlighted in the following paragraphs.
To update the application firmware file follow these steps:
- Disconnect power from the Model 372A. This will entail removing the Ethernet connection that is providing PoE power.
- Remove the cover from the Model 372A. Begin by removing the four Phillips-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 pushbutton and then lift it off.
- Locate the USB receptacle on the main circuit board. It’s near the front, adjacent to the pushbutton and level controls. Insert the prepared USB flash drive into the USB receptacle.
- Apply power to the Model 372A by connecting to a Power-over-Ethernet (PoE) Ethernet source.
- After a few seconds the Model 372A will run a “boot loader” program that will automatically load and save the new application firmware file (M372A.bin). This will take only a few seconds. During this time period the talk pushbutton’s LED will flash slowly in alternate colors. Once the entire process is over, taking approximately 10 seconds, the Model 372A will restart using the newly saved application firmware.
- At this time the Model 372A is operating under the newly saved application firmware and the USB flash drive can be removed. But to be conservative, remove PoE power first and then remove the USB flash drive.
- Confirm that the desired application firmware version has been correctly saved. This can be done by pressing and holding the talk pushbutton, applying PoE power to the Model 372A, and then “reading” the application firmware version number by observing the talk pushbutton’s LED. Alternately, the STcontroller software application can be used to identify the application firmware version number. Whatever method you use, ensure that the desired version is present.
- Once the update process has been completed reverse the steps and reattached the cover using the four machine screws.
Note that upon power being applied to the Model 372A, if a connected USB flash drive doesn’t have the correct file (M372A.bin) in the root folder no harm will occur. If the correct file is not present upon power up the talk pushbutton’s LED will flash rapidly, alternating green and orange, for a few seconds to indicate this error condition after which normal operation using the unit’s existing application firmware will begin.
Ultimo Firmware Update
As previously discussed, the Model 372A implements Dante connectivity using
the 2-input/2-output Ultimo integrated circuit from Audinate. The Dante
Controller software application can be used to determine the version of the
firmware (embedded software) that resides in the Ultimo “chip.” The
STcontroller software application can also be used to identify Ultimo’s
firmware version. (Use the Version selection under the Device tab.) The Ultimo
firmware can be updated by way of the Model 372A’s Ethernet connection. The
latest Ultimo firmware file is available on the Studio Technologies’ website.
The Dante Firmware Update Manager (FUM) application program has traditionally
been used to install the Ultimo firmware. The Dante Controller software
application also includes an automated method of updating Ultimo firmware.
Both applications are available, free of charge, on the Audinate website
(audiante.com).
Restoring Factory Defaults
A command in the STcontroller software application allows the Model 372A’s
configuration to be reset to the factory default values. From STcontroller
select the Model 372A for which you want to restore its defaults. Select the
Device tab and then select the Factory Defaults feature. Then click on the OK
box. Refer to Appendix A for a list of the Model 372A’s factory default
values.
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: single- or dual-ear broadcast-style with
dynamic or electret (low-voltage DC-powered) microphone: pin 1 mic common; pin
2 mic; pin 3 phones common; pin 4 phones left; pin 5 phones right
Compatibility Headset B: CTIATM/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: 3.3 volts DC via 2.00 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: 2 dB above nominal level (19 dBFS)
Slope: 2:1
Stabtus 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: 2.8 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: 5-pin female XLR
Headset B: 4-conductor (TRRS) 3.5 mm jack, per Japanese standard
JEITA/EIAJ RC-5325A
Ethernet: Neutrik NE8FBH etherCON RJ45 jack
USB: type A receptacle (located inside Model 372A’s enclosure and used
only for application firmware updates)
Configuration: requires Studio Technologies’ STcontroller software
application
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 and information contained in this User Guide subject to change
without notice.
Appendix A: STcontroller Default Configuration Values
STcontroller default Model 372A configuration values:
Microphone Input Electret Power: Off
Microphone Input Gain: 36 dB
Headphone Output Channel 1 Input Routes to: Left
Headphone Output Channel 2 Input Routes to: Right
Headphone Output Sidetone Level: Medium
Button Operation Talk: Push to Talk/Tap to Latch
Issue 2, June 2023
Model 372A User Guide Studio Technologies, Inc.
Documents / Resources
|
studio-tech 372A Intercom
Beltpack
[pdf] Instructions
372A Intercom Beltpack, 372A, Intercom Beltpack, Beltpack
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References
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- Audinate - Pioneering the future of AV
- Home - Studio Technologies, Inc.
- STcontroller Application - Studio Technologies, Inc.
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