Studio Technologies 44D User manual

Copyright © 2023 by Studio Technologies, Inc., all rights reserved
studio-tech.com
50032-0223, Issue 6
User Guide
Issue 6, February 2023
This User Guide is applicable for serial numbers
M44D-01151 and later with application rmware 2.2 and later
and Dante rmware 4.6.0 (UltimoX2 4.2.2.3) and later
Also applicable to units with serial numbers
M44D-00151 to 00250; see Appendix A for details
Model 44D
Audio Interface
Dante®to and from Analog Audio

This page intentionally left blank.

Model 44D User Guide Issue 6, February 2023
Studio Technologies, Inc. Page 3
Table of Contents
Revision History ............................................................ 4
Introduction................................................................... 5
Getting Started.............................................................. 10
Conguration ................................................................ 14
Operation ...................................................................... 18
Technical Notes............................................................. 22
Specications................................................................ 26
Appendix A: Original vs Updated Model 44D .............. 28
Appendix B: Interfacing with RTS®
Matrix Intercom Systems .............................................. 31
Appendix C: Interfacing with Riedel®Artist™
Matrix Intercom Systems .............................................. 32
Appendix D: Interfacing with Clear-Com®
Matrix Intercom Systems .............................................. 33

Issue 6, February 2023 Model 44D User Guide
Page 4 Studio Technologies, Inc.
Revision History
Issue 6, February 2023:
• Claries tone generator frequencies versus sample rate.
Issue 5, April 2021:
•Added Appendices B, C, and D. Details how to interface the Model 44D with matrix
intercom systems.
Issue 4, June 2020:
•Documents deletion of pull-up/pull-down capability.
Issue 3, August 2018:
• Documents change of tone frequencies from 1 kHz and 18 kHz to 18 kHz and 20 kHz.
Issue 2, November 2017:
• Documents addition of operating mode conguration (audio interface and tone
generator).
Issue 1, September 2016:
•Initial release.

Model 44D User Guide Issue 6, February 2023
Studio Technologies, Inc. Page 5
Introduction
The Model 44D Audio Interface provides a
simple yet high-performance means of in-
terfacing two channels of analog line-level
audio to and from applications that utilize
Dante®audio-over-Ethernet media net-
working technology. Two Model 44D units
can also provide one-to-one signal paths,
two in each direction, over a standard
local area network (LAN). In addition, the
unit supports transport of status signals or
contact closures between Model 44D units
and other compatible products. There are
two general-purpose inputs (GPI) and two
general-purpose output (GPO) on each
Model 44D.
A special operating mode allows the
Model 44D to serve as a tone generator
rather than an audio interface. When
congured for the tone generator mode
18 kHz and 20 kHz sine-wave audio sig-
nals are available in both the analog and
digital domains. These frequency values
are applicable when the Dante sample
rate is congured for 48 kHz. When the
Dante sample rate is 44.1 kHz, the tone
generator output frequencies will be
16.5375 kHz and 18.375 kHz, respectively.
The Model 44D is a fully professional
product that offers the audio quality, fea-
tures, and reliability required by 24-hour,
on-air, and commercial applications. The
two line-level audio inputs use standard
3-pin female XLR connectors for easy
interfacing with balanced and unbalanced
sources. The input audio signals are
converted to 24-bit digital and then trans-
ported via the Dante interface. Two digital
audio signals arrive into the Model 44D via
the Dante interface and are then converted
to analog. Two 3-pin male XLR connectors
on the Model 44D’s back panel provide
balanced line-level outputs.
The Model 44D is designed as a bridge,
using Dante to link analog or other Dante
interfaces found on devices such as matrix
intercom systems, broadcast routers, and
audio consoles. An Ethernet connection is
all that’s required to make the Model 44D
part of a sophisticated, networked audio
system. Dante audio-over-Ethernet has
Figure 1. Model 44D standard “throw-down” front view
Figure 2. Model 44D back view

Issue 6, February 2023 Model 44D User Guide
Page 6 Studio Technologies, Inc.
found wide acceptance as an audio “back-
bone” due to its ease of use, high perfor-
mance, strong interoperability, and wide
adoption by a large number of equipment
manufacturers. The Model 44D is a gen-
eral-purpose “tool” that helps to expand
Dante’s capabilities to facilities and equip-
ment that primarily supports signals in the
analog domain.
Careful attention to circuit design and
component selection ensures that excellent
audio quality is maintained. Extensive lter-
ing helps prevent damage or less-than-
optimal performance should DC voltage,
ESD (“static”), or strong RF signals be
present on the associated analog signals.
Conguration switches allow several Model
44D operating parameters to be selected.
The nominal audio levels of the line input
and line output functions can be inde-
pendently selected. In this way compatibil-
ity with SMPTE®and EBU nominal signal
levels is supported. Audio level meters
provide conrmation of system perfor-
mance during setup and operation. Two
general purpose input and two general
purpose output functions allow support for
installer-selected applications, including
party-line intercom call-light functions. Two
LEDs provide a direct indication of the sta-
tus of the GPO functions.
The Model 44D can be powered by Power-
over-Ethernet (PoE) or an external source
of 12 volts DC. Standard connectors
are used for the line inputs and outputs,
Ethernet, GPI/GPO, and DC power inter-
connections. The Model 44D’s enclosure
has a “1/2-rack” 1U form factor and weighs
less than two pounds, making it well suited
for use in portable applications. Alternately,
using one of the optional rack-mount front
panels, one or two Model 44D units can be
mounted in a single space (1U) of a stan-
dard 19-inch rack enclosure.
Dante Audio-over-Ethernet
Audio data is sent to the Model 44D us-
ing the Dante audio-over-Ethernet media
networking technology. Audio signals with
a sample rate of 44.1 or 48 kHz and a bit
depth of up to 24 are supported. The two
line input channels are converted to digi-
tal and then routed to transmitter (output)
channels on the Dante interface. Two
transmitter (output) channels from an as-
sociated Dante-enabled source device can
be assigned to the Model 44D’s receiver
(input) channels using the Dante Control-
ler application. These are then converted
into analog outputs.
Applications
The most basic application for Model 44D
is for transporting analog audio signals to
and from one location to another using
the data transport resources of a local
area network — there’s really no simper
means to getting high-quality audio from
“point A to point B” and back. With stan-
dard connectors and PoE power, setup
can be completed in just a few minutes.
This makes Model 44D units effective in
both xed and portable applications.
The Model 44D can also nd use when
an application already supports Dante.
For example, ports on a matrix intercom
system that directly supports Dante, such
as the RTS®ADAM®with OMNEO®, can
be routed to a Model 44D’s Dante output
(transmitter) and input (receiver) channels.
The Model 44D will then provide two ana-
log input and two analog output interfaces
for use in a variety of applications. These
can include interfacing with audio inputs

Model 44D User Guide Issue 6, February 2023
Studio Technologies, Inc. Page 7
and outputs associated with audio con-
soles, providing talent cueing (IFB) feeds,
and interfacing with the audio outputs of
aerial camera systems.
The Model 44D’s tone generator mode
enables the unit to create 18 kHz and
20 kHz analog and digital sine-wave audio
signals. The 18 kHz tone is provided as
a resource when supporting remote-
production (REMI) applications that use
the Studio Technologies’ Model 5422
Dante Intercom Audio Engine. The tone
can be used by a matrix intercom system
to facilitate creation of voice-with-tone
interruptible foldback (IFB) signals. When
routed to the Model 5422’s interrupt inputs
these specialized IFB signals will allow ex-
cellent talent cueing performance to occur.
The 20 kHz tone is provided for use in ap-
plications where generation of a party-line
call signal is desired. For example, the
20 kHz tone can be connected to a matrix
intercom system which would be cong-
ured such that a button press will cause
20 kHz to be sent out an intercom chan-
nel. This can serve as a “trigger” signal for
visual or audible alerting devices, such as
the Studio Technologies’ Model 391 Dante
Alerting Unit.
Note that the frequencies described
(18 kHz and 20 kHz) are effective when
the Dante sample rate is congured for
48 kHz. When the Dante sample rate
is 44.1 kHz, the tone generator output
frequencies will be 16.5375 kHz and
18.375 kHz, respectively.
Line Inputs
The Model 44D provides two analog
line-level input channels. A conguration
choice allows the nominal level of the
input signals to be +4 or 0 dBu. When
congured for +4 dBu the unit will be
compatible with SMPTE applications
where the nominal digital signal level is
–20 dBFS. In the 0 dBu conguration the
line inputs are optimized for EBU applica-
tions where the nominal digital signal level
is –18 dBFS.
The electronically balanced (differential)
input circuits are capacitor-coupled and
ESD (static) protected for reliable opera-
tion in a variety of applications. They are
also protected from damage should a
moderate DC voltage be accidentally con-
nected. Sources can include analog I/O
cards on matrix intercom systems, audio
consoles, wireless microphone receivers,
and broadcast routers.
Line Outputs
The Model 44D provides two analog line-
level output channels. As with the line
inputs, a conguration choice allows the
nominal level of the output signals to be
+4 or 0 dBu. This allows compatibility in
applications where SMPTE (+4 dBu =
–20 dBFS) or EBU (0 dBu = –18 dBFS)
standards may apply. The outputs are
electronically balanced, capacitor-coupled
and ESD (static) protected. The outputs
are compatible with virtually all balanced
and unbalanced inputs with an impedance
of 2 k ohms or greater.
General Purpose Inputs and
Outputs
The Model 44D allows the sending and
receiving of status signals using high-
frequency audio tones that are included
with within the Dante audio channels.
When two Model 44D units are intercon-
nected using an Ethernet network and
Dante, two status signals will be transport-

Issue 6, February 2023 Model 44D User Guide
Page 8 Studio Technologies, Inc.
ed in each direction. Each general purpose
input (GPI) is compatible with contact clo-
sures provided by equipment such as ma-
trix intercom systems or routers. A closure
on a GPI on one Model 44D unit will result
in the closing (shorting) of a solid-state relay
contact on the other Model 44D. To assist in
implementing specialized GPI and GPO ap-
plications a source of low-current DC power
is also provided.
The GPI and GPO functions can be espe-
cially useful in party-line intercom applica-
tions where call-light signals are utilized.
Contact closures on matrix intercom sys-
tems can be “repeated” by Model 44D
units that are located anywhere within the
associated local area network (LAN). The
Model 44D is also directly compatible with
the call-light signal support provided by the
Studio Technologies’ Model 45DC and
Model 45DR Intercom Interface units.
With a Model 44D appropriately intercon-
nected with a matrix intercom system full
call-light support can be provided to and
from RTS and Clear-Com®party-line inter-
com circuits.
Pro Audio Quality
The Model 44D’s audio circuitry was de-
signed in the spirit of professional audio
equipment rather than that found in typi-
cal broadcast or commercial audio gear.
High-performance components are used
throughout, providing low-distortion, low-
noise, and high headroom. Care was taken
so that signal integrity is maintained in both
the analog and digital domains.
Audio Meters and Status LEDs
The Model 44D provides four 5-segment
LED meters. The meters, located on the
front panel, display the level of the audio
signals associated with the two line inputs
and two line outputs. At the time of instal-
lation and setup the meters are invaluable
in helping to conrm correct operation.
During normal operation the meters of-
fer direct conrmation of the unit’s audio
signal levels, helping to ensure that optimal
audio quality is maintained. Additional LED
indicators are provided on the front panel,
offering status indications of the incoming
power and general purpose output (GPO)
functions.
Tone Generator Mode
For special applications the Model 44D can
be congured to serve as a tone generator.
Instead of functioning as an audio interface
device, the Model 44D will generate two
sine-wave audio signals, one 18 kHz and
the other 20 kHz. These signals are avail-
able both as line-level analog and Dante
digital audio (transmitter) outputs. The 18
kHz tone is intended for use with matrix
intercom systems that are used with the
Studio Technologies’ Model 5422 Dante
Intercom Audio Engine. This tone will be
connected to a matrix intercom system
using either analog or Dante inputs. The
matrix intercom system will be congured
such that it will combine voice audio with
the 18 kHz tone to create specialized IFB
signals. These voice-with-tone signals will
be routed, by way of an audio transport
system, to Model 5422 interrupt inputs
associated with tone operated (TOX) IFB
channels. The Model 5422 will detect the
18 kHz tone and “trigger” the associated
IFB function. In this way high-performance
IFB functions can be implemented for REMI
(remote-production) applications.
The 20 kHz tone is provided for use in
applications where generation of in-band
signals that are compatible with the call

Model 44D User Guide Issue 6, February 2023
Studio Technologies, Inc. Page 9
function on RTS TW-series party-line (PL)
intercom channels is desired. One example
would be for the 20 kHz tone to be con-
nected to an analog or Dante receiver (in-
put) channel on a matrix intercom system.
The intercom system would be congured
such that a button press on an intercom
“key” panel would cause 20 kHz to be sent
out an intercom channel. This would then
serve as a call “trigger” for devices such as
a Studio Technologies’ Model 391 Dante
Alerting Unit. Another interesting example
would be for the 20 kHz tone to be used to
serve as an activation signal for contact clo-
sures. Using Dante subscriptions (routes),
the intercom channel from the matrix in-
terface would be connected to additional
Model 44D units. When those units receive
the 20 kHz tone signal they would enable
their associated GPO contact closure.
Both the 18 kHz and 20 kHz tones are pre-
cise in terms of frequency and level accu-
racy, as well as being very low in harmonic
distortion.
Ethernet Data, PoE, and DC
Power Source
The Model 44D connects to a data network
using a standard 100 Mb/s twisted-pair
Ethernet interface. The physical intercon-
nection is made by way of a Neutrik®
etherCON RJ45 connector. While compat-
ible with standard RJ45 plugs, etherCON
allows a ruggedized and locking intercon-
nection for harsh or high-reliability environ-
ments. The Model 44D’s operating power
can be provided by way of the Ethernet
interface using the Power-over-Ethernet
(PoE) standard. This allows fast and ef-
cient interconnection with the associated
data network. To support PoE power man-
agement, the Model 44D’s PoE interface
reports to the power sourcing equipment
(PSE) that it is a class 1 (very low power)
device. The unit can also be powered
using an external source of 12 volts DC.
Four LEDs on the back panel display the
status of the network connection, Dante
interface, and PoE power source.
Simple Installation
The Model 44D uses standard connectors
to allow fast and convenient intercon-
nections. An Ethernet signal is connect-
ed using a Neutrik etherCON RJ45. If
Power-over-Ethernet (PoE) is available
operation will commence immediately.
An external 12 volt DC power source can
also be connected by way of a 4-pin XLR
connector. Line input and line output con-
nections are made using 3-pin XLR con-
nectors. A 9-pin female D-subminiature
(DE-9F) connector provides access to the
two GPI, two GPO, and auxiliary DC out-
put functions. The Model 44D is housed in
a rugged yet lightweight aluminum enclo-
sure that is designed to be “eld tough.” It
can be used as a standalone portable unit,
supporting what’s known in the broad-
cast world as “throw-down” applications.
Rack-mount options are also available
allowing one or two units to be mounted in
one space (1U) of a standard 19-inch rack
enclosure.
Future Capabilities and
Firmware Updating
The Model 44D was designed so that its
capabilities 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 rmware
(embedded software) to be updated using
a USB ash drive.

Issue 6, February 2023 Model 44D User Guide
Page 10 Studio Technologies, Inc.
To implement the Dante interface the Model
44D uses Audinate’s Ultimo™ integrated
circuit. The rmware in this integrated cir-
cuit can be updated via the unit’s Ethernet
connection, helping to ensure that its capa-
bilities remain up to date.
Getting Started
In this section signal interconnections will
be made using the variety of connectors
located on the Model 44D’s back panel.
Connections to the two line inputs and two
line outputs will be made using 3-pin male
and female XLR connectors. An Ethernet
data connection will be made using either a
standard RJ45 patch cable or an etherCON
protected RJ45 plug. A 4-pin XLR connec-
tor allows the connection of an external
source of 12 volts DC. Interfacing with the
GPI, GPO, and auxiliary DC output func-
tions can be made using a 9-pin female
D-subminiature (DE-9F) connector.
System Components
Included in the shipping carton are the
Model 44D Interface and instructions on
how to obtain an electronic copy of this
guide. If a rack-mount front panel is going
to be used as part of the installation it will
typically be shipped in a separate carton.
If the installation or specic application re-
quires an external source of 12 volts DC
it needs to be provided separately. A com-
patible power supply, the Studio Technolo-
gies’ PS-DC-02, is available as an option.
Locating the Model 44D
The location of the Model 44D will primar-
ily depend on being within the 100-meter
(325-foot) twisted pair Ethernet cable limita-
tion. But that can be overcome by using a
ber-optic interconnect between the Model
44D-related Ethernet switch and the other
Ethernet switches in the local-area-network
(LAN). The analog line input and line out-
put connections, typically being wired as a
differential (balanced) pair with shield, can
support lengthy cable runs with negligible
impact on audio quality.
Protecting the Enclosure
The Model 44D is shipped as a self-con-
tained unit suitable for portable use or
placement in a semi-permanent location.
Installed on the bottom of the chassis are
screw-on “bump on” protectors (also known
as “rubber feet”). These are useful if the unit
is going to be placed on surfaces where
scratching of either the Model 44D or the
surface material could take place. The “feet”
can be removed, without the use of a tool,
when rack- or custom-mounting the unit.
Rack Mounting the Model 44D
For permanent or mobile applications it
might be desirable to mount one or two
Model 44D units into one space (1U) of a
19-inch rack enclosure. A range of rack-
mount front panels, each purchased
separately, are available from Studio Tech-
nologies. The following provides details
on how to install Model 44D units to these
panels.
To attach a Model 44D unit to the single-
unit rack-mount panel, begin the process
by using a 5/64-inch hex wrench to remove
the four 6-32 thread button-head cap screws
that hold the standard front panel to the
chassis. Note that the screws might be
quite tightly afxed. Ensure that a good-
quality hex wrench is used and press and
hold it rmly into each screw head while
turning counterclockwise. Unless this

Model 44D User Guide Issue 6, February 2023
Studio Technologies, Inc. Page 11
recommendation is followed the hex
wrench could “cam out” and the head
could be damaged (“stripped”).
Using the screws that were just removed,
attach the rack-adapter front panel to the
Model 44D’s chassis. To prevent damage
care is required when aligning the front
panel with the LEDs that protrude slightly
through both the Model 44D’s chassis
and front panel. Tighten the four screws
only after a careful inspection ensures
that all of the LEDs protrude through the
front panel without interference. To allow
vertical clearance in the associated rack,
remove the four “bump on” protectors from
the bottom of the chassis. They are re-
moved by using the ngers to rotate them
counterclockwise; no tool is required. It’s
probably a good idea to carefully protect
and store the standard front panel, along
with the “bump on” protectors, for possible
later use.
Mounting a Model 44D to a dual-unit rack-
mount panel follows the same procedure
but will apply to two units. Store both of
the removed standard front panels and the
eight “bump on” protectors for possible lat-
er use. Note that on the rack-panel’s graph-
ics the Model 44D unit that’s on the left is
designated as A while the unit on the right
is designated as B. This is provided so that
each can be easily identied during installa-
tion, troubleshooting, and operation.
Once the desired one or two Model 44D
units have been installed in a rack-mount
front panel, the assembly can be mount-
ed into the designated equipment rack.
One space (“1U” or 1.75 vertical inches)
in a standard 19-inch equipment rack is
required. Secure the front panel into the
equipment rack using two mounting screws
per side.
Ethernet Connection
An Ethernet connection that supports
100BASE-TX (100 Mb/s over twisted-pair)
is required for the Model 44D’s Dante
audio-over-Ethernet connectivity. A
10BASE-T connection is not sufcient
for Model 44D operation. A 1000BASE-T
(“GigE”) connection is not supported
unless it can automatically “fall back”
to 100BASE-TX operation. An Ethernet
connection that supports Power-over-
Ethernet (PoE) is preferred as it will pro-
vide both data and operating power for
the Model 44D. To support power man-
agement functionality on an associated
PoE switch (PSE) the Model 44D will
enumerate itself as a PoE class 1 (very
low power) device. If PoE is not available
an external 12 volt DC power source can
be connected. This will be discussed in a
later sub-section of the guide.
The 100BASE-TX Ethernet connection
is made by way of a Neutrik etherCON
protected RJ45 connector that is located
on the back panel of the Model 44D. This
allows connection by way of a cable-
mounted etherCON plug or a standard
RJ45 plug. The Model 44D’s Ethernet
interface supports auto MDI/MDI-X and,
as such, using a crossover or “reversing”
cable will not be required.
External 12 Volt DC Input
An external source of 12 volts DC can be
connected to the Model 44D by way of a
4-pin male XLR connector which is locat-
ed on the back panel. While the require-
ment for the external source is nominally
12 volts, correct operation will take place
with any source that has a range of 10 to
18 volts DC. The Model 44D requires 300
milliamperes maximum at 12 volts DC for

Issue 6, February 2023 Model 44D User Guide
Page 12 Studio Technologies, Inc.
correct operation. The DC source should
be terminated to a 4-pin female XLR con-
nector with pin 1 negative (–) and pin 4
positive (+). Purchased as an option, the
PS-DC-02 power supply is available from
Studio Technologies. Its AC mains input
allows connection to a 100-240 volts,
50/60 Hz source and its 12 volt DC, 1.5
amperes maximum output is terminated
on a 4-pin female connector.
As previously discussed, an Ethernet con-
nection that provides Power-over-Ethernet
(PoE) can serve as the Model 44D’s power
source. Alternately, an external 12 volt DC
source can be connected. For redundan-
cy, both PoE and an external 12 volt DC
source can be connected at the same
time. If both PoE and an external 12 volt
DC source are connected, power will be
drawn only from the PoE supply. If the PoE
source becomes inoperative the 12 volt
DC source will provide the Model 44D’s
power with no interruption in operation.
(Of course, normal operation will cease if
both PoE and data transport fails on the
Ethernet connection.)
Line Inputs
The Model 44D provides two line in-
puts that are intended for connection to
line-level analog audio signal sources
associated with professional audio and
video equipment. It’s expected that the
nominal level of the analog sources will ei-
ther be +4 dBu for SMPTE applications or
0 dBu for EBU applications. (Refer to the
Conguration section for details.) Com-
monly-used sources could include analog
I/O ports on broadcast matrix intercom
systems, audio consoles, video storage
and playback systems, wireless micro-
phone receivers, and audio testing equip-
ment. The circuitry associated with the line
inputs is analog, electronically balanced,
capacitor coupled, with an impedance of
20 k ohms.
Two 3-pin female XLR connectors, located
on the Model 44D’s back panel, are used
for interfacing with the source signals.
Prepare 3-pin male XLR mating connectors
such that pin 2 is signal high (+), pin 3 is
signal low (–), and pin 1 is common/shield.
It’s also highly possible that an unbalanced
source will interface correctly. With an
unbalanced source begin by connecting
signal high (+) to pin 2 and signal low/
shield (–) to both pins 1 and 3. If this results
in hum or noise, next try connecting sig-
nal high (+) to pin 2 and signal low/shield
(–) only to pin 3; leave pin 1 unconnected
(“oating”).
If the Model 44D has been congured to
operate in the tone generator mode the
two analog line inputs will not be active.
As such, no connections should be made
to either line input channel 1 or line input
channel 2.
Line Outputs
The Model 44D provides two line outputs.
These analog outputs are designed for
general-purpose use which could include
connecting to analog inputs on devices
including matrix intercom systems, trans-
mitters associated with wireless in-ear
monitors, audio consoles, or amplied
speakers. The circuitry associated with the
line outputs is analog, capacitor-coupled,
and has a source impedance of 200 ohms.
It will perform optimally when driving loads
of 2 k (2000) ohms or greater. The nominal
level of the line outputs is congurable to
be either +4 dBu or 0 dBu, corresponding
to SMPTE or EBU applications. (Refer to
the Conguration section for details.)

Model 44D User Guide Issue 6, February 2023
Studio Technologies, Inc. Page 13
Two 3-pin male XLR connectors, located on
the Model 44D’s back panel, are provided
for interfacing the line outputs with asso-
ciated equipment. Prepare 3-pin female
XLR mating connectors such that pin 3 is
signal high (+), pin 2 is signal low (–), and
pin 1 is common/shield. To connect to an
unbalanced load use pin 2 as signal high
(+) and pin 1 as low/shield; do not connect
anything to pin 3. Do not short pins 3 to
pin 1 on the Model 44D’s line output con-
nectors as it will stress the output circuitry.
Connections made to the line outputs will
be the same whether the Model 44D has
been selected to operate in the audio
interface mode or in the tone generator
mode. In the latter mode a continuous
18 kHz sine-wave tone will be present on
line output channel 1 and a continuous
20 kHz sine-wave tone will be present on
line output channel 2. The nominal level
of both signals will be +4 dBu.
Note that the frequencies described
(18 kHz and 20 kHz) are effective when
the Dante sample rate is congured for
48 kHz. When the Dante sample rate is
44.1 kHz, the tone generator output
frequencies will be 16.5375 kHz and
18.375 kHz, respectively.
General Purpose Inputs (GPI)
The Model 44D provides two general-pur-
pose input functions that are referred to
as GPI 1 and GPI 2. These functions allow
transport of the status of relay contacts or
open-collector logic signals. The Model
44D’s GPI inputs use logic circuitry, “pulled
up” to 3.3 volts DC by way of resistors,
which are active whenever they are brought
to their logic low state. While the GPI input
circuitry is protected from over-current and
static discharge (ESD), care should be
taken to minimize the chance that “nasty”
signals can reach them.
The GPI inputs are active only when held
in their low state; they can’t be congured
to change state (“latch”) in response to
a logic pulse or momentary closure. Pins
on a 9-pin female D-subminiature con-
nector (DE-9F) are used for interfacing
with the GPI inputs and system common
connections. This connector is located
on the Model 44D’s back panel. A GPI is
only active when its corresponding pin
is connected to system common. GPI 1
is accessible on pin 3 and GPI 2 on pin
4. System common is available on pins
8 and 9. Refer to Figure 3 for connection
details.
Figure 3. GPI, GPO, and Auxiliary DC Output
connections
Pin Function
1 GPO 1-A
2 GPO 2-A
3 GPI 1
4 GPI 2
5 Aux DC Out
6 GPO 1-B
7 GPO 2-B
8 COM
9 COM
Note:
Connector type on Model 44D is a 9-pin
female D-subminiature (DE-9F). Installer
must provide a 9-pin male D-subminiature
(DE-9M). Connector uses 4-40 threaded
inserts for locking with mating plug.
If the Model 44D has been congured to
operate in the tone generator mode the
two GPI inputs will not be active. As such,
no connections should be made to pins 3
and 4 of the 9-pin connector.

Issue 6, February 2023 Model 44D User Guide
Page 14 Studio Technologies, Inc.
General Purpose Outputs
(GPO)
The Model 44D provides two general-
purpose output functions that are referred
to as GPO 1 and GPO 2. These functions
provide contact closures that respond to
trigger signals transported over the Dante
input (receiver) audio paths. The trigger
signals are in the form of high-frequency
audio tones (typically 20 kHz) that travel
along with the normal audio signals. The
normally-open (not shorted) contact clo-
sures are isolated from system common.
They are provided by solid-state relay con-
tacts which are intended to control low-volt-
age/low-current DC functions. The contacts
are rated for a maximum current of 400
milliamperes and a maximum of 60 volts
DC or AC. They are not intended for direct
connection to AC mains (high-voltage AC
signals.).
Pins on a 9-pin female D-subminiature con-
nector (DE-9F), located on the Model 44D’s
back panel, allow interfacing with the GPO
connections. Two connections are provided
for each GPO, pins 1 and 6 for GPO 1 and
pins 2 and 7 for GPO 2. Refer to Figure 3
for connection details.
Auxiliary DC Output
A source of low-voltage, low-current DC
is available for support of special applica-
tions that use the GPO functions. The auxil-
iary DC output has a nominal voltage of
12 and is referenced to system common.
During normal operation the output can
range from 10 to 18 volts DC if an external
power source is connected to the Mod-
el 44D and is providing operating power.
Circuitry associated with the auxiliary DC
output limits the maximum current to 25
milliamperes. The auxiliary DC output is
accessible by way of pin 5 of the 9-pin
female D-subminiature (DE-9F) connector
that’s located on the Model 44D’s back
panel. System common is provided on
pins 8 and 9. Refer to gure 3 for connec-
tion details.
The exact use of the auxiliary DC output
will depend on the needs of the specic
applications and the capabilities of the
installer. The auxiliary DC output can, for
example, be connected in series with a
GPO’s relay contact and used to directly
light a status LED, enable an optical cou-
pler, or provide a “GPO active” voltage
output. Be careful to limit the load placed
on the auxiliary output. Its circuitry will limit
the current to 25 milliamperes but keeping
it from reaching that maximum value is a
good idea.
Conguration
Back-Panel DIP Switches
A 4-position DIP switch assembly, labeled
Cong, is located on the Model 44D’s
back panel. The switches are used to set
operating parameters, including line input
nominal level, line output nominal level,
low-pass lter on/off status, and operating
mode.
Line Input Nominal Level
Switch SW1 is used to congure the nom-
inal level of the Model 44D’s two line input
channels. When SW1 is in its off (down)
position the line inputs are congured
such that connecting an analog signal
at a level of +4 dBu will result in a digital
signal at –20 dBFS being present on the
corresponding Dante output (transmitter)
channel. This would allow compatibility

Model 44D User Guide Issue 6, February 2023
Studio Technologies, Inc. Page 15
with SMPTE standards. When SW1 is in its
up (on) position connecting an analog sig-
nal at a level of 0 dBu will result in a digital
signal at –18 dBFS being present on the
corresponding Dante output channel. This
is compliant with EBU standards.
The choices provided by SW1 are primar-
ily intended to allow the Model 44D’s line
input gain structure to be matched to the
needs of specic applications. Most North
American (SMPTE) applications will follow
+4 dBu in the analog domain being equal
to –20 dBFS in the digital domain. While in
Europe (EBU) it would be typical in modern
installations for 0 dBu (analog) to be equal
to –18 dBFS (digital).
But SW1 can be used as a coarse lev-
el adjustment function if necessary. In a
SMPTE-compliant installation (+4 dBu =
–20 dBFS) setting SW1 to its on (up)
position will provide a 6 dB increase in
input sensitivity. This could be useful if the
average level of the signal connected to the
line inputs was a little low. And in an EBU
application setting SW1 to its off (down)
position would provide a 6 dB decrease in
input sensitivity. This could be useful if the
analog signals connected to the line inputs
were especially “hot.”
Line Output Nominal Level
Switch SW2 is used to congure the nomi-
nal level of the Model 44D’s two line output
channels. When SW2 is in its off (down)
position the line outputs are congured
such that a Dante input (receiver) channel
with a signal level of –20 dBFS will result
in an analog signal at the corresponding
line output channel having a level of
+4 dBu. This conguration would allow
compatibility with SMPTE digital-to-analog
level-relationship standards. When SW2 is
in its up (on) position a Dante input (receiv-
er) with a signal level of –18 dBFS will result
in an analog signal at the corresponding
line output channel having a level of 0 dBu.
This relationship will make the line output
compliant with EBU standards.
The choices provided by SW2 are primarily
intended to allow the Model 44D’s line
output gain structure to match the needs
of specic applications. Most North Ameri-
can (SMPTE) applications will follow
–20 dBFS in the digital domain being equal
to +4 dBu in the analog domain. While in
Europe (EBU) it would be typical in modern
installations for –10 dBFS (digital) to be
equal to 0 dBu (analog).
SW2 can be used as a coarse level
adjustment function if necessary. In a
SMPTE-compliant installation (–20 dBFS
=+4 dBu) setting SW2 to its on (up)
position will provide a 6 dB decrease in
input sensitivity. This could be useful if
it’s desirable for the average level of the
line output signals to be less than typical.
Figure 5. Analog outputs nominal level
conguration switch
Figure 4. Analog inputs nominal level
conguration switch

Issue 6, February 2023 Model 44D User Guide
Page 16 Studio Technologies, Inc.
This can be useful when a true “+4 dBu”
output is simply too “hot.” And in an EBU
application setting SW2 to its off (down)
position would provide a 6 dB increase in
input sensitivity. This could be useful if the
average level on the Dante input (receiver)
channels is lower than expected and a
“hotter” analog output is desirable.
Low-Pass Filters
Switch SW3 allows a low-pass lter func-
tion to be enabled or disabled as desired.
The function consists of four digital lters,
two applying to the audio signals from
the line inputs and two applying to the
signals destined for the line outputs. When
active the lters will eliminate most of the
audio content above 10 kHz that enters
the Model 44D by way of the line inputs
and exits the Model 44D by way of the line
outputs. When SW3 is in its off (down)
position the low-pass lters are disabled.
Full bandwidth audio signals will past
through the Model 44D’s line inputs and
line outputs.
When SW3 is in its on (up) position the
low-pass lters will be enabled. Enabling
the low-pass lters can improve the per-
formance and possibly the intelligibility of
audio signals that consist mainly of voice
content. In this case audio content in the
extend high-frequency range will typical-
ly provide little enhancement to system
performance and can often contain extra-
neous nose or other unwanted artifacts.
Also, in situations where a Model 44D’s
GPO functions are used, enabling the
low-pass lters will prevent the signaling
tones (typically 20 kHz) from being part of
the signals that are presented on the line
outputs.
Operating Mode
Switch SW4 is used to congure the
Model 44D’s operating mode. When SW4
is in its off (down) position the Model 44D
functions as an audio interface. This would
be considered its normal mode of opera-
tion. When SW4 is in its on (up) position
the tone generator mode is selected. In
the tone generator mode the Model 44D
generates 18 kHz and 20 kHz sine-wave
tones. Analog output 1 and Dante trans-
mitter (output) channel 1 will have a con-
tinuous source of 18 kHz present. Analog
output 2 and Dante transmitter (output)
channel 2 will have a continue source of
20 kHz present.
Note that the frequencies described
(18 kHz and 20 kHz) are effective when
the Dante sample rate is congured for
48 kHz. When the Dante sample rate is
44.1 kHz, the tone generator output
frequencies will be 16.5375 kHz and
18.375 kHz, respectively.
SW4–Operating Mode
1234
ON
1234
ON
Tone Generator
Audio Interface
Figure 7. Operating mode conguration switch
Enabled
Disabled
SW3–10 kHz Low-Pass Filter
1234
ON
1234
ON
Figure 6. 10 kHz low-pass lter conguration
switch

Model 44D User Guide Issue 6, February 2023
Studio Technologies, Inc. Page 17
Dante Conguration
To integrate the Model 44D into an audio
interface application several Dante-
related parameters can be congured. At
a minimum, signals must be routed to the
two Dante input (receiver) channels and
from the two output (transmitter) channels.
The conguration settings will be stored
in non-volatile memory within the Model
44D’s circuitry. As such, power-down and
power-up activities will not impact the
unit’s settings. The Model 44D uses the
Ultimo 2-input/2-output integrated circuit
to implement the Dante architecture.
The two Dante receiver channels will be
assigned to the desired Dante transmitter
channels on other devices. The two trans-
mitter channels associated with the Model
44D’s Dante interface must be assigned
to the desired destinations (Dante receiver
channels on associated devices). This will
typically be done with the Dante Control-
ler software application which is available
for download free of charge ataudinate.
com. Versions are available to support
Windows® and OS X®operating systems.
Within Dante Controller a “subscription” is
the term used for routing a transmitter ow
(a group of output channels) to a receiver
ow (a group of input channels). Note that
as of the writing of this guide the Ultimo
integrated circuit limits the number of
Dante ows to two. These can either be
unicast, multicast, or a combination of the
two.
The Model 44D has a default Dante device
name of ST-M44D followed by a unique
sufx. The sufx identies the specic
Model 44D that is being congured. The
sufx’s actual alpha and numeric charac-
ters relate to the MAC address of the Ulti-
mo integrated circuit that’s present in the
specic Model 44D. The two Dante receiv-
er (input) channels have the default names
of Ch1 and Ch2. The two Dante transmit-
ter (output) channels also have the default
names of Ch1 and Ch2. Using Dante
Controller these names can be revised as
appropriate for the specic application.
The Model 44D supports audio sample
rates of 44.1 and 48 kHz with no pull-up/
pull-down values available. The desired
conguration can be made using the
Dante Controller software application. The
Model 44D can serve as the clock master
for a Dante network but in most cases that
would not be optimal.
Switch SW4, located on the back panel, is
used to congure Model 44D’s operating
mode. When selected for the tone gen-
erator mode (SW4 on (up)) normal audio
interface operation will not take place.
The unit’s internal processor will generate
two sine-wave audio signals (tones). The
two Dante transmitter (output) channels
should be assigned to the desired desti-
nations. The two Dante transmitter (out-
put) channels will have the default names
of 18kHz and 20kHz. Signals routed to
the two Dante input (receiver) channels
will not cause any Model 44D activity to
take place. The two Dante receiver (input)
channels will have the defaults names of
Ch1–Inactive and Ch2–Inactive.
Note that the frequencies described
(18 kHz and 20 kHz) are effective when
the Dante sample rate is congured for
48 kHz. When the Dante sample rate is
44.1 kHz, the tone generator output
frequencies will be 16.5375 kHz and
18.375 kHz, respectively. The default
names will not change.

Issue 6, February 2023 Model 44D User Guide
Page 18 Studio Technologies, Inc.
Operation
At this point the Model 44D should have its
Ethernet, line input, line output, and GPI/
GPO connections implemented as desired
for the application. Depending on the capa-
bilities of the Ethernet connection an exter-
nal 12 volt DC power connection may have
also been made. The two Dante transmitter
(output) channels and two Dante receiver
(input) channels should have been routed
using the Dante Controller software appli-
cation. Normal operation of the Model 44D
can now begin.
The Model 44D is designed for continuous
operation with no adjustments required.
Maintaining the correct signal levels com-
ing into the line inputs and Dante receiver
channels is important. This will ensure
that proper signal levels are presented to
the Model 44D’s circuitry and associat-
ed equipment, leading to optimal audio
performance. The audio level meters and
GPO status LEDs will provide assistance in
conrming that correct operation is taking
place.
Initial Operation
The Model 44D will begin its initial function-
ing a few seconds after its power source
is connected. As previously discussed,
the unit’s power source can be provided
by Power-over-Ethernet (PoE) or an ex-
ternal source of 12 volts DC. If both are
connected the PoE source will power the
unit. Should PoE power subsequently no
longer be available, uninterrupted opera-
tion will continue using the external 12 volt
DC source. (This will probably prove to be
a “hollow” victory since a loss of PoE will
probably also mean a loss of the required
Ethernet data connection!)
Upon Model 44D power up the status LEDs
will light in various manners. The PoE, Dan-
te, and Ethernet status LEDs, located on
the back panel, will light in various ways.
On the front panel the input power, GPO
status, and audio level meter LEDs will light
in a sequence. Once the test sequence has
completed the two columns of level meter
LEDs associated with the line outputs will
momentarily display the version number of
the unit’s application rmware (embedded
software). Details on how to “read” the ver-
sion number are provided in the Technical
Notes section.
The Model 44D will now begin normal
operation. The way in which the back-panel
LINK/ACT, SYS, SYNC, and PoE LEDs light
will depend on the characteristics of the
connected Ethernet signal and the cong-
uration of the unit’s Dante interface. Details
will be covered in the next paragraph. The
user is presented on the front panel with
two input power status LEDs, two GPO sta-
tus LEDs, and four 5-segment LED audio
level meters. These resources are simple to
understand and should prove to be useful
as will be highlighted in the following para-
graphs.
Ethernet, PoE, and Dante
Status LEDs
Four status LEDs are located below the
etherCON connector on the Model 44D’s
back panel. The LINK/ACT LED will light
green whenever an active data connec-
tion to a 100 Mb/s Ethernet network has
been established. It will ash on and off
in response to data packet activity. The
PoE LED will light green whenever Pow-
er-over-Ethernet (PoE) associated with the
connected Ethernet signal is providing op-
erating power for the Model 44D. The SYS

Model 44D User Guide Issue 6, February 2023
Studio Technologies, Inc. Page 19
and SYNC LEDs display the operating sta-
tus of the Dante interface and associated
audio-over-Ethernet network. The SYS LED
will light red upon Model 44D 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 audio
data with another Dante device. The SYNC
LED will light red when the Model 44D is
not synchronized with a Dante network. It
will light solid green when the Model 44D
is fully synchronized with a Dante network
and an external clock source (timing refer-
ence) is being received. It will slowly ash
green if this specic Model 44D is serving
as the clock master for the Dante network.
How to Identify a Specic
Model 44D
The Dante Controller software application
offers an identify command that can be
used to help locate a specic Model 44D.
When identify is selected for a specic unit
its audio level meter LEDs will light in a
unique pattern. In addition, the SYS and
SYNC LEDs, located directly below the eth-
erCON connector on the back panel, will
slowly ash green. After a few seconds the
LED identication patterns will cease and
normal Model 44D level meter and Dante
status LED operation will again take place.
Audio performance will not be impacted by
the use of the identify command. As such
it’s perfectly acceptable to use the identify
command any time it would be useful.
Line Inputs
The Model 44D’s two line inputs are elec-
tronically balanced (differential), capacitor
coupled, with a nominal impedance of 20 k
ohms. The nominal analog level of signals
presented to the line inputs should match
the Model 44D’s conguration. If the nom-
inal input level is congured for –20 dBFS
this will equate to a nominal analog input
level of +4 dBu. If the nominal input level
is congured for –18 dBFS this will equate
to a nominal input level of 0 dBu. As such,
if the nominal level of the Dante output
(transmitter) channels is 6 dB different
than expected, either high or low, a user
should conrm that the Model 44D’s input
conguration has been set correctly.
The line input circuitry is protected from
damage should a moderate DC voltage
be accidentally connected. For example,
no damage will occur if a powered analog
party-line intercom circuit (typically 28 to
32 volts DC from 3-pin XLR pin 2 to pin 1)
be accidentally connected. This protection
would also be effective should P48 phan-
tom power associated with a microphone
signal be accidentally connected.
The frequency response of the line inputs
will depend on the conguration of the
low-pass lter function. If the lter is en-
abled most energy above 10 kHz will be
removed. This will be effective for voice-
applications such as intercom or talent
cueing (IFB). If support for high-quality,
full-bandwidth audio is necessary ensure
that the low-pass lter function has been
disabled. This will also apply if 20 kHz
nominal “call light” or signaling tones
need to pass through the Model 44D’s
line input to the Dante output (transmitter)
channels.
Line Outputs
The line outputs are electronically bal-
anced (differential) and intended to be
connected to various analog inputs with
nominal impedances of 2 k (2000) ohms
or greater. The nominal analog level of

Issue 6, February 2023 Model 44D User Guide
Page 20 Studio Technologies, Inc.
signals present on the line outputs will
depend on the Model 44D’s conguration.
If the nominal output level is congured
for –20 dBFS this will equate to a nominal
analog output level of +4 dBu. If the nomi-
nal output level is congured for –18 dBFS
this will equate to a nominal output level
of 0 dBu. As such, if the nominal analog
output level is 6 dB different than expected,
either high or low, a user should conrm
the Model 44D’s conguration.
No special precautions are necessary
when using the line outputs in settings
where a variety of signals are present. As
with the line inputs, the line output circuitry
is protected from damage. For example,
no damage will occur if a powered analog
party-line intercom circuit or a microphone
signal with P48 phantom power present be
accidentally connected.
Similar to the line inputs, the frequency
response of the line output will depend
on the conguration of the low-pass lter
function. If the lter is enabled most energy
above 10 kHz will be removed. This will be
effective for voice-applications such as in-
tercom or talent cueing (IFB). If support for
high-quality, full-bandwidth audio is neces-
sary ensure that the low-pass lter function
has been disabled. This will also apply if 20
kHz nominal “call light” or signaling tones
need to pass from the Model 44D’s Dante
receiver inputs to the line outputs.
Level Meters
The Model 44D contains four 5-segment
LED level meters, two associated with the
line inputs and two associated with the line
outputs. The meters are provided as
a support aid during installation, congura-
tion, operation, and troubleshooting.
General
The meters are organized into two groups
with one group representing the two line
inputs and the second group represent-ing
the two line outputs. The two meters asso-
ciated with the line inputs are calibrated in
reference to the conguration of the nomi-
nal level of the line inputs. When congured
for +4 dBu nominal a meter’s 0 LED light-
ing will indicate that an analog signal with
a level of +4 dBu is present on the associ-
ated line input. This would translate to an
output (transmitter) level of –20 dBFS being
sent to the Dante network. When the line
inputs are congured for 0 dBu nominal a
meter’s 0 LED lighting will indicate that a
signal with a 0 dBu is present on the line
input and the corresponding Dante output
(transmit) level will be –18 dBFS.
Similar to the line inputs, the two meters
associated with the line outputs are cal-
ibrated in reference to the conguration
of nominal level of the line outputs. When
congured for +4 dBu nominal a meter’s
0 LED lighting will indicate that a Dante
input (receiver) level of –20 dBFS is present
along with a corresponding signal on the
line output with a level of +4 dBu. When
the line outputs are congured for a 0 dBu
nominal level a meter’s 0 LED lighting will
indicate that a Dante input (receiver) level
of –18 dBFS is present. And the corre-
sponding analog output signal present on
the line output will have a level of 0 dBu.
Each level meter contains four green LEDs
and one yellow LED. The four green LEDs
indicate audio signal levels at or below the
selected nominal level (+4 dBu or 0 dBu).
The top LED is yellow and indicates a sig-
nal that is 6 dB or greater than the selected
nominal level. An audio signal that causes
the yellow LED to light doesn’t necessarily